sd_iconoclast Posted June 5, 2004 Report Share Posted June 5, 2004 I have a '97 Gran Prix GTP with the supercharged 3.8. Recently it has started missing under load. I know it is #6 missing because I get a code P0306 : Misfire, Cylinder 6. I have tried replacing the plugs, wires, and coil pack. No luck. I am also getting code P0102 : Mass or volume air flow circuit, low input. I assume the two are not related as I sometimes get the first code without the second. In trying to diagnose this problem, my big question is "How does the ECM know that #6 is misfiring?". Is it somehow watching the emissions from cylinder 6 via the O2 sensor? Does it have some electrical means of sensing a misfire? If it is sensing emissions, then I think my problem can be mechanical or fuel delivery. If it is sensing the miss in the electrical circuit, then I can be pretty well assured that the problem is in the ignition side. Your suggestions would be appreciated. Quote Link to comment Share on other sites More sharing options...
Heza Posted June 6, 2004 Report Share Posted June 6, 2004 clubgp.com. go there for 3800 SC questions. most of us cant really answer them here. Quote Link to comment Share on other sites More sharing options...
digitaloutsider Posted June 6, 2004 Report Share Posted June 6, 2004 I know the problem.. it's a 97 GP. Electrical problems galore. Quote Link to comment Share on other sites More sharing options...
Gearhead43 Posted June 6, 2004 Report Share Posted June 6, 2004 And You Shuan want one..LOL Quote Link to comment Share on other sites More sharing options...
DaveFromColorado Posted June 6, 2004 Report Share Posted June 6, 2004 honestly, sounds like it could be a bad valve, that'd cause a misfire, how does the spark plug look that came outta that hole? --Dave. Quote Link to comment Share on other sites More sharing options...
Canada Posted June 6, 2004 Report Share Posted June 6, 2004 Could be a flithy injector. Quote Link to comment Share on other sites More sharing options...
WhiteOut Posted June 6, 2004 Report Share Posted June 6, 2004 The ECM knows it cylinder 6 due to a knock sensor. Usually when you get a misfire code and a MAF code in conjunction you'll get an EGR code as well. And needless to say, its a faulty EGR valve thats at fault in this case. Since however your not getting an EGR fault code and still gettting a MAF code I'd guess that its a vaccum leak, and since its only cylinder 6 I would guess its on the lower intake gasket right next to cylinder 6. Assuming that your car has near 100k on it an intake leak is pretty likely for a 3800 series. Thats my idea anyway, shoot me if I'm wrong. Quote Link to comment Share on other sites More sharing options...
sd_iconoclast Posted June 6, 2004 Author Report Share Posted June 6, 2004 The spark plug that came out of the #6 Cylinder looks fine. Same as all the others, light brown powdered look, no oil. Actually, the car has about 150K miles on it. Quote Link to comment Share on other sites More sharing options...
Gearhead43 Posted June 6, 2004 Report Share Posted June 6, 2004 Possible bad coil? Quote Link to comment Share on other sites More sharing options...
sd_iconoclast Posted June 6, 2004 Author Report Share Posted June 6, 2004 We tried swapping the coil with one of the working ones. We also tried replacing the plugs and ignition wires. No luck there. Quote Link to comment Share on other sites More sharing options...
WhiteOut Posted June 6, 2004 Report Share Posted June 6, 2004 It can't be a coil, those engines still use the waste spark ignition which means two cylinders would be misfiring. Oh, and the plastic intake on that engine is known to be prone to cracking which could also introduce a vacuum leak and cause a misfire. Try doing the propane or starting fluid check. All you've got to do is spray starting fluid on the area where the vacuum leak is suspected to be and see if the idle changes, if a change in idle is seen you've located the vacuum leak. Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted June 7, 2004 Report Share Posted June 7, 2004 It can't be a coil, those engines still use the waste spark ignition which means two cylinders would be misfiring. Oh, and the plastic intake on that engine is known to be prone to cracking which could also introduce a vacuum leak and cause a misfire. Try doing the propane or starting fluid check. All you've got to do is spray starting fluid on the area where the vacuum leak is suspected to be and see if the idle changes, if a change in idle is seen you've located the vacuum leak. The plastic intake is on the L36 3800's, not the L67's which have no "upper intake"(the composite/plastic piece on the L36's). The L67 has a cast aluminum intake manifold(lower). Quote Link to comment Share on other sites More sharing options...
WhiteOut Posted June 7, 2004 Report Share Posted June 7, 2004 I suppose this is what I get for thinking my experience with L36's would transfer over to L67's. I suppose had I thought about it for a second I would have known the supercharger is the uperintake. DUH!!! Thanks for the corrections mfewtrail. :oops: I still vote vaccum leak on this one though. Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted June 7, 2004 Report Share Posted June 7, 2004 I suppose this is what I get for thinking my experience with L36's would transfer over to L67's. I suppose had I thought about it for a second I would have known the supercharger is the uperintake. DUH!!! Thanks for the corrections mfewtrail. :oops: I still vote vaccum leak on this one though. No problem, I've made my share of mistakes and will continue to do so as well. :shock: I'd also vote for a vacuum leak w/ that many miles on a 3800...on a side note sd_iconoclast, how bad are your valve covers leaking w/ THAT many miles on them? I've seen those plastic valve covers(not sure whether it's the fact that they're plastic/composite or the gasket design) leak w/ less then 40K on 3800's. Quote Link to comment Share on other sites More sharing options...
sd_iconoclast Posted June 7, 2004 Author Report Share Posted June 7, 2004 My front valve cover is definitely leaking, but not too bad. It is really hard to see how badly the rear cover is leaking. I will look more closely when I check for the vacuum leak. Thanks fro all the advice guys. Quote Link to comment Share on other sites More sharing options...
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