420SEL Stalling. Help with the diagnosis! - PeachParts Mercedes-Benz Forum

Panzermann · #1 09-21-2007, 11:48 AM

So, my 1991 420SEL with 202,000 on it. Problem is that occasionally, seemingly at low speed, the engine will shuts off. It happened this AM. Just stops.

Recent stuff that's been done
1) EZL Ignition control module failed about 3,000 mi ago (the engine just stopped while car being driven), replaced with used one.
2) New rotor, distributor cap, spark plug wires 10K ago.
3) New spark plugs, 1,000 mi ago
4) New Fuel distributor 500 mi ago. Engine was running rough at idle. Number 1 and 3 cylinders were not firing. Back to baseline after replacement.
5) Fuel injector seals and air feed tubes replaced.
6) Fuel injectors tested and good (after 200K!)
7) Fuel filter replaced

Machanic told me that idle speed not being as well regulated as it should be, and I sometimes observe it running a little high (900-1100 on the dash tach). suggested this could be a problem with the idel control module or idel control valve (which has a little electric motor in it and would surprise me to still be running normally).

Thoughts????

#2 09-21-2007, 12:13 PM

Check your ovp relay, Steve Brotherton has written an article about this. I can't find it right now, but it's around here somewhere.

Oracle12345 · #3 09-21-2007, 02:25 PM

Yeah I can help send me your vin and email addy so I can send you some documents.

raymr · #4 09-21-2007, 02:54 PM

Check that the idle control module is plugged in tight. A loose connector will cause fluctuations.

Clean the idle control valve by removing it and spraying the inside thoroughly with carb cleaner.

Panzermann · #5 09-25-2007, 04:16 PM

well, I changed the idle control valve for a nice fresh juicy one and made sure the idle control relay was in place. Seems to be idling at the correct speed, based onthe dash tach. Will need to drive it around a bit to see if it stalls at low speed. I still don't understand how the OVP relay would lead to a stall at low speed.

zcc · #6 09-25-2007, 06:10 PM

Check the following:
OVP
Fuel relay (most likely)
Ignition coil

raymr · #7 09-25-2007, 06:46 PM

The fuel relay can also cause some hard starting, ie repeated twists of the key before the engine fires. I also had the stalling problem but it seems to have gone away since I replaced the fuel relay.

saumil · #8 09-25-2007, 08:44 PM

The power for the idle control valve comes via the OVP relay. A bad contact of the OVP relay in its socket can cause intermittent idle failure. Remove OVP relay, clean it properly, check that the female contacts in the socket have not widened excessively, push the OVP relay back in properly.

raymr · #9 09-26-2007, 10:00 AM

The ICV thing has me a little confused. When you remove power from the ICV, the idle speed goes up to around 1500. So losing power to the ICV should never cause a stall, right? You would just have an abnormally high idle speed.

david s poole · #10 09-26-2007, 10:19 AM

crankshaft position sensor,at the bell housing,single shielded wire running to the ignition module as a single pin plug in.classic symptoms,seen it 10 times this year already.

zcc · #11 09-26-2007, 11:05 AM

Panzermann! Did you get your problem fixed?

Panzermann · #12 10-01-2007, 06:23 PM

Quote:

Originally Posted by david s poole

crankshaft position sensor,at the bell housing,single shielded wire running to the ignition module as a single pin plug in.classic symptoms,seen it 10 times this year already.

So, I thought everything was wonderful, my payback for a life well led. Having changed my idle control valve, it had not happened in about a weeks. But this PM, it's back, while waiting at a stoplight, having just started the car after leaving it for 45 minutes in a parking lot. Car stalled in gear 3 times in a row at the same light. The rest of the drive was uneventful, although the idle speed was about 500.

It is interesting that the crankshaft position sensor is mentioned, as I recently had to change a failed ignition control module for a new (used) one. I will check the plug on the ICM to make sure the sensor is plugged in well.

I will look now at the OVP as the next culprit.

Will keep y'all posted as to outcome.

CamelotShadow · #13 10-01-2007, 10:23 PM

Quote:

Originally Posted by saumil

The power for the idle control valve comes via the OVP relay. A bad contact of the OVP relay in its socket can cause intermittent idle failure. Remove OVP relay, clean it properly, check that the female contacts in the socket have not widened excessively, push the OVP relay back in properly.

I changed my OVR today
didn't read this first

The contacts to accept the ovr are recessed
How would one know if they were too wide?

I did notice a few relays rock in there sockets
The old ovr had stable prongs so it must be the base that rocked.

If the relay rocks when you wiggle it from above should I remove it and try to crimp the connection socket tighter that is if I could get to it?

Did see one prong on old OVR was darker
could that have been a sign of a problem?

I didn't check the 10A blade fuse yet in the old one...
but I just shook the ovr & sometimes something inside it rattles & is loose?????

Maybe it was broken?

Should anything mmove inside of it????

Thanks

zcc · #14 10-02-2007, 10:52 AM

Quote:

Originally Posted by Panzermann

It is interesting that the crankshaft position sensor is mentioned, as I recently had to change a failed ignition control module for a new (used) one.

Of course it must be used, who will pay more than 3k$ for a new module???

Anyway did you check the FUEL PUMP RELAY??? It's a common failure for your car's symptom.

BTW, After searching and experience, a malfunction coil would damage the ignition control module.

Panzermann · #15 11-14-2007, 07:33 PM

So, here is how I proceeded:
1) Changed Idle control relay (having already changed the valve). Went OK for a while, then...stall
2) Had an extra used EZL ignition control module laying around. Had changed to a new used one. Hypothesized that it could be the used EZL that was put in to replace the one that burned out. Placed the spare used EZL in. Drove around. Seemed to be doing well over about 250 miles...stall (in a bad place too, as I was making a left turn in a busy intersection)
3) Replaced...yes, I know, you told me so...the fuel pump relay. Drove so far about 150 miles so far. No stall yet.
4) Had ordered a new OVP relay. figured what the hell, put that one in too.

So, if I stall again, then I guess I look at my ignition coil. Put a new one in about 7K ago. Old one had not failed, but figured it was getting up there at 200K. Will keep posted.

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