Nate's 1998 Z28 Project

[JoeliusZ28]

If you got one of the bad batches, yes but I think thats unlikely and I also think you would know if you had a broken spring. best case scenario youll get some noise, worst case scenario the motor goes kaf**ingboom.

[nascarnate326]

What else could it be? Piston/rings?

[Atrus]

If you got one of the bad batches, yes but I think thats unlikely and I also think you would know if you had a broken spring. best case scenario youll get some noise, worst case scenario the motor goes kaf**ingboom.

When I snapped a spring on my 3800 W-Body, I got a misfire code as the valve wasn't seating fully anymore. Not saying his problem couldn't be a spring, but I agree with you - unlikely.

[s.reef]

Could it be a wire to the coil? I would think a broken spring would be pretty obvious

[WMCCjames]

Sorry you are having issue...I'd run a comp check ASAP.

[sman]

Could it be a wire to the coil? I would think a broken spring would be pretty obvious

THIS. I chased a problem like this for several weeks. Swapped the coil harness, problem solved.

[JoeliusZ28]

a broken spring would only escape obvious detection if it was broken near the top or the bottom of the spring so that the majority of would still be functioning.

[hoogiesngrinderz]

It could very well be a broken wire in the coil harness. I'd still do a compression check first. If compression is low or non existent then you will have a different path to go. I might even have a spare harness, albeit from a truck (not sure if they are interchangeable)

Quick spark test - Pull the INJ-1 and INJ-2 fuses then take one of the spare spark plugs from the bench and hook it into #7 plug wire and ground it out. Have someone crank the car over to see if you have spark. Then try with #1 cylinder. If #7 is dead and #1 sparks, most likely harness. Replace INJ-1 and INJ-2 fuses.

If you have spark from #7 coil, I'd then put a noid light in the #7 injector connector. If #7 is dead, check 1-3-5. If 1-3-5 are good, you will have to check continuity between the #7 injector ground wire and PCM as well as check for voltage on the power side.

[98blackbeauty]

9 out of 10 times when engine runs and idles ok but misses under load its valve train. compression check, and visual inspection of valve springs, then check timing chain marks to verify cam is in proper time.

[nascarnate326]

9 out of 10 times when engine runs and idles ok but misses under load its valve train. compression check, and visual inspection of valve springs, then check timing chain marks to verify cam is in proper time.

Did all that, appears to be fine. Had 165 pressure.

Just verified that my o2 extensions are correct.


I feel like this is just a simple problem that I am somehow missing.

[hoogiesngrinderz]

Did you get spark or a pulse at the injector connector?

[nascarnate326]

confirmed cyl 7 is getting injector pulse.

Tonight I am going to test all cylinder injector pulse, and all coil packs.

May remove the injectors from the rail to see if there is junk in the fuel rail.

[hoogiesngrinderz]

I highly doubt there is anything in the fuel rail considering how quickly and how much fuel came out of the rail when I pulled #7 injector.

Best case scenario left: Exactly what Sam and Spencer mentioned, a problem with the coil harness. You have confirmed everything except for spark. The problem didn't follow the injector or coil when it was moved so it rules out a faulty component. Compression looked good, injector is pulsing, so that leaves spark.

[nascarnate326]

The saga continues.

Checked all coils, they all spark like they are supposed to.
Checked all fuel injector wiring with noid light - they all blink
Just took a look at the push rods for cyl 7 - they look perfectly normal/ straight.


So we know the injector is good, the coil is good, both are getting signal. Pushrod looks good.

At this point whats left to check? lifters? take the head off?

[hoogiesngrinderz]

I assume you checked the pushrods/rockers when both valves were fully closed? If so, and there wasn't any play in the pushrod, then the lifters should be fine.

Leakdown test and PCM swap would next on my list.

These PCM's are pretty robust but they have been known to corrode at the connectors or get moisture inside.