Austin91

I was wondering whether or not it would matter if I have a positive backpressure EGR on my 91 5.0 TBI when the manual calls for a negative backpressure EGR? I have done some reading on the topic and found the following (correct me if I'm wrong):

Positive EGR valves - use exhaust backpressure and manifold vacuum to open valve
Negative EGR valves - use manifold vacuum to open valve and negative backpressure to close valve.

My question is: if I have a heavily modified exhaust (3 in pipes all the way back, headers, free flowing cat and muffler), wouldn't this limit the flow of my positive EGR valve? Should I buy the negative valve from GM?

Thanks for all your help.

dimented24x7

iTrader: (2)

ive heard of some instances where people have had the computer set a code 32 because the positive back pressure egr isnt recirculating enough exaust gasses with a low back pressure system w/o a cat. If you have a cat and a full exaust it probably wont be a problem. id jsut leave it and get teh exaust. if you have problems down the road, you can always look into it then, after all, its just an egr valve.

Grumpy

The EGR valve's amount of flow for a given opening is a function of intake vacuum, and exhuast pressure. While changing the exhaust will slightly effect it, there are plenty of systems that get the CARB good House Keeping Seal of Approval. Based on that I'd suggest just using the oem one. EGR design takes ALOT of effort to get right, it would take alot of luck to back into something that work well. BTW, there are some lies about the way EGRs work. If you have a real curiousity about exacting how yours is working build a *cat's whisker* movement detector, and use it to monitor the EGR pintle posistion.

burnouts4ever

the egr is easy to replace also, i replaced mine

Austin91

Dumb question, but how do I build a "cat's whisker" motion detector for my EGR? Thanks for the reply.