Misfire on 1992 440 GLi 1.8 (B18U) engine

Please help. My 92 1.8i 440 is suffering from a persistant misfire at 2000-2500 rpm, under gentle acceleration, or holding steady revs. It disappears when revving or accelerating hard. I have changed plugs, leads, distributor cap and coil, and all the rubber hoses at the back of the injector unit have been renewed. The injection unit has been taken off the manifold, and the gasket here has been renewed. Despite the misfire, the car has just flown through the MOT emissions test with no problems at all. The engine has covered 129000 miles. Any suggestions, short of putting car into main Volvo agent and/or nearest canal!

[Daniel M]

Hi Mike...
Im not going to lie-im no mechanical genius and i don`t have the answer, but my friend had a similar problem. He has a (dare i say it!)N plate Ford (boo!) Fiesta Si, and had the same problem as you, but he also lost a bit of power too. After some careful consideration and fiddling, cut fingers etc etc, he took it to a garage and they told him he needed a new engine management system. He got one. Problem solved. May not be the same problem/outcome as yours, but def. something you may have to consider-and he wasn`t charged much either. Sorry its not like mega helpful advice-just thought i`d share the experience...! Hope it all goes well.

Dan.

Hi Dan
Hadn't thought of that one. Have located new ECU from scrappers for £20, returnable if problem not solved, so will try that out on next day off (sometime next week). Just for interest's sake, also priced ECU at Volvo main agent. Quote -- £614 + vat. for the ECU, and 2 hours labour at £61 + vat for fitting. I only paid £600 for the car! And they were a bit put out when I told them no!
Anyway, will give the ECU a go -- there's not a lot else it can be. Thanks for your time, will post results when the job's been done. thanks again
Mike

Just tried a different ECU from the scrappers. Seems to have cured the problem. Despite Volvo wanting over £600 + 2 hours labour to fit, it cost me £20 cash, plus about 15 minutes to do the job. Most time consuming bit was replacing the trim after I had finished.
Anyway, thanks Dan for the thought. Much appreciated.
Mike.

Found out what the REAL problem was. When I got the car, the factory sunroof panel rubber seal was corroded, and the roof was leaking. At the time, I just spent £15 from a salvage to replace the sunroof panel, and forgot the problem ever existed. HOWEVER --- Water must have been running down into the front pillars -- on taking the old ECU to bits, there was evidence of water damage to the circuit board inside. Worth noting if you have a persistant problem that nothing else cures. Who would have thought that a leaking sunroof could cause rough running????