I have a cylinder in my truck I am trying to diagnose. Cylinder #5 a balance rate of +4.5. I ran a compression test and it tests 340# cold, 380# hot. Swapped out for two different injectors and the numbers are consistent. Any ideas on this?
Good compression - Bad balance rate
- Thread starter Trgglynn
- Start date
I hope you’re right. I had issues getting it plugged back in. The weatherpak insulator seemed to slide back and the connector wouldn’t connect easily. Seems like the inside of the connector had some sort of residue in it. I cleaned with QD. I guess this might coincide with the suspected FICM issues.
If it’s not that I am wondering if the injector seat is bad… but I suppose if it was it wouldn’t of passed a compression test?
What would your thoughts be on a bad valve adjustment/bad valve?
Please educate us what a balance rate of +4.5 means? What is the ECM attempting to do and why? I think I know, but sometimes I'm wrong.
As far as I understand the cylinder power output is low, and the ECM is trying to add fuel to that cylinder to compensate for the imbalance in the engine cycle. OR I suppose other cylinders could be causing the ECM to try to compensate for them.
Edit: also, the balance rate is subject to the main fuel rate AFAIK
I think I may have found some useful information. I have an updated GM harness I installed about two years ago (from LDS). I I’ve picked injector #5 and removed the weatherpak insulator, no love there. I then hooked up my Flashscan, went on a drive to get the engine up to temp. As before, balance rates were +4.5 on cylinder #5. Also, my truck has had a “quirk” where the fueling rate would drop low and you could not read the balance rates hot. Off and on but mostly off. Well, I may have just found the issue. I took the Flashscan under the hood and thought about my possible FICM issue, and started pushing around the top loom of the big bale connectors. And sure enough the 0.00 balance rates started jumping around and the slight miss at idle became intermittent.
Any ideas on a replacement bale connector/repair? Seems like something there is intermittent. Not enough to break connection but enough to be an issue.
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Does anyone know of a way to get a part number for the pins themselves for c107/c108 and its counter parts on the other harness?
Much of the connector info is available from the Electrical Manual at GM Upfitter. Google for it because the web site does not have correct labels on the older trucks
If you're talking the bale connectors on the DS of the engine, just unplug them and check that the pins are all pushed out into the connector. They will sometimes back out of their spots and make intermittent connection. It happens.
If you're talking about the wire harness above the FICM, there is also the infamous rub point above the FICM bracket. The wires wear thru and -bingo- truck has misfires and runs rough. Harness repair, install thicker insulation around wiring (slit heater hose), and moving it away from the bracket are in your future.
I hate giving Dmax Forum credit, but the Place threads have no pics: https://www.duramaxforum.com/threads/ficm-harness-rub-fix.147783/
If the injector plugs have never been replaced, then at a minimum you should be ice-picking the connectors (thank you, Rick Lance) to get them to make a better connection. https://www.dieselplace.com/threads/lly-injector-harness-repair.142114/
Again, all of these problems are things that are 20+ years old now and all have proven repairs. This is not rocket science, nor has anyone over the years found a better way.
If you're talking about the wire harness above the FICM, there is also the infamous rub point above the FICM bracket. The wires wear thru and -bingo- truck has misfires and runs rough. Harness repair, install thicker insulation around wiring (slit heater hose), and moving it away from the bracket are in your future.
I hate giving Dmax Forum credit, but the Place threads have no pics: https://www.duramaxforum.com/threads/ficm-harness-rub-fix.147783/
If the injector plugs have never been replaced, then at a minimum you should be ice-picking the connectors (thank you, Rick Lance) to get them to make a better connection. https://www.dieselplace.com/threads/lly-injector-harness-repair.142114/
Again, all of these problems are things that are 20+ years old now and all have proven repairs. This is not rocket science, nor has anyone over the years found a better way.
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https://www.duramaxforum.com/threads/help-me-understand-injector-balance-rates.931706/ Post #9 by MrWizzard explains a lot about balancing for my understanding. For those who really understand, it is probably elementary school.
Ron, here's Ferm's original post about checking balance rates using main rate:
www.dieselplace.com
Info: - Proper way to check balance rates
www.dieselplace.com
Thanks. I saw that one too, very informative. I thought that I remembered something like if a cylinder had a high + number, that could be because the previous one in the firing order slowed down the engine and was the cause for the next firing cylinder to have a high number, to even out the engine speed.
Yes. The balance rates you see won't mean that that exact injector is at fault. More of in indicator of overall health. I don't think GM/Bosch ever intended on people swapping one injector out. Either one bank or all
Here’s a report so far:
Checked the Injector 1, 4, 5, and 6 control circuits and am getting 12.1V to the FICM key on engine off. Also tested resistance and am seeing 0.00.
Checked the Injector 1, 4, 5, and 6 control circuits and am getting 12.1V to the FICM key on engine off. Also tested resistance and am seeing 0.00.