170,000 miles. Misfire on number 8. Spark at the plug. 185 psi compression. Pops and misses badly under light load. Smoothed out under heavy load/acceleration. 60 psi at rail ign on engine off. 55ish engine running at idle. The fuel pressure gauge does wiggle quite a bit (1 psi) very rapidly. Cap, rotor, plugs and wires were changed with no improvement. Is there anything you would try before changing the spider? I have not read the codes yet but I’m sure the usual suspects are there.
always read the codes first. It could be the ‘usual suspects,’ but make sure before you start tearing into things.
Does the 5.7Lhave coil packs? If so, I’d swap #8 with #2 and see if the misfire moves.
You say “pops and misses badly”. If it’s popping back through the intake, I would suspect a bad valve spring. The injectors should be flow tested instead of simply replaced. This will take a fuel pressure gauge and either a scanner or an injector tester that pulses the individual injectors. Test don’t guess.
It is not popping through the intake it is through the exhaust. It does not have coil packs. As I stated it has a standard distruibutor. I do not have access to the equipment to test each injector through the computer. I would need to pull the upper manifold to access them and I think for 250 dollars I will swap out the “spider injector” and be sure rather than pull it off again. Thanks for the advise.
Before you pull the intake manifold and replace the spider assembly, check for a stretched timing chain.
Remove the distributor cap, and while someone watches the rotor in the distributor, put a socket/breaker bar on the crankshaft bolt and rotate the engine by hand. Stop and rotate the engine in the opposite direction. If you can rotate the engine in the opposite direction 5 degrees or more before the rotor in the distributor begins to rotate the timing chain is stretched and causing the misfire.
Tester
GM had some problems with valve guides on the 4.3, 5.0 and 5.7 engines. A misfire would intermittently occur under load. The problem was that the guides were causing the valves to stop rotating. I’ll post the TSB number when I find it.
Check that the distributor rotor doesn’t have excessive play. That could mean a worn distributor gear.
@Eddo that engine is old school. It has a distributor and wires.
The new spider unit took care of it. It runs like a scalded dog and idles very smoothly. Thanks guys.
@Jgarewal congratulations!
Did you set the cam retard with the scanner after you started it up again?
I did not. I do not have a scanner to do those sort of things. What would I gain/lose from doing/not doing it?
@Jgarewal if you put the distributor back EXACTLY where it was, more than likely you’re okay.
If you ever get a check engine light with a P1345 ckp/cmp correlation code, you’ll need to check and adjust the cam retard (the relationship between the crank and cam).
Technically, that code can because of a worn distributor, loose distributor rotor, worn chain, etc.
But it more commonly sets after engine work involving removal of the distributor.
I did my absolute best to do so but I will keep an eye out for it. Thanks
@Jgarewal if several days go by and there’s no check engine light and no P1345, it probably won’t set and you’re fine.