My 454 Rebuild

[yevgenievich]

I am thinking on splitting exhaust in to duals to run two stock mufflers. Stock 454 exhaust has a bit of a drone at 2300rpm. Was planning to try two mufflers from 2015+ HD trucks.

 

[Spareparts]

Hmm. My stock exhaust is totally quiet at all speeds.

 

[OutlawDrifter]

Maybe 2 of the big round Dynomax Super Turbos...or just use whatever muffler flavor you want to hear and do a helmholtz resonator like I did on my Suburban. Kills drone for good.

 

[Spareparts]

I have not mentioned it for a while cuz i just had better things to work on and am tired of it anyway but just in chase ANYONE has a suggestion im listening.
Yup the misfire and rough idle.
I believe the entire problem is ignition related. It's worse when cold. Better when hot.
So to recap.
I have replaced the Distributor with new. No real change.
2 Sets of new plug wires. AcDelco stock style, Second set Taylor 8MM. No real change.
2 New sets of plugs. No real change.
3 New caps and rotors. No real change.
New crank sensor, Properly gaped. No real change.
New ICM. No real change.

Here's what i know.
When i hook up a timing light it should have a rhythmic flash, flash, flash on all cylinders. #7 is just flashing WAY to often, almost constant.
The other cylinders are doing it a slight amount.

Leads a guy to think bad cap/rotor, right? Problem is i have tried 3 new sets with no change. I find it hard to believe i have gotten 3 bad ones in a row.

What could i be missing?

 

[Schurkey]

L29 Vortec 454?

There was a guy some months ago that had a TBI. Injectors sprayed fuel any time the ignition was on. Turned out to be a failed ignition module sending false signals to the ECM, which then triggered the injectors.

I wonder if you're not getting false signals to the computer, and the computer is then triggering extra sparks.

RFI interference on wires that should be shielded but aren't?
Faulty ignition module (but you've replaced that already.)
Faulty computer?
Faulty wire harness between crank sensor and computer, or between computer and ignition module?

This is one of those engines that would be fun to look at on an ignition oscilloscope, searching for "extra" sparks that shouldn't be there.

 

[Spareparts]

I have replaced the Computer. Made no difference.
From watching the timing light flashing there is definitely extra sparking going on compared to other cylinders that are not misfiring.
Im sure i have a ignition problem but every single part is new and not fixed a thing.
I can say for certain though if you get zapped by a plug wire doing a cylinder drop test you're gonna know it for a while!

 

[yevgenievich]

Sounds like a trace cross over in a cap where number 7 gets spark same time as other cylinder. Maybe carefully inspect all the caps on hand?

 

[BeXtreme]

I agree. With a Vortec, the only way you could be getting extra spark on ONE wire is if the cap is bad. I would suggest a different brand cap from a completely different source than the one you have gotten the other caps from.

 

[BNielsen]

Can confirm that it's not uncommon to get multiple duds in a row. Had some issues with my 96 when I had a tune-up done.

First was an Accel cap and rotor that was a no start, second was an MSD cap and rotor from Advanced Auto, ran fine but burnt through after 5 minutes, there's a NAPA/Echlin cap and rotor on there now and it's been over a year with no trouble.

 

[Spareparts]

I took the cap/rotor off. I could not see a thing wrong with the cap. It's a summit blue cap with bronze contacts. Less than a year old. The rotor was a new one but i can't remember the brand. I put a new AcDelco rotor on it and it did help. Probably 50% better.
I would have changed the cap also but had to order it and im not so sure that will change anything
Most cylinders get random misfires but #7 was pretty consistent. The other cylinders are way better also but still a few.
Over all just changing the rotor and adding dielectric grease helped but did not fix it totally. I think im on the right track to fixing it.
The wires are 8MM Taylor wires and they are in the factory looms but i'm also going to separate them further where possible.