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Hey guys, I'm running out of ideas here so I could use a hand. My LS3 A6 GS developed a missfire in cylinder 1. Thought it was just a fouled plug at first so I replaced it (it came out black) Drove for 10 mins, came back it was black again... I swapped coil packs around as well as wires, same result. Cyl 1 is a dead hole. Next logical step was to pull the valve cover make sure nothing was out of place, springs were good, valve seals were good, did a compression and a leak down test and it passed both with flying colors. Then just to be certain cause we had an extra one laying here we through a new injector on it too (i know thats not the best way to diagnose things but we had the stuff laying around so figured it was worth a shot. Cylinder still wont run clean and fouls the plug within 10 mins of runtime. I'm at a loss... Coil harness wiring all checked out, we seem to have spark. Which I guess means its a fuel issue. I just cant fathom why it would be on only one Cylinder and not multiples. No codes being thrown either. Just not sure where to go next. I have a scan tool, I need to go out and do a log and see if anything looks odd. Just wondering if anyone had any other direction you could point me in. Any help is greatly appreciated. Much Thanks!
Hey guys, I'm running out of ideas here so I could use a hand. My LS3 A6 GS developed a missfire in cylinder 1. Thought it was just a fouled plug at first so I replaced it (it came out black) Drove for 10 mins, came back it was black again... I swapped coil packs around as well as wires, same result. Cyl 1 is a dead hole. Next logical step was to pull the valve cover make sure nothing was out of place, springs were good, valve seals were good, did a compression and a leak down test and it passed both with flying colors. Then just to be certain cause we had an extra one laying here we through a new injector on it too (i know thats not the best way to diagnose things but we had the stuff laying around so figured it was worth a shot. Cylinder still wont run clean and fouls the plug within 10 mins of runtime. I'm at a loss... Coil harness wiring all checked out, we seem to have spark. Which I guess means its a fuel issue. I just cant fathom why it would be on only one Cylinder and not multiples. No codes being thrown either. Just not sure where to go next. I have a scan tool, I need to go out and do a log and see if anything looks odd. Just wondering if anyone had any other direction you could point me in. Any help is greatly appreciated. Much Thanks!
Next thing I'd do is something you already did, but with the coils. I'd swap a known good injector from a different, non misfiring cylinder, and see if the problem moves. Sure, you had an extra injector laying around, but it is possible you simply changed the problem from one bad injector to another bad injector. Who knows. But if you swap the injector to a cylinder that has no issues, if the problem moves, bingo! If not, it could be something in the PCM. if it doesn't start misfiring until warmed up/10 minutes, could be something electronic that only happens when the internal components get 'warm'. Just an idea. Hope this helps you out. Sucks when a problem is unusual. I have one myself in the A/C system electronics my LS7 C5. Best of luck to you....
Not a bad idea with the injector, worth a shot I suppose. I think the miss is present even on cold start, just saying within 10 mins it will foul the plug every time. I considered possible computer issue too, maybe a bad injector driver or something to that avail but seems like a rare problem. I've had a couple folks say o2's but seems unlikely it would just affect one cylinder on one bank. I guess I need to do some datalogging of an actual drive and see what happens between closed and open loop. I'm completely shooting in the dark at this point, wish the thing would throw a code and give me a direction. The weird thing is if you put some load on it it seems to clear right up... Doesn't feel down on power at all. That being said though you can put a laser temp gun on each of the primaries and on average Cyl 1 is 100 degrees cooler than the other primaries .
The black plug would indicate unburned fuel. I think you are getting fuel, but not getting sufficient ignition. You said you seem to be getting spark, but I would follow up on that some more. Maybe buy a spark detection tool. I think they are quite inexpensive.
What do your long and short term fuel trims look like at idle ??...remove the #1 fuel injector connector and with a 12 volt test light connected to battery positive probe the injector connector terminal that isn't the pink wire...that is the injector control wire...when the engine is running the test light should be blinking when probing that wire...sometimes "swaptronics" isn't the best way diagnose a misfire...with the fouled plug maybe an ignition issue...there are some mechanical issues that would not be picked up with a compression or cylinder leak down test...worn cam lobe for instance...what does the injector resistance look like with a ohm meter ??...with an injector misfire your long terms will be quite high...somewhere around 15% or so...sometimes you really need a lab scope or perform an incylinder pressure testing to quickly and accurately diagnose this...maybe find a diagnostic shop in your area...they will find your issue within 30 minutes !..an incylinder pressure waveform below on my 01..I can see ANY mechanical issue with the engine with this waveform...no engine disassembly requiured !! !!
Could also be commanding too much fuel, Thats my current thought process, but not entirely sure why only one cylinder is effected.
I just recently had an upstream O2 stuck lean on my 01...it was a bad O2 sensor...both long and short term fuel trims were MAXED out...misfires on all 4 bank 1 cylinders...exhaust stunk bad !!
What are you referring to as "primaries" when you say: "That being said though you can put a laser temp gun on each of the primaries and on average Cyl 1 is 100 degrees cooler than the other primaries ."? Do you mean the ignition coils?
What are you referring to as "primaries" when you say: "That being said though you can put a laser temp gun on each of the primaries and on average Cyl 1 is 100 degrees cooler than the other primaries ."? Do you mean the ignition coils?
I believe he's referring to the exhaust header primary tubes.....
So it finally decided to throw a code after a month and a half of this mess. P0154 o2 sensor no activity detected. My theory though I haven't had time to check is I have an o2 wire on the passenger side of the car that has some mangled wiring. When I was in Tennessee and this issue developed I ran over a trailer hitch in the road that got stuck under the car and drug for a few 100 feet... The issue started on the way home from that trip so my guess is thats where my problems going to be. I'll update tomorrow after I have a chance to get into it.
So it finally decided to throw a code after a month and a half of this mess. P0154 o2 sensor no activity detected. My theory though I haven't had time to check is I have an o2 wire on the passenger side of the car that has some mangled wiring. When I was in Tennessee and this issue developed I ran over a trailer hitch in the road that got stuck under the car and drug for a few 100 feet... The issue started on the way home from that trip so my guess is thats where my problems going to be. I'll update tomorrow after I have a chance to get into it.
You probably have the same issue I had but mine was a bad sensor…your issue sounds like wiring…yes, you should data log and see what your O2 sensor on bank 2 is doing…it will be lean (below 450mv) so a quick check is to disconnect the sensor after shutdown and if it goes from say 100mv to 450 it’s the wiring !!
Need some help: Odd misfire issue on LS3
