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Discussion Starter #1 (Edited)
Parts I've changed:
-idle control valve, tested and works fine
-tested the coolant temp sensor, is within spec
-changed airflow sensor potentiometer with new one
-replaced o2 sensor
-checked all vacuum hoses, fine.
-adjusted the EHA clockwise about 1/4 turn and even swapped with another, yet no difference in warm start.
-replaced OVP relay
-fuel filter
-spark plugs
-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?

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.

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.
 

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Discussion Starter #3
Cap and rotor
if its the cap and rotor, wouldn't that cause the hard start problem all the time? And like I said, even if the engine is actually hot, and I trick the computer to think the engine is cold, it starts up fine, which makes me think its not mechanical but electrical (ie: the computer probably sends the engine more fuel when thinking it is cold, so it starts eaiser)

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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2011 GLK,2007 S550,2003 S55,2008 CLK,2009 C300,1996 E300,2005 E320,2002 E3
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I had one of my w140's that drove me nuts. The car would start perfect cold, but after it got warm it wouldn't restart, and ran horribly when warm. I tried everything like fuel filter, fuel pressure regulator etc... The distributor caps were bad. My 260e ran very well over 400k miles, but did need to be tuned up to maintain that nice running quality.
 

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Discussion Starter #5
I had one of my w140's that drove me nuts. The car would start perfect cold, but after it got warm it wouldn't restart, and ran horribly when warm. I tried everything like fuel filter, fuel pressure regulator etc... The distributor caps were bad. My 260e ran very well over 400k miles, but did need to be tuned up to maintain that nice running quality.
yea a problem like this surely will drive anyone crazy. It runs fine while driving, just in idle sometimes its fine, sometimes too low, and the warm start trouble.
 
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