Uneven Idle

[crafty]

Lately my truck has developed an "uneven idle" which seems to be more obvious once it is warmed up. If you watch the tach it may move somewhere between 50 and 100 rpm. (Normal idle is about 600 rpm so it jumps to near 700.) Sound wise it is very noticable. Maddmatt, I was wondering, is this a sign that I am developing injector problems? The mileage has been excellent with the last two tanks coming in at over 23 mpg (imperial gallons))and there is no shortage of power or acceleration.
I had the flywheel replaced two years ago and I think it is going again. Could this cause the idle to be off? I have a clattering noise when I depress the clutch with the tranny in neutral (only noticed this in the last week) and a vibration occasionally. They won't work on the flywheel until I can give them some proof but it didn't act up when I went to the dealer a month ago.
I was thinking of having the dealer check the injector balance rates. Is there any other things I need to have them check?
I should also add that for the last few months I have had an noticeable engine knock when starting up or making the engine work at an idle. This doesn't happen all the time but it is there.
Thanks for any help you can give.

[ 07-25-2005, 03:58 AM: Message edited by: crafty ]

[Kennedy]

The varying rpm at idle is typicaly caused by a failing fuel pump regulator which is varying the rail pressure.

The rattling sounds like the dual mass flywheel. Fairly common thing as I understand.

Both have 100k warranty if you are still that low on the clock.

[madmatt]

if your milage and power is still good I'd side w/ JK and say you've got a sticking FPR. There is a bulletin on this that states if contamination is found in the end of the FPR, replace the entire pump. When they give you a diagnosis if they don't mention a bulletin or replacing the pump, simply ask them about this bulletin and procedure. Don't TELL them about anything, you'll just ****'em off. Trust me service advisors hate being told how to do their job or being questioned.

[crafty]

I went to the dealer today and the tech there took a balance rate reading of the injectors.
Here are the numbers.
Cyl 1 0.5 mm (Cubed)
Cyl 2 -1.2 mm "
Cyl 3 -2.9 mm "
Cyl 4 -0.4 mm "
Cyl 5 -0.7 mm "
Cyl 6 0.5 mm "
Cyl 7 7.0 mm "
cyl 8 -2.5 mm "

Fuel rail pressure was 35.0 MPa
FRP Regulator Command 38%

After finishing that the tech said injector 7 was bad and needed to be replaced. He is to call GM in the morning to see if he should replace them all or just one. (When he shut off the number 7 injector the engine was much quieter and the knock was gone.)

As for the clattering noise, they say it is the throw-out bearing but the service manager thinks it could be the flywheel as well.

My feeling is that I should get all eight injectors done and a new flywheel as well. What is the opinion of anyone here who has been through this already? (I have 93,000 kms on the truck and 5 months left before my main warranty runs out.)

All opinions are welcome. Thanks,

[More Power]

It is my understanding that GM issued a service advisory some time back, stating that all eight injectors were to be replaced whenever one or more were found to be defective.

As far as the FW, let them look at it. The flywheel is specifically mentioned in the engine warranty coverage, so you'll not be responsible beyond the deduct if the mileage is under 100K (or equivalent kms).

Jim

[copperhead]

I just had my FPR replaced for the exact symtoms you are describing. The dealer, after hooking my truck up like a patient in the OR said, we are going to have to replace the injectors. Then after working with GM for a good part of the day said that they would replace the regulator. That fixed the idle surging and I don't know that it has ever sounded better. I have read alot indicating that the injector failure rate may have been skewed by misdiagnosis. I am nervous though about the injectors because of all the HOOPLA. However, I see alot of older model DMaxs and say to myself, all these guys can't have had their injectors replaced. I have 77+k miles and was able to get my regulator replaced for $0 under the emission warranty, after I had GM call the dealer and explain it to them. Both provided an excellent service experience.

[madmatt]

I've e-mailed you but if you come here first....Have your dealer check out PIP3292. They may want to fix your flywheel first. The vibration caused by a worn dual mass can cause skewed balance rate readings. heres part of the bulletin...

Complete SI diagnostics for Rough, Unstable, or Incorrect Idle and Stalling.

Complete SI diagnostics for any DTCs found.
Inspect the fuel system for excessive contamination.

If the vehicle is equipped with a manual transmission, a worn or damaged Dual Mass Flywheel may cause excessive crankshaft speed variance. This will cause the cylinder balance rates to fluctuate or read zero. Diagnose and repair Dual Mass Flywheel concerns using current SI procedures.

[madmatt]

also have the dealer reset everything and recheck the balance rates to see if #7 reappears as the weak hole. have them do a power balance test and see what happens then have them. Then have them read this...

The numbers below refer to the step numbers on the diagnostic table.

If the majority of the balance rates are positive and high, the dual-mass flywheel is causing a harmonic vibration that is affecting the engine fuel control system.

A dual mass flywheel concern will cause the balance rates to be inaccurate. The transmission concerns must be repaired before any fuel system diagnostic can be performed.

....guess I'm the only one in the world who actually reads any of this info in dealerworld. your dealer has the same access to this info as I. ask them to check it out sometime...good stuff ;)

[madmatt]

this is when we're supposed to replace all eight...

If fuel return flow on either the right or left cylinder bank is above the initial fuel injector bank return flow value, then replace all eight (8) fuel injectors using the Fuel Injector Replacement procedure in the Engine Controls section of the appropriate Service Manual.

[crafty]

Well, I have a smooth running engine again after three days in the shop and some money spent.
The dealer replaced the flywheel for a second time. ( The first was July of 2002) The throwout bearing was noisy so that was replaced as well. This part was not under warranty so it cost me $275 and I opted to change the clutch while it was all apart since that would save me the labour costs if I had to do it later down the road. (I got the old clutch etc so if I do need another I can always put the used one back in)
After all that work, the number 7 injector was still reading off the normal range so that was replaced as well.
The result is a smooth running truck and all is well. I pulled my trailer last week after the repair and got 15.5 mpg (imp gal.) with a 10700 lb load. That is the same mileage I got last summer on the same trip.
I have a feeling that I may be back for the rest of the injectors at some point in the future and with the fuel filter recall I now have 3 filters to throw out.
I'm glad it is fixed and I will hope for the best. Thanks Madmatt and Jim for your help and to all the others who posted suggestions as well. :D :D :D