Re: 91 Burb w/ 7.4L

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Posted by Frankenbiker ( on 22:17:09 07/19/07

In Reply to: Re: 91 Burb w/ 7.4L posted by 92sub

: Agree that clogged EGR passages could also pose a problem. I wouldn't expect that type of issue to only manifest while towing but 'stranger things' have happened.

Not so strange, really. EGR is used to reduce NOx formation, and to allow for "decent" fuel economy by reducing detonation at light throttle; thus the engine can run really advanced timing. (it does both of these by reducing peak combustion temps.)

Conditions for the formation of NOx aren't really present during light-load cruise. Thus the amount of exhaust gas required to effect the timing is low.

During heavy towing, however, conditions for NOx formation are present almost all the time: high peak pressures, and high temperatures. The amount of exhaust gas flow from a clogged valve would not be sufficient for either NOx reduction, nor timing changes.

: Fords were terrible for plugged EGR passages. I used to cut a length of old speedo cable and chuck it in a drill and 'whip' the intake passages into submission. Start the engine with the egr off (warning! engine will rev high very very quickly - be fast on the key!) a couple of times to blow out the chunks.

Interesting method. Too bad I don't have a vehicle with an easy EGR system any more. :-)


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