Re: 91 Burb w/ 7.4L


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Posted by Frankenbiker (32.128.147.149) on 21:58:44 07/17/07

In Reply to: 91 Burb w/ 7.4L posted by PeterW

: Guys, I'm spent! My 91 Burb, R2500, 7.4L, 3.73 rear and 133k on the clock has me going in circles.
: Here's the deal; She's my tow beast and typically is used only for that purpose. She does weekly trips to the dump but that's about it. Towing my trailer is her primary job.
: Without towing, she runs beautifully, never a hiccup anywhere. However, hook up the travel trailer (5.8k lbs.) and the check engine light comes on with DTC 32 stored. This indicates an EGR problem. I've replaced the EGR solenoid and EGR valve itself and without fail, each and everytime I tow, I get the same code. Never a code when not towing.
: I don't notice any dimished power or performance when the light comes on, yet it's on and driving me NUTS!
: Anyone have any idea's on why it comes on while towing and never anytime otherwise?
: Where do I begin? What to look for?
:
: TIA.....Peter

Something else I'm being reminded of as I search is that GM's TBI EGR systems are notorious for clogging up with carbon. The 5.7L motors needed a good cleaning of the valve and the intake passages every 100K miles or so, and I suspect the 7.4L engines are similar in this respect.

Your ECM may be throwing a fit because it can't see enough response to activating the EGR valve.

Assuming that your EGR passages in the manifold are clogged, you may wind up having to remove the manifold to completely clean them out. You can clean out SOME of the gunk W/O removing the manifold (perhaps enough to make the computer happy), but I'm not sure you can get it ALL out. As I recall, a sharp screwdriver was an effective tool for knocking out some of the gunk. Having carbon chunks falling back down the exhaust manifold isn't really a problem, but that's not the case if they fall down the intake.

(It's been long enough since I messed with a GM EGR system that I don't remember all of the specifics.)

-blaine



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