My NA 1991 240 with LH 3.1.

Started stumbling a bit over bumps. When driving, or when coasting at idle, the engine just bogs down when I hit bumps. In the past this was a Crank sensor, but I just checked it and the cable is good, not shorted. I pulled a 232, lean fuel, code off the OBD, but I am thinking this is a different problem. Fuel/RPM drops regardless of where the pedal is. If running it won't drop low enough to die, but if coasting, moving but at engine idle, it will flash all the lights and nearly die.

So about 3-5 months ago I was blowing fuel pump fuses all the time. I finally realized I was running 8a not 16, so I fixed that and have not blown one since. But the 16 does get hot. Around the same time my MPG went from 24ish to 20ish, no change on anything else. Now at best, high way miles, I can only get 21-22. So I'm thinking maybe a dying fuel pump or a short in the wire where the pump line comes into the cabin, under the back seat. TB needs a good cleaning too.
Any other thoughts?

Hi,

I had the same problem with a 91 245 (LH3.1) I've been working on--stumble going over bumps, or when slamming either front door. After putting in a new pump relay I was still getting the same problem. Replacing all of the fuses didn't help either.

When I started tracing the wiring to/from the fuel pump relay and I found an intermittent open in the red wire leading to the pump relay. On our car there is a splice in the wire about 14" up from the relay where 4 or 5 smaller wires joint the bigger wire going to the relay.

I found that if I flexed the wires around the splice while the car was idling, it would stumble. I took the original splice apart, cleaned everything and used a new connector to put all of the wires back together. So far it appears to have fixed the problem.

BTW remember to disconnect the battery before starting the work, as on our car the red wire(s) to the pump relay are always "HOT" and are not protected by a fuse.

Hope this helps!

Best,

Steve A-