5.7L Gen I misfire causes?

[pronstar]

I’ve got a 99 Suburban with a 350 Vortec. I was getting slight spark knock (also CEL for misfire) at 3,000-ish rpm / large throttle openings, so I’m running 89-93 Octane to keep it in check.

 

No more audible knock, but still throws a CEL. Codes initially were for Cyl 7 misfire, but now I get a multiple-cylinder misfire code.

 

CEL turns off after a drive cycle or two, but the code is still stored.

 

Truck runs great, burns maybe a quart every 3k miles. No power loss at all when it throws a CEL.

 

Plugs, plug wires, cap/rotor are all 1 year old (threw same code before parts were replaced).

 

Have not yet pulled the plugs.

 

Some folks say this is common when there’s an air leak in the intake manifold, bad valve/worn cam.

 

Do you guys have any thoughts on how to diagnose this?

 

While I’d love to use this as an excuse to drop a 383 stroker in there, I’ve got too many things tugging at my bank account to make that happen LOL

 

 

Sent from my iPhone using Tapatalk Pro

[pronstar]

No love for my Gen I SBC?

 

IIRC this was the year for the last bodystyle that retained this iconic engine.

 

 

Sent from my iPhone using Tapatalk Pro