Backfiring and eratic idle. Video...
#17
IHI KING!
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I would double check your vacuum hoses. I had a VW bug with dual carbs and it would pop like that when it was cold (no chokes). The issue was the mixture was excessively lean which is slower burning. The flame within the cylinders is still burning when the intake valves open.
Another theory - Does it backfire when the engine is hot and cold or just cold? Could it be a bad cylinder head temp sensor? Do you have access to a scantool or hammer?
Another theory - Does it backfire when the engine is hot and cold or just cold? Could it be a bad cylinder head temp sensor? Do you have access to a scantool or hammer?
#19
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How would coils make backfire in the intake ?
I can see how crossed wires might , but he said the wires went on and the car ran OK for two weeks .
I'm thinking an intake valve is leaking fire into the intake system .
I would do a quick test of removing the two sparks to one cylinder at a time to try and find what cylinder is sending fire into the intake system and then check the valve clearance for that cylinder . Or I might try a quick/dirty "leak down" to try and find a leaky intake valve .
Another thing might be cross talk between wire causing a spark to show up at a time when an intake valve is off its seat .
I can see how crossed wires might , but he said the wires went on and the car ran OK for two weeks .
I'm thinking an intake valve is leaking fire into the intake system .
I would do a quick test of removing the two sparks to one cylinder at a time to try and find what cylinder is sending fire into the intake system and then check the valve clearance for that cylinder . Or I might try a quick/dirty "leak down" to try and find a leaky intake valve .
Another thing might be cross talk between wire causing a spark to show up at a time when an intake valve is off its seat .
Hope it's not a sticky or broken valve part. I'd do a compression test before driving it again, or it could look like mine in the pic below.
However,........ Other than the really bad backfire, it sounds exactly like mine did a couple of weeks ago after an engine rebuild and a cleaning of the intake system. But mine had only a mild and less frequent backfire. I cleaned the ISV thoroughly (for a third time) and removed / carefully reinstalled the intake. It ran beautifully on first startup. I think the problem was an intake leak at the breather hose. So, if above doesn't check out, don't forget the possibility of an intake leak. Those intake connectors and large hose connections are pretty easy to check.
#20
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Thanks for all your help so far guys. I'm going to dive into it this afternoon. Your info will help me in what to look for. I hope I can get this worked out by our club's first autocross on the 18th in Hershey. If not, hopefully it will be ok for the swap meet. My wife and I will be at the entrance gate 9am-1pm on Saturday.
I'll let you know if I find anything...
I'll let you know if I find anything...
#22
Burning Brakes
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Hi, I had an intermittent misfire on my car for months which, after replacing coils, dist caps, rotor arms, etc. turned out to be either a dodgy o2 sensor or the cylinder head temp sensor. Not sure which as the garage replaced both at the same time but o2 sensor was most likely suspect. Just another couple of checks you can make... HTH.
#23
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After checking all the things that could have been, those were fine. The intake manifold came loose only on the right bank. I put it back on and purrs again....
Thanks for all the help!
Thanks for all the help!
#25
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Thanks. I ran through all the plugs and wires. Pulled the intake valve covers off to check the rockers and valves. I got it to hold a good idle but couldn't build the revs from the throttle body. Listened a little closer and the intake manifold wasn't seated right. I'm really not sure how that happened...but it's working fine now.
#27
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I understand that it would pop off the manifold from the pressure coming back up. I don't understand what caused it do that in the first place. Unless I missed something? Was it an engine hick-up? Once I fixed the manifold, it ran perfectly. Could something else cause it in the future?