mystery miss, please help me!

[morgspothead]

Gday guys. My name is Morgan and I work in a small workshop. The reason I'm asking for help is that I serviced a VT commodore 99 stock standard 3.8 and ever since it has had a miss. The miss is more evident in drive and it's not a constant miss. When you experience it, it makes you think it's the coil.All I did in the service was plugs, fuel filter, and oil and filter. The only thing I did do wrong was mix up 2 leads which was a stupid mistake. Since the service I've been chasing this problem by replacing all the leads in case I'd cracked a plug, replaced all leads, tried 3 brand spanker coil packs, o2 sensors, scanned it for codes and nothing comes up. Soon after the service I was chasing this problem and gave it a tk test for the head gasket and it was positive. We did the head, had them serviced and all, put them back on and the miss is still there. I am out of ideas and curious as to why it's doing it. We had the same problem with another vt commodore wagon. Same type of miss. car drove fine once u were driving. Wouldn't notice a thing. So if anyone could shed some light on this you'd be a great help!

Cheers.

Morgan

[Pub247]

have you tried different plugs one might be defective from new all-all it v6 and they do it at one stage or another dfi module might be worth checking too

[Tom_1569]

Yeah as Pub24/7 said, DFI and plugs. I would start with the plugs, a few brands are well known for quite often having dodgey plugs when new. Try the old plugs if they worked fine. If its not that, replace the DFI module.

[ephect]

interesting problem, so it only happend after the service. im thinking that one of the vacuum hoses must be cracked, prolly happend after it was disturbed.

while the engine is running, spray some crc on the vacuum hoses, and if the revs increase you have a hole in it.

[morgspothead]

cheers ay! I got a feeling its gotta be the dfi module. Coz everything else has been ruled out. Coz the old plugs gave the same problem. But thanx for that.

[Doctor Bob]

i have seen a dfi cause this sort of misfire

[big m]

sorry if i sound like a bit of a tard but what and where is the dfi??

[Tom_1569]

sorry if i sound like a bit of a tard but what and where is the dfi??

DFI is the block under the coil pack. NOt really sure what is does, but ut has wires going to each cylinder plug on the coil if that makes anysense.

[Garth]

i can safely say your issue will be spark related.

check the coil pack, you will find there is one that is starting to die.

[Doctor Bob]

DFI is the block under the coil pack. NOt really sure what is does, but ut has wires going to each cylinder plug on the coil if that makes anysense.

Direct Fire Ignition... its the module under the coils that controls them
if you have tried coils etc try swapping this module.

Rob

[blownba]

I have seen injectors block after missfires when leads are on backwards. Its like the pressure created in the manifold blocks them up or something.
If its there on acceleration but it will rev or cruise at a constant OK then it really sounds like injectors to me.

[natas.308]

mmmm.... have you checked the injectors or givin them a good flush?

[Emackulation]

I would definately try another DFI first.