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1997 S420 stalls when hot

3K views 4 replies 4 participants last post by  paxpeter 
#1 ·
My 1997 S420, 70k miles, stalls when hot. Also will drop RPM on highway, but usually picks up and keeps running. Off highway will drop RPM and just die. Feathering the throttle helps some, but not always. Cruise control will catch falling RPM with a large jolt (seemingly not a good situation for transmission etc.). Recently replaced fuel pump relay for similar problem and intermittent no-start condition, worked for two weeks. New plugs and fuel filter at 60K. No engine codes at all.

The previous problem was motor would sometimes no-start, but frequently stall when warm (55-60C) such as after sitting for an hour, but would perform okay when fully hot. Now the stalling is when hot. Ran fuel injector cleaner/MB Carbon remover (no effect).

So far two dealers stumped. I suspect fuel pressure regulator.
 
#4 ·
Fuel pressure

Thanks for the info.

They're telling me I have fuel pressure, and it's not the regulator (if the diaphragm is kaput, I would supposed the pressure would be too high?) They say the pump is working, but do they get intermittent? (Obviously it works most of the time). I'm wondering about the Oxygen sensor, but my impression that also dumps more fuel, not less if defective.

So, are there other sensors in the fuel line that affect flow? An electronic control that doesn't throw engine codes?
 
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