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Discussion Starter #1
w140 s600, 1993 Hi guys and I presume Girls?

I have a V12 which starts, runs, idles and takes full throttle without any problem. however when I gently depress the gas pedal, immediately, the ASR lamp comes on. the electric throttle bodies go to manual, and the engine loses its power.This is whilst stationary.

I have swapped throttle bodies, air mass meters, I have swapped the 2 ECU's across. changed air induction temp sensors. swapped O2 sensors, removed the wiring harness, inspect for damage and traced for open circuits. I have run it with the o2 sensors disconnected, it doesnt change.

My thinking being that at idle it runs slightly rich, at full power it is very rich, but is leanest at mid range, light throttle. But I could be on a wrong track here?

I think the ASR comes on because the engine is in limp home if I run it with the ASR ECU removed, the lamp stays on. but the engine behaviour is the same. All parts were swapped from a running car that has no issues.

any suggestions would be appreciated

Al. :bowdown:
 

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Outstanding Contributor Always Remembered RI
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Because you have been swapping parts for testing purposes, I would suggest you have the fault codes read first and then cleared. Road test the car and read the fault codes again, I think you will find this the easy way to go.

Even swapping parts will not take the fault codes away from the computer, so you are achieving zero. As long as there are (stored) fault codes on the computer then the ASR light will come on and loss of power will ensue.;)
 

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Discussion Starter #3
I have a launch scanner, it is great on these cars, but I should have added that I cannot get comm.s with the ECU's. the quick test, scans then freezes. the ECUs are different between cars, as this one is US spec my others are Euro spec. so I cant swap them over. Incidentally you are mistaken about swapping units, as long as the power is off when it is done, it does not instill codes. The codes are for reference and a car will run perfectly well with codes in the ECU, it is only once they have entered into the second stage of memory that they can become troublesome. I do these cars every day with some problem or another,so I am always swapping things to diagnose. but this car has thrown me right off track.

thanks for your reply

Al.
 

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Outstanding Contributor Always Remembered RI
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I have a launch scanner, it is great on these cars, but I should have added that I cannot get comm.s with the ECU's. the quick test, scans then freezes. the ECUs are different between cars, as this one is US spec my others are Euro spec. so I cant swap them over. Incidentally you are mistaken about swapping units, as long as the power is off when it is done, it does not instill codes. The codes are for reference and a car will run perfectly well with codes in the ECU, it is only once they have entered into the second stage of memory that they can become troublesome. I do these cars every day with some problem or another,so I am always swapping things to diagnose. but this car has thrown me right off track.

thanks for your reply

Al.
Hi Al, Im an MB Tech, here in sunny china (the sunny was not a pun excuse me). To give you an example, at one time I knew the EZL unit was not ok so I changed it with a part that was a from the same model and hey presto - nothing.
So I brought the test equipment and cleared the fault codes and hey presto everything normal.

Then I put the old EZL back on and same problem re-occured. If you try this type of diagnostics without a computer then, you understand:thumbsup:
 

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On the gas pedal is a small switch that is tied in to the electronics. I believe it monitors idle/off-idle position of the pedal and compares it with the position of the throttle bodies. The wires from the switch run down the back of the pedal and then under the carpet to a plug on the side of the transmission tunnel. The wires flex continually as you manipulate the pedal and are a wear point.
 

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Outstanding Contributor Always Remembered RI
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so many things can cause this, its better to start with a fault code read out and go from there.
 
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