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strange stumbling/backfiring problem

This is not exactly a follow-up to the thread begun on Nov. 3 by Mark Stonecipher, but my version of maybe the same thing, which is not yet resolved.

I have a 1986 240 DL wagon (Canadian model) with 382,000 km on it, and it is the fuel-injected model, with the air mass flow meter. As I read the Haynes manual, this is the 230F engine with the LH Jetronic

2.2 fuel injection system. It has had a recurrent problem with stumbling and backfiring. Now that it's colder, does it nearly every day. The symptoms sound similar to what Mark described, but with a twist. Every morning the car starts fine, and will accelerate fine if you apply the gas slowly, but only up to a certain point. Then it bogs down and if you press harder on the gas, it backfires. The twist is that if you drive it this way until it warms up and then shut it off for 10 or 15 seconds and restart it, it runs fine! Absolutely fine! Lots of power, good passing gear, no hesitation! If you then park it and let it cool down, it misbehaves again when you start it up.

I have had it worked on twice for the bogging down and backfiring, to the accumulated tune of nearly $1000 now, and it is not fixed. Both fuel pumps and the fuel pressure regulator and the engine thermostat have been replaced, the throttle body has been serviced, and both a new ignition computer and a new air mass flow meter have been installed temporarily (neither fixed the problem).

The last thing the last mechanic (a Volvo dealership) wanted to do was try a fuel computer (which apparently costs much more than the car is worth), and I demurred.

Anybody got a clue? The turning it off and back on fix is a bit tantalizing - it seems to me as if some running state is being set when you start it cold, which doesn't work right, and only if you shut it off and back on once warm does it get set correctly. I have to point out that merely warming up does NOT solve the problem - you actually have to shut the engine off, but really only for 10 or 15 seconds. I saw from the Stonecipher thread that someone suggested the fuel pump relay - does this sound like that?

Also - are the fuel computer and ignition computer different beasts?

And where is the fuel pump relay and how does one test it?

Many thanks for any hints.

Edge

Reply to
Mark Edgley
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My thought on this is there is something loose in the exhaust system that blocks the flow, and can fall out of the way when it's warm and there's no exhaust pressure on it.

Reply to
Mike F

Has anyone tested or replaced the coolant temperature sensor for the injection? Also when it's cold does unplugging the air mass meter make any difference? I suppose it could have a cracked solder joint in it.

Reply to
James Sweet

I have nearly the same symptoms, except I don't have to turn it off for

10 or 15 seconds. Otherwise it sounds identical.

In my case, at the very instant the coolant temp gauge shows full temp the engine gets a surge of power (well, comparatively at least :-) and runs normally. And not at a hair under full temp. If you shut the engine off for 3 minutes to run in the store the symptoms return, but only for a short time since full temp is resumed very quickly.

I have suspected and others have suggested the AMM. However, that's what everyone says when the engine runs poorly and there are no better ideas...

So is there a way to open the AMM to check for and repair cracked solder joints (without destroying the unit obviously) ?

Also, is the temp sensor that runs the injection the same one that runs the gauge on the dash ? If not, which is which ? I think I know which one runs the gauge, under the intake manifold near the center of the engine, I think it has a yellow wire.

Reply to
David

You're right regarding the gauge sender. Assuming you have a B230F, the sensor for the injection is under the intake runner for the 4th cylinder. It has the same electrical connetor as the injectors, the body is either blue or black depending on year.

Reply to
Mike F

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