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Loping or surging at idle...it seems like my truck has a big cam in it.

Max Attitude

Max Attitude

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I have noticed once in a while my truck will lope like it has a big cam in it or something. That's the best way I can describe it. I was reading old posts over at the place and some suggested that it was a bad fuel rail pressure regulator (FRPR) or it could also be a loose reluctor wheel on the crankshaft sensor. Anybody have any ideas on what it would for sure be? I have 97,xxx miles on it and need to get it in soon before warranty is up at 100k.

Could any of this be caused by the recent head gasket replacement at 93k miles?

Other than the weird idle it runs fine.
 
You know, its funny you mention that because I've felt it in mine recently too. Its only in idle though, park or drive and when I start rolling, its fine. Its happened 4 or 5 times since I've owned it.
 
Even my future bro in law asked me why it did that. I just told him that's the way it was but I want to get it fixed if something's wrong so I'm not stuck with the bill later.
 
x2 on the fuel pressure regulator,that will cause an erratic idle, if the fuel pressure relief valve goes bad the vehicle will fall flat under hard acceleration.
 
If you have a scantool look at the actual rail pressure and the desired rail pressure when you have the problem. If they stay close together its not a regulator if the Actual is high by more than 500 psi you've got a regulator issue.
 
Diesel Tech said:
If you have a scantool look at the actual rail pressure and the desired rail pressure when you have the problem. If they stay close together its not a regulator if the Actual is high by more than 500 psi you've got a regulator issue.
Click to expand...


Thanks for the reminder... I'll check that with my Predator. Last time I looked, it was close but that was a while ago.
 
Diesel Tech said:
If you have a scantool look at the actual rail pressure and the desired rail pressure when you have the problem. If they stay close together its not a regulator if the Actual is high by more than 500 psi you've got a regulator issue.
Click to expand...

Here's what I found via the Predator.

Fuel Rail pressure- desired 30.00mpi
Actual bounced between 27.2 and 31.4mpi

Fuel Pressure regulator- jumped around from 1000 to 1700 ...it did not state the desired level.

What do these #'s mean? What does mpi stand for?
Thanks
 
I will bring it to the dealer soon but can anyone tell me about the #'s I posted above?

I'll keep in mind the 2 cycle oil thing just in case the dealer won't fix it but I run fuel additive from time to time so I don't think it's anything the oil will help.
 
If you have read the unit properly then they have a typo as it should be mPa. That is a unit of measure for reading pressure

30 mPa = 300 bar = 4350.9 psi

The Desired is what the ECM is telling the pressure to be at and the Actual is what it really is. Those number look fine so it's not a rail pressure issue. If it's going to be awhile before you get to the dealer dump 1 qt of ATF into a full tank of fuel. See if that settles it down. If it does my guess would be you are starting to have injector issues.
 
Diesel Tech said:
If you have read the unit properly then they have a typo as it should be mPa. That is a unit of measure for reading pressure

30 mPa = 300 bar = 4350.9 psi

The Desired is what the ECM is telling the pressure to be at and the Actual is what it really is. Those number look fine so it's not a rail pressure issue. If it's going to be awhile before you get to the dealer dump 1 qt of ATF into a full tank of fuel. See if that settles it down. If it does my guess would be you are starting to have injector issues.
Click to expand...

Man I would hope not seeing it's an LLY...but there have been a few LLYs with bad ones. Would it show now by reading the balance rates? I'll check them out too I guess.
 
Well guys, finally got my truck in... 99,933 miles on the odometer. They found out that #1 injector was out of spec so they replaced it under the 100,000 mile engine warranty. I just had to pay the $100 deductible. Hopefully that fixes the problem. :thumbsup: Glad I brought it in when I did.

Looks like you were right about the injectors Diesel Tech. Hopefully that will be the last of that issue for a long while.
 
the lly injectors are not common thing. especially if you run additive every tank. after a few tanks a bio a buddys truck on original injectors and 80k had balance rates of .5 or so. having the extra lube and cleaning agent helps alot.
 
From what they explained to me is was a seal that went bad. 1 injector and head gaskets before 100k.....I sure hope that's the last of major issues but the future isn't looking too bright at the moment.

Oh, and my rough idle is still there. They think it might be because of the unplugged and blocked egr. They were aware of all my mods and and did not care. I have a great dealer in that respect. Dealer doesn't think my idle issue is anything to worry about. It's not bad, I just happened to notice it.
 
I know I am an LB7 guy but mine did the lope thing real bad. It was horrible to try and hook up to a trailer. You would slowly back up but the surge would just rush you back. I started using Stanadyne again and it seemed to go away. See my post about Stanadyne. I have been lazy lately and not used it and it seems to be coming back. It is not as bad as it was but the last time i started to with a slow surge/lope. Can't hurt...
 
Clark20ry said:
I know I am an LB7 guy but mine did the lope thing real bad. It was horrible to try and hook up to a trailer. You would slowly back up but the surge would just rush you back. I started using Stanadyne again and it seemed to go away. See my post about Stanadyne. I have been lazy lately and not used it and it seems to be coming back. It is not as bad as it was but the last time i started to with a slow surge/lope. Can't hurt...
Click to expand...

I can't find that stuff around me. I have run the Power service stuff before and it didn't help the idle thing. Mine isn't anything like you describe....yet. I can just hear it good with the straight pipe exhaust. If I sit real still I can feel it in the seat but it doesn't lurch forward if I let off of the brake.
 
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