M103 300E runs like crap. And I'm out of ideas! - PeachParts Mercedes-Benz Forum

tbomachines · #1 03-08-2012, 03:12 PM

My 300E developed a problem early last summer where sometimes it would misfire at lower RPMs and stall out. It idles fine, but the moment you put the engine under load (i.e. going from park to drive), the RPMs drop, it begins to misfire, and eventually stalls if you don't put your foot down. Then, after starting it back up again it will misfire on the startup and immediately stop the rotation of the engine (like a preignition or something, not quite sure). I think I've tackled all the usual culprits. So far:

- replaced ovp with new unit
- replaced cap and rotor, just inspected them again today to see if there was anything wacky there...cap had some usual corrosion on contact points but nothing out of the ordinary
- replaced wires, checked again for arcing today and nothing
- replaced EHA (was leaking wildly, had to be done anyways)
- checked engine temp sensor, appears to be fine
- checked the flywheel crank sensor (which goes to EZL), came out to 880 ohms, which is well within spec
- replaced O2 sensor
- fuel pump is always on during this so that rules out FPR
- replaced spark plugs (proper style - ordered from here)
- checked vacuum connections, seems fine

Today before I started it (it had been a week or so), I replaced the EHA and in doing so I checked the MAF plate. It did not spring back to the top but stayed wherever I pressed it to (and I had to pull it back to the top). However after starting the engine and having it run like crap, I checked it again and it sprang back up to the top--so I don't think that is the culprit.

Also this is completely intermittent. After it ran like crap today, I shut it off, let it cool down a bit while I checked the cap, rotor, CPS, and wires. Started it back up again with its temp roughly 40*C and continued to run fine as if nothing ever happened. Shut it down and started a few times and it was still good. I hadn't replaced anything in between these two times I had it running, just disconnected/connected the aforementioned things.

Emissions test for this bad boy is er....tomorrow.

I need to get it so I know it will not stall out on me on the way over to the testing facility or worse run like crap on the wires.

Any thoughts? I checked the duty cycle not too long ago and it looked fine...I am going to check it again now but I don't suspect anything to be wrong since it was ok before.

lorainfurniture · #2 03-08-2012, 03:29 PM

Do you feel low on power? When was the last time you replaced the fuel filter?

I had (still have) a power issue, along with poor mpg. dropping a bottle of redline fuel additive helped a lot.

Intermittent problems suck.. They get expensive too.

My last guess would be to change injectors.

tbomachines · #3 03-08-2012, 05:07 PM

Quote:

Originally Posted by lorainfurniture

Do you feel low on power? When was the last time you replaced the fuel filter?

I had (still have) a power issue, along with poor mpg. dropping a bottle of redline fuel additive helped a lot.

Intermittent problems suck.. They get expensive too.

My last guess would be to change injectors.

I replaced the fuel filter about a year and a half ago, the old one appeared to be the original. When its working, it runs fine and gets good mpg, its got to be something electrical somewhere in the system since its intermittent but I feel like I've checked all the boxes. BTW that EHA valve worked out great - got it on this afternoon and it doesn't leak a drop, turns out the smaller O rings were right. Thanks!!

Edit: also, duty cycle today (while running ok) was fluctuating between 48-51% which is very good. Hmmm

lorainfurniture · #4 03-08-2012, 05:31 PM

I would check vacuum, however I doubt it is an issue.

What is the idle difference normal vs bad, park and in drive?

johnflight1 · #5 03-08-2012, 05:40 PM

sounds like a vacum leak check the hoses that go to the Idle control valve! Mine were shot! as soon as I put it in gear it would want to die,even worse the warmer the eng was. replaced the hoses and all is well

cth350 · #6 03-08-2012, 07:48 PM

The two hoses to the idle valve get loose, crack, etc. I have a new pair on the counter that I will install this weekend hopefully. Another place to find leaks are the injector seals and the rubber boot that makes up the underside of the air flow metering chamber.

-CTH

tbomachines · #7 03-08-2012, 11:31 PM

Thanks guys - I guess I will double check the vacuum lines again, the intermittent state of it is what really throws me for a loop but it can't hurt to eliminate one more variable.

nulu · #8 03-08-2012, 11:39 PM

Possible ignition coil going bad when hot, removed coil wire and check spark while sombody cranks , hold about a3/8 inch gap , spark should be blue, if its orange = weak, should jump a 1/4 gap with no problem, and be cafefull dont shock yourself , use insulated plyers or wooden clothing clip to hold wire

tbomachines · #9 03-09-2012, 02:33 PM

Just passed emissions, and it was well within the boundaries in every field. Not surprising since its AFR/duty cycle was pretty much perfect when it was running okay. Thankfully it didn't stall out on the rollers!

brentsmith · #10 03-09-2012, 05:32 PM

I recently had similar problems that I had a hard time finding. It turned out to be a bad idle control valve and badly cracked hoses connected to it. The idle control valve has a shutter that moves to control air. It would stick at one position. I bought a used one on eBay and replaced the hoses. It runs perfectly now.

Brent Smith
Atlanta, GA
1986 300E 274,000 miles

pawoSD · #11 03-09-2012, 06:25 PM

Idle control valve, hoses, and possibly the fuel pressure regulator could be bad.

anziani · #12 03-12-2012, 12:23 PM

Had a similar problem with an '87 300E. Turned out it was the coil. I'd try as replacement to make sure.
Anziani

tbomachines · #13 07-09-2012, 05:44 PM

Alright, just an update on my situation here. It has gotten worse, unfortunately

the car now barely runs and can't really be taken anywhere. There's a misfire at idle and low RPMs when you give it the beans, but once the revs go up it works fine (as stated before). Since it is fairly consistent now I was able to get the duty cycle off of the car WHILE it was misfiring and all associated weirdness. Interestingly, the DC never fluctuated beyond 45-55% while this was happening. When it'd skip, it would go up to about 55% quickly and then come down. Makes sense since there is then unburned fuel going through the system. With this in mind, it is almost certainly electrical. Since I've already gone over the cap, rotor, and wires today, that leaves me with bad plugs, bad coil, or bad ignition control module. I have to dig out the EZL troubleshooting guide (I know I have it somewhere) and rule that out. Not sure how to test the coil other than resistance for the different wire winds (any thoughts?).

Also verified:
Wires are low resistance (1k ohms, printed on the terminals and verified as 1.1k though multimeter). Again I have to verify with the manual as to the correct overall resistance spec but from searches on here, having 1kohm wires should necessitate resistor spark plugs, rather than the resistors being in the wire. I don't want this to turn into a resistor v. non resistor post but I am just looking for the TOTAL spec from cap-end-terminal to the tip of the spark plug. I am going to test this out before spending any more money (I am also planning on pulling each individual plug to make sure they're not fouled...the 2 I pulled today looked almost new, which is great since I replaced them 15k ago).

tbomachines · #14 07-09-2012, 05:45 PM

Oh, also should note that I have a homemade LED OBD flasher but I'm not sure it's hooked up right. I stuck it on pins 1 and 3 of the 16-hole diagnostic port per basic troubleshooting and got...a solid light with no flashes. hmm....

tbomachines · #15 07-09-2012, 05:52 PM

Quote:

Originally Posted by lorainfurniture

I would check vacuum, however I doubt it is an issue.

What is the idle difference normal vs bad, park and in drive?

In park, it now misfires when idling (didn't do that at the time of my first post). Giving it some gas makes it misfire but the RPMs still rise up, about 2500-3000rpm there's no more misfire and its as happy as could be. Putting it in gear causes it to misfire and stall.