91 silverado 350 preignition and detonation woes

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91 silverado 350 preignition and detonation woes

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Chevrolet Forums >> Chevy Trucks, Vans & SUV's >> Silverado >> 91 silverado 350 preignition and detonation woes

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91 silverado 350 preignition and detonation woes - 9/9/2006 6:13:32 PM

Andrew_350

Posts: 2
Joined: 9/9/2006
Status: offline

OK, so I first bought this truck with an EGR problem which I fixed with a new valve and solenoid, passage cleaning etc. after that there were no more EGR codes and no more preignition.

Still had some spark knock under initial full throttle.

I recently put on headers and dual exhaust and now im getting the occasional code 32 EGR on the highway.

ive still got spark knock and preignition under light throttle. I do recognize that headers and duals can cause egr problems, and I do recognize that headers can sound like preignition.

However this preignition seems to happen in the same manner it did when I initially bought the truck.

The preignition (rattle) stays no matter what fuel i use, the spark knock almost goes away when i put in 94.

Ive had the truck to a shop and their scanners pick up the knock, blah blah, but they have no idea where its coming from.

So far, ive put in new plugs (the proper ac delco, proper gap) wires, cap, rotor, esc module, fuel filter, checked timing, egr valve works fine, when i apply vacuum the engine stalls as it should, fuel pressures good.

I cant think of any thing else and I'm all out of ideas any ideas as to what would cause this, and whether or not my preignition really is preignition or just headers would be greatly appreciated.

Post #: 1

RE: 91 silverado 350 preignition and detonation woes - 9/9/2006 9:43:00 PM

kcb37

Posts: 504
Joined: 7/3/2006
Status: offline

If you feel like spending a little more money try a knock sensor. It should be some where around $20. What it does is senses the vibration from a cylinder firing to early and it adjusts the timing to prevent this. When you say it runs better off 94 this seams a likely cause to me. You shoudn't have to run anything but unleaded, but I do know my 96 runs better off of mid grade. The less combustive the gas the less the knock sensor works. I hope this make sense. what I don't know is if it will change anything.
Good Luck.

(in reply to Andrew_350)

Post #: 2

RE: 91 silverado 350 preignition and detonation woes - 9/10/2006 10:03:53 AM

Andrew_350

Posts: 2
Joined: 9/9/2006
Status: offline

Thanks, I'll try that tomorrow and see what happens

(in reply to kcb37)

Post #: 3