1993 300E 2.8 Cold Throttle Response
 

Hello,

I have a 1993 300E with a 2.8L gas auto and 180k miles. My main issue with the car is throttle response when the engine is cold. Until the engine is fully warmed up, when driving the engine slowly accelerates without regard to how far down I push the accelerator. Once the engine is hot, throttle response is fine.

A couple strange issues are when the engine is cold, the throttle response is poor until I hit 2800 RPM. Once the engine hits 2800 RPM, the engine finally "takes off" and accelerates dramatically. I'm thinking the issue may be a vacuum leak issue but I have yet to find any visible leaks or cracked hoses.

Also, I have some hard starting in cold weather. If the engine does not start on the first crank without any throttle, then I have pump the throttle to get the engine to start. I don't think I should have to use throttle when starting a fuel injected vehicle.

I have a code reader with the blinking light from Ebay (works great), but after I reset the faults and fixed some issues, I'm showing no current faults for several weeks. I have also replaced the spark plugs, plug wires, air filter, water temp sensor, and air intake temp sensor.

I've done a lot of research on these boards and in books but before I pay to have a tech to go hunting for the problem, I would appreciate any possible suggestions you might have.

Thanks,

John B

Weird. Sounds like you might have an issue with the cold start injector. Anyone know how this works?

Typical of some M103 engines.
You may want to have your mechanic adjust the fuel distributor lower chamber pressure to .45 bar ( 6.5psi ) instead of .4 bar ( 5.8 psi )
This will compensate for the years of operational wear.
You'll need a CIS-E fuel pressure gauge to make the adjustment.

<<You'll need a CIS-E fuel pressure gauge to make the adjustment.>

The car is HFM/SFI w/104 DIS engine.
Check codes on pin 8 of Diagnostic Module and post.

Arthur and Ed,

Thanks for the replies. I ran the diagnostic on Pin 8 and it came back with one blink, no faults found. Any ideas on where I should check next?

Thanks,

John B

14

Arthur,

Thanks for the response. I checked pin 14 and I had one new fault I have not seen before: Fault 11.

My fault book reads "Pin 14 Fault 11 - Closed Throttle recognition signal to engine control module (HFM-SFI or Left LH-SFI); Fuel safety shut-off to engine control module (HFM-SFI or Left LH-SFI)."

I cleared the fault without a problem. Any idea what this means?

Thanks,

John B

Check that you have a little slack in the throttlew cable at idle and check that you have the new style OVP.

Arthur,

Yes there is play in the throttle cable while at idle. As for the OVP, I think I have found it after reading some of the other posts. Mine sits behind the battery, close to the firewall. It is a small, square black plastic box with a white plastic top along with a clear plastic cover. Under the clear plastic cover is one fuse, although it looks as though there is room for two fuses. The fuse is a 15 amp, blade-style fuse. Not the regular tube, bullet style like in the main fusebox. The fuse appears to be in good shape. What should I do next?

Thanks again for the help,

John B

OVP is the tall, rectangular one..should be aluminum body.

Pull it and see if it is the Modified relay 000-540-67-45.

If it is 000-540-52-45 , change it regardless.

That could be your start problem, and might have a running problem.

http://catalog.worldpac.com/mercedesshop/sophio/image.jsp?title=Overload%20Relay&url=http%3A//img.eautopartscatalog.com/live/P205670038APA.JPG

It sounds as if the fuel mixture is not sufficiently enriched for a cold engine. I have the same car. I once accidently left the coolant temperature sensor disconnected and had similar symptoms. The engine would die when started cold, usually several times. I don't recall what the cold drivability was like. In my case the diagnostic codes pointed directly to the ECT sensor; the ECU knew the value was implausible.

I wonder if there is a failure mode here where the ECU thinks the engine is warm even though it's not? I don't know the specification for the sensor, but expect it can be checked with a simple DVM. Is the wiring harness original or replaced?

- JimY

Missed the year...you are correct !

Arthur,

I will remove the OVP and check to see if it has been updated. I will post here tomorrow what I find.

JimY,

Not sure if the wiring harness has been replaced. It hasn't been replaced since I've owned in the last year. It looks as though the temp sensor is working though.

It has been suggested that I might have a bad O2 sensor or a vacuum leak. Would either of these cause the sluggish performance?

Thanks for the replies,

John B

Arthur,

I removed the OVP and checked the part number. The car has the new OVP 000-540-67-45. I also re-checked my diagnostics after driving the car for two days and both pin 8 and 14 had no faults. Please let me know if you can think of anything else to check.

Thanks again for the relies,

John B

<<both pin 8 and 14 had no faults.>>

Did a single flash come up on both????

Arthur,

Yes, one flash each on pins 8 and 14. I'm starting to think that I have air/vacuum leak that seals up once the engine heats up and things start to expand. Possibly in the air intake after the Mass Air Flow sensor. Or maybe a wore out O2 sensor that isn't faulting yet. What do you think?

Thanks again,

John B

After you get the single flash, wait 2 secs and then hold the button 6 secs..then turn off key for 50 secs , on for 10 and then restart.
That will reset the HFM memory to mean..then drive the car for a couple of days for it to re-adapt see how it then runs ... and then check if any codes come back on 8 and 14.
The big power change at rpms comes from both the variable cam advance and the runner length change as rpms increase..you are aware of that????

Arthur,

Sounds good. I will give that a try. What pin do I use to reset the HFM? 8 or 14 or do it to both? Also, I guess I'm not sure how the variable cam advance system works. I will do a little research to get up to speed. I'll do the reset of the HFM and post in a few days.

Thanks again,

John B

Do them both..
As I stated on a previous post , 8 is HFM and 14 is EA . You have to reset each module, one at a time.

You may also want to clean the MAF , but I would prefer you do nothing until you follow the steps I mention so we know where you are at from the get-go....
And I am assuming from your post that you have no codes on the DM....................

Arthur,

I did as you suggested and re-set the EA and the HFM. After driving for a few days I checked for fault codes. There were no faults on the Pin 14 EA. The HFM on Pin 8 returned one code: #9 O2S 1 - Voltage too high, circuit open or voltage implausible. I think I have only one O2 sensor one my car. Do you think this O2 Sensor could be bad?

If so, I've read on some posts that generic O2 sensors or O2 sensors from late-model Mustangs work the same as the OEM but are much cheaper. Any idea if these other units would work on my '93 300E 2.8L?

Thanks again for the replies,

John B

Disconnect sensor under rug on passenger side and monitor the voltage output on green wire as you take the vac line off the fuel pressure regulator for high v.and create a vac leak at engine for low v. reading.
Post what you get.

Arthur,

Sorry for the delay, I got sidetracked for a while with the repairs. I tested the voltages with the vehicle idling on the O2 Sensor as you suggested, here is what I found:

1.) On the smaller green/blue wire to the O2 Sensor, I had a reading of 12.6 Volts. The reading was the same with the vacuum line connected and disconnected from the fuel regulator. (I'm a novice with the voltage reader, please let me know if these values are incorrect)

2.) There was another larger, separate green wire heading to the O2 Sensor, which I believe is for the O2 heater. The reading on that wire was a constant 0.6 Volts with the vacuum line connected and disconnected.

3.) Just for testing, I drove the vehicle with just the O2 Sensor disconnected and then again with the just the vacuum line disconnected.

4.) With just the O2 Sensor disconnected, I couldn't notice a difference in perform. Still sluggish.

5.) With just the vacuum hose disconnected from the fuel regulator, I still couldn't notice a difference in performance. Still sluggish, but I did notice a small vacuum pressure coming from the disconnected hose.

Now I'm kinda lost with what to do next. Any help would be greatly appreciated.

Thanks again,

John Bjork

Your wire understanding is incorrect.

There are two plugs for the 02 sensor...one is a single wire plug and the other is a 3 wire plug.
They are right next to one another..under rug
The single wire one has a green wire coming from the engine [ ECU] and it plugs into the single wire connector.. THAT connectors wire is the signal wire coming from the Sensor and that is the wire you want to monitor.[ not the green one]
The 3 wire plug contains the heater circuit and the ground wire. Leave those plugged in.
You unplug the single wire connectors green wire so that the 02 sensor sig can not report back to the ECU.
Now, normal running coolant temp and engine @ idle, you take the vac hose off the FP regulator, that causes the fuel pressure to increase and when it does , more gas gets thru the injectors and causes a RICH condition...so, YOU are MANUALLY making the engine run RICH by increasing the Fuel Pressure beyond spec, and you should see the 02 sensors V increase to about .9v ...meaning it is RESPONDING/RECOGNIZING the rich condition you have created. [ You must plug the vac hose you took off the FP reg for this test so you do not have a lean input thru that open hose at the same time].
Now, note the 02 V for this test and then put that hose back on Reg.... this time, pull off another/different vac hose and create a vac LEAK... the 02 should now respond and show a lean condition by reading a low V [ like .2v]
So, what you are doing is basically manually changing the rich/lean condition of the engine and seeing if the 02 picks up on your changes..if it does , it is working..if it doesn't, it's not....you are just using the engine as a lean/rich generator of sorts..and b/c you have unplugged the green wire going back to the ECU, the ECU can not correct the imbalanced air/fuel mixture that you are creating b/c it sees NO 02 SIGNAL.
This is just a simple 02 sensor test, where YOU are manually controlling/changing the air/fuel mixture and watching the sensors reaction to your inputs.
When you do the lean test, you can actually put your thumb on/off the vac hose you are using to make the engine lean out and as you open/close that hose end , you can see the 02 sig jump up/down with those inputs..verifying the sensors speed for change.
Pretty simple trick...

Get it ????

Arthur,

Thanks for the response. I attempted the voltage reading as you suggested, but I was unable read a change in the O2 Sensor voltage with the fuel regulator hose unhooked. I did however see a significant change when I would press the accelerator. At idle, the reading on the O2 Sensor was 0.06 volts. As soon I hit the gas, the reading shot up to roughly 0.80 volts at 2000 RPM. The voltage from the O2 Sensor varied up and down as I throttled up the engine up and down. Once the engine came back to idle, the O2 Sensor reading slowly leveled back to 0.06 volts after about 20 seconds. Does this mean the O2 Sensor is working? Its strange if the O2 Sensor is working, then why does the car seem unaffected when disconnected?

Thanks again,

John Bjork

<<

I assume this .06v is a typo?????

I just read through your ordeal and have an idea. When did this problem first occur? All of a sudden or ? After some other repairs? It sounds like your valve timing may be off. I've seen it a couple of times on the 104 engine b/c it is not the easiest engine to time properly. If you have a late cam it will be very sluggish but will pick up power in the higher revs. Since it would be a basic mechanical problem you won't have any fault codes pointing directly at the problem. O2 sensor codes, adaptation codes, and random logic chain codes could be caused by the late cam due to the engine dynamics with the late cam will not give the expected responses that a properly timed engnie will. The best check would be to pull off the valve cover and confirm valve timing. If you have acces to a compression tester, check the compression first. I'd expect the cranking compression would be low if the valve timing is off. If compression is low, then pull the valve cover and check the cam timing.

Arthur,

Like I said, I'm kind've a novice with the volt meter. With the dial set to 20V, the reading at idle was between 0.04 volts to 0.06 volts, with the average being about 0.06 volts . As the RPM's increased, the voltage steadily rolled up to between 0.75 to 0.85 volts, with the average being about 0.80 volts.

If I am correctly reading the volts, what does a reading of 0.06 volts mean? Is my engine starving for fuel at idle?

Thanks again,

John Bjork

duxthe1,

Thanks for the suggestion, I've considered having the compression checked. I just haven't pulled the trigger yet for the cost. I'd like to exhaust all my ability first, then hire someone. I may be close to that point, heh. I bought the vehicle with somewhat sluggish performance, so I'm not sure how it began. I'm trying to rule out vacuum leaks and O2 Sensors before I crack open the head.

Thanks again,

John Bjork

OK

Your sensor is not putting out a decent signal at low rpm...so, we have either a bad heater circuit or a bad sensor.
The heater input should be 12 v....thatwould be the two same colored wires [ probably white] on the 3 wire connector.
Check for V and then unplug the connector and check the sensor for heater OHMS. probably open circiuit on heater, allowing the sensor to go open loop at low rpm ..meaning a new sensor is in order.

If valve timing were off , I would expect to see a Cam Position Sensor/ Crank Position sensor relationship code...HFM/SFI are Sequential Injected via cam sensor timing.

Arthur,

I checked the voltage on the heater circuit, it reads 12.6 volts. I checked the resistance on the two white wires leading from the O2 Sensor, it read 3.3 Ohms with the meter set to 200 Ohms setting. What do you think?

Thanks again,

John Bjork

Well, you have heater, but the sensor may be getting weak..
The true heater test is to see if it draws 1.2-2.2 Amps
The sensor has to be kept at 600 degrees to work, so sometimes the exhaust can't maintain that at idle , so the heater is an aid for that, plus it gets the sensors into closed loop fast at cold start.
But , it is not uncommon to see a drop of 02 readings after 20 secs or so at idle as a sensor ages. Some new sensors even have a low reading at idle . You want to do my rich/lean test after a 1 or 2 min/2500 rpm run to be sure the sesor is good and hot. Then do both rich/lean right away. That will tell for sure.
Then an actual in-situ test is 02 monitor at a 2K rpm and watch for sensor to cross count the 4.5 v line at least 1 htz when ECU is hooked back up.

You may also want to clean the MAF. MAFS get dirty film on them and tend to run rich, specially at lower rpms.. MAF cleaner aeresol at any parts place.

On the later engines I would agree, but the early hfm cars tend to not throw codes that readily. I have seen timing off on a 104 without any cam position codes present, just similar symptoms as described in this scenario.

Maybe ...
The problem I find here is he does not have the problem once the car has warmed up to temp..........

quote:

<<<I have a 1993 300E with a 2.8L gas auto and 180k miles. My main issue with the car is throttle response when the engine is cold. Until the engine is fully warmed up, when driving the engine slowly accelerates without regard to how far down I push the accelerator. Once the engine is hot, throttle response is fine.>>

My specs show a currect draw of 1.2-2.2 amps for heater, so that would equate to an R factor of from 6 to 10 ohms.. Your 3.3 ohm would be almost twice the spec. amp draw.
so, if your ohm readings/values are correct, you may have a shorted heater element. Try to redo that ohm test on a lower range setting, if your meter has one.... a better reading would be current b/c most low end meters have a hard time with accurate low ohm readings.
Amp draw will require meter in series with circuit..........

Arthur,

I've got two things I'm going to try. First, I'm going to go to the parts shop and check how many Ohms the resistance is on a new O2 Sensor to check if the old one and a new sensor have similar resistances.

Second, I've been reading about the resistor spark plug problem. I replaced the plugs about a year ago with whatever Bosch was recommended by my local parts store. I pulled one out today and sure enough, it was a resistor plug: FR8DC. I think the proper plug for my car is an F8DC4. I'm going to order some of the F8DC4's and see if there is a difference in performance. I'll post what I find.

Thanks again,

John Bjork

Must have missed that Arthur, I thought it was a problem all the time, not just cold.

FR8DC's are Bosch's replacement for the F8DC4, which is on the way out. We havn't had any real issues running them. I wouldn't be surprised if the spark plug connectors go out a little sooner due to the resistance but other factors influence their life too so it would be hard to quantify.

Yes , no more F8's...my concern with R plugs on that engine is it is both a waste spark system , and they are known for weak plug connectors from the get-go, plus he has the early version which had the Blue coils..they were not the best and the later ones seem a lot better. The real prob seems to be when they use palts, and I think that is b/c the second plug has to fire from ground back to electode ..and the plats electrode is quite small..but that is just my theory.
Might want to have a look at both MAF and IAT sensor......

OK so heres where I'm at now. After testing the O2 Sensor, I cleared any faults with my code reader. I ordered a compression tester and a new set of the correct F8DC4 spark plugs. I drove the car for about a week to check for any fault codes, and then when the plugs and compression tester arrived, I changed the plugs and tested the compression. Here is what I found:

1.) I retested the O2 Sensor heater by putting the Meter in series with the heating circuit. It started at about 2.0 Amps then fell to a constant 1.4 Amps. The O2 Sensor seems to within its operating specifications.

2.) I checked for fault codes after driving the car for a week. No faults at all, on any system. All came back with 1 flash.

3.) The spark plugs that I removed look very good. Nice clean look, a little bit of white and very minimal carbon buildup after about 1 year in the car. All plugs looked alike.

4.) The compression test results as follows, done with all plugs removed, the throttle full open, and the engine hot:
- Cylinder #1 = 82 PSI
- Cylinder #2 = 80 PSI
- Cylinder #3 = 80 PSI
- Cylinder #4 = 80 PSI
- Cylinder #5 = 77 PSI
- Cylinder #6 = 77 PSI

5.) New Bosch F8DC4's installed. The car runs better with these plugs but the problem is not completely solved.

6.) Note on the current performance, when I first started this post, it was late winter here in Minnesota. Now its summer time and the car has been running a bit different. Basically the car is very sluggish at low RPM's then at about 2800 RPM, it seems to really kick-in and take-off. In the summer heat, the engine seems to run better just before it completely warms up. On hot days the car is at its sluggish worst and when the AC is turned on the car accelerates at a snails pace. When I hit the accelerator, the engine sound reminds of an old Chevy V8 with the ignition timing too retarded. Not snappy but rather fighting to increase RPM's.

7.) Also while working on these problems, I've noticed that I am leaking a little oil from what looks to be the head gasket. The leak is at the back of the engine on the drivers side. I do not have any milkiness in my coolant nor do I have any smoke coming from the tailpipe.

Any ideas? Thanks in advance for the help.

John Bjork

Yep, it does indeed look as if the cam timing is off.

To check the cam timing you have to pull the valve cover and set the engine at TDC. If your cam lobes on #1 aren't pointing somewhat upwards and towards each other then rotate the engine another revolution.

Once you are sure you are at TDC then take a pair of channel locks and grab the intake cam 1/2 way down it's legnth and turn it towards the exhaust cam until you feel it stop. If it doesn't move at all then all the slack is already out but pull it a bit clockwise and then back counterclockwise to make sure you feel the stop. This takes out any slack from the variable cam timing.

Now you need to locate the timing marks, the marks are actually small holes in the back side of the camshaft gear flanges. The holes are approx. 3mm and will be located toward the outside of which ever cam you are looking at when the engine is near TDC. There are several holes visable on the back side of the gears but the timing hole is the only little one. To check the timing you insert a 3mm rod a few inches long (I use a 3mm allen wrench) into the hole. The allen wrench should lay close to flush with the top of the head if the cam is in time. Don't fret if it isn't completely flush as chain wear will have the intake a little above flush and the exhaust a little below flush. If you have one that is a lot less than flush (I seriously suspect you do) you need to eyeball it and determine if moving it one tooth will put it back nearer to flush with the top of the head.

Once you have found which cam is out, (most likely the intake) you will need to re-time the eninge. That isn't any fun as the front upper timing cover has to come off. Trust me, although it looks as if you can slip the chain over the gear with the tension off, I assure you that you can not. But you can worry about re-timing the engine after you know it is out.

You may want to unplug the cam advance solinoid at idle and see if there is a change.....could possibly be getting an sig input for cam advance when it should not..

Arthur and Dux,

Thanks for the replies. I think the cam timing is a little out of my league, I'm going to look for an independent mechanic in the Minneapolis/Saint Paul area and get a quote.

I am unfamiliar with the Cam Advance Solenoid. Can you give me a rough idea of where and what to look for?

Thanks again for all the help,

John Bjork

As Dux has stated , you have low compression all the way across...so...
that would point to a jump in cam/valve timing..most likely chain.

But...
This car has a variable cam timing feature and that is done by The ECU sending an electrical sig down to the cam advance magnet [ solinoid] That is at the front of the head .. round device w3 cap screws... two wire plug goes to it.
I have never seen one stick, but I have read about them failing right here on this forum. There shoud be NO sig to this actuator unit until a certain RPM [ 3K in N or P..] at which time the intake cam advances valve timing for more power. However... If this gets a sig at idle, the cam will advance when it is not supposed to, or the mechanism inside could be stuck..
The test for cam advance magnet is to unplug the connector and bring a 12V battery jumper over to the solinoid at idle ... that will cause the cars idle to be adversely effected b/c you are advancing the cam manually at too low a RPM .. it will run like crap, but that will confirm the mechanism is working. Or, if one suspects a sig to it at idle [ causing the same complaint, unplugging it would see that difference...if it is working as it should [ electrically] there should be no change at idle. In other words, there should be NO 12 V at those wires at idle.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2EI1B4MYE2EN1CY8CT&year=1993&make=MB&model=300-E-003&category=A&part=Camshaft+Adjuster+Magnet


But again, this is just a quick test to rule that possible out before going in there for possible chain jump....

One quick question.

When doing comp test...did you let the engine crank several turns for each
test..

Arthur,

Thanks for the response. I tested each cylinder twice and I rolled the engine several times on each test.

I found the cam advance solenoid. I pulled off the 2-wire connector and I tested each lead for voltage. At idle, one lead had 13.5 Volts, and the other had 0.5 Volts. I know you said there should be no volts at idle, so I left the unit disconnected and test drove the car and it ran very poorly, no power.

I'm not really sure what to think now. Maybe a prior owner "hot-wired" the lead to compensate for a valve timing issue. I don't know. I haven't found any splices and all the wires in the car look good, no cracking or flaking that I can see.

I will test the solenoid itself with a 12 Volt lead from the battery tomorrow and see if I can hear the solenoid activating. Also I will see if it affects idling.

Thanks again,

John Bjork

You don't test each lead to ground ..you test across the leads b/c the ECU does the switching on the ground side.

The best test is the 12v jumper test b/c that also checks the inner mechanical workings of the advance mechanism. As you switch that jumper power on/off , you will see if it is working by engine response.
I am not eliminating the possibility of a jumped chain and that is a very likely cause, [although rare on a 104]....I am just telling you that a jumped chain one tooth off is an 18 degree valve timing change and the advance feature on that chassis is a 20 degree change...so my common sense tells me that I would do a simple advance solinoid test before ripping anything apart...just a simple test ..hate to see you take it all apart and then see the problem was not a jumped chain.
Kinda like taking out your starter before turning on the headlamps to test for a dead battery..............

OK, so I tested the Cam Advance Solenoid today with a hot lead wire connected to the battery terminals. With the engine off, I connected a positive and a negative lead to the two prongs of the solenoid. I could hear a click-clack sound inside the head.

When I started the engine and connected these hot leads again to the solenoid, the engine idled down a little. I could definitely tell that engine experienced a change when the solenoid was manually activated.

The strange part of this is that even though I had current in the connector plug that I had previously disconnected, I could not hear a change in the engine idle when I reconnected the connector plug to the solenoid.

I tested for fault codes and I found that I had fault #38 on pin 8. This is the fault for the Cam Solenoid. It looks like the car knew the solenoid was unhooked.

I figured that maybe the 13.5 Volts that I had measured from the solenoid connector plug could be the engine diagnostic trying to read a response from the solenoid. So I reconnected the solenoid plug but I left a sliver of room to test the prongs on the solenoid when the connector plug was reconnected. With the car running and the solenoid connected, I could not measure any volts across the two leads connected to the solenoid.

Any idea what this means? Maybe I should try to wire in a hot lead to the solenoid so that I can test not only the idle, but how well the car drives when the solenoid has been artificially activated?

Thanks again for all the help,

John Bjork

Like I said....There is always 12 pos at the cam solinoid. The switching to activate the solinoid is done on the neg side by the ECU..it is a SWITCHED GROUND circuit.
In a S/G circuit, the switching to complete the circuit is done on the ground side of the circuit, so just cuz you have battery voltage on the pos side of the solinoid does not mean the solinoid has a complete circuit..it does not have a complete circuit until the ECU grounds the other leg. Only then will the solinoid activate. This is quite common on ECU switching..same as your blower or ign, etc..they are SWitched Ground circuits , not switched positve circuits.

The criteria of the cam advance on that chassis is:

No Load/ N or P
3000 RPM activation/advance /20 degrees/intake valve cam

Under Load :
1500 RPM to 4200RPM/Load Dependant Advance Range - advance 20 degrees
4200 and above RPM.- Cam Advance Retard

When those criteria/demands are met , the ECU will ground the return leg of the solinoid circuit and you will have cam advance b/c you now have a completed circuit. [ pos to sol.> thru sol coil >back to ECU> ECU to ground/ neg]

If you are testing the solinoid for activation in N or P , you can hook up your meter to your 2 wires at the plug [ back-probe] , but you must meet criteria of 3K RPM. When the engine reachs 3K, you should read 12v on meter.
The reason that I have you jumper 12 v to the cam solinoid when it is at idle is b/c there is no criteria for cam advance at that RPM, so if we manually induce some, we will see an idle change IF the cam solinoid AND mechanism are activating..it is just a test that we trick the engine with...just like when you want to test your EGR valve ..the egr is designed to NEVER opens at idle, but if we MANUALLY open it at idle with a hand vac pump, the engine will run very rough..that tells us that the EGR is in fact OPENING and the passages are clear..it is just a test that is out of the NORMAL engine running condition and it's results tells us what is working inside w/o taking stuff apart.
That's all.... the cam should not advance at idle , so we make it advance just to see if it works...the engines responce to our cam input tells us if it is working..if it did NOT work, the engine would do NOTHING different, even though we have brought 12v directly to the solinoid, thereby eliminating all controls..you are the ECU and you are looking for the engine to respond....the ECU is out of the picture b/c you do not have it plugged in.

So, if you have a definate change in RPMs with a jumper to cam sol. from battery [ pos and neg] at idle , the advance is working and the test has passed...so, suspect is now timing chain. If your car did not have this advance feature, I would have gone with the timing chain right from the start, but you can see why this test is performed with cam advanced engines. When one notices that surge of power that the 104 HFM engines are so well know for, it is the cam advance along with the intake variable runner length kicking in...it's like a whole new power-plant....kinda cool..........

Arthur,

Thanks for the reply. It makes a lot more sense now that I know how Mercedes set of the pos and neg to the sensor. I would not have guessed that.

I'm going to start looking for a good MB tech here in the Minneapolis/St Paul area. Do you think I should look at replacing the timing chain along with the adjustment job? I was thinking about what else would be an easy, accessible job since the engine going to be opened up for valve timing adjustment.

Thanks again,

John Bjork

If the timing chain has jumped . it is definately going to have to be replaced.
So, any rails and chain tensioner should be looked at then too.
And make sure whoever does the job is aware that the tensioner is a ratchet design and has to be reset when re-installed or the new chain will break the cams right in half.
Many guys [ even Techs] do not know about that until they learn the first time.
I might add that I am almost surprised that the engine runs at all with comp that low...those engine are high comp and usually run close to 200psi.
[ Although that spec would be on the 3.2 version, so maybe on the 2.8 the comp is much lower ]

Also, The code for cam advance was b/c you had unplugged the sensor, so that diagnostics module is working nicely.


Might want to read this article by SB ..Kinda covers the ins and outs of 104 top end well..

http://www.peachparts.com/Wikka/M104HeadGasket