if nothing has been changed recently, ie a tune or injector nozzles, it may be a sign you need to start saving your pennies and invest in a cp3.

 

Start by diagnosing the supply side. Restriction and air intrusion can contribute to what you are seeing. If you have a plastic wix filter change that to anything steel. Measure supply side restriction and consider adding a lift pump.

 

The fitler that I am running is a steel WIX filter. I dont think that it is air in the system as it will run fine and then all of a sudden just start to surge.

Start by diagnosing the supply side. Restriction and air intrusion can contribute to what you are seeing. If you have a plastic wix filter change that to anything steel. Measure supply side restriction and consider adding a lift pump.

 

What is a CP3? Also it has an edge insight programmer on it running in the economy mode.

 

The first thing to do is verify supply side restriction plain and simple. Just because the filter has been replaced does not mean there is not an issue here.

This follows along the same lines as the LBZ P0087 diagnostic outlined here:

http://www.kennedydiesel.com/docs/Duramax LBZ and LMM P0087 Low Fuel Pressure code.htm

Bottle test:

http://www.kennedydiesel.com/docs/Shim mod Bottle Test etc.htm

The main injection pump is called the CP3. They seldom fail. Regulators can get flaky and cause surging idle, but this is typically consistent. Air/foam in fuel can also cause a rough idle/surge condition.

 

Kennedy,
Been meaning to ask you and since this is related: your simple pressure pump you sell, is there any reason to run 2, under fairly stock conditions? You have the option for two, but I don't want to spend the extra money if not needed. It would seem on a vac system, under stock to mostly stock programming, just a small amount of pressure would be sufficient enough to help the system.

Just thought I'd ask before purchasing. Might help others decide too.

 

Kennedy,
Been meaning to ask you and since this is related: your simple pressure pump you sell, is there any reason to run 2, under fairly stock conditions? You have the option for two, but I don't want to spend the extra money if not needed. It would seem on a vac system, under stock to mostly stock programming, just a small amount of pressure would be sufficient enough to help the system.

Just thought I'd ask before purchasing. Might help others decide too.

High volume, low pressure. The second pump simply boosts the pressure to help compensate for drop across the filter(s) allowing you to run better with added restriction.

Years back I did a dyno run on a legit 500 RWHP LB7 (550-600 by most modern standards) and plotted multiple runs with identical curves with my lift pumps on and with them off.

It's not so much about the power it's more about keeping a constant supply of low psi fuel at the inlet of the CP3. I run the twin pumps on my 2002 at 1050RWHP and have no issues keeping up.

 

How does one know whether to change out the FPR or FPRV? I recently got the code P1093, and it has been surging at idle. Also i noticed that under hard acceleration that the fuel rail pressure drops way below what the desired pressure should be. Any help is appreciated.

As far as checking both, the FPRV is done by bottle testing at WOT (if the bottle is filling up then you need to shim or replace it.
The FPR is checked via the OBD at idle with engine warm. More than +/- 0.1k psi variation between actual and demand rail pressure and I would replace it.

Kennedy,
Been meaning to ask you and since this is related: your simple pressure pump you sell, is there any reason to run 2, under fairly stock conditions? You have the option for two, but I don't want to spend the extra money if not needed. It would seem on a vac system, under stock to mostly stock programming, just a small amount of pressure would be sufficient enough to help the system.

Just thought I'd ask before purchasing. Might help others decide too.

I'm not John but I do have his setup. The number of pumps IMHO would depend on the amount of HP (fuel flow) you are trying to achieve.....one pump is more than enough in stock form. As you start building your trans and maxing out your turbo, then I would definitely switch to the dual pumps.

 

I'm not John but I do have his setup. The number of pumps IMHO would depend on the amount of HP (fuel flow) you are trying to achieve.....one pump is more than enough in stock form. As you start building your trans and maxing out your turbo, then I would definitely switch to the dual pumps.

I figure one pump would be enough. I'm not after 'big power'. If I want power/speed I'll jump on my Ducati. Hell, I have EFILive and haven't touched my tune in 5? 6? years now. It's mostly to bypass the EGR codes from the exhaust work, and that's about it. I don't even have the computer that has my EFILive stuff on it. ):h

Thanks for the input though. This is one mod I forgot about back in the day, just revisiting and probably do it sometime soon.

 

At idle with the engine warm I am seeing upwards to .4 difference and it is bouncing everywhere.

 

I would go ahead and replace the FPR in that case.

 

Surge at idle

I have the surge at idle many complain about. I'm convinced it is the FPR. I have read many DIY threads on replacing this animal and my head hurts. From remove everything to it's not that difficult. Can anyone tell me where the FRP is located? Passenger side, driver side fore, aft? I hate to be stupid but I see zoomed in pics & I can't tell which way is up. Thanks for any help. 2005 LLY, 220,000 miles. No major problems so far except for the transfer case pump eating a hole thru the case.

 

I have the surge at idle many complain about. I'm convinced it is the FPR. I have read many DIY threads on replacing this animal and my head hurts. From remove everything to it's not that difficult. Can anyone tell me where the FRP is located? Passenger side, driver side fore, aft? I hate to be stupid but I see zoomed in pics & I can't tell which way is up. Thanks for any help. 2005 LLY, 220,000 miles. No major problems so far except for the transfer case pump eating a hole thru the case.

I think you should be able to do it by removing the entire aluminum intake up to the Y bridge. I never had to attack the LLY on an assembled engine, but the LMM works this way.

BTW we keep the genuine Bosch regulators on the shelf.

 

FPR

I believe its on the drivers side and you do have to remove a few parts to get at it.

 

I believe its on the drivers side and you do have to remove a few parts to get at it.

Thanks. I see some recommendations for removing the AC compressor & some say loosen the alternator & some say none of that is necessary. I will find it soon. Thanks again for your reply.