5.7 vortec misfire at idle

Wwildman

Wwildman

Never Give UP
Joined
Apr 16, 2005
Location
Garner, NC
Ok so ihave been through the entire ignition and fuel system the only thing I have not replaced but checked is the spider injector the engine runs fineoff idle but misses at idle . The static and dynamic compression isgood . Also was doing this before tune up.

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un cross 5 and 7 plug wires at Dist cap

EDIT: just reread the OP's post, at first read it as it wasn't doing this before ( the 5/7 wire swap is very common tune-up gaff ) sorry about that
 
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If the plug wires are on correct, check the valve springs on the cylinder that is missing. Very doubtful the injector will cause a miss at idle. I have had the distributor cause this. They are crap plastic and the housing will wear causing the ingition pickup to produce an erratic signal to the PCM.
 
yes, Dizzy is plastic housing, cam gear inputs a side load to the distributor drive gear, which over time does wear the plastic housing. pull distributor shaft up and rotate slightly, then wiggle in all directions, any side to side play of the shaft in the housing can very well cause a mis-fire.

any codes ? is possible to get a cam sensor code from this as well, the breaker plate under the rotor can contact the cam sensor and damage or even wipe it out, and the engine will still run ( poorly, but it will run )

have you tried spraying carb cleaner along the intake checking for leaks? these engines are very good for sucking/cracking intake gaskets.
 
may sound dumb but i had one do that cause egr had carbon holding open a smidge.
 
EtodaJ said:
may sound dumb but i had one do that cause egr had carbon holding open a smidge.
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Not dumb I checked that first because I have see that too . not the case I actually plugged off the port to see if it helped
 
Ive seen quite a few spiders do this over the years. Some say a fuel clean or decarbonizer will fix it but from my experience the spider will always end up being the fix. In the cases I'm speaking of its never a driveability issue, mainly cel and inspection troubles.

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Ok I replace the spider injector , upper and lower intake gaskets found 3 and 7 pulling vacuum on crank case side . After I finished all of that it still has a misfire on #4 now :shaking: because I have no scanner I there was no change on #4 until I Fixed all the other issues , tried swapping plus no change then wires no change then ran compression on right bank 2,4,6,8 all had 150 except #4 it had 60:handed: so tomorrow I pull off the right valve cover and find out what is wrong
 
Ok after I finally figured it out
1. rocker arms off valves I could get 100 PSI
2. Set lash on rockers and get 60
Pulled head and found #4 exhaust valve bent only 0.002 of an inch just enough to create low compression and a misfire at idle but run good just off idle .
 
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