I am having a rough idle and I did plug my EFI live into it to see what was going on and found that my fuel rail pressure is averaging about 65psi higher than desiered. I did a search and found that most of the topics discuss bad injectors. I just has some replaced under warantee and I checked my balance rates and they are all under 2mm3. So that can't be the probem either. What else can cause this problem? Also if it helps it doesn't do it all of the time. My truck voltage is at 14.2vdc. I dont know where else to check. Is there a notorious ground connection or something?

65psi above desired won't cause any odd idle characteristics -typically.

Is the idle messed up on all tune positions or just one in particular? Does it idle rough on the stock tune?

Nick

65psi above desired won't cause any odd idle characteristics -typically.

Is the idle messed up on all tune positions or just one in particular? Does it idle rough on the stock tune?

Nick

like nick said, see what it does on the stock tune.

The stock tune idles rough and so does the rest of the tunes I have loaded into my DSP5

The idle has now smoothed out. I haven't done anything to it. What do you think could have happened... any ideas?

Rough idle started back up again today... Any idea's???

did it start after the lift pump install??

It did. I did a search on here and found that some lift pumps provide too much pressure and causes the engine to lope. I adjusted the bypass spring so that my fuel rail pressures as logged by EFI Live were less than 200 psi more than desired pressure. I have also logged while the rough idle is present and seams that I am only about 65 psi higher than what I should be. Wondering if that could have been the problem I removed the fuse for the lift pump thus taking it out of the loop and no change was noted. Are you thinking something else?

just trying to narrow things down. what about the fpr?? if its surging, this could be the culprit.

how can I check the FPR? i logged something to do with it but am not sure of what it means. It showed a consistant 35%?????

the % would fall slightly during an acceleration

I have had a rough idle and a smooth one ... It seams to change once a day. Any ideas?

My 02 was doing the same thing so i took it to the chevy house and they said it was the fuel pressure regulator and it is $900 instaled.

the bad idle has been comming and going. I have ran some diesel kleen through it and still no fix. it does seem to idle rough only when at a complete stop. If I am parked or at a redlight. If i let off of the brake in drive it smooths out. has anyone else experienced this problem?

how can I tell if it is a FPRV?

This idle is getting worse. Is there any vacuume hoses I can check? I am shootin in the dark here? Help

What about leaks in the intake or something? Could the MAF sensor be a cause of this as well??? I need some help

I have a K&N intake and I have read that the oil from the filter will get onto your MAF sensor and cause funny things to happen. I have never had a problem before but what does oil on your maf do and what symptoms does it cause?

I have seen a few MAF sensors that were covered in oil and dirt from over oiling the filters at most it caused a hesitation in acceleration but i dont think it would have much to do with a roudh idle. mine does it once about ever month and a half or so. i give it a good dose of 2 cycle on about a 1/4 tank of fuel and it goes away for awhile.

I have put in a couple of healthy doses of diesel kleen. Should I also try some 2stroke oil? if so then what kind and how much is good?

I have pulled some DTC from my computer... didn't realize there were any on there
b2610
b0229
b3770
c0035
c0055
u1300
p0089
p0101

I have looked up what they mean and for the rough idle problem it looks like maf and fpr Where should I start?

ideas???

anyone?

hello??? Is this thing on?

Turn off the lift pump and see what happens ? Did you check what the psi was on the lift pump ?

I have pulled some DTC from my computer... didn't realize there were any on there
b2610
b0229
b3770
c0035
c0055
u1300
p0089
p0101

I have looked up what they mean and for the rough idle problem it looks like maf and fpr Where should I start?b2610 dimming circuit-b0229 hvac door actuator-b3770 ?-c0035 front wheel sensor-c0055 rear wheel speed sensor-u1300 data link shorted-p0089 fuel pressure reg. performance-p0101 maf sensor performance

Ok cleaned the maf and let it run for a while. As of yet no dice. When I press the accelerator to (efi live says) 0.4% the funny idle goes away and runs smooth. I have attached a log file and I placed notes into the file. Between the two notes (where the tp is higher than 0) shows what the engine is doing while the rpm feels smooth. Before and after the notes the idle feels like I have a big cam in it or something.
Thanks for looking

I also have this DTC summary that maybe could help someone help me.
Again thanks for looking

I don't know exactly what this psi is but unpluggin it doesn't help the idle. My rail pressures are about 65 - 100 psi above what they should be so I am not sure if that would cause the problem. It may cause the FPR code though. I am trying to find me a 15psi pressure guage so I can find out for sure. When the MAF is disconnected it doesn't change anything about how it runs. Should i suspect a bad MAF? I cleaned it and still no better???

please help????

What is your balance rate ? How old is the fuel filter,My be bad fuel ? and 60 to 100 psi off on your rail psi is ok

all balance rates are less than 2.5. Fuel filter was replaced (trying to fix this problem) about 2 weeks ago. I have gone through 3 tanks of fuel from different gas stations???

Did you get it fixed ??

alright guys sorry about the delay. I have been troubleshooting as much as i can but work has had me on the road alot.

So I am sitting here with my EFI Live up and my hood popped trying to figure this thing out. I was watching my rail pressures as I disconnected my lift pump and guess what my rail pressure dropped over a 25 second period all the way to stall. WTF does that mean? I guess my CP3 is going bad??? I continued to watch rail pressure and it seamed to loose about 5 pounds or more a second. Does that mean regulator? I have recently changed my fuel filter again but still didn't fix the idle... Any help????

i would guess that your fuel pressure regulator is sticking. i have seen this on a couple of trucks. the disconnecting the lift pump and it dying just tells me that your lift pump is not flow through

I was under the impression that the AIR dog was flow through. I have disconnected it before but I don't recall how long I did leave it disconnected.

I see that you have the same lift pump. Does yours die if you turn off the pump?

sorry didnt even look at your sig. yes airdogg is flow through

what can I do to try and fix this problem? I figured that if the FPR is bad then i should see some fluctuations in my fuel pressure. What is the tolerance for the fuel pressure difference? How else could I check to be sure that is the problem. $400 regulator is pretty expensive to replace if you know "know" it is the problem...

well with efi i think you can go in and command max pressure or less and see if it changes. or you can unplug the connector from the back of the fpr and it should spike to max pressure

and you can get a modded regulator way cheaper than 400. i think they can be had for about 150

I have used EFI to increase and decrease fuel pressure and the funny idle didn't go away. Where is this connector That i should pull??? (newbie)

its hard to find it is on the back of the cp3 pump in the valley of the motor. behind the below the alternator

when I get this disconnected what will this tell me?

I think I see a connector way down there.. how the heck do i get to it? Is there another place to disconnect? (if i am even looking at the right thing)

you just have to reach down there and un hook it. truck should be running rail pressure should max out and you should have a really lopey idle. if not then regulator is sticking

finally got it with the aid of a long screw driver. Well I took a log of it and the pressure jumpped up to 26106. does that mean my regulator is good???

Ok I learned a lot today.

1. My bubbling lift pump was because I was low on fuel... Got some fuel and no more

2. Increasing the current to the regulator using table B1010 did nothing to the commanded current for the regulator. I also tried the table on maximum duty cycle in conjunction with B1010 and still did nothing as observed with the scan tool. Still maintained 1480 or so ma of current. I used DVT to control rail pressure and it did control my regulator current. I went down to about 2000 psi and still the idle remained weird. (1800 or so ma of current to regulator)

3. I found something really interesting and enclosed a log to show you. I logged main injection PW and found that it is all over the road at an idle and when I press the throttle to .4% or above the PW maintained a more consistent number.

What controls main injection pw during idle mode? If it is not the tune then I would think that one of my sensors could be bad. It would have to only be used at 0% throttle though. What could I log to at least rule out some things?

Again thanks for all of your help
Justin

Been looking through the tune file while running the log and I can't for the life of me figure out why the pulse width is changing. Am i Missing something here???

i am still leaning towards the reg sticking

think so??? Is the pw supposed to "bounce" at an idle then not with some throttle? Sorry to be so hard headed I just don't want to throw $400 at a part I am not 100% sure that its the problem.

well no it isnt suppose to bounce around, but what could be happening is the ecm says that it is not getting enough fuel because the reg is sticking but it doesnt know that. so it bumps the pw up to compensate for not getting enough fuel. then once it goes up ecm says ok every thing is fine know so it goes back to normal. then all of the sudden it does it again. it is a viscious circle :D

I thought about that and my rail pressures are fairly constant so i then looked at mm3 per stroke (calculated) and it is also fairly constant. They do bounce around but the psi is bouncing around but it bounces less than 150 psi which it also does when i push on the accelerator so i "assume" that bounce is normal. The mm3 is pretty constant at 6mm3 except for when I press the accelerator then it will jump to 9mm3

anyone else have any opinions or know of a cheap place to find a FPR?

So did you get it fixed yet?

No still have a bad idle. I am still driving it. I am just not sure that the regulator is the cause. If it was I would think that i could log some rail pressure fluctuations??? Still trying to figure out a good way to measure airdog pressure (just been really busy at work getting ready for hurricane season)

Beach said in post 41 that you can get a modded FPR for 150ish. Where can that be bought, beach? I just discovered that I get a rough ("Lopey") idle when I max my fuel rail pressure out. I am pretty sure I have a CP3 going bad though. My CP3 maxed, is only producing 11,300PSI. I am leaning toward it being your FPR. I wonder if they can be removed and cleaned? I have good detailed replacement instructions I can send you. Compliments of a DP member.

I have those instructions stareing me in the face. The FPR can not be purchaced for 150. That is how much it takes to modifiy the one you have. I have checked into that from Fleece perf.

Oregon Diesel has FPR's for 150 plus shipping. Stock FPR. Could be new, used, rebuilt, dont know.


You'll have to check the website it has been a while since I searched for one.

I purchased mine from StewieTuned, or Nelson Diesel Performance. Brand new GM.

Ok guys been a long day... I have finally installed my new FPR from Gillet diesel. I am pretty upset though. Still have this rough idle. Someone please tell me how I can figure out what is causeing my MIPW to jump anywhere from 289 to 562. It jumps only when at an idle. If i increase Throttle to say 0.4% the PW smooths out and also the idle smooths out but RPM does not change. This is really agravating and my mood keeps worsening. I am currently refilling my coolant with my logger going. I will stick around for a while if anyone has any responses.
TIA

Raise your idle.

I have commanded the idle to anything between 500 to 700. The roughness is still there but is harder to notice. On a side note I just got the truck back from GM they replaced all 8 injectors with new ones and it still has same symptoms. I also logged my MAF while tapping on it and found that my readings were anything inbetween 43g/s to 46g/s. What should it be. What are the tolerances for it. What else can I check??? I have another thread going about a cough at hard acceleration that I am also trying to fix. I need the truck for hauling on the 9th. Please help me solve this riddle.

I was talking with a tech at a gm garage here a while back and he said they had a guy with a suncoast tranny with loose flywheel bolts??? He also said something bout a crosspin in the crankshaft being worn or something, maybe look into that to see if those could be the problem. He said the rough idle was a balancing issue. Just a thought, problem is none of those are an easy fix. I feel for you dude, hang in there!!!

how would i check those?

I am still under warrantee from suncoast but I wouldn't even know how to dictate why they would need to look at that cause they would have to drop the whole tranny because it could be a problem???

My suggestion would be give them a call and tell them about yr problem, explain to them all the things youve done and see if and I say if the flywheel bolts were loose could that cause a rough idle problem and see what they say, its worth atleast a phone call.

One thing Im thinking would be if it is a mechanical balance issue wouldnt yr balance rates be funny? By the injectors trying to make up the difference of the rough idle by changing the balance rates to smooth out the idle, without me going back and re reading the other posts does it smooth out when you pick up the throttle in a few 100 rpms?

it smooths out when i add .4% of throttle possition. The pw are all over the road 200us to 600us at an idle. if i press throttle in 1/4inch (.4-.8% tps) the pw evens out and rough idle goes away. If i command different idle speeds the problem is still there yet less noticeable.

Any ideas?

Any ideas