Fuel pressure causing rough idle when warm.... - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 16 (permalink) Old 07-09-2008, 01:53 PM Thread Starter
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Fuel pressure causing rough idle when warm....

Recently I pulled my injectors to replace the o-rings. I was pretty sure that I had an injector that was leaking a little oil by an o-ring because of these symptoms:

I had a rough idle when the engine is up to temp. When the engine is cold it would idle silky smooth. One of my chip positions has a 600 RPM idle and it was much more noticeably rough idling than the rest of the positons which have a 750 RPM idle. At the 600 RPM idle I even had some problems with the engine stalling when I was slowing down to a stop or slowed down to turn a corner. If I revved the engine up to 2000 RPM (trans in neurtal or park) and let off the pedal quickly the engine would stall 95% of the time when the engine was warm but when cold it would return to idle perfectly.
--All of these symptoms started the day that I removed my stage 1 injectors and installed the B-codes. I bought the B-codes used and the o-rings looked good on them so I just decided to save my 50 bucks and reused the o-rings. Also it is note worthy to say that I saw absolutely no change in this condition when I went from a stock HPOP to the Stealth (dual IPR).

After dealing with these issues for a few months I finally decided to pull the injectors out and put new o-rings on them. While changing the o-rings I didn't find any of them that I thought were real bad, but there were one or two of the square cut o-rings that were a little suspicious looking.

I got everything back together and running last night but much to my displeasure my choppy idle when warm remained...I was more than a little peved to say the least

After I was done test driving, and I cooled off a little, I decided to try messing with my fuel pressure some and see if that helped any. I have been running 65 psi so I backed it off to about 55 psi and saw no change. So I backed it down a little more to about 48 psi and what do you know it doesn't stall every time you let off the accelerator at 2000 RPM in neutral, but it still struggled to stay running. So now I figure lets try it a little lower and go to 35 psi. Now the truck idles pretty much like any stock PSD (you know they aint quiet) and I can not get it too stall when revving the engine to 2000 RPM and letting off the accelerator quickly. I probably tried 20 times and every time it came to an idle effortlessly, and this is in my 600 RPM idle program.

I am somewhat at a loss at how higher fuel pressure can cause a rough or choppy idle only when the engine is warm but I guess you don't have to understand it if you know it works. I was so 100% sure I had an oil side problem whether it be o-rings or within the injectors them selves but it turns out to be fuel pressure Also even more confusing is that the stage 1 injectors idled perfectly and didn't have any stall issues with the constant 55 to 65 psi of fuel pressure.

What I plan to do about this issue is to run about 35 to 37 psi fuel pressure at idle and hook my boost reference port on the fuel pressure regulator to the regulated side of my ITP Overboost Annihilator. That should get me to 55 psi of fuel pressure any time I am at 20 psi or higher boost. This will probably extend fuel pump life as well I would imagine since most of the time I am under 15 psi boost cruising down the road.


Long (extremely long) story short, if you have some idle irregularities it may be a good idea to try a fairly low fuel pressure to see if that cures it. Especially before pulling injectors to replace o-rings or sending them back to the builder. My next step was going to be to send them all out to have bench tested because CCT would not show me any problems with a specific cylinder.

Oh, I would like to give props where they are deserved. Thanks to Geoff (aka GTSMotorsports aka Hot Wheels) for recommending that I try some extremely low fuel pressure to cure it. He has to run about the same pressure as I am to cure some idle issues on his truck.

Eric
96 F-350 CC Dually
300/100% B codes, Stealth dual pumps, H2E, BTS trans, ARP head studs, Comp 910 valve springs, Tyrant Tunes
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post #2 of 16 (permalink) Old 07-09-2008, 02:43 PM
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Re: Fuel pressure causing rough idle when warm....

I have noticed some idling irregularities lately. I can feel the truck shake ever so slightly when running in park or at a traffic light. It has just recently began. I am running around 60-62 psi on the fuel, with stock injectors. It does it in each program as well as stock. I will try adjusting the fuel pressure to see if it changes.

2003 7.3 XLT FX4, AFE Stage 2, Regulated Return, Bowl Delete, 3/8" line from tank to heads, Pre/Post Filters, Tank mods, DP F5: 60T, 80E, 120R, 6.0 IC, 6.0 Trans Cooler, Suncoast Shift Kit, Wicked Wheel, ITP Boost Annihilator, Di Procol Optix, Straight Pipe, CCV, 285/75/16 BFG AT's
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post #3 of 16 (permalink) Old 07-09-2008, 10:22 PM
 
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Re: Fuel pressure causing rough idle when warm....

I would guess your rough idle is coming from ICP.

Take a reading when it's bone cold, then compare that to when it warms up.

Jody played with the ICP @ idle on my truck during live tuning and got it to idle awesome!
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post #4 of 16 (permalink) Old 07-09-2008, 10:30 PM
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Re: Fuel pressure causing rough idle when warm....

Jody bumped my icp up some at an idle and she purrs like a kitten now.
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post #5 of 16 (permalink) Old 07-09-2008, 10:47 PM
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Re: Fuel pressure causing rough idle when warm....

I have the same issue recently like in the past year.I blame my injectors or an injector for being out of spec and causing icp issues.I have checked mine and the computer never sees more than 2900 at WOT and 600 at idle.It use to be 800 idle and 3600 at WOT so something is fubar.

I would check your ICP if you can and duty cycle.


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post #6 of 16 (permalink) Old 07-10-2008, 12:39 PM Thread Starter
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Re: Fuel pressure causing rough idle when warm....

I've got a scan gauge and my Commander reads ICP as well. I'm still running the same tunes as I was with the stage 1 injectors, but I gues idle ICP could be the issue. IIRC I am at about 700psi in the 600 RPM idle program and about 750 to 800 in the 750 RPM idle programs.


Whether the ICP at idle is the problem or not I feel like a pig in sh!t with my truck idling like it is now. It's been 6 months since I could pull in some where with it and not have people looking at me like WTF is wrong with that thing.

Now my bigger problem, I pulled the turbo to fix what I thought was an oil leak at the EBPV actuator. I'm not sure if it was leaking or not but now I have a fair amount of oil leaking from under the pedestal. F###in OBS turbo

Eric
96 F-350 CC Dually
300/100% B codes, Stealth dual pumps, H2E, BTS trans, ARP head studs, Comp 910 valve springs, Tyrant Tunes
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post #7 of 16 (permalink) Old 08-03-2016, 03:52 PM
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Re: Fuel pressure causing rough idle when warm....

How did you lower your fuel pressure?
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post #8 of 16 (permalink) Old 08-03-2016, 04:06 PM
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Re: Fuel pressure causing rough idle when warm....

welcome to the forum! this being an 8 year old thread, you may never get an answer from them. but, i read the first post, and i'm kinda guessing that he put in a modified spring in the fuel pressure regulator (maybe either shorter or weaker)... otherwise, i'd like to know the answer as well!


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post #9 of 16 (permalink) Old 08-03-2016, 04:59 PM
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Re: Fuel pressure causing rough idle when warm....

ya I just noticed I have a very similar issue and I just put new fuel bowl in my truck and that's when it started, so I took the old spring assembly and installed in the new bowl and still no change!!!! not sure what pressure I have though
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post #10 of 16 (permalink) Old 08-03-2016, 05:04 PM
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Re: Fuel pressure causing rough idle when warm....

i hear that worn out injectors on 7.3s are kinda known for this, where at OP Temp the idle is all over the place because of fuel leaking past the pintle. i'm just assuming that the lower fuel pressure could be a bandaid for the symptoms.


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