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

Panzermann · #1 09-21-2007, 12:48 PM

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, 01:13 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, 03:25 PM

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

raymr · #4 09-21-2007, 03:54 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, 05:16 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, 07:10 PM

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

raymr · #7 09-25-2007, 07:46 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, 09:44 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, 11:00 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, 11:19 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.

CamelotShadow · #11 10-01-2007, 11:23 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 · #12 09-26-2007, 12:05 PM

Panzermann! Did you get your problem fixed?

Chadahar · #13 11-14-2007, 10:08 PM

It may well be your ICU. They get Cold Solder Joints. I futzed with a bad/no idle and stalls. Cleaned the ICV twice with no results, replaced the OVP with no results, then bought a used ICU and VOILA! It fixed it and it has idled and not stalled for almost 2,000 miles.
I just happened to noticed that when my car did idle it was high, then would cut out or drop too low. I rapped on the ICU and it died. Thinking it may be a coincidence, I started up , it idled high, I rapped on the ICU and it cut out again. Did it two more times with the same result. Got a used ICU off Ebay and it purred. Have not resoldered the original ICU yet, but it is on the list.