Miss at an idle 12 valve

kole32

kole32

New member
I’ve got a 12 valve that has a miss that is only at an idle. Once it’s warm and you’re driving the miss goes away. It doesn’t feel down on power and starts easy as well. It made 1157hp on the engine dyno on a stock bottom end ?. I’ve narrowed it down to cylinder 3 I’ve moved injectors around, and it stays at cylinder 3. I did a leakdown test today to eliminate a valve issue. And that checked out good. Didn’t hear anything out of the exhaust or intake. And it would push the piston down after a few seconds. Checked the delivery valve and holder didn’t see anything abnormal either. Thanks for any help


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Sooo after Messing with it some more today, cylinders 3 and 5 are dead at an idle. If I take it on the road and spool it up. The miss goes away.


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Mine has always had a chop to it I guess youd call it. Been that way ever since I went to a 13mm pump and high timing.

It kinda comes across as a skip at light throttle. But has been the exact same way from when I first installed the pump.
 
Do a compression check on it. It may have bent a rod and once warm there is enough heat in the cylinder to fire the fuel or pull the injectors and use a dial indicator in a good cylinder then the dead ones to make sure the piston is coming up all the way. Double check your valve lash also. Cold vs hot plays with tolerances
 
DISTURBED said:
Do a compression check on it. It may have bent a rod and once warm there is enough heat in the cylinder to fire the fuel or pull the injectors and use a dial indicator in a good cylinder then the dead ones to make sure the piston is coming up all the way. Double check your valve lash also. Cold vs hot plays with tolerances
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I’ll check that out. Bent rods has been in the back of my head.


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Checked valve lash again, it was checked out good, pulled the pushrods on cylinder 3, they’re straight, did another leakdown test, it was good. Checked compression, everything was within 20 psi of each other. But I used a cheap Harbor freight tester, and it was reading 180-200psi which seems awfully low. But the adapter in there needed a little grinding to get it to fit. I’m guessing maybe it’s not sealing all the way. Also talked to Seth about it being a pump issue, and he said to check the DV’s. They move freely and I didn’t notice anything out of the ordinary.


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