Poss Fuel Delivery Problem?

[CCR91]

Hello,

I have a stock 01 LB7/Allison with 51,000 miles on it that has a problem I hope someone can help with.

When cold, the engine almost seems like it surges but it's more of a tone change. It is most noticeable at about 1,500 RPM @50 mph. It is quite bizarre because the tach does not register an RPM change and it doesn't sound like the engine is changing speed. When I stick my foot in it from a stop up to 75 mph, the engine pulls hard and smooth up through 3,000 RPM. No smoke (black or white) and no oil in the crankcase, the oil is nice and clean. Coolant level remains normal. No Check Engine/SES lights. No problem starting.

Once the water temp passes 150, the problem is just barely detectable but still occurs.

It is almost as if the pilot injection is not working. Usually, when I hit about 2,500 RPM the engine noise becomes quite louder as the pilot injection kicks off. Now, when I exceed 2,500 RPM, I notice no change in engine sound. My wife also noted she thought it sounded louder at idle.

Any ideas?

Thanks for the help.
Corey

[More Power]

Might be a good idea to change the fuel filter as a first step to determining the cause of the problem.

The fuel pressure regulator (FPR) can produce surges (barely detectable or more significant) and it could cause some change in sound.

Your dealer tech can use a Tech II scan tool to look at fuel rail pressure.

Jim

[Kennedy]

Generally, a lope/surge when cold is related to programming and warm is the regulator. The 2001 seemed to be the most common year to do this and had a programming update early on. I've had guys add a bunch of my FPPF Total Power to the fuel and this condition lessened and often disappeared. If it is the regulator it may well come back, but using a quality lubricity additive lessens it indicating that there is a definite need/benefit to using it...

[CCR91]

Thanks for the help.

I had the filter changed about 2 months ago as part of the recall.

What is the proper pressure?

Does the 7yr/100,000 injector warranty cover the regulator? If not how much does one cost? I have exceeded the 5-yr warranty.

Thanks again,
Corey

[More Power]

Fuel rail pressure can vary, depending on RPM and load. A dealer tech can look at two values for fuel rail pressure - Commanded & Actual. If there's a fluctuation in pressure, the "actual" will varyup/down, while commanded will remain more steady (or it could change in an attempt to compensate).

Jim

[CCR91]

The SES light cam on today. I will take it in next Tuesday to have it looked at. Will be interesting to see what it is. I sort of hope injector because they are warrantied. I don't thing fuel pressure regulator is.

Corey

[CCR91]

Update:

I got my hand on a Genisys scan tool for a few hours today, nice piece of gear.

The SES came on due to the DTC code P0089A. I looked that up in my manual and it corresponds to "Fuel rail pressure sensor indicates a pressure more than 20 mPa greater than desired."

I have a few more questions now.
1. According to the Scan tool, the desired pressure was 34 mPa. While idleing, the pressure fluctuated between 29 and 41. Is the 34 Mpa correct, or is this a value that is manually inserted from a previous test? The fluctuation directly corresponded to a RPM change and surge (from 570-620 RPM), which I originally thought was just a tone change. Sometimes, the actual rail pressure stayed at 34 mPa. When that happened, the idle was very smooth and rock solid at 600 RPM, no surge.

2. When I ran the engine up to 2,000 RPM, in accordance with the test procedures, the actual rail pressure did not fluctuate and remained at 88 mPa. Now that I got home and read the test procedures closer, I can see I did the test wrong. I thought I was looking for a min of 20 Mpa, not a difference of 20 Mpa between desired and actual. What should the desired pressure be at 2,000 RPM? I only have the surge problem at idle or when cold around 1,500 RPM. Above that no issues.

3. The next step in the test, assuming that I saw more than 20 mPa difference is Go to Diagnostic Aids." I can't seem to find that in the P0089 section. Some other DTC's have a Diagnostic Aids section. What are the diagnostic aids for this DTC?

4. Assuming I saw less than 20 mPa differnce, I am to use a vacuum gauge to check to see if the fuel filter is clogged. I did not have access to the J 44638 vaccum tool so I could not run that part of the test. However, I did pull the cap off where the gauge attaches. Is this the fitting that is just above the accesorry belt idler pulley? If so, when I pulled the cap off, I noticed a small amount of liquid puddled inside. It smelled like diesel. Is this normal?

5. So far, the indications point to Fuel Pressure Regualtor (assuming filter is good). My 5yr/100,000 mile warranty has expired. Does a separate 100,000 mile warranty apply to the fuel pressure regulator?

Thanks again for the help.

[jbplock]

... I did not have access to the J 44638 vaccum tool ... I did pull the cap off where the gauge attaches. Is this the fitting that is just above the accesorry belt idler pulley? If so, when I pulled the cap off, I noticed a small amount of liquid puddled inside. It smelled like diesel. Is this normal?

Yes, you have the correct fitting - the Schrader valve test port ... a little diesel in the fitting is normal ... Click Here for some pics of GM (Kent Moore) gauge...

JK sells a better one ...
Fuel Filter Restriction/Lift Pump Psi Gauge Kit for Duramax

As MP suggested you might want to just change the filter to rule it out ...

[CCR91]

Update:

I replaced the FPRV and that has solved all the problems, although I have yet to connect a scan tool to verify the fuel pressure. The SES light went out and the idle is very smooth.

FYI, here is a run down on how I did it (The Helm's manual for my truck states that the FPRV must be replaced as part of the fuel pump. Accordingly, the manual states procedures corresponding to removing the entire pump assembly which is way more than needs to be done).
1. Drain coolant.
2. Disconnect batteries.
3. Remove black plastic inlet duct that connects airbox and turbo inlet.
4. Remove serpentine belt.
5. Remove 4 AC compressor bolts and unplug two electrical connectors, roll compressor off to side.
6. Unplug the two large bail connectors and remove bail support bracket. A small electrical connector is located on the bottom of the bracket and must be unplugged. (Note: I think I could have done without this step but installing the upper radiator hard pipe is difficult. I know because I forgot to install the hard pipe before the bail support bracket).
7. Remove upper radiator hard pipe and thermostat assembly as one piece.
8. Remove turbo turbo inlet pipe (Note: a few rubber hoses may need to be removed to gain access).
9. Remove FPRV bolts and remove FRRV (Note: I did not have to remove any fuel lines or other components. I used lots of patience and a 1/4" drive ratchet and torx bit with multiple lentgh extension combinations and swivels. I may have saved time by removing other components but did not want to break fuel lines, etc).

Assembly notes:
Reverse the procedures but here are a few tips:
1. Have a long magnetic and/or grabber handy, you will drop small parts into the valley for sure.
2. You will need a new gasket for the turbo inlet pipe to turbo connection. It is part # 97318441 and cost about $8. I have seen it for $3 - $5 on the internet.
3. This is a great time to replace the thermostats. The rear thermostat body is not centered and needs to rotated to clear the housing.
4. I destroyed two "banjo" clamps to remove a hose to gain access to the turbo inlet pipe and a hose connecting to the coolant hard pipe. I had two 3/4" "normal" hose clamps available.
5. Refill of coolant was about 2.5 gallons of 50/50 mix.
6. I pumped the primer at the fuel filter just for kicks. Not sure it it helped but it fired right off.

This was my first time to do this. Total time was about 4 hours, this includes showing my 9-yr old son how to do it. Probably could have been done in three by myself.

Thanks to all on this board that have provided insight to this. I had forgotten how smooth my truck is supposed to run. I figure dealer cost would be in the $500 plus range. Doing it myself was $240 for everything.

Corey