Misfiring

[vince944red]

Misfiring Symptoms Erratic misfire recently worsened to also be lumpy at tickover. But it comes and goes and sometimes not there. Sometimes acts as a sort of rev limit under hard acceleration. Investigated: New fuel filter New air filter New vacuum lines to all except heater controls Plugs cleaned and ok New rotor and distributor cap HT leads part but not all replaced Timing belts replace 1500 miles ago MAF dismantled and sweep arm modified to pick up clean tracks ( 2000 miles ago) I do have an exhaust problem I need to fix - the centre box is disintegrating internally I've not tested the fuel pressure I have a refurb kit fo the injectors but not yet fitted them Is it the head gasket? ( I had overheating problems last year) engine supposed to have 80k miles on it Not losing any water No water in oil or at least nothing visible in the filler cap Very occasionally a tiny puff of white smoke on starting up from exhaust , barely visible and clears in seconds. Not always and not often. Cylinder compression 115,115,120,125 Cyls 1-4. ( well within the 10% range) Once had a super clean plug (#1) as if it had been steam cleaned but the day I did the compression test all 4 plugs looked perfect - light brown centre, slightly darker around the edge. I intend doing a leak down test when I can get the bits together. I have not got the chemical block tester. I do not want to make a wrong diagnosis - I once replaced the cylinder heads on a V8 based on a compression tester and its problems ( crankcase compression and oil blow out) turned out to be a blocked rocker breather. Any ideas anyone?

 

[craig2105]

Wow - pretty comprehendsive list of checks there! All I can say is that my S2 had an erratic misfire that used to come and go. It mainly afflicted the car at start-up from cold but also very occasionally did it at other times too. On mine, it did turn out to be the head gasket, which went big style very suddenly, but I suspect it was a growing problem for quite a while beforehand. Have you done a sniff test?

Best of luck...

 

[pauljmcnulty]

New rotor and distributor cap HT leads part but not all replaced

Is this because some bits were perfect already? Life has taught me that the one thing you don't change is the only faulty bit. [&:]

 

[dac68]

Hi Vince,
I experienced something similar recently, low speed misfire but cleared up at higher rpm. dropped it in to the local specialist and he checked all of the things you mention, eventually he found that the main valve springs on cyls 2 and 3 had failed. This apparently was a reasonably common problem some years ago. i can only guess that my car had until I got it had a relatively quiet life (it's now doing 500 ml/wk) and the increased usage had brought it on. incidentaly the leakage/ compression test showed that everything was fine. Now sporting new springs she's back to her old self. Hope this helps
Regards,

Dave.

 

[DivineE]

I'd do the rest of your HT leads. Also am I dreaming or did someone recently say flywheel sensors cured his misfire? Not sure if I imagined that, I am tired.