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Limp Mode and Defuelling

mfgguru

mfgguru

Makin' it better!
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Winkler, MB, Canada
When Dieseldad and I were working on his truck, we were discussing the results of the our trucks going into limp mode. Each of us had some questions that I could not find the answer to in the ref. material, so maybe some of you brilliant all knowing people can shed some light the the subject.
At what conditions specifically cause it to defuel ie. PSI etc.
The other day I pulled 20' covered cargo trailer about 200 miles with no issues at all. I don't have a boost fooler. I ran 12 PSI sustained while pulling and 60 mph at 1800 rpm without issue. It wasn't windy, so that may have been a factor. It didn't defuel at all. The only mod I have done since pulling similar loads is the T/M. In the past I have had big issues with defuelling. Why the marked improvement? What PSI will it defuel at?
Now Dieseldad (Gerald) had his truck defuel on him when his W/G actuator was not working pulling a similar trailer, why?
Any explanations would be great.
 
High boost, or high IAT will cause defuel, have never seen the published limit when it occurs, only seen it aftger the fact, happens when PCM commands lowered boost, and doesn't happen because mechanical means (TM) prevent the boost from being lowered so next thing PCM does is lower max fuel, no code is set but 50mm^3 is all you see as max fuel. truck that haven't been reflashed/chipped may need a MAP fooler in addition to TM to make sure this does not occur.
 
In addition to what Turbine Doc said I have a gm document for the DS4 that states that PCM de-fuel will happen when the coolant temp reaches 210, or above. This is designed to limit the heat build up.
 
Thanks guys, that explains a lot. Any idea what sustained PSI will cause too high of egt's? Don't have a guage yet. Should I be worried about my current settings?
 
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