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hi guys, im having some diagnosis issues with my l67 running poorly. ive been trying to troubleshoot the issue for months but cant seem to work it out. its had a solid misfire since ive had it rebuilt which has me baffled. I have basically replaced everything almost twice over and i cant find any vaccum leaks. im a very persistent man and i hate to say it but this ones got me beat.
A few weeks ago i decided it was time to stop guessing and start looking at some log data. Unfortunately im just as baffled. Drivers bank is running rich, along with some knock retard and high spark advance. I was thinking my misfire is coming from the drivers bank but i cant seem to isolate it by unplugging the injectors.
the following is a list of items ive managed to test/swap out to eliminate from the suspect list.
-Pushrods
-Coils/DFI
-Injectors
-Oxys
-MAF
-AIT
-PCV
-Fuel Pump
My latest thoughts are maybe the engine builder has buggered up the timing sprocket as it was one of the adjustable type. Or my headers are cracked/slightly leaking. If anyone would be willing to take a quick squiz at the data log for me and share their thoughts or perhaps even be able to steer me in the right direction, it would be greatly appreciated. Ive uploaded the latest log i have. Any ideas would be great. cheers guys

Have you done a compression test?

Have you looked at ignition leads?

I had a case once where one cylinder on a v6 was misfiring due to bad leads, somehow the other plug on the same coil pack was still firing despite the other not. If you get one bad lead on coil packs, both cylinders drop as they are in series, yet somehow it was only one in this case and becasue of this I dismissed the leads as the problem and changed the injectors and plugs instead before I finally tried the leads.

Charlescrown wrote:Have you done a compression test?

I havent yet, that was one of the next steps i was gonna do to check out my valves. the reason i havent yet is because my coolant levels havent budged and the oil is clean. i was pretty confident the valves were ok, lapped them all and changed the stem seals while the bottom end was getting done. no signs of damage and all lapped up nicely. also i could feel good compression when i was turning the motor over by the crank. regardless, ill probably crack the guage out shortly as im stumped.

vlad01 wrote:Have you looked at ignition leads?

I had a case once where one cylinder on a v6 was misfiring due to bad leads, somehow the other plug on the same coil pack was still firing despite the other not. If you get one bad lead on coil packs, both cylinders drop as they are in series, yet somehow it was only one in this case and becasue of this I dismissed the leads as the problem and changed the injectors and plugs instead before I finally tried the leads.

yeah i chucked new leads on it when i dropped it in the car, although i havent eliminated it from my list. i threw the originals out beforehand because everything is rubbish until you need it. ive just been swapping out parts to see if it affects my oxy readings. have you guys had issues with eagle leads before??

I had the same problem when I did my l67 conversion into my vs, I fixed it by doing the earth mod.

https://forums.justcommodores.com.au/th ... lem.98628/

Good call, I'd completely forgotten about that problem.

Comcal76 wrote:I had the same problem when I did my l67 conversion into my vs, I fixed it by doing the earth mod.

https://forums.justcommodores.com.au/th ... lem.98628/

Thanks mate. will look into it. would changing the oxy before doing the mod have any affect on the readings though? as ive swapped the drivers out twice already while watching the data with no difference at all.

mine is alsoconverted, perhaps ive missed a ground somewhere. Or maybe the l67 comes with an extra ground somewhere that the normal v6 doesnt come with. hmmm

Have you used a VS wiring loom? The fault is in the loom with a shared earth for both the heater circuit and sensor circuit. Simply changing the sensor doesn't fix the issue. If you are happy to sacrifice a O2 sensor you can cut the earth wire for the heater circuit (effectively turning it into a 2 wire O2 sensor) at the sensor plug before the body loom plug. If the AFR's than come right the wiring is an issue.

I had the same problem on our old VS but instead of cutting wiring at the PCM I made an interceptor plug to go between the O2 sensor and body loom and put the earth wire for the heater circuit directly to the engine block.

You can also try cleaning all the earth points on the block. There is one on the back of the passenger head and another on the front drivers side head on one of the studs that holds the tensioner bracket.

immortality wrote:Have you used a VS wiring loom? The fault is in the loom with a shared earth for both the heater circuit and sensor circuit. Simply changing the sensor doesn't fix the issue. If you are happy to sacrifice a O2 sensor you can cut the earth wire for the heater circuit (effectively turning it into a 2 wire O2 sensor) at the sensor plug before the body loom plug. If the AFR's than come right the wiring is an issue.

I had the same problem on our old VS but instead of cutting wiring at the PCM I made an interceptor plug to go between the O2 sensor and body loom and put the earth wire for the heater circuit directly to the engine block.

You can also try cleaning all the earth points on the block. There is one on the back of the passenger head and another on the front drivers side head on one of the studs that holds the tensioner bracket.

im using a vs l67 loom and ecu for it.

oh right. is that essentially doing the same thing as earthing it at the ecu? i prefer to do things that way rather than chopping factory wiring.