really rough idle
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Posting Guru
Joined: Nov 2005
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From: La Grande, OR
really rough idle
My truck developed a real rough idle in the past couple weeks. The first one was because of a bad (not closing all the way) EGR. Replaced it.....now Im thinking it might be the FPR. It idles down to about 800 and idles just fine, then it will kick down to about 650 and start idling really rough. If I go and take off the vacuum line to the FPR and cap it, it comes back up to 800 and idles just fine again....ideas???
Post Fiend
Joined: Mar 2002
Posts: 19,402
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From: Bonita Springs FL
The only really good way to test the FPR is with a fuel pressure gauge that you can buy at about any parts store. Most of the time when they're bad, there will be gas in the vacuum line. If there's no gas then it's probably OK.
The fact that the idle returns to normal without the line says to me that the fuel pressure is too low. The only way to check that is with the pressure gauge.
The fact that the idle returns to normal without the line says to me that the fuel pressure is too low. The only way to check that is with the pressure gauge.
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Posting Guru
Joined: Nov 2005
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From: La Grande, OR
ok, will see if I can rent a fuel pressure gauge....would the FPR be making the pressure too low, and how does it really work? thats one of the things I dont really understand yet....I was guessing that as the RPMs go higher and more vacuum is applied, the higher the fuel pressure would be, but maybe its the other way around.
Post Fiend
Joined: Mar 2002
Posts: 19,402
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From: Bonita Springs FL
If you take the vacuum line off, the pressure increases. Under heavy engine loads, there is less vacuum, so therefore there is more fuel available at the injectors. The computer monitors the exhaust stream via the O2 sensor and tweaks the pulse width (amount of time the injectors stay open) based on the amount of unburned O2 it measures.
Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
Originally Posted by nighthawk285
well, I cant rent a FP gauge and/or a hand vacuum pump.....will try some more places tomorrow, could this be from a bad O2 sensor?
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Posting Guru
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From: La Grande, OR
ok, what do you mean by a dial-type....would it just be any kind of pressure gauge, because no one here knows what I mean by that.
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Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
Originally Posted by nighthawk285
ok, what do you mean by a dial-type....would it just be any kind of pressure gauge, because no one here knows what I mean by that.
Here is an image of one.
http://i54.photobucket.com/albums/g9...gaugeLarge.jpg
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