'91 965 still wont drive after 1m of warm-up

MarkRobinson · 10-19-2010, 11:30 AM

Ok, so my '91 245k mile 965 is still reluctant to improve. So far I've replaced/ruled out the following:
plugs, wires, cap, rotor, distributor
Crank trigger,
Turbo Control Unit
O2 sensor (in case it had an internal short).

What happens is that the car starts up perfectly normal, idles perfect for almost exactly one minute: then something is switched on/switched off and the idles goes to about 3-400 & spark (apparently) is cut: car is very reluctant to rev or even hold a lower RPM & spits flames if you rev it up at all & let up.

What led up to this: the rough idle, or rough driving (dropped spark here/there or very weak spark) in small doses, then got worse, & worse until now, the car is not driveable. Starts & warms up nice, but after 1m it won't drive: has this excessively rich issue.

I plan to swap in an EZ69 tomorrow night as the first one I tried was not working correctly & my car wouldn't start at all. Anyone have any other thoughts??

Thanks, Mark.

Turbohead · 10-19-2010, 07:20 PM

Mark
WUR and or AAV
Elliot

RarlyL8 · RarlyL8's Garage

I would also diagnose the fuel system. Stick some gages on it and see what your cold/warm pressures are.
For example, is the WUR is not getting power the car will run great cold until the AAV stops diverting the air flow from around the throttle plate and an overly rich condition is exposed. The fuel pressure in this scenario is not increasing as it should. You then check the voltage going to the WUR. Other things can cause this but that is a start.

DA VINCI · 10-20-2010, 11:49 AM

I had a similar problem on my '92 965. It started well but the mixture was getting richer and richer (slowly) as the seconds pass by to finally get a died engine. I was able to see this clearly with my Zeitronix lambda meter.

The problem was that I had the mixture screw (top of the distributor- 7mm allen) set too, too, rich. When I leaned it the problem dissapeared.

Hope this helps.

MarkRobinson · 10-20-2010, 01:15 PM

I haven't tuned my mixture in 10 years...been running perfect until now.

Keep in mind this issue started showing itself intermittently while driving, then would clear up, then would return, then would clear up. Now it happens 1m after started & never goes away; so it progressed to this point :/

Mark

RarlyL8 · RarlyL8's Garage

Is this car 425WHP?
If so what fuel system mods are present?
Have you checked the fuel pressure cold and warm?

IMONBOOST · IMONBOOST's Garage

I would say WUR or ECU issues. Have you considered disconnecting the lambda to keep the car in open loop? Remember it will go closed loop like after a minute or so.

DA VINCI · 10-21-2010, 01:09 PM

The days before my WUR died, the car did strange things with the mixture. The tendendy was to have over-rich conditions but not always. Check (if you didnt) if your WUR flows fuel through the air filter box (it shouldnt) or check the pipe that links the wur with the air box.

175mph951 · 10-21-2010, 08:01 PM

+1 wur check the pressures

MarkRobinson · 10-26-2010, 01:34 PM

My issue presents itself exactly 60 seconds after startup: I've timed it twice. If the WUR is not getting power, then that's only 1/2 the battle: why is it not getting power?

I'll check "power" tonight to the WUR if I can figure out how to get a test light on the wires with the IC in place. :/

MarkRobinson · 10-26-2010, 01:35 PM

Ps, I've tried 2 other EZ69's from another '91 965; my car won't start with either of them in place: odd I feel...same PN's.

pjv911 · pjv911's Garage

Sounds to me like your ignition coil is shorted, overheating and then going open circuit.
I would ohm test the coil before and after. If you need a coil take note that most 90's Mercedes benz cars use the exact coil.
Another place to check is your rev limiter which is in a module under the seat. If it burns out you will lose the ground to your ez69.
To easily check this just wait till the car wont run, locate the green power relay in the engine room and see if it engages when the key is turned to run. Also consider the relay itself could be bad.

Kurt Williams

wjfk32 · 05:54 AM

Sounds like your car is starving for fuel.....Once you step on the gas it gets worse. I had a similiar situation, the fuel head was STICKING/GUMMED/CLOGGED. I went nuts also when my car wasn't right. Chked plugs/connections,electrical,oil,hoses,timing,etc..etc.. etc....nothing...Even my wrench was baffled at first.

The fuel head had to come off.

POOR MANS Solution-Marvel Mystery Oil in the gas/mix..Extra dosage..will produce white smoke out of the exhaust...Thats when you know its working. It clears up within minutes.

I use it every fill-up--low dosage...Never had a problem since. Knock on wood.

Walt

MarkRobinson · 10-28-2010, 07:34 AM

Quote:

Originally Posted by pjv911

Sounds to me like your ignition coil is shorted, overheating and then going open circuit.
I would ohm test the coil before and after. If you need a coil take note that most 90's Mercedes benz cars use the exact coil.
Another place to check is your rev limiter which is in a module under the seat. If it burns out you will lose the ground to your ez69.
To easily check this just wait till the car wont run, locate the green power relay in the engine room and see if it engages when the key is turned to run. Also consider the relay itself could be bad.

Kurt Williams

Hi Kurt, I've tried another coil, does the same thing: starts up perfectly for exactly 60 seconds & then barely runs.

I have the two other modules adjacent to the TCU but they're for a '94 3.6 so I elected not to try them. I have tried an additional ground to the aluminum chassis the EZ69 mounts to: as a friend had luck with this, but have not tried what you've said, though I've also switched around all the similar relays in hopes of finding the culprit. I'll check the green relay tonight though.

Mark

MarkRobinson · 10-28-2010, 07:38 AM

Quote:

Originally Posted by wjfk32

Sounds like your car is starving for fuel.....Once you step on the gas it gets worse. I had a similiar situation, the fuel head was STICKING/GUMMED/CLOGGED. I went nuts also when my car wasn't right. Chked plugs/connections,electrical,oil,hoses,timing,etc..etc.. etc....nothing...Even my wrench was baffled at first.

The fuel head had to come off.

POOR MANS Solution-Marvel Mystery Oil in the gas/mix..Extra dosage..will produce white smoke out of the exhaust...Thats when you know its working. It clears up within minutes.

I use it every fill-up--low dosage...Never had a problem since. Knock on wood.

Walt

Thanks Walt. This car is my wife's daily driver. Interesting spark of memory from reading your post: THis issue started very intermittently, as we noticed it was common when the fuel level was very low. I Even pulled the sender & looked to ensure the screen was not full of crap: very clean! I replaced the fuel filter too.

Being that this issue happens exactly 60 seconds after the car starts makes me think Elliot has it nailed down with the power to the WUR 60 seconds after startup: I'll work on it tonight.

Mark

wjfk32 · 10-28-2010, 09:59 AM

Try chking your GROUND WIRE under the RIGHT SIDE BACK WHEEL..Should be attached to the body of the car. Between the transmission & in front of the right back wheel.
Also double chk your wiring plug diagram.

Walt

MarkRobinson · 10-28-2010, 12:43 PM

I'll check that strap: it's been a while since I have...I remember it when doing my clutch.

"wiring plug diagram"???

Mark

wjfk32 · 12:52 PM

Plug connections/numbered correctly to the Distributor cap...

Double chk.

Walt

MarkRobinson · 10-28-2010, 12:58 PM

Oh, no that's fine. LIke I said this issue started in a very subtle fashion: acting like a fuel issue (running rough/low idle, rich) when fuel was low in tank.

Then got worse, worse, where even with full tank would exhibit symptoms every now & then & then getting more & more problematic. Replaced old cap & rotor< discovered disty was failing (bad bearings, had axial play & hard to spin from bad bearings). Replaced it, cap & rotor, no change in behavior.

swapped relays, fuses, tried a fellow PP'er's coil, crank trigger, EZ69 (two of them, but my car wouldn't crank with either in place).

pjv911 · pjv911's Garage

You may also be losing the rear fuel pump. If the rear pump stops the line flow becomes very restricted and the car wont have enough fuel to idle.
You should have a relay for each pump. You could pull the pump relay for the rear pump (when the car is running correctly) and see if it mimics the failure. If it does then you can follow up with pump diagnosis.
The car will run somewhat fine on the rear pump only so be sure to pick the correct relay for proper results. Im assuming you know where the pumps are located?