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Old 07-05-2021, 09:00 PM   #1
LiqTenExp

 
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Bad injector, lifter, or?

2017 ZL1 with H/C/LT and 2300. Cylinder #3 has started reporting misfires. It is fine at idle and high rpm, issue exists mostly around 2000-4000 rpm. Issue is worst when cold and goes away nearly completely when up to temp. Have already:
  • replaced plug
  • replaced plug wire
  • swapped coil pack
  • inspected under valve cover (didn't observe anything like cracked springs or hot spots on top of valve, everything's tight)
Take a listen while watching this log go by and see if you can come to a conclusion:



Attached is a photo off log when car is fully up to temp, notice no more misfires comparably.
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Old 07-05-2021, 11:18 PM   #2
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You can definitely hear it during the video. Any unusual loud clicking? Usually a bad lifter will let you know audibly.
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Old 07-06-2021, 06:58 AM   #3
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Nothing obvious from inside cabin.
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Old 07-09-2021, 11:24 AM   #4
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  • When you hear the misfire you feel the loss in power, car hiccups slightly
  • No issues misfires at idle, hot or cold
  • No issues past like 4200 rpm, seems to be in the 2000-4000 rpm band only

Some bore scope photos attached. Ignore what look like scratches/lines, they are from borescope. Had it on a dyno a month ago with this issue and it made more power than it did the last time thanks to meth/water injection, it doesn't drive like it is hurt.
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Old 07-10-2021, 09:53 AM   #5
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I would inspect the injectors. Either pull them and have tested or swap the one out on the misfiring hole and go from there.
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Old 07-10-2021, 10:32 AM   #6
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I'm going to do a quick compression test just for sanity.

I have a set of new injectors and hardlines coming. I have no intentions of going under there again in the near future. I could just replace the one if that is what is is but when will the next one be questionable?... I've played that game before, there are no winners.
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Old 07-10-2021, 11:28 AM   #7
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Quote:
Originally Posted by LiqTenExp View Post
I'm going to do a quick compression test just for sanity.

I have a set of new injectors and hardlines coming. I have no intentions of going under there again in the near future. I could just replace the one if that is what is is but when will the next one be questionable?... I've played that game before, there are no winners.
Probably a good call in my humble opinion.
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Old 07-10-2021, 03:19 PM   #8
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Ran compression test on Bank1, pulled fuses 62/64 for coils and held pedal down (flood clear mode so the injectors don't fire).

All the cylinders on Bank1 were between 155-150 psi so pretty balanced, this was on a cold engine so would be higher I'd believe at hot. Since my issues happen at cold I was interested in testing here. Cylinder #3 was @ 154 psi so was towards the top psi wise.
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Old 07-11-2021, 01:28 PM   #9
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its very difficult to find actual compression test numbers for these engines. i know my na LT1 should come back a little higher, but my compression results are over 100 lbs higher than yours. factory stock long block. i have tested several cylinders over the course of 8 months or so. cold engine, hadnt been ran in over a week.
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Old 07-11-2021, 05:46 PM   #10
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Have you disabled injectors (disconnected or holding throttle pedal to the floor)? Have you used another gauge or validated that gauge somehow?

I wouldn't expect anything over 200 on NA motor.
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Old 07-11-2021, 06:33 PM   #11
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Just waiting on parts now...
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Old 07-11-2021, 07:32 PM   #12
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ive had 2 different gauges on it. i flood cleared it the first time with everything together, sat 2 weeks before then, mid november in the midwest.

second time i had all of the plugs out (+ flood clear) and it cranked over slow as hell. only sat for a week on that one. (the pic)
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Old 07-12-2021, 09:17 PM   #13
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Parts are pouring in, dripping, maybe oozing. May have everything by this weekend to reassemble it.

One of the parts I was considering buying a new TMAP but good luck finding one in stock that doesn't require special order first. Trying the dealer tomorrow. Nothing wrong right now with current one, just realized how hard it would be to replace if I had to (blower comes off!).

Also looking at replacing the following while I have access to them:
LT4 injectors (x8) - ordered
Canister purge valve (hangs off of TB) - received
Supercharger lid oring (x1) - installed
New supercharge lid hardware - received
Intercooler brick to blower orings (x2)
Supercharger to heads orings (x8)
Supercharger to head seal washers (x10) - ordered
Spark plugs, trying Brisk RR14S (x8)
SC Belt (x1)

Some good points to consider:

1) The SC heat exchangers need to have their hardware tight and Loctite applied to keep them sealed and not leak coolant. This is an easy spot to develop a leak into cylinder 1 or 2 and lose IC coolant. The passenger's side had a tiny seeping leak that I discovered during this disassembly. Cleaning up, priming, and Loctite application will fix it and prevent the hardware from backing off tq preload and getting loose. Also looking at replacing the seal for good measure, not required.

2) Take the time to inspect all contacts (pins/receptacles) prior to complete reassembly. Don't want to find a contact connector lock broken on an injector after putting it all back together.
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Old 07-13-2021, 05:20 PM   #14
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Wound up ordering one of these kits to install injectors: https://www.amazon.com/Injector-Repl.../dp/B08F7T59LV
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