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In my Build thread, over the last 6 months I have I've refreshed the car inside and out. Engine wise I only pulled the intake and did the LS6 PCV conversion of the 04+ Valley Pan new acdelco knock sensors and harness and painted almost everything. Once I got everything back together, fired it up now it's misfiring on cylinders 5 and 7 with p0300 code. I've done everything I can to test and swap driver side coils, wires, and injectors. Compression is 150-160 on driverside odd bank. Put in two new spark plugs also and yet no change to the misfiring cylinders. Used a new noid light to make sure the injectors were receiving a signal from the Pcm. Tested wires between PCM and the coil signals
I've done everything I can think of. Car ran just fine before I parked it
If theres any of you that can think of next for me to test I would greatly appreciate it. I have hptuners also
Are there rodents where you parked it? Look for broken/chewed up wires. Check all connections and grounds. Time has a habit of making bad connections.
No rodents here. I did combine the front driver corner grounds to the one by the abs bracket frame rail. I checked the backside of driver head for the 3 grounds there and they dont look or feel broken. I did loosen them to move the harness to be able to run some wires under the intake.
Good connections are important here. Grounds need to be very solid connections.
Check all connectors in the coil/injector harnesses. It has to be in there somewhere...
Good connections are important here. Grounds need to be very solid connections.
Check all connectors in the coil/injector harnesses. It has to be in there somewhere...
Im getting 12v to 5 and 7 coil between pink and ground and 12v from pink and brown. What is the reference low signal exactly? An extra positive or negative? What should I be seeing from the brown? I've checked continuity of signal wires from pcm to coils and all checked out
This sounds silly, but a long time ago, I had an issue with a tune that caused P0300.
Removed battery cables and shorted them together to drain all power in the system, re-connected, reloaded the tune, and was good to go. For an engine that hasn't been opened, and everything else you have checked, I would at least give this a try.
This sounds silly, but a long time ago, I had an issue with a tune that caused P0300.
Removed battery cables and shorted them together to drain all power in the system, re-connected, reloaded the tune, and was good to go. For an engine that hasn't been opened, and everything else you have checked, I would at least give this a try.
I can try this easily enough. I did have the pcm and battery out for like 5 months.
No rodents here. I did combine the front driver corner grounds to the one by the abs bracket frame rail. I checked the backside of driver head for the 3 grounds there and they dont look or feel broken. I did loosen them to move the harness to be able to run some wires under the intake.
I just reread and saw this. If you can, try grounding to the driver side head and see if it helps. TBH, I'm not aware of any engine-front grounds on the LS harness, unless they were extended for easy access.
I just reread and saw this. If you can, try grounding to the driver side head and see if it helps. TBH, I'm not aware of any engine-front grounds on the LS harness, unless they were extended for easy access.
that's what I was thinking was those grounds were for the lights, abs, cruise control, and ground strap so I thought it would be safe to combine them and hide them away.
The only thing that's left to diagnose really is to see if the coil is being triggered by the PCM. Is there any practical way I can measure it with a regular DMM?
I tried the battery drain and re-wrote the pcm to no avail. Would a test-light light up when pcm triggers the coil on the signal wire like a injector noid light? I tried it and it wouldn't light up. With the DMM hooked to ground and positive on coil plug red wire, I wiggled the harness around with zero fluctuations on voltage. Same with the 2 ground wires (black and brown wires). I'm at a complete loss on what to try next. Wish I had another pcm to try.
All I did was pull the PCM and store it in my top drawer toolbox for about 5 months and then reinstalled it. There's no way I damaged it or anything.
Here's a screenshot and quick log file of a cold start
I know you tested the wires and swapped coils. At this point I would try a new passenger side coil harness. The only other thing I can think of is the connection at the coil harness itself. With the wires passing continuity checks, there might be a weak connection there that checks out when off, but a bit of vibration at startup distorts the signal which you can test by checking for spark at 5 and 7.
I know you tested the wires and swapped coils. At this point I would try a new passenger side coil harness. The only other thing I can think of is the connection at the coil harness itself. With the wires passing continuity checks, there might be a weak connection there that checks out when off, but a bit of vibration at startup distorts the signal which you can test by checking for spark at 5 and 7.
I did think about this at first because I wrapped over them with electrical tape to hide them better, I thought maybe I twisted or bent them to much and broke some of the wires but with the continuity test I let it go. Theres some cheap ones ebay that are for relocating and it would hide the bulk connector at the back of the engine to clean up around the fuel rail and valve cover.
When it comes to wrapping wires, worry more about functionality than appearances. Looks don't matter if it isn't running.....
Ya I get what your saying.
How come the scanner says it's 5 and 7 misfiring, but when I command injectors 5 and 7 off it starts stumbling worse?
I found its 3 and 6 with zero idle change and the popping stops which is the exact same result when I unplug injectors 5 and 7. So what's right and what's wrong?
What's correct is your unplug test. 3 and 6 are misfiring. Might be worth checking the plugs and cranking compression on those two cylinders. Easy way to verify spark is to unplug the injector and leave the spark plug attached to the spark wire, but out of the motor with the ground strap touching the motor. Get someone else to crank the starter and you will either see it spark or not.
From: Halfway back on the Highway to Hell...again!
OK, just for the hell of it. You said you had your coil harnesses apart. Look at your harness for each side. The reference wires for each end, one will be a purple and one will be red. They need to be opposite from each other on either side of the engine. bascially, #1 cyl will have a purple ref wire, #2 cyl will have a red ref wire. You may have accidentally crossed up your harnesses if you took them off the brackets. The wire colors for both harnesses are the same, but have to be reversed for either side.
OK, just for the hell of it. You said you had your coil harnesses apart. Look at your harness for each side. The reference wires for each end, one will be a purple and one will be red. They need to be opposite from each other on either side of the engine. bascially, #1 cyl will have a purple ref wire, #2 cyl will have a red ref wire. You may have accidentally crossed up your harnesses if you took them off the brackets. The wire colors for both harnesses are the same, but have to be reversed for either side.
I didn't have them stripped down to the wires. I only wrapped on top of the factory wrap, so the form of the wire harness stayed in the exact same shape. I did depin the bulk connector to paint the white plug but I took pictures of the wires and triple checked I put them back in the exact same spot.
What's correct is your unplug test. 3 and 6 are misfiring. Might be worth checking the plugs and cranking compression on those two cylinders. Easy way to verify spark is to unplug the injector and leave the spark plug attached to the spark wire, but out of the motor with the ground strap touching the motor. Get someone else to crank the starter and you will either see it spark or not.
I don't follow the first part. If I physically unplug cylinders 5 and 7 injectors while running, there's no change in the idle and the popping in the exhausts stops. Makes sense cause the unburned fuel is no longer being dumped in. Hptuners scanner says those are the cylinders misfiring. So then if I plug them back in and go into the functions, why is it I have to command injectors 3 and 6 off in Hptuners but in reality it is actually 5 and 7 injectors turning off? Are they labeled wrong under the functions?
I've already unhooked the the plug wires on 5 and 7 while running and there is spark
I don't follow the first part. If I physically unplug cylinders 5 and 7 injectors while running, there's no change in the idle and the popping in the exhausts stops. Makes sense cause the unburned fuel is no longer being dumped in. Hptuners scanner says those are the cylinders misfiring. So then if I plug them back in and go into the functions, why is it I have to command injectors 3 and 6 off in Hptuners but in reality it is actually 5 and 7 injectors turning off? Are they labeled wrong under the functions?
I've already unhooked the the plug wires on 5 and 7 while running and there is spark
Originally Posted by Dark_Side
Ya I get what your saying.
How come the scanner says it's 5 and 7 misfiring, but when I command injectors 5 and 7 off it starts stumbling worse?
I found its 3 and 6 with zero idle change and the popping stops which is the exact same result when I unplug injectors 5 and 7. So what's right and what's wrong?
Based on this earlier post, cylinders 3&6 are the problem.
Either way, if you have spark and fuel and still misfire then compression is the next check.
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Misfiring and popping with p0300 code 
