alley_dog_77

I have a 93 Z28 and recently had a fire underneath from a bad Cat-converter, the fire screwed everything up, so I removed the CAT for a straight pipe, and I've change the speed sensor, its wire harness, the shifter cable, and the vacum lines to the EGR valve. The EGR will not hold any pressure pressure at all though and I'm getting detonation. Is there any way to easily remove the EGR valve? It's exetremely hard to reach considering it's DUMB location!!!!

Also, does anyone have any suggestions on anything else that could be causing the detonation? I'm pretty sure its the EGR considering when I'm on the throttle I spit out white/gray exhaust.

PLEASE HELP

shoebox

Use a mirror and feel around to get to the EGR. It's not that hard to get off, IMHO.

alley_dog_77

Got the EGR Valve changed but there is still detonation. Could that be caused from a lack of back pressure due to having no catalytic converter on the exhaust?

Exhaust is the following: K&N mass air-flow package, Edelbrock headers, and no catalytic converter. The rest is stock (93 Z28)

LiENUS

No its not from lack of backpressure. You sure you dont have a vacuum leak or damaged FPR? Check the fuel pressure while driving with a gauge taped to the windshield.

The Engineer

When headers are added and/or Cats removed it is "very common" to have a DTC (code displayed) related to the EGR (I'm too lazy to look up the actual DTC #). Which is due to a lack of EGR flow and caused by "no exhaust back pressure."

WD

LiENUS

But it doesn't cause detonation. if hes hearing detonation hes got serious issues somewhere.

alley_dog_77

I changed the vacum line to the EGR but that's it so far. But what is the FPR? Also, what other vacum lines are there to check. (please give location if possible.)

turnin20s

FPR=Feul Pressure Regulator

check out www.shbox.com for the vacum lines and their locations

alley_dog_77

How would I test for "no exhaust back pressure" without actually buying a new cat and installing it? Im speding money left and right and cant see to get the damn detonation to quit!!

LiENUS

You wont get detonation from no exhaust backpressure. If it throws an EGR code after removing your cat and you know your egr valve is still functioning then that is caused by reducing backpressure, however it still wont induce detonation. your detonation is likely caused by something unrelated to the EGR valve but likely related to the fire. Are you sure its detonation and not something more serious like a knocking rod?