LBZ: Rough Idle, No Related Codes

[Cknight199]

Needing some help diagnosing a rough idle. Truck starts and then the balance rates will get progressively worse and then level off around -4. However cylinder 2 and 8 continue to climb to -12 and -10.

After seeing this my first thought was injectors, so I switched them with other cylinders and the rates remained the same in cylinder 2 and 8.

I then did a compression test in cylinder 2, 6 and 8 which resulted with 350 psi +/- 5psi.

Then, I used DVT in EFI Live to individually turn off each injector and see if I could notice a change in idle. When I turned 3 and 7 off (individually), there was no noticeable change. However if I unplug the injector itself on both of those cylinders, the idle gets more rough.

Any input is greatly appreciated.

Truck is an LBZ with a tune and exhaust.


Sent from my iPhone using Tapatalk

 

[02greysixer]

Egr valve and cooler still present?

Sent from my SM-G930P using Tapatalk

 

[Cknight199]

Egr valve and cooler still present?

Sent from my SM-G930P using Tapatalk

Yes.

Will be testing each injector circuit tonight.


Sent from my iPhone using Tapatalk

 

[stibuilder]

Have my truck in the shop for a similar issue right now. It idles file but #8 is out of line +6 upwards of 10. Once you drive it you notice a miss. I also moved injector 8&3 as they both were new and it stayed in #8 i then replaced the whole engine harness with the same affect. I have even gone as far as the ECU and still nothing. Good Luck! my truck is also a LBZ/LLY its in a Kodiak.

 

[gmduramax]

Is it giving you the rates for the correct injectors? On a LBZ that had a bad injector I couldn't turn it off with the DVT but if I unplugged it the knock went away. Why wouldn't you check the comp in all the cylinders?