Hi my 85 240dl wagon starts well and seems to run well so long as you dont have your foot down hard on the gas pedal. When the pedal is depressed hard as to pass or for more power needed on a hill the car merrily downshifts then no power...it sounds like it should be picking up speed but does not. As you let up and it shifts back into a higher gear you feel that it has power again? I dont think its an ECU problem, this has been replaced. I also dont think its fuel pump or filter related either. Filter is brand new and the pumps have both been replaced in recent years. I recently replaced the AMM with a used part but this seemed ok for quite a while before this latest power issue.

I would have thought plugged car or plugged fuel filter too.

Couple of possibilities, maybe some things to rule out-
if you can rig up a fuel pressure tester, with a long hose on it, you would be able to monitor pressure while driving. Stick it right out of the back of the hood, at the cowl and observe pressure from the driver's seat while the problem occurs.

Could be a weak fuel pump I guess or a problem with the in-tank pickup, either a split line or a failed in-tank pump causing a little starvation.

Also go over the ignition basics: just worked on a VW Golf with some similar problems and it seemed to be ignition breakdown mostly- some old wires and crappy plugs. We found 2 burnt plug wires and yet it didn't idle badly and always started. Have a look inside the spark plug end of your wires with a flashlight, see if there's any burning or damage.

Good luck with it!
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Rob Bareiss, New London CT ::: 87 244DL, 88 245DL, 90 745GL, 84 242DL project, 89 244 parts, 88 244DL to replace the 87

It sure sounds like insufficient fuel. Did the trouble start shortly after replacement of the fuel filter? I'm thinking improperly assembled filter or simply a kinked pressure pipe. If it started before that work was done, then you may have an ignition weakness (worn plugs, failing coil, arcing rotor). A partly blocked exhasut system is next on the list for high speed power loss.

Anything related to late camshaft or ignition timing would affect power at all speeds.

I replaced the fuel filter thinking it was plugged due to a situation where it would start seem to run fine for a bit then quit. Found it was the AMM cause it would run, all be it badly, with it unplugged. Relpaced AMM with an ebay part and it ran again. Worked fine for a month or so then started acting up again this past weekend. Im going to swap ECU's, I have several, and see if this makes a difference. When I was diagnosing the AMM problem I swapped the ECU and put the old coil back in (I do a lot of diagnosis through replacement...LOL)...they are still in as the car seemed to run fine with the AMM replaced. Ill put the new coil back in and the ECU and see if anything improves...thanks for the help.

Oooohhh, I just realised the model year of your car. 1980-88 used degradable insulation in the engine wiring harnesses. What you may have is failing insulation on the hall sensor, AMM or coolant temp sensor wiring. The failure may only occur when the engine mounts are torqued under acceleration and the harness flexes. Try holding the brake hard and gas it while in drive to see if you get a similar symptom. You might be lucky enough to find the bad area by moving the harness around while it's idling and listening for a change in running.

This is, unfortunately, a common problem that rears its head as any of dozens of symptoms - depending which wire is touching which other wire.

If by some chance your replacement AMM is damaged in the same way as the first, it may be that one of its wires shorting to 12v or ground and damaging it. In other words, you'll have to repair the harness or keep feeding it AMMs.

Some possibilities (pretty hard to really pin anything down based on internet descriptions)

- plugged catalytic convertor: power will seem fine at lower throttle settings, but power will fade badly as engine throughput increases due to excessive backpressure
- slipped cam belt: retarded cam timing makes the engine very weak at higher rpms
- clogged air filter: air can't get in, the motor can't make much power
- retarded timing: Engine won'tmake much power, exhaust manifold will get very hot as still-burning fuel gets dumped into it
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I'm JohnMc, and I approved this message.

Thanks for the hints...not a plugged CAT I got rid of that years ago for similar simptoms that turned out one time to be a faulty ECU then later on an AMM problem. I'll swap back in another ECU, I have several, and a coil. Ill also check the timing.

Thanks.