Looks like one of my "new" injectors is going out on me. Doesn't even have 1,500 miles on the truck since all 8 injectors were repalced. Truck just crossed 50,000 miles last week.
Number 6 is already into the mid 3's while the rest are sitting around +/-.5

Funny thing is, after about 3-5 minutes of idleing it pulls down into the 2 to 2.5 range. I've never seen this much movement of balance rates on an injector. Is this normal or a sign of it going out?? What a bummer. I don't want to sound like PC, but WTF!! :mad: :(

Funny I just started seeing something similar...but I need to be careful in raising a flag.

I have about 35k on the new set of 8 injectors on my 2004 LB7 and Injector 1 is around 3...it started out at around 1.8. Injector number 3 is around high 2's...and was around 1.5 new.

But fuel affects them and we are in the midst of new fuel here in California so I am hoping the changes are due to the fuel being blended into the system.

I also noticed that Chevron is the best for balance rates.

I have 3 sets of new injector, cuz they kepy going bad!!! i first got my new set @ 64k and now have 72k and #1 is in the +4 range. Looks like "NEW" injector's and not "REBUILT/REMAN"

Thanks for the input so far guys. I am just really bummed that one of the "new" ones is already showing a higher balance rate. I filled up at FlyingJ a couple of weeks ago, so I'll try somewhere else next week. I have been adding fuel additive to every tank since these "new: injectors went in. Figured clean fuel (CAT pre filter and new updated OEM filter) as well as additive would have made 'em last a little longer!

Well, I checked the rates after I got home yesterday and number 6 was dancing around the +1.75 to +1.83. Still on the same tank of fuel. Crazy. I guess I was a bit too quick to raise the red flag myself! I'll keep an eye on it, but it looks like things are well in injector land for me at this time...

good deal man :ro)

4X4man,

I have noticed that the values jump around even on the same tank....but I have noticed that some injectors will change more than others.

I guess what you should have you eye on is a general trend....

Injector balance rate is not necessarily a sign of a bad injector.Balance rates can be higher on a cylinder with low compression or other mechanical issues. The balance rate is calculated to get the engine to idle smoothly in a representation of crankshaft speed verses time.If a cylinder is not doing it's fare share, more fuel is injected into that cylinder to get more heat/work out of that cylinder to balance the idle speed.
Balance rates should only be checked on a fully warmed up engine and with the proper specific gravity.To condem an injector just because of balance rates is not proper diagnosis and is the reason so may trucks get multiple sets.You must understand and figure out why the balance rate is high or low first.
Injector balance rates in the 5-6 range should have driveabilty issues and to use just the balancing rate as your reason to replace injectors is not allways the the cause.Be aware of proper diagnosis and fix the CONCERN, not the data that you think is incorrect.The problem, not the result of the problem. Tim

Tim

Great post on injector balance rates and what needs to be checked first.

Injector balance rate is not necessarily a sign of a bad injector.Balance rates can be higher on a cylinder with low compression or other mechanical issues. The balance rate is calculated to get the engine to idle smoothly in a representation of crankshaft speed verses time.If a cylinder is not doing it's fare share, more fuel is injected into that cylinder to get more heat/work out of that cylinder to balance the idle speed.
Balance rates should only be checked on a fully warmed up engine and with the proper specific gravity.To condem an injector just because of balance rates is not proper diagnosis and is the reason so may trucks get multiple sets.You must understand and figure out why the balance rate is high or low first.
Injector balance rates in the 5-6 range should have driveabilty issues and to use just the balancing rate as your reason to replace injectors is not allways the the cause.Be aware of proper diagnosis and fix the CONCERN, not the data that you think is incorrect.The problem, not the result of the problem. Tim


good info thanks Tim. Although how does the engine know which cylinder is the trouble one, and to adjust its individual injector accordingly??

Tim,

Good info. I do understand that the balance rates reflect the cylinders ability to idle. Fuel is added or removed to obtain the idle charactoristics demanded. However, I was told by the diesel tech that worked on my truck, that an injector that is plugging would cause high balance rates as well. This is why only the injectors with high balance rates were replaced the first time the truck had to go under the knife (one was at 5, the other over 8 with no driveability issues, just an audiable knock at idle). The reason why all 8 were replaced this time was due to high fuel flow return rates which mandates all 8 be replaced.

I have had no driveability issues with this new set of injectors. I checked the balance rates just after replacement and none were over 1.5 (I don't remember the exact numbers but they were all low). However to see one injector jump up to the mid 3's caught my attention and made me wonder if something was up already. GM's limit is +/-4 at idle and after a couple thousand miles I was getting rather close to this number already... I have been checking with the engine warmed up. Lowest engine temp I have checked rates at was 189 degrees.

Bob

good info thanks Tim. Although how does the engine know which cylinder is the trouble one, and to adjust its individual injector accordingly??
The crankshaft reluctor/sensor and the camshaft position sensor give the pcm information on crankshaft position and which cylinder. The pcm watches crankshaft speed verses time to determine the cylinders/engine balance.
There has been some issues with rough runing trucks and erratic balance rates caused by a loose crankshaft reluctor.Once again do not try to correct the data, correct the SYMPTOM.These trucks are very often misdiagnosed because of cause and effect.Understanding principles of operation is crutial in proper diagnosis.
I have replaced hundreds of injectors if not thousands and can count on one hand the number of trucks that have needed multiple sets of injectors.I bet it's less than 2 trucks that had failure in 30k miles or less.Most multiple sets are high mileage trucks of 180k or more.
Alot of injectors are replaced only due to balance rates and no driveability or symptom.The GM special policy is for injectors with high return rates or cracked injector bodies (the cause). The SYMPTOM would be hard/no start, fuel in crankcase etc.It is not for balance rates being high with NO SYMPTOMS.
Once again balance rates out of spec is NOT fault line to replace injectors.
I personally am a firm believer in valve lash adjustment when injectors are replaced and feel could be the MECHANICAL problem most trucks have with high balance rates after injectors get some time on them.I think new injectors can mask slight mechanical issues with a perfect spray/atomization pattern.A little carbon on the injector and there go your balance rates. Just my 2 cents TIM

4x4man
It is very unlikely that the injector is actually plugging.The injectors ability to properly control fuel delivery is likely the cause, but yes it is still the injector.You stated you did not have a driveability issue but you did. You said it had a knock which is fuel delivery control problem and therefore driveability related.Understand I am not saying all cases but several injectors are needlessly replaced for balance rates.Drive your truck several miles, and let the engine stabilize at idle for a few minutes and recheck.Verify the specific gravity of your fuel first as fuel quality is very crutial to this test.Make sure A/C is off. Repost with questions. Tim

Tim - :ro)

Tim-

AWESOME INFO!!!! Ok, I'm screaming, but thanks for all the info, learned a lot more about how this stuff works.
Good point about the driveability issue, I took driveabilty to mean low power, loss of mileage, but you are right a knock falls into that category as well.

I'll continue to monitor as the miles rack up.
Bob