M104, 95 E320 "Missing" or Rough running
 

I am now at a dead end.

While driving to breakfast this morning, the engine began "missing"; running very rough. After getting home, I pulled the plugs with hope of identifying the problem cylinder. All six plugs looked the same. I checked the resistance on the plug wires and "plug stub" and they were 1.5 to 2K ohms (within spec).

I then checked the fuse on the over voltage protection relay and it was good.

I also checked for malfunction codes; pin #8 (HFM-SFI) responded with one blink (no malfunction). The check engine light is not lit.

The wiring harness has been replace on this car.

The only other clue is that the exhaust smells rich.

Could this be an over voltage protection relay?

Anyone have other tests or ideas?

Hey Jim,

Long time since.

Pull the OVP and see if it is 000-540-52-45..
If it is , change it to the new part # 000-540-67-45

Arthur .... Yes, it has been a while. With your 5K responses, I can see where you have spent your time after your 2K responses on the pagoda board. I am slow, I only have 3K with the 190SL Group.

Anyway, the OVP was also my guess as that would explain the lack of a malfunction code (still with the reader you send me in 2001). So I have a new 00 540 67 45 in my hand that I'll install tomorrow. If that dosen't work (or change anything) I am not sure where to look. I'll post the results tomorrow morning.

Thanks again, you always seem to be around when I need assistance.

Very good..I think the OVP will do it..if not , we will go to the next step, but those HFM/SFI OVP set-ups are infamous and where we always start b/c that chassis is full Electronic and OVP is mandatory..if you pull it, the car will not run , whereas on the earlier models the car would still run b/c OVP was just on the control side. It is nice to see you have a single flash on pin 8..that is a real good sign on that chassis ..most have somethin in there..I think that new harness took care of that.
Have not been at Pagoda much..but I do go over once in a while to read some of those long -winded post.....:)......and I mean Looooong..
Nice talkin' to you again.

Arthur ..... I need "plan two". I installed the OVP this morning and it is still "missing" or running very rough.

You might want to visit the 190SL site and see my current "Barn Find" project project. It had last run in 1988.

My next thought would be in the fuel pressure area (probably not trip a malfunction code). Could it be the fuel pump or pressure regulator?

<<My next thought would be in the fuel pressure area (probably not trip a malfunction code). Could it be the fuel pump or pressure regulator?
>>

I would check it... These HFM will fool you b/c if the HFM module sees an ignition misfire , it automatically cuts fuel to that cyl. injector for CAT protection, so an ignition failure on these seems like a fuel issue.
But fuel pressure is a next step.
On the top of the fuel rail, you will see a test port cap..That is where you can hook up a gauge. That fitting is the same as an R12 fitting, in case you do not have one.
So, first check is to start the engine and let it idle..now, pull the vac line at the regulator and see if any gas is shooting out that port on the reg. There should be none and if there is, the diaphragm is leaking and you need a new regulator. [ raw, unmetered gas getting sucked intio intake.]. Also check for any evidense of fuel in that vac line..again, you want none.
If all is well, then hook up gauge and do this simple 3 part test.
1-Engine @ idle, Vac line ON-- FP should be 3.2-3.6 Bar
2- " " , Vac line OFF-FP should jump to 3.7-4.2 Bar
3-Engine OFF , wait 30 min. -FP should maintain at least 2.5 Bar
*Bar = 14.5 PSI... [ you already know that, but this winds up in archieves]

See what's up w/FP...
..next suspect would be the 3 Resistor under the coils if we have a missing/misfire condition, or a vac leak could fit a Rough running condition.
If intermittant, that could be a sticking EGR [ common on 104] . I have a simple test for that after we see where you are w/FP.
You may aso want to try the DM led/sw [ the built-in one] while at idle in case there are any impending codes...
Are you using Bosch F8DC4 plugs?

i HAVE BEEN THRU THIS AND WILL BET YOU IT IS THE OXYGEN SENSOR EVEN THOUGH THE LIGHT IS NOT LIT....GET ONE OFF EBAY FOR CHEAP AND IT WILL MAKE YOUR CAR RUN LIKE NEW.

Arthur ..... Great use of my old R12 gauges (I sold my last R12 car).

It does not appear to be a fuel pressure problem; Idle with vacuum, 55 psi; without vacuum, 61 psi; with engine off, 50 psi. Possibly a little high but very close.

Checking the plug "thing" under the coils was one of my first checks. I tested them with an ohm meter and they, and the wires had 1.8-2K ohms. I believe that I replaced them long ago at your recommendation.

I am not sure of the plug numbers but they are Bosch copper from my local dealership (they give me good prices so I buy a lot from them. With my discount, even 190SL parts are cheaper than the speciality suppliers).

I guess that ERG is next.

I checked the LED (in the DM) readout with the engine idling and received a 7 code, "Ignition System failure". This sounds promising but I am not sure what it really is saying. After a search and some reading, I'll pick up three of the connectors under the coils and a new set of F8DC4 plugs.

Is there a way to test the coils? There is no resistance between the center tap and ground.

The oxygen sensor is another "easy" replacement part. I'll pick one up next time that I am out.

<<Arthur ..... Great use of my old R12 gauges (I sold my last R12 car). >>

Yes, that is why I mentioned it..I just use the R12 ends on a good fuel gauge..very nice.. if using your old gauges , you can also use the manifold valves for fuel flow rate test...cool.

<<It does not appear to be a fuel pressure problem; Idle with vacuum, 55 psi; without vacuum, 61 psi; with engine off, 50 psi. Possibly a little high but very close.>>

Fine...........

<Checking the plug "thing" under the coils was one of my first checks. I tested them with an ohm meter and they, and the wires had 1.8-2K ohms. I believe that I replaced them long ago at your recommendation.>>

Ok ..here is what to look for on those connectors..[ just the ones under the coils].. They don't "snap connect" to the plugs like the other 3 wire lead plugs that stand alone ..and b/c they are under the coil, benz used a simple spring arrangement that just pushes down on the top of the plug connectors from the force of the seated coil..not a good connection set-up, but I see why they did it with the coils being on top of the plugs...anyway, if you look in there and see any heat fatique or grayish ash type residue, or spring degeneration on that spring and connection, that is where the failure and misfire has/is occurred.. look for any carbon type tracking right there and around the plug base....an ohm reading of the connector does not address this condition. Each coil fires 2 spark plugs at the same time [ Waste Spark System] in Series, so a poor connection at this point will cause a misfire very easily ..which is why most Techs [ knowing this failure rate] just change those 3 connectors when changing plugs. As I posted earler, once the HFM [ ignition] module sees this misfire , it cut off injection, so the misfire is pronounced and often erratic. A scope does pick these up , but if one does not have that, a close look at those connections may show the condition.. I am pretty sure I advised you when you did the harness to go with the Bosch Super Coppers , so it is most likely that you do have/ did go w/F8DC4's ..and I only stress that point b/c 104 are very fussy about plugs being a Waste system.. and they HATE plats!!!!
I also use a little die'electric grease on these connectors.
On the EGR, there was a Benz TSB for sticking valve and it was remedied by replacement to one with a smaller shaft dimension. I have that Campaign Info, if you need it , but a simple EGR hand test should suffice.
With car up to temp and @ idle, take a hand vac capable of pulling 12-14" vac and apply that to the vac port of the EGR and hand vac open the EGR..the engine should immediately try to stall/run rough . Now the trick..With hand pump, quickly release vac supply and listen for the EGR to SNAP shut. The engine should return to perfect idle if all is well an egr is completely closing..do this several time and actually try to get it to hang up..if NO, then I would not suspect EGR leakage. But that test would not eliminate other possible vac leaks. It is just possible EGR confirm.
[ if no change in rpm with this test, you have another problem, but will wait for results on this one]

Finally , I doubt you have an 02 sensor problem , but they are fairly easy to test on that model b/c it is full electronic engine management.
Under the passenger rug is the 02 wires. The green one gets unplugged so that no sig goes back to ECU . Now , the blk wire that plugged into the green is 02 sensor output. You can connect a DMM + there and a good ground.
Now , with engine @ temp and a decent idle, watch your meter as you remove the vac line to the FP regulator [ cap the line with your thumb so you don't create a vac leak while doing this test].
This will make the reg increase the FP and that increased pressure will cause a manually induced RICH condition to the engine and will show right up on the 02 as a high voltage [ .8-9v].. That is the rich test for 02. The engine can not correct for this b/c it does not have an 02 input sig. going back to the ECU b/c you disconnected the green wire..
Now , hook the vac line back up to reg and then take a good sized vac line OFF somewhere and watch your meter go LEAN..[ .1-.2 v].. That test 02 ability to read LEAN condition....now , to test the switching speed , I take that line you are using for the lean test and put my thumb over it , on and off, while watch the DMM..it shoud react to your on/off input of air through that vac line pretty fast. If so, you have a decent 02.
A scope pattern is much better, but this is a viable DIYer test on HFM systems..what you are basically doing is using the engine as a Lean/Rich generator and simply seeing if the 02 has the ability to react to you manually causing a rich or lean condition.
I would start with a closer inspection of the connectors under the coils and then the egr test..both simple...and check the plugs while you are there.
...and see if any pending codes on DM

<<<I checked the LED (in the DM) readout with the engine idling and received a 7 code, "Ignition System failure". This sounds promising but I am not sure what it really is saying. After a search and some reading, I'll pick up three of the connectors under the coils and a new set of F8DC4 plugs.
>>

Jim,

I did not see this added info when I wrote you my last posting b.c you added it while I was answering the original posts..

.... but , with that new info, that would certainly help confirm my suspect of the coil connectors under each coil...
If the N59 DM sees a malfuntion from the HFM ignition system, it brings on a pending code before CE lamp activation ..if it does not see subsequent repeat failures , it will drop it as a viable fault before it activates the CE. [ intermittant problem]
If you have coil problems , they are output/current monitored by HFM Ignition Module via pin 8 and would show as a code 21/22/23, depending on which one was in question..
So , with this added info from the DM, we are back to coil connectors as first possible suspect...and plugs while you are in there... this will most likely turn out to actually just being your basic/common HFM/104 ignition connector failure complaint/remedy.
Have fun..............

Arthur ..... From you description, it is easier to change the oxygen sensor than to throughly test it. I would just put a digital volt meter on it and watch the voltage; if it cycled up and down, it is OK.

When I inspected the coil bottoms, there was some gray power that I just ignored. I'll replace them before doing anything else. It will be Monday before I can get the parts.

Thanks again.

<<I would just put a digital volt meter on it and watch the voltage; if it cycled up and down, it is OK.
>>

I agree.. The posted procedure is actually harder to read than to do..I just posted the full procedure if anybody with HFM really wants to know how to get a close check w/o a DSO wave pattern from a scope... by simply removing or adding a couple of vac hoses at the engine while watching the 02 sig.
I use/have some nice equipment , but I try to give the DIYer the same diagnostic abilities using what he would mostly have in his Tool box..which is usually just a DMM , with maybe freq and duty cycle at the most...
So, I have to tone it down, but at the same time try and get the general idea across..
With the 02 sensor wires right there under the rug, it is a simple matter to hook up and monitor while driving..some guys hook a permanent meter right on the dash. Some also use that connection to hook those a/f mixture Led readout gauges you see around.
One thing that should be mentioned on 02 sensor replacement on this or later Benz chassis [ both OBD1/2] is the fact that using a generic sensor
will cycle fairly well for fuel mix control, but the other systems [ Like AIR] require the correct relacement OEM b/c they are capable of reading the ultra lean conditions the ECU looks for on Emmissions mandates and if one does not use a sensor with this quality and precision, he runs the risk of codes when the ECU does its self testing procedures.

We will see what happens when you change out the connectors...
See ya

I have been following this post--I have a 95 E320 with similar symptoms.

While reading, it once again occurred to me that the readers of this forum are very lucky to have someone like Mr. Dalton as a regular contributor.

Thanks again from a very appreciative forum member.

J. M. van Swaay

Danke J. M. van Swaay...................

Arthur ....
 

I always admire your very scholarly input re member problems and have often wondered about your background related to these cars. Would you mind sharing a little bit of that with us?

Well,
Nothing special..just a Motor Head kid from the '50s who started working on Old Benz's starting around early '60s. I was the Kid in a small New England town that was referred to by the neighbors as that guy who " Works on those damn GERMAN cars " ...:)
That was the era of the Ford/Chevy Rivalry days and most did not pay much attention to a Benz...
I had worked at repair shops in and out of the '60s and finally owned a couple of small shops the 70/s/80's..
Also Collected several chassis, including several 113 chassis cars and they are probably my Tech Speciality. Had several of them thru the years and worked on so many that I became fairly well versed on all models.
My favorite of that bunch is the 250SL..and I still own a 1967 Early Euro version which has been with me forever.
So, I am basically still just a veteran Benzhead , still tinker , have a few Tech friends that share info and hang with , still drive Benzs, and I have somehow kept up technically... probably just my progressive nature and curiosity in all things Benz...
The Forum is just a way for me to spread what I learned or forgot to the next generation of Benzers.. I do write on several other sites , [ not all Benz related/other Hobbies] ....but this is my favorite Benz one.
I work on-line many hours , so it is easy for me to sneek over here in between my work.
There are several members here that are Pro Techs and Shop Owners and they deserve the credit for this fine group..
That's about it......

I might add that Arthur has been posting here a LONG time, on this site before 2000 when I first came on-line. Over the years, I have floated in and out as I spend more time on other sites but I always come back when I have a "hard" problem. This is by far the best Mercedes technical site. Thanks in part to Arthur, MBDoc, stevebfl and several of the other very knowledgeable folks who spend their time here.

Now to continue the saga. I replaced the plug wires and stubs and installed a new set of Bosch copper plugs. Nothing significant changed.

I did notice one more interesting symptom; the engine will not rev above 4000 RPM (in neutral). The computer starts cutting out either fuel or spark.

My parts guy mentioned that the mass air sensor on these cars is a commonly replaced item. I would think that a bad air sensor would trip a code.

Just to verify; I checked the pin #8 for codes with the ignition on but the engine not running. The check engine light is still not on (but the bulb is good, lights with key on but the engine not running).

<<I did notice one more interesting symptom; the engine will not rev above 4000 RPM (in neutral). The computer starts cutting out either fuel or spark.>>

That is Normal 4K rpm cut-out in N or P . That is the torque converter load protection safety feature. If you tried N while the car was moving a few MPH, you will notice that feature would be disabled.

>>My parts guy mentioned that the mass air sensor on these cars is a commonly replaced item. I would think that a bad air sensor would trip a code.
>>

Possible, but before changing it , I would get some MAF cleaner and try that.
You really need a scope or adaptation #s to properly diagnose the MAF

Do a search on MAF cleaning and I will post some other info shortly.
I would also pull the vac line OFF the purge valve and run the car with that line plugged to be sure it is not causing an internal vac leak..just disregard any purge code in the meantime..

PS --Jim,
I saw you are now are on Utube with some 113 suspension tutorials..very cool.. maybe I can be your Agent....:)
Here is another video that explains the basics of MAF management that is cool too..I like this guys style ....:) [This uses later style wide band 02 sensors rather than the one in your car, and may be a little Technical for the diy guy , but still some good info for the curious]
Check it out..............

http://www.picotech.com/auto/automotive-oscilloscope-guide/lambda-sensors.html

Arthur ..... The video was of my suspension presentation at the Pagoda Gathering in Blacklick. There is another Blacklick presentation video on Pagoda drivability modifications on you-tube. I have also done six videos that are for sale in the 190SL Group store. Fun stuff and a good revenue producer for the club.

I checked the EGR with a vacuum pump and it does not leak vacuum. I plugged the line and drove the car without change.

I watched the MAF video, very interesting and a good sales pitch for a two channel laptop interface.

I searched cleaning the MAF sensor and it looks straight forward; remove it and the gently spray the flat plain sensor with a MAF cleaner and then replace it. I happen to have the torx with a center hole for the screws (I needed one to replace the MAF on my Porsche). So I will head out for some "MAF cleaner".

I tried to find a "purge" valve but the best I could see is a "Regeneration switchover valve" but I couldn't locate the actual valve. It controls vacuum to the "activated charcoal filter, which I also could not locate.

Arthur .... Since you caught me modifying a previous posting, I'll just post another post.

I found the purge valve on the driver's side fender with a vibration mount and two large black tubes. I disconnected and plugged the tube; no effect.

<I tried to find a "purge" valve but the best I could see is a "Regeneration switchover valve" but I couldn't locate the actual valve. It controls vacuum to the "activated charcoal filter, which I also could not locate.
__________________


Purge is Regeneration.. Same guy , different name.

OK..on that chassis:
Behind the driver headlamp is the ABS pump..and behind that pump is a little valve that says "MOT" on top of it. That is it and there is a vac line [ fairly good sized] feeding that to the intake. The other vac line goes to the canister.
That valve is suppose to pulse rapidly [ 5-20htz ] to allow canister fumes to re-enter the engine [ regeneration]...but they do it in pulses so the engine does not see this as a large gulp of air, [ they meter it ], as to not effect the idle and A/F mixture control system. What can happen on these is they get crap in them and they intermittantly stick open and the engine sees this as a vac leak, resulting in intermittant rough idle. So, if you just disconnect/plug it and the engine acts nicely to that change, you can assume the valve was at fault and you do not have to do all kinds of Purge control test. It is fairly common and this is just a shot/stab at your condition before condemning the MAF, as any unmetered intake air will cause your complaint and I hate to see a MAF changeout before checking some of the other simples...
Worth a try. Just diss the purge code youare going to create.

OK
You are ahead of me on that one too.. my problem is I am a 2 finger typer and it takes you less time to search in the archieves as it does for me to get this keyboard crankin'.....

You are using the search feature , ain't ya ????

Ok
Look everywhere for vac leaks and check for codes again.
Might want to unplug the MAF while at idle and see if any change too.

Arthur ... Yes ... I search everything to verify that I am doing things correctly. I found "Purge" in numerous places but none corresponding to a location or other terminology.

Well, I got a can of CRC MAF cleaner, removed the sensor and sprayed it down according to the directions. Again, no change.

I took your advice and checked the codes again. This time I got a code 23 on plug #8 that I believe indicates a misfire on coil #2 for cylinder 3/4.

I listened to the injectors click with a mechanic's stethoscope and they all sound the same with a nice audible click.

When I was changing the plugs, I checked the resistance of the coils; all were about 0.6 ohms. This seamed low but it was consistent across all three coils.

<<I took your advice and checked the codes again. This time I got a code 23 on plug #8 that I believe indicates a misfire on coil #2 for cylinder 3/4.
>>

Ok ...I like that.....:)

Now, clear the codes . swap that coil and connector to another location and watch to see if the code follows that coil/connector to the new location.........or, do you have a DSO ??????

Arthur, thanks a bunch ...
 

for the background info. You sound like the kind of guy I'd like to have for a neighbor.

Arthur ..... Bingo! I swapped coil #1 with coil #2 and the problem moved to a malfunction code #22; indicating a misfire of cylinders #2 oand #5 which says that the coil that I moved from position #2 to position #1 is bad.

So, I'll make another parts run tomorrow morning for a coil.

By the way, I forgot to connect the MAF sensor wire after swapping the coils. The engine ran worse and it showed a malfunction code #4 (Duh). After clearing that code and another test drive is when I got the code #22.

[QUOTE=Jim Villers;1824368]Arthur ..... Bingo! I swapped coil #1 with coil #2 and the problem moved to a malfunction code #22; indicating a misfire of cylinders #2 oand #5 which says that the coil that I moved from position #2 to position #1 is bad.

So, I'll make another parts run tomorrow morning for a coil.

Cool ... I think that could well fit your problem..
These early 104 HFM/SFI had coil problems and the ones that ususally were troublesome were the ones with the Blue sticker on them..most have been changed by now.

Hope that works out.

One can see where a Scope is a nice tool for these full Electronic systems...
I sometimes see those Sun LS2000 DSO's on ebay for short money now [$250]

Arthur .... A scope would be nice. I tried testing the coil with my inductive timing light. I should have done this before but I kept putting the cover on before I reinstalled the air duct and then it was too late.

The results were not what I was expecting. With the pickup over the plug wire from the coils, the "bad" coil flashed but appeared to flash at about half the rate of the other coils and not consistent. I had expected that the bad coil would not flash at all. I can't imagine why a "bad" coil would flash at a different rate; either it should flash or not. I thought that the high voltage plug wires would come from the same point within the coil. Could the computer be not firing the coil because of something else?

Anyway, I'll get a new coil tomorrow and hope that an "Eureka moment" occurs in the driveway.

It is common to have an intermittant coil problem , and usually that would be on the secondary windings side [ but not always]. The ECU actually triggers the primary and spark occures when a pre-determined current is reached, [ spark circuit Ramp] so one could also have a bad trigger threshold in the ECU. That is why I had you try another location for the coil. If the code follows the coil , you can assusme the coil /connector is bad ..if it did not , it would point to that trigger Transistor circuit in the ECU..[ which does happen] or a bad plug/injector/etc at that same cylinder....this swapping stuff around to make a diagnosis is commonplace if one does not have the proper diagnostic equipment and even a good shop will use these quicky test...
The oddity of the Waste Spark system this chassis uses is that the 2 plugs are wired in Series with one coil, meaning the flow goes from coil to electrode of first plug , fires to ground and then on the second plug it goes from ground to electrode for fire and back to the single coils secondary winding to complete the circuit...so, that is quite a path and a couple of plug gaps to overcome..Of course , the second plug offers no load demand [ b/c it has no compression/fuel mix], so it has an easy jump, but even still, there is that contention... knowing this , one can see why the coil to plug connectors are so important, as they can effect both plugs firing as they are always in the circuit, regardless of which cylinder is under compression load................. [ any weak link/connection in a Series circuit shuts down the complete circuit].
I also believe that this plug firing arrangement is the reason these models do not take a likeing to Plats with their ultra-thin electrodes..[ but that is just my guess and may not be a viable reason, even tho its seems to make sense]
The later coil over plug versions use coils on each plug.
I used to be able to just see the electrons path until I got a lethal dose of that Kriptonite stuff...now I have to use a DSO....The Scope allows you to see the signals and wave patterns just as the ECU sees and reads them..so that narrows it right down simple.
Give me a schematic, a jumper , and a test lamp and I am all set to go at it
on the older cars , but these High Techers need equipment to really get it down w/o some guessing, as you could see on that Video..............

Arthur ..... Eureka arrived. The magic of the correct part was instantaneous and the car was back to its old normal self.

It shows again that the diagnosis is more important than the mechanic. Swapping out the coil was a 5 minute job; finding the correct part took several days.

Thanks again for all of you assistance.

Now that the action seems to be over, may I toss in an aside? The waste spark system with the two plugs in series is quite common, in my experience. For many years I drove a Ford sedan equipped with a Yamaha built DOHC V6. It used three coils on six plugs, also setup in series. Interestingly, from the factory it was equipped with three each of two different part number platinum plugs. One part number had a platinum center electrode, the other a platinum side electrode. As you would guess, each circuit had one of each. I've also worked on a number of GM cars which used the same design.

- JimY

Very Good..

You may want to clear any codes and might even want to reset the HFM modules memory back to normal base line ..[ that will readapt by itself, but it is easier and better to reset everthing after that type repair b/c the ECU was adapting to the old misfire condition], so you know it is spec now.

The new plugs and connectors are maint. items anyway, so no loss there .. and the OVP is changed to the new part# regardless ..I would stash the old one in the Glovebox/trunk as a spare in case you ever need one on the road b/c a bad OVP on an HFM/SFI can stop the car dead.
You may also want to compare your old coils to the new for Resistance values , with the secondary windings being the ones of most concern.
They will be in K-ohm.

..PS

<<Boxster 'S', >>

I see you have another addition aside from the 121 barn find..........
How do you like/dislike the Boxster???
I am thinking about one.

See ya

<<One part number had a platinum center electrode, the other a platinum side electrode. As you would guess, each circuit had one of each. >>

That is interesting..so the second plug would have that extra electrode and that would be an improvement on the bosch plug ..
That makes me think my hypoth of why the 104s like the regular coppers over the standard plats has more crediability...that extra electrode on the neg side would possibly aleaviate that firing to the electrode problem of the second in series plug...

Arthur ... The old and new coil have the same static resistance on both the low voltage side, 0.6 ohm, and the high voltage side, 6.3K ohm. The only visual difference is some swelling around the center bar of the steel core on the sealed end.

The 2001 Boxster 'S' is an OK car but after a couple of years, it still doesn't "fit" me. My thoughts are to "recycle" the Porsche and to try a SLK32. The Porsche is fast, handles like glue, fun on the track but I don't find it comfortable to drive around town, to get into and out of and it is clumsy if you need to carry anything (not much room, even for a cup of coffee). On the other side, friends say that "I look good in it" (it is speed yellow with a hard top). Since it is newer with OBD2, fixing it is easier that this old E320.

<The 2001 Boxster 'S' is an OK car but after a couple of years, it still doesn't "fit" me. My thoughts are to "recycle" the Porsche and to try a SLK32. >

That's basically what I wanted to know...

Thanks for the info.

Thanks for this thread guys, it's been very helpful - I've been having the same problems with my '95 E280 M104, now finally sorted with new coils. Arthur, you're a veritable fountain of knowledge on these cars. Thanks for sharing it.

This has been an interesting problem. I had posted the initial problem on the MBCA froum and then posted the final solution. There were two people on that board that anre utilizing this information in their trouble shooting.

Coil(s) seems to be the common cause of this problem for M104 engines. Had the same problem in my '96 E320 a month ago and it turned out to be a bad coil. Ran perfect one day then started intermittantly missing on the way to work and progressively got worse.

I wonder if it makes sense to just replace the coils once in a while and what that schedule would be. As far as I know, the one that failed on me was original, so that's 245,000+ miles. Surely if they were replaced every 100,000 miles you could avoid having them fail.

A lot of things, particularly the harness problems, are age-related as well as mileage-related, and the youngest of these cars is now 12 years old. Even non-moving parts can degrade over time. But 100,000 miles for the coils seems about right - mine failed at 113,000.

My thoughts on these coils [ and connectors] is they are prone to a high fail rate due to extreme engine heat b/c they sit right on top of the engine and then they throw an engine cover over the top. This is definately heat fatique situation and one will notice that these coils are NOT oil cooled..like the old car were..and those old coils , being liquid cooled and remotely located from the engine where they had airflow would last a lifetime..so, not surprizing that a coil that has little cooling AND has to fire 2 plugs in a high compression engine does not have a life time that one would expect from a remote/cooled coil..
One will also notice that the plug connectors that always give the trouble are only the 3 under the coils ..they other 3 are not a as heat trapped b/c they are in the open air and not under a HOT coil..[ that is why we always
point to the 3 connectors under the coils as a first possible on 104 Waste Spark systems

Plus the fact that the originals were weak to begin with [ the blue stickered ones]
This problem can be diagnosed in 5 min with a scope, but for the diyer, persistance and parts swapping, along with some code observations and analytical thinking will get to the bottom of it..

Arthur .... And a little help from our friends.

My car has 175K miles.

Thanks Jim,
I will let the other members know that you get special treatment b/c you have been a Collector Friend for many years and I love the 190SL Group Cap you sent me ..
I was wearing it one day while driving my 250SL and I pulled into a Convenience Store and a guy checking the car out and said "Hey Dude, how come you are driving a 250 and wearing a 190 cap ? " in a smart-ass tone..
I said "Well, I just can't drive both of them at the same time "

" So, do ya' wear a 250 hat when you drive the 190 ? "

" NO , that is when I take the GullWing out ! "

great thread.

I'm thinking under GP, it's best to replace all coils and their "stubbies" at 150K miles, and keep the rest for spares . . .

:-) neil

I will second that.

After following this thread, I changed the connectors under the coils and my engine misbehavior disappeared! Now I actually notice the poor shocks in the front of the car and the non functional AC. Before I was too busy hiding behind the wheel trying to drive the backfiring beast back and forth to the airport each week.

Surprisingly, my car just hit 149,000 miles to boot. Perhaps the interval for the stubbies should be 125K.

Great Thread and thanks for the bump - I thought I lost this in the sea of posts. I now have bookmarked for further notes and evaluation.

Most interesting post! I just changed the coils of my 1996 E320 at 135K preventively. With "stubbies" do you mean the connectors, wires or plugs?

http://catalog.worldpac.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=2EI1B4MYE2EK12P51I&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1996&product=F1010-84561&application=000357357

Stubbies.

Altough I have never heard them referred to as such..

If you change them every few years , you might not need coils.
Most Techs change them with every plug change b/c they know what a problem they can be for misfires on a Waste Spark system.
Just the ones under the coils.

Most owners change the plugs and leave the old connectors on the coil , when in actuality, it is usually the connectors that are the problem and should always be considered the first suspect on 104 engines w/DIS ignition systems.

I"m reviving an old thread by saying that I have a 95 S320V with the same problem. My first order of business was to check the spark plug gaps, and see how she runs tomorrow. If still missing, I'd probably do new plugs and wires.
Interesting thing is, that when I restarted the car (just shut off and restarted) it was almost gone......
I might start a new thread on this problem.....

FWIW, I used the inductive timing/strobe light (hooked to coil output plug wires #1, #3, #5 (seperately) ) to find the bad coil, which flashed both slower than the good coils (half the rate?) and intermittently.

For kicks, I hooked-up the inductive timing light to the coil input wire, and it flashed at the same rate as the GOOD coils' output. I'm thinking this would be a good test to see if the coils are receiving a good input signal and if it is a wiring harness issue.

:-) neil

I, too, found a bad coil pack on a '95 E320 with NO apparent codes with the homemade reader. Used the ignition timing light tip -- mine flashed on the good ones, did not on the bad -- to isolate the bad coil without swapping.

I know it's only OBDI, but it has defective ignition coil codes...hmm?