decelerating - Ford Powerstroke Diesel Forum
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Old 09-11-2009, 07:02 PM

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Ok, this may be a dumb question, but this is the first Powerstroke I've owned..

When you decelerate (coast) to a stop sign in the country, it sounds like the engine is actually shutting down part of the time and only firing occasionally. It isnt running bad, and it sound like it is by design..
I was wondering, 1) is that what its doing? The truck has an aftermarker muffler, tailpipe, turbo downpipe, and chip, so you can generally hear the engine pretty well
And 2) if it is doing that, is that a Powerstroke design, or being done by the aftermarket chip... We have no idea yet what chip is in it.. We were told the former (original owner, we're second owners) put a chip in, but no one was sure which one.. If it is doing it, for which ever reason, it definetly helps the deceleration with the horse trailer... This has no exhaust brake, but it controls the decel better than any other diesel I have driven without an ex brake.

And a quick 3)... where is the computer in the '97 CC F350.. I'd like to take a look and see if I can tell which chip is in it, but I dont know where it is on this model.

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Old 09-11-2009, 09:49 PM Fanatic

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This is totally normal. All 7.3's do it whether they are chipped or not. The engine is not actually shutting down, the injectors just quiet down because of the lack of load and therefore, fuel demand required to keep the engine running. Most of the engine noise that the 7.3 makes is from the injectors firing, so their state of operation ( i.e. how much fuel they are delivering) largely determines how loud the engine is...until the rpm's get in the higher range and other noises such as exhaust and turbo begin to dominate. The ecu is located in the firewall on the driver's side. It can be accessed in two ways. One is from under the hood, but is a pain to get out that have to remove part of the inner fender well, so don't do this unless you need to change the ecu for some reason. The other way and better way since you are just looking to remove the chip for inspection is to remove the three nuts that hold on the parking brake pedal. Push it aside after removing the nuts and you will find a hole behind it which looks right at the end of the computer and therefore, the chip. Good luck!
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Old 09-12-2009, 07:41 AM
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That is perfectly normal. The computer quits injecting fuel all together when it doesn't need to. If you are decelerating, and you have your foot off the petal, it will stop all together till the RPM is getting close to idle. It should pick back up before the RPM falls below idle speed.
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Old 09-12-2009, 07:52 AM
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Yep and its not just the 7.3s, the 6.0ls do it as well. Its a pretty cool sound if you ask me
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