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Old 03-02-2010, 11:33 AM   #1 (permalink)
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Question Is DFCO bad for fuel pumps??

I recently had to replace my fuel pump in my van lying on my back in the middle of a snowstorm in a hotel parking lot in Frisco. Granted, the vehicle has 194,000 miles on it, and I don't know if this part had ever been replaced, but I do an awful lot of engine-on-DFCO coasting here in the mountains.

I've had this van since 10/09 and the previous owner had told me that he averaged about 17 MPG. Since October I've been averaging about 26.5 MPG, so that's about a 55% improvement.

I'm wondering if the fuel pump was just at the end anyway, or if I led to it's premature demise by engaging DFCO whenever possible, and letting that pump pressurize a fuel system that wasn't getting it's normal release through the injectors?

Any expert opinions on DFCO??

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Old 03-02-2010, 03:30 PM   #2 (permalink)
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The system is designed for DFCO. I'd say it doesn't have any adverse effect on the pump.
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Old 03-02-2010, 03:35 PM   #3 (permalink)
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DFCO would be built into the ECM. Do you mean DFCO, or EOC (Engine-Off-Coasting)? If it was bad for it, I think we would have seen a LOT more problems/complaints from the general public; end result being a recall. Seeing as that isn't the case, I'd say DFCO is totally fine.
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Old 03-02-2010, 03:41 PM   #4 (permalink)
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Not an expert but:
At idle my car uses 0.2-0.3 GPH, at full throttle it uses 3-3.5 GPH. A look at the replacement fuel pump for my car shows a pump output of 7 GPH. So the fuel system should be designed to return anywhere from 4 gph all the way to the full output of 7 gph back to the tank depending on what the fuel injectors use. I can't see how the fuel return system sending 6.8 gallons back to the tank at idle and 7.0 gph back to the tank during DFCO should make any difference.
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Old 03-02-2010, 04:49 PM   #5 (permalink)
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Busypaws - That depends on whether or not the car uses a return type fuel system. Not all do. Some use a variable speed pump (or a pressure switch and regulator) that only feeds as much fuel is needed. Therefore, during DFCO, these systems would turn the pump off, as no fuel is required.
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Old 03-02-2010, 05:30 PM   #6 (permalink)
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190K miles is a pretty good life for an electric fuel pump. My '88 Escort with 505K miles on it is on it's 3rd of 4th fuel pump, I don't remember which. Running the tank low on fuel is supposed to be one of the biggest causes of premature fuel pump failure, because the gas in the tank helps prevent the pump from overheating.


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