Home » Public Forums » GMCnet » Re: [GMCnet] Rear Brake Shoes
| Re: [GMCnet] Rear Brake Shoes [message #245581] |
Fri, 28 March 2014 19:17  |
rallymaster
Messages: 662
Registered: February 2004
Location: North Plains, ORYGUN
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What's a DFCO engine, Corley?
On Fri, 28 Mar 2014 18:05:21 -0500 Corley Wooldridge <corley@corleyw.com>
writes:
I am trying to clarify if in fact Manny does not recommend down shifting
a DFCO engine coach.
> And finally, why is it that I continually seem to be misinterpreted
> in things that I post, then accused of being ignorant?
> --
> Corley
> '76 Glenbrook
> 29 other vehicles
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Ron & Linda Clark
1978 GMC Eleganza II
North Plains, ORYGUN
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Ron & Linda Clark
North Plains, ORYGUN
78 Eleganza II
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| Re: [GMCnet] Rear Brake Shoes [message #245609 is a reply to message #245581] |
Fri, 28 March 2014 22:12  |
corleyw
Messages: 130
Registered: June 2007
Location: Battle Ground, WA
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| rallymaster wrote on Fri, 28 March 2014 16:17 |
What's a DFCO engine, Corley?
On Fri, 28 Mar 2014 18:05:21 -0500 Corley Wooldridge <corley@corleyw.com>
writes:
I am trying to clarify if in fact Manny does not recommend down shifting
a DFCO engine coach.
> And finally, why is it that I continually seem to be misinterpreted
> in things that I post, then accused of being ignorant?
> --
> Corley
> '76 Glenbrook
> 29 other vehicles
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
Ron & Linda Clark
1978 GMC Eleganza II
North Plains, ORYGUN
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Ron,
Thanks for asking, it's been explained several times now, but I don't mind explaining it again, so here it is again. DFCO stands for Deceleration Fuel CutOff. That is, when you let up on the gas pedal, but he engine RPMs are still above idle, (as in descending a hill) the EFI system stops sending ANY fuel to the engine. The other option, of course would be since the throttle goes to idle when you let up on the pedal, a non-DFCO system would provide the engine with the amount of fuel that would normally be provided for idle conditions.
EBL enters into it in that EBL (an addition to GM TBI EFI), EBL can be configured to provide DFCO. Also, most factory EFI systems shipped today also use DFCO, to keep the engine from getting fuel when it's not getting air, due the throttle plates being closed. Several of the GMC MH guys have installed EBL, so they could set it to DFCO.
Rob stated that he thought that Manny said that you should never downshift a coach with EBL/DFCO on a decent, instead you should just use the brakes. I honestly believe that advise, as stated, is dangerous, and irresponsible. (Further, it's such BAD advice, I have to question if that is really what Manny said.) The stock brakes alone on a GMC coach are simply not capable of holding back the 12k lb coach at hiway speeds, for extended periods. Personally, I would never even consider heading down the grapevine, for instance, without shifting down, DFCO or no, and especially when towing. When the road signs tell the trucks to downshift, it's time for us to downshift too.
I hope this is not talking over anyone's head, and is clear to all, but if it needs further explanation, just let me know. I do apologize for seeming abrupt on this, but after several people answering with answers that did not apply to my question, because they did not understand the question, I start to get testy. Especially when told I am not smart enough to even ask the question.
One more clarification: My question has nothing to do with the speed of when you downshift. I recommend slowing to between 40-45 for the downshift, but I did not 'build' the transmission. (And by the way, when/if my trans goes, I'll be calling Manny, regardless of his answer, and I'll be downshifting it on steep hills as well.)
Again, thank you for asking, and not just guessing and based on a bad guess, giving a bad answer, as several others have done.
Corley
'76 Glenbrook
29 other vehicles
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