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740GL engine problems

hello everyone

I have a 16 y.o. Volvo 740 GL (no lambda sensor) that had already made

180K miles (290K Km). it is a very sturdy and reliable car, not rusty. engine is B200E, Constant Injection System.

the only problem I am having with it is that it is misfiring badly on idle. driving range is fine, no power loss, no twitching on acceleration. idle is really bad though, I suspect the engine at times is running on two cylinders. when heating up after cold start (additional injector in action), seems to run much more stable, but once warmed up, starts to misfire. afaics, exhausts smell petrol.

I checked the ignition system and replaced most of it - it is not to blame for sure. recently I replaced the cylinder head gasket and other gaskets that go with this procedure. compression is fine, even a bit higher than the manual says.

I suspect either injectors, or fuel distributor or insufficient vacuum in the inlet manifold. I tried taking injectors out to check fuel atomisation, the engine won't start. perhaps I should have plugged the injector hole to keep vacuum ?

any ideas ? is it common for these injectors to get clogged ? I asked local injector cleaning specialists and they told me that they don't clean this type of injectors. maybe I can clean them myself with a little acetone ?

thanks very much in advance guys. I really like this car and don't want to drive it to the scrapyard yet because of such a stupid problem.

/max

Reply to
maxim naumov
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My first guess would be vacuum leaks. Start with the boot from fuel distributor to throttle body, then everything connected to the intake manifold. This type of fuel injection bakes the seals that go between the injector holders and the head, that's a common problem.

Reply to
Mike F

Hi Mike, It is very possible that it could be your idle air motor. It is cylendrical about 1 1/2 inches, and about 5 inches long. it has an electrical connection at one end and 2 connections for hoses (about

1/2" inside diameter), one in and one out. The "in" hose attatches to the air intake plenum, post air flow sensor/pre throttle body. The "out" hose attaches to the intake manifold, post throttle body. Use a hose pincher, or a pliers and a couple of pieces of wood to block air flow through this loop(preferably, post idle air motor.) if idle changes, especially if it drops/stalls, this is not the problem, or the Idle air bypass valve should be adjusted. This valve is the large thumb screw located below the throttle body. If adjusting this valve with the hose clamped seems to help, then it is just out of adjustment. It should be adjusted until the idle is 500 rpm with the hose clamped. If no change occurs, you may want to disassemble the idle air motor mechanism and clean it with BRAKE PAD CLEANER, nothing that leaves a petroleum residue. IE engine brite etc. that stuff will mess it up. For more detailed instructions about this part, jot a line back, and I'll tell ya' how to clean it step by step.

regards, and best of luck,

-Zeke-

Reply to
Zeke

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