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Brent you already replaced your FPR though, right?

Does your actual vs demand rail pressure go up and down with the lope?
thats a good indication, if the lope causes the desired and actual to change, it could be the FPR

Just out of curiosity, Brent, what are your balance rates?
 

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I seem to be having the same issue. Last night I had less then a quarter tank and when I got home it was loping in park before I shut it off. This morning I drove to get fuel and at that time I put my additive in. After driving multiple places today it hasn't acted up once.
what additive and what mods do you have on your truck, that help us
 

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I use power service diesel supplement. I have an 05 lly has straight pipe side exit exhaust. Previous owner said it was ppe tuned but I'm petty sure it's on a stock tune right now. Motor is completely stock 120k on it
 

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Brent you already replaced your FPR though, right?

Does your actual vs demand rail pressure go up and down with the lope?
Yep, FPR has been replaced. Which did fix the lope in gear and trying to push through stop lights. This lope is certainly different from that one, in that it only lopes in neutral or park and smooths out the instant you put it in gear.

At the time it was happening I didn't actually monitor the rail pressures, but looking back in this thread in post #23 I have a log file where I did. Since now it's not loping I can't monitor it currently, but I doubt it would be any different than that log.

I'm trying to think why would the additive have such a drastic effect on this issue. Obviously the first thing that comes to mind is an FPR, but like you said it has been replaced and from my previous log actual vs demand FP seems to be good. My injectors are basically new so whats left other than a CP3? I doubt there is anything wrong with the CP3. So what else could fuel lubricity and cetane be affecting? or I could just be reading too much into this also. Maybe my truck just really hates winter fuel...:)

thats a good indication, if the lope causes the desired and actual to change, it could be the FPR

Just out of curiosity, Brent, what are your balance rates?
My balance rates are all good no more than +/- 1. I replaced all my injectors at Christmas back in 2012 so they are still pretty new. At most can only have about 30,000 miles on em.
 

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Mine was doing this. I reolaced the fpr and all is fine now, smoother idle and increased take off power
 

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Just thinking out loud...
- It only lopes in park or neutral
- It only Lopes above 140ish degrees, sometimes not till 160ish
- the main fuel rate and rpm are bouncing around while "loping"
- putting a load on engine whether brake pedal, steering or AC the lope goes away
- everything on the CS looks good when in gear/not up to temp/while under load
- the fuel rail pressure is not fluctuating more than +/- 0.1k at all times
- no air in fuel lines/ no fuel leaks
-injectors are in spec according to balance rates

Im sure I missed something...

But I am thinking some sensor has got to be sending the computer misleading information, which in turn causes the main fuel rate to fluctuate, and is ultimately causing the lope. (my theory at least)

If any part of this "theory" is correct, then looking for the sensor sending this bad info is what I need to be looking for.

...BTW I bought a Haynes Duramax rebuild book thing off Amazon today, should have it Wednesday, gotta love Amazon Prime. maybe it will give a little info on the electrical monstrosity that are these engines.
So we still haven't figured anything out on this? These symptoms above are the same exact for my truck. My 05 is bone stock. No mods. The lope/shake in park is more of annoying than anything.
 

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Close friend is having these same issues currently. Bone stoke LLY w/180k. Lope/Surging getting worse. Bout to help him tackle this problem. Will follow up in weeks ahead.
 

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2005 Duramax Rough Idle

I have the same problem I replaced all of the injectors at 102000 miles and one week later it started missing again a guy told me it is my fuel pump on the engine when the fuel is cold the fuel is denser and when the fuel is hot it is thinner and the pump can build pressure better when the fuel is denser and I said the truck idles really good in the winter when the temp is around 10 degrees and the engine temp is around 185 degrees. My truck started that problem at 8000 miles and the dealer where bought it could not find the problem for years that I took it in intill the warranty ran out and today at 128000 miles on it it still has a rough idle the guy said wait intill your truck gets to where you have to fix it because it is exspecive to fix it.
 

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Did anybody solve this? We have a 2005 lly in the shop now with a rough idle in park and neutral only and only after it’s warmed up. Balance rates all drop to 0 when this happens you can shift it back into gear and it’s perfect. All new injectors harness fpr and sensor. We have a parts truck here and have swapped all the modules over that we could think of.
 

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Mudtruck1, did you figure your issue out? I have a 05 LLY that didn't do this on original motor. It dropped a valve at 220k, found a very clean 102k motor and swapped it out...runs stronger than ever but I too have been bitten by the rough idle bug. Can't seem to find the solution. I checked all wiring, swapped harnesses, changed NSBU, ice picked all injector plugs on both harnesses, changed FPR, swapped fuel filter heads and filters. It definately has to be electrical. Once there is any kind of load on the motor it will smooth right out. No surge in gear.

Also a little info on the rig(new here). 05 LLY, EFI Live by Kory, stock trans, 30% injectors from LDS, PCV re-route, EGR delete with LB7 up-pipe, BD driver side manifold, MA motor mounts, Garrett Stage 1 VVT turbo, 4" MBRP exhaust, MBRP Downpipe.

All said parts were swapped from old motor to new...no issues other than this rough idle in park or neutral and balance rates wont read unless in gear. Any help is appreciated!
 

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I should also add that the old motor did not do this, but it didn't have EFI Live for all of 2 days before valve gave way. Before EFI, it had Edge Evo on it for over a year and no issues. Since new-to-me motor has less than half of my original I figured all sensors has that much less wear on them...so I'm kinda thinking it's a tuning issue. Like others my desired and actual fuel pressure is good. At a loss here...
 

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I am in the same boat....replaced 6 of the 8 injectors (over time) was told some were causing my "knock"...well still knocks but now lopes in park and neutral....and if I turn the defrost on it seems to stop for a while....
 

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FIX Update! To all that has tried to put a new harness on with no luck, I strongly suggest you take the one you took off...go thru EVERY wire carefully. Ice pick (and I mean pick em deep) EVERY injector plug. I bought a roll of plastic corregated wire protector and redid the entire harness. Taped up everything really good. Swapped them back out last night and now she runs quieter (less injector ticking) and so far no more rough idle in park/neutral. I did check my reluctor wheel will I was at it and it was tight, no loose or missing bolts. Everyone kept saying it was some kind of electrical problem, and they were right. Hope you guys have already found your fix as well!
 

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LLY05D, the defrost will clear it up...as well as brakes, put in gear, and a/c. For me it was some kind of connection issue. I had a spare harness and went thru every wire, ice picked injector plugs, wrapped it all back up and swapped it out. Solved all issues from rough idle in park/neutral to loud injector ticking at most all rpm range with slight loss in power. Hope this helps!
 

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So another update. The issue is coming back, and is very intermittent. I'm still convinced it is the wiring harness issue...so I just ordered all new 8 injector connectors. Once they come in, I am going to go thru the harness I took off and reseal it all up like I did the one I put on. Then splice all the new connectors on. Swap them back out and report back. Will be about a week or so I'm guessing. I came across another post of another guy having exact issue, he ice picked #7 and it didn't fix it. He bought a new connector and it did in fact fix it. So I'm going with that little bit of hope, that and the fact it ran perfect for about a week before doing it again. Will post up results.
 

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Any word on this?
I'm still having the same damn issue...I have all 8 new injectors, new fpr, new filter head and filter, installed a race plug, replaced both lines going to filter head (all parts came from Lincoln diesel).....I do not have a problem with the truck starting even after sitting for a week in negative temperatures....she will fire right up...it only lopes when it gets close to operating temp as stated above....my problems started with a knock while driving (balance rates looked great!)....replaced 1 injector and didn't fix it....took it to a shop and was told to replace 3 injectors that looked a little off...replaced them and I started getting the lope and still knocking...bit the bullet and replaced the other 4...the hard knock Is gone but still loping and seems to have a "rattle" upon acceleration....I installed clear lines going to filter head and found a large amount of air coming out of filter head...replaced the whole unit..amazingly nothing changed!!( I reinstalled clear lines on new filter head to check for air and found very little bubbles)
So I replaced the fpr because that is a known culprit...nothing...
Instead a plug in place of the fprv...nothing...
Truck is still loping at idle only in park and neutral and only when warm...and I still have this (what I suspect to be injector rattle)...
No lift pump...
Small ecm tune (previous owner)...
New injectors...
Have checked wiring, ice picked all 8 injector plugs and added dielectric grease to them
 

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So we still haven't figured anything out on this? These symptoms above are the same exact for my truck. My 05 is bone stock. No mods. The lope/shake in park is more of annoying than anything.
Did you guys figure this out?? My truck is doing same thing rough idle above 160
 
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