98 5.7 Timing all over and misfires

[LastOne]

I have swapped plug and wires 6 with 5,moving suspect to other side of engine. No change. Compression 175-180 on all 8 cyl. Vac gauge steady at various rpm levels. I have read that cyl6 is sometimes picked on as a default. Before rerouting plug wires I recorded miss on cyl 3, 6, and 8.
TPS checked with meter and observed live on scanner. No problems. Shake it at several different TPS positions.

[MT-2500]

Sounds like a hard one.
I would try to get the camshaft retard setting checked or set.
Some scanners can run a injector balance test to check for clogged injector.
Also one that will read history and present misfires.
Make sure MAF sensor is not dirty and reading good.
Also hook a fuel pressure gauge up and drive it with gauge on the road.
Make sure pressure remains 60/66 at all times.
Good luck MT

[Bob B]

You're not using Autolite spark plugs are you?

[Blue Bowtie]

Originally Posted by MT-2500

...Some scanners can run a injector balance test to check for clogged injector.

So can a guy (or girl) with a tachometer. Idle the engine hot, disconnect the IAC, then pull injector connectors one at a time and record RPM drop. Move along to the next hole.

Then you can use that "high end" scanner to clear the DTCs you just set, or do that the old fashioned way, too.

I'll second the thought about testing fuel pressure, but also monitor pressure after shutdown. That CPFI "spider" may have a bladder control problem.

Inspect the distributor for radial play. Axial play is less of a problem. Cam gear wear is also not normally a problem, since the load of the oil pump tends to take up most of the lash while running. I've seen them running just fine with an iron gear on a billet replacement cam with teeth so thin and sharp you'd think they belonged to a musky.

[LastOne]

Using AC DELCO platinum plugs. I don't think I can disconnect the injectors 1 by 1 as they are inside the upper intake manifold and are in 1 large connector. I forced GM to replace the CSPI with the improved MFI injectors about 20K ago. Had the miss problem before and after the switchover so I would say most likely not an injector issue. I will check for play in the dist. Planning on taking it to a guys shop to pay an hour labor to test set the cam retard and double check fuel pressure. Thanks for all the info so far. I will post results back. Any new ideas, keep them coming.

[Blue Bowtie]

If you were really ambitious, you could use a pin rejection tool at the PCM to lift the injector sinking output wire terminals one at a time.

I didn't say it would be easy, or efficient, but it can be done. You will set DTCs, however. The scanner is the fastest/easiest way to go.

[LastOne]

Cam Retard was way off, shop used a Snap On scanner. No more miss or shudder going up hill. even with A/C on!

[MT-2500]

Thanks for posting back with the fix.
Glad all is well and going.
MT