Misfire 3,4,5
Thread Starter
Joined: Jan 2008
Posts: 597
Likes: 9
From: Tequesta, FL
Misfire 3,4,5 Hey guys, this is driving me nuts, I've spent a ton of time trying to figure this out but it is kicking my ***. Hoping for some insight. First the car in question is a 2000 Camaro, LT's ORY, AIR! EGR! 224/224 .563 .563 112lsa. I built the engine and installed it about 7 years ago and have put 40,000 miles on it with Zero issues. In the past 3 years the car has sat for extended periods of time and had slowly developed a misfire at low RPM high load. At first it was light and intermittent, Now it is aggressive (heavy shaking and popping). I First thought it was fuel related but hooked up a fuel pressure gauge while duplicating the misfires and the pressure was right at 58psi. I then found a few wires that were suspect so I replaced all plugs and wires (tr55's .050) and MSD wires, no change to the symptoms. I've then started logging and found that I consistently have cylinder's 3,4,5 misfiring at low rpm high load only. They do not misfire at idle or at higher rpm/load situations. I then moved all the corresponding coils to other cylinders and that made no change. I then moved the corresponding injectors to other cylinders also with NO CHANGE! The misfires are sill on 3,4,5. I have no DTC's and all sensors MAF, MAP, TPS etc... respond normally in the scans but I did unplug the MAF to force SD and it made no change. I'm starting to think the the drivers in the PCM for those coils are starting to go bad? It just seems crazy that 3 would go bad.... Any thoughts I'm at a loss? See attachment.
TECH Senior Member
Joined: Jun 2016
Posts: 22,295
Likes: 3,617
From: Central Cal.
I would be checking wires in the harness and all connections plus ALL grounds. And I mean ALL grounds. Since you eliminated coils and injectors, it's wiring. Make sure a mouse or rat hasn't chewed any of the wires. It happens! lol
Thread Starter
Joined: Jan 2008
Posts: 597
Likes: 9
From: Tequesta, FL
There are no visible Rodent markings on the harness anywhere, I also checked the major grounds on the back of the cylinder head and they were tight with no visible issues. I'll have to bring my dmm home from work to ohm it out to be sure but i feel confident they are ok.
TECH Senior Member
Joined: Jun 2016
Posts: 22,295
Likes: 3,617
From: Central Cal.
Good call! Just curious, wouldn't a low-compression miss be a "softer" miss than an ignition/fuel miss? Because in the low-compression miss, something is still be lit off and burned, just under lower compression, whereas in an ignition/fuel miss, NOTHING is happening.
Thread Starter
Joined: Jan 2008
Posts: 597
Likes: 9
From: Tequesta, FL
Did a compression check this morning i've got 200 - 210 psi on all cylinders. I went for a drive and its still there. when I did the compression check I compared the plugs of the misfiring cylinders to the other cylinders and cyl 3,4,5 look like they are starving for fuel and the other cylinders look normal. If you look at the log above it looks like when its happening the STFT's start adding a bunch of fuel, I've got to figure out why these cylinders are not getting proper fueling under load.
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Verdad Gallardo yea if it had low compression it would still run half decent. With an ignition/fuel miss u would defiantly know something wasn't right.
could be bad lifters, weak springs, etc. check all the normal stuff. How is oil pressure? Does it run fine or act like its got a miss? Could be like u said a bad pcm. Do u have access to a spare u could try?
Thread Starter
Joined: Jan 2008
Posts: 597
Likes: 9
From: Tequesta, FL
It runs fine other than being in a high gear around 1500 rpm and give about 40% throttle, dead miss violent shaking and popping out the exhaust.
Thread Starter
Joined: Jan 2008
Posts: 597
Likes: 9
From: Tequesta, FL
So I wanted to update this as I finally got the car fixed. I made a few mistakes in that I did not immediately put the car on the scanner to see what cylinders were misfiring, i just looked under the hood and found 2 wires that were starting to crack from their close proximity to the headers so I put a complete new set of plug wires on the car and still had the mis fire so I then dove into all the diagnostics above and assumed that my "new" wires were not causing the problem. Well come to find out the plug wire on #4 had an improper crimp which was causing an arch internally under a High load and was the culprit of the misfire. I fixed the original misfire but created a new one with a bad "new wire" See the attachment I have circled the area were the arch was present you can see some carbon tracking in there.
Take aways from all of this,
-The mis fire counter showed multiple misfires but only #4 was actually misfiring, the other 2 cylinders were reporting misfires due to them being before and after #4 in the firing order.
-Always scan first
-Never assume new parts are not an issue.
Take aways from all of this,
-The mis fire counter showed multiple misfires but only #4 was actually misfiring, the other 2 cylinders were reporting misfires due to them being before and after #4 in the firing order.
-Always scan first
-Never assume new parts are not an issue.