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Vy commodore develops a miss when hot

cracky11234

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Hey guys iv got a vy v6 commodore that has had a miss for some time which i thought i had fixed, but i have noticed the miss comes back once the engine is hot.

Originally i replaced coil packs, dfi module, plugs and leads and the car has been running great.

I have recently got the car registered and was driving around most of the day with no issues, but once you start opening it up a little and the engine gets hot it develops a miss and only runs on 5 cylinders or maybe even less. All the coil packs are still sparking so id assume thats not my issue. I think it could possibly be my leads, the leads i brought are to fat to fit the heat shields so i put them on without them, is it possible that the heat from the manifolds are causing the leads to fail? Once the car cools down it runs fine again.
Any help or ideas would be greatly appreciated. Cheers
 

lowandslow

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I've never had luck with aftermarket leads. If you still have the old ones, put them back on and see if its any better.
I chased a miss like you described. Ended up being a cracked plug. Must have either been faulty or i cracked it upon installation.
 

cracky11234

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Update: so this morning the car started and ran fine, driving down the street and it dropped to 5 cylinders again. So i went and got a new set of plugs and leads with heat shields but it made no difference. I took the plug out of cyl number 4 and it was wet, so this tells me its number 4 thats not firing... i then swapped the number 4 coil pack over with another good working one and had the same problem so my guess is the dfi module? This is the 3rd dfi module i have been through in a couple of months, is there any reason why i am going through so many? The car is currently at a holden wreckers/mechanics hopefully they can tell me whats going on.
 

cracky11234

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Could a faulty o2 sensor or crank angle sensor cause the engine to fire on only 5 cylinders?
 

cracky11234

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Another update: so i swapped out the dfi module for another know working one and it made no difference, tried another 2 different set of coils and still no luck. Cylinder number 4 just wont fire, occasionally when you floor it it will rev up and run and all cylinders but only for a very short period then goes back to running on 5. The mechanics didnt get a chance to look at it today so i am taking it back in the morning. Does anyone know how much psi each cylinder should be at?
 
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