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Discussion Starter #1 (Edited)
Parts I've changed:
-idle control valve, tested and works fine
-ovp relay
-tested the coolant temp sensor, is within spec
-changed airflow sensor potentiometer with new one
-fuel filter
-spark plugs
-replaced o2 sensor
-replaced valve cover gasket due to small oil leak
-checked all vacuum hoses, fine.
-adjusted the eha clockwise about 1/4 turn and even swapped with another, yet no difference in warm start.
-checked fuel pressure and fuel leak down; all within spec even hours after car was off, so no sign of any leaking fuel or bad accumulator or check valves.

car is 6-cyl 89 260e.

Starts fine when car has been sitting overnight (cold engine), starts up on first try, idle is above 1,000 until it warms up and stays smooth around 700-800.



When starting warm, fires up and cuts right off.

Tested the coolant temp sensor (for the computer) and tested fine at every temp listed in alldata temp chart.

When grounding the green/red wire for the coolant temperature switch with a 10k ohm resistor (simulating a cold engine) car starts fine on first try, even if engine is hot. This tricks it to think the engine is cold. And it starts up on first try and idle is close to 1500rpm.

Tested cold start valve and harness.


Any suggestions?



BTW, the car drives fine and has full power throughout on highway as well, just stalls sometimes when coming to a stop if I don't give it gas it stumbles and hesitates and cuts out.


Also, the engine (when hot), starts fine when tricking the ECU to think its cold (with a 10k ohm resistor), even starts fine if I disconnect the cold start valve in this case.
 

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89 300E; 00 E320
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You can rule out the O2/lambda sensor and the fuel mixture adjustment in about 10 -15 minutes. Click on the links to see tests.

That cold start throws extra fuel, maybe when the extra fuel stops the ECU is getting some conflicting info. And there are several input and output signals flowing in the ECU including: power from OVP, Idle speed air valve, EHA, Deceleration Shut off, A/C Compressor "On" , Coolant Temperature , Air Flow Sensor , Altitude Correction , O2 Sensor , RPM, vehicle speed, Check engine, Coolant temp...
Fuel Pump Relay behind battery
EHA: Electro-Hydraulic Actuator - Trims amount of Injection Fuel, Also controls Maximum engine Speed to 6200 RPM +/- 50 RPM; Top of engine, rear of fuel distributor

See the wiring diagrams for a better list.

Wiring Diagram: Electronic Engine Controls 118 118-1
 

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Discussion Starter #3
You can rule out the O2/lambda sensor and the fuel mixture adjustment in about 10 -15 minutes. Click on the links to see tests.

That cold start throws extra fuel, maybe when the extra fuel stops the ECU is getting some conflicting info. And there are several input and output signals flowing in the ECU including: power from OVP, Idle speed air valve, EHA, Deceleration Shut off, A/C Compressor "On" , Coolant Temperature , Air Flow Sensor , Altitude Correction , O2 Sensor , RPM, vehicle speed, Check engine, Coolant temp...
Fuel Pump Relay behind battery
EHA: Electro-Hydraulic Actuator - Trims amount of Injection Fuel, Also controls Maximum engine Speed to 6200 RPM +/- 50 RPM; Top of engine, rear of fuel distributor

See the wiring diagrams for a better list.

Wiring Diagram: Electronic Engine Controls 118 118-1

Yea I replaced the o2 sensor with new one and checked duty cycle of the air/fuel mixture and it was a bit lean in idle, so I adjusted it to be within spec on the tower adjustment 3mm hex screw.
 

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2008 E350 4M, 2016 Audi Allroad, 2019 Audi Q5
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The fact that your idle is above 1000 shows something is wrong. You should never see a start, cold or warm that is above 800-900. 650rpm +-50 is the correct idle speed once the car is warm and happy.

Check your idle control valve is not gummed up. Clean it out with some carb cleaner.

Car is stalling when coming to a stop...Was your OVP replacement a new or used? Stalling when coming to a stop is a dead classic OVP symptom....
 

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Discussion Starter #5
The fact that your idle is above 1000 shows something is wrong. You should never see a start, cold or warm that is above 800-900. 650rpm +-50 is the correct idle speed once the car is warm and happy.

Check your idle control valve is not gummed up. Clean it out with some carb cleaner.

Car is stalling when coming to a stop...Was your OVP replacement a new or used? Stalling when coming to a stop is a dead classic OVP symptom....
I replaced the Idle control valve with a newer one, cleaned it, and made sure it works.

Thats the thing, it doesn't always stall, sometimes the idle is higher and sometimes lower. The OVP was new aftermarket but used.
 

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OVP has signals to or from: fuel pump relay, alternator, idle speed air valve, CIS-E Control Unit (ECU) and the anti-lock braking system.
 

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Discussion Starter #7
OVP has signals to or from: fuel pump relay, alternator, idle speed air valve, CIS-E Control Unit (ECU) and the anti-lock braking system.

Right, but I've tested the OVP and replaced it, also the problem is it idles low sometimes but other times higher, when low it does have a chance of stalling when stopping.

could the OVP be working right sometimes and not others? I never get the ABS light on even in these situations
 

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Right, but I've tested the OVP and replaced it, also the problem is it idles low sometimes but other times higher, when low it does have a chance of stalling when stopping.

could the OVP be working right sometimes and not others? I never get the ABS light on even in these situations
The point I was making is that so many important components count on the OVP being good. Not sure how you can test one but i would never replace mine with anything but a brand new OVP.

I was a little confused about what "new aftermarket but used" really meant.
Sometimes these things look new and the fuse on top is not burned out, but still the circuit board inside burns out a solder joint and your screwed.
 

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Discussion Starter #9
The point I was making is that so many important components count on the OVP being good. Not sure how you can test one but i would never replace mine with anything but a brand new OVP.

I was a little confused about what "new aftermarket but used" really meant.
Sometimes these things look new and the fuse on top is not burned out, but still the circuit board inside burns out a solder joint and your screwed.
There is a test sequence on the service manual. By aftermarket: this is a KAE? I believe and not the OEM MB one, also it was used.

I'd rather test components before just replacing.
 

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Never, ever buy a used OVP. You are asking for problems with that. First thing you need to do is replace it with a new one. KAE is fine.

The ABS light generally means the fuse is toast and/or the relay is dead. It is != a functioning OVP if the ABS light is off.

Start with buying a new one and go from there. Like I said, I've experienced personally every stalling issue in the book related to the OVP, on both my cars.
 

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Discussion Starter #11
Never, ever buy a used OVP. You are asking for problems with that. First thing you need to do is replace it with a new one. KAE is fine.

The ABS light generally means the fuse is toast and/or the relay is dead. It is != a functioning OVP if the ABS light is off.

Start with buying a new one and go from there. Like I said, I've experienced personally every stalling issue in the book related to the OVP, on both my cars.

The ABS light is not on, not even when these things happen
 

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It might be your ignition coil. It used to happen to me. When ever my car got warm, it was hard to start and eventually it quit on me. I suspected the cranckshaft position sensor but turned out being my coil :)
 

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Discussion Starter #13
It might be your ignition coil. It used to happen to me. When ever my car got warm, it was hard to start and eventually it quit on me. I suspected the cranckshaft position sensor but turned out being my coil :)
I forgot to list it, but I did replace the coil as well and same problem still
 

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Discussion Starter #15
have you considered the crank position sensor? although those things rarely get damaged
Yes, I've gone through the diagnosis steps, and tested the CPS and it tested fine with ohm-meter.

Like I said the problem is weird, as I can get the warm engine to start on first try perfectly if I bypass the coolant temp sensor and trick the computer to think its -10 degree C. I do this by using a 10k ohm resistor.
 

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The ABS light is not on, not even when these things happen
again, just because the ABS light is not on, does not mean the relay is good. Replace it or you will be chasing ghosts.
 

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Discussion Starter #17
again, just because the ABS light is not on, does not mean the relay is good. Replace it or you will be chasing ghosts.
well thats the thing I have changed it with a KAE one and it seemed the idle control valve functioned better with that one in, but even with this OVP I can get it to start fine cold and when the engine is warm if I trick the ECU to think its cold.

In that sense I can't see the OVP being the problem
 

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All I am saying is that stalling when coming to a stop is probably not related to your issues and is solely OVP. I've stated my recommendation so up to you.

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when you replaced the airflow potentiometer, did you position correctly and use the voltage as your guide? It must be very specific for position.
 

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Discussion Starter #19
All I am saying is that stalling when coming to a stop is probably not related to your issues and is solely OVP. I've stated my recommendation so up to you.

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when you replaced the airflow potentiometer, did you position correctly and use the voltage as your guide? It must be very specific for position.
Yes I followed a guide which the link was provided on this forum, and adjusted it to the right voltage.
 

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I wish you would use a new OVP.

There is another component in the diagram with the coolant sensor:

N1/2 Electronic ignition control unit (EZL) Left side of engine compartment, on fender 251-1

Ignition 113
 
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