Fuel Pump Relay Help Needed - Mercedes-Benz Forum

 
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post #1 of 1 (permalink) Old 02-02-2010, 03:31 PM Thread Starter
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Date registered: Apr 2005
Vehicle: 2005 S55; 2003 ML350; 2002 C240; 1997 C280 Sport; 1991 300SL; 1986 190e 2.3 16V (2); 1968 W30 442
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Fuel Pump Relay Help Needed

I have posted the entire problem on the 126 forum here, and have had some responses. 1987 420SEL. I am thinking the operation of the FPR is the same on this car as other models that vintage. Mybe a non-126 tech could help. I hope.

Problem - car starts fine, idles fine, hits about 50c, seems to go into closed loop, the idle jumps up to the 2200rpm range, and after 20-30 seconds it dies. If restarted immediatly, it will almost immediately jump up into the high idle and die almost instantly. If we wait a while, and restart, the time to race/die is longer.

Jumped FPR. Car runs fine.

Tried a known good FPR in place of existing one, issue is the same.

I have the schematics for this car; FPR is shown on page 106, 108, 108/1, and 110. Many things are feeding or are fed by, or just passin' through the FPR.

Does anybody know, or can send a document, on how to troubleshoot the various items connecting to the FPR socket that could cause the above problem? I am thinking both FPRs are ok, but something connecting to it is somehow disconnecting it.

Or am I completely off and need to buy a new FPR? I still don't understand why, if the FPR is bad, it races like it does when in closed loop.

What if I left the FPR in, let it get to 50c, and when it races, pull the plug on the "thermoswitch" to trick the car into running cold? If it settled down in cold mode, would that indicate anything?

Thanks in advance for your time. This is a tough one for me. Besides, it's my son's car and he's driving the 202 now. Need to get him back into his car.

Thanks!
Fred
2005 S55
2003 ML350
2002 C240
1997 C280 Sport
1991 300SL
1986 190e 2.3 16V (2)
1968 W30 442
1988 46' Cougar US1 with Triple blown 572s
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