Misfire can’t find the issue.

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dshaff45

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I have a 2012 GMC Yukon SLE with 5.3L. My problems started with a P0300, and since the vehicle has high miles, I ordered new coils, plugs, and wires. My #4 spark plug was wet, and the rest looked fine. I changed the plugs and wires at this time. Two days later, I got an MAF code, which I proceeded to replace the MAF, and the code cleared immediately. About a week went by, and as I was leaving for work, the car died while driving. I was unable to get the vehicle started. After verifying I had fuel pressure and spark, so I assumed it was the cam or crank position sensor. I replaced those, and after a long crank, I got it started. I got access to a Tech 2 scan tool and did a crank relearn procedure. The next day, the car seemed to be running fine, and then I got a low oil pressure message. The gauge would start normal and slowly drop to zero. I replaced the screen and sensor and haven't had an issue since (I believe this may be unrelated to other problems). Next, I took the Yukon for a test drive to monitor oil pressure, and once I was warmed up. I gave the vehicle heavy acceleration. Then, I got a flashing check engine light, traction control, and a noticeable misfire. I got my car home, and I was worried I hurt the engine during acceleration I proceeded to do a dry compression test, which was 160 psi, close to all the others. I also did a cylinder leak-down test, and it was around 3% leak-down. My coils arrived, so I replaced those with no improvement. I was getting P0304 and another code for the rich fuel mixture Bank 2. I checked the #4 cylinder with a timing light, and it seemed like I had a consistent spark, so I decided maybe the fuel injector was the culprit. I replaced that with no improvement, as well. The next time I went to start the vehicle, it was a long crank followed by P0335 (Crankshaft Position Sensor "A" circuit), so I felt like I finally had something to go off of. I looked up the troubleshooting instructions for the crank circuit, and everything tested fine. Checking ground and the 5v signals, I moved around the harness to try and find a possible open or short, but the signal never fluctuated. This has been very frustrating, and I'm running out of ideas. So, right now, I am showing a consistent #4 cylinder misfire, CKP circuit code, and long cranks. Also, I removed the valve cover to inspect the upper valve train and watch for proper rocker operation on Bank 2. And I’ve also replaced the ECU with same issues following. Any help would be greatly appreciated, I’m at a dead end right now.
 

Geotrash

Dave
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I have a 2012 GMC Yukon SLE with 5.3L. My problems started with a P0300, and since the vehicle has high miles, I ordered new coils, plugs, and wires. My #4 spark plug was wet, and the rest looked fine. I changed the plugs and wires at this time. Two days later, I got an MAF code, which I proceeded to replace the MAF, and the code cleared immediately. About a week went by, and as I was leaving for work, the car died while driving. I was unable to get the vehicle started. After verifying I had fuel pressure and spark, so I assumed it was the cam or crank position sensor. I replaced those, and after a long crank, I got it started. I got access to a Tech 2 scan tool and did a crank relearn procedure. The next day, the car seemed to be running fine, and then I got a low oil pressure message. The gauge would start normal and slowly drop to zero. I replaced the screen and sensor and haven't had an issue since (I believe this may be unrelated to other problems). Next, I took the Yukon for a test drive to monitor oil pressure, and once I was warmed up. I gave the vehicle heavy acceleration. Then, I got a flashing check engine light, traction control, and a noticeable misfire. I got my car home, and I was worried I hurt the engine during acceleration I proceeded to do a dry compression test, which was 160 psi, close to all the others. I also did a cylinder leak-down test, and it was around 3% leak-down. My coils arrived, so I replaced those with no improvement. I was getting P0304 and another code for the rich fuel mixture Bank 2. I checked the #4 cylinder with a timing light, and it seemed like I had a consistent spark, so I decided maybe the fuel injector was the culprit. I replaced that with no improvement, as well. The next time I went to start the vehicle, it was a long crank followed by P0335 (Crankshaft Position Sensor "A" circuit), so I felt like I finally had something to go off of. I looked up the troubleshooting instructions for the crank circuit, and everything tested fine. Checking ground and the 5v signals, I moved around the harness to try and find a possible open or short, but the signal never fluctuated. This has been very frustrating, and I'm running out of ideas. So, right now, I am showing a consistent #4 cylinder misfire, CKP circuit code, and long cranks. Also, I removed the valve cover to inspect the upper valve train and watch for proper rocker operation on Bank 2. And I’ve also replaced the ECU with same issues following. Any help would be greatly appreciated, I’m at a dead end right now.
How many miles?

Next step: remove, clean and reattach the ground on the front of the pax-side cylinder head. After that I would start looking for breaks in the loom and damaged wiring to the injectors or coils on that bank.
 

Doubeleive

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check battery & grounds and alternator
add a ground from block to frame
re-check coil/injector harness, particularly when the code appears, use a noid light and also check for open ground while wiggling the wire
check ecm harness (wet or corrosion)
check fuse box (lift it and check for corrosion/wet)
use the tech2 to monitor the misfires it has a long cable you can place it right by you while wiggling wires and watch the screen
if none of that results in a fix report back and we can start looking at other potential issue's
 

Doubeleive

Wes
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I have a 2012 GMC Yukon SLE with 5.3L. My problems started with a P0300, and since the vehicle has high miles, I ordered new coils, plugs, and wires. My #4 spark plug was wet, and the rest looked fine. I changed the plugs and wires at this time. Two days later, I got an MAF code, which I proceeded to replace the MAF, and the code cleared immediately. About a week went by, and as I was leaving for work, the car died while driving. I was unable to get the vehicle started. After verifying I had fuel pressure and spark, so I assumed it was the cam or crank position sensor. I replaced those, and after a long crank, I got it started. I got access to a Tech 2 scan tool and did a crank relearn procedure. The next day, the car seemed to be running fine, and then I got a low oil pressure message. The gauge would start normal and slowly drop to zero. I replaced the screen and sensor and haven't had an issue since (I believe this may be unrelated to other problems). Next, I took the Yukon for a test drive to monitor oil pressure, and once I was warmed up. I gave the vehicle heavy acceleration. Then, I got a flashing check engine light, traction control, and a noticeable misfire. I got my car home, and I was worried I hurt the engine during acceleration I proceeded to do a dry compression test, which was 160 psi, close to all the others. I also did a cylinder leak-down test, and it was around 3% leak-down. My coils arrived, so I replaced those with no improvement. I was getting P0304 and another code for the rich fuel mixture Bank 2. I checked the #4 cylinder with a timing light, and it seemed like I had a consistent spark, so I decided maybe the fuel injector was the culprit. I replaced that with no improvement, as well. The next time I went to start the vehicle, it was a long crank followed by P0335 (Crankshaft Position Sensor "A" circuit), so I felt like I finally had something to go off of. I looked up the troubleshooting instructions for the crank circuit, and everything tested fine. Checking ground and the 5v signals, I moved around the harness to try and find a possible open or short, but the signal never fluctuated. This has been very frustrating, and I'm running out of ideas. So, right now, I am showing a consistent #4 cylinder misfire, CKP circuit code, and long cranks. Also, I removed the valve cover to inspect the upper valve train and watch for proper rocker operation on Bank 2. And I’ve also replaced the ECU with same issues following. Any help would be greatly appreciated, I’m at a dead end right now.
and welcome to the forum!
 
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dshaff45

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How many miles?

Next step: remove, clean and reattach the ground on the front of the pax-side cylinder head. After that I would start looking for breaks in the loom and damaged wiring to the injectors or coils on that bank.
240k miles, but the top end was rebuild previously as well. Heading to the part store to get fuel pressure tester and noid lights as well. It’s been quite the project I guess I didn’t post everything we’ve done. But grounds have also been replaced. Will keep you posted when I get back with the pressure tester and lights.
 

Geotrash

Dave
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240k miles, but the top end was rebuild previously as well. Heading to the part store to get fuel pressure tester and noid lights as well. It’s been quite the project I guess I didn’t post everything we’ve done. But grounds have also been replaced. Will keep you posted when I get back with the pressure tester and lights.
Fuel pressure I would expect to affect all cylinders. Though if you're on your original fuel pump at 240K, you're due.
 

mikez71

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If the CKP code and long cranks are related... maybe double check the CKP wiring to ECM or try to datalog that signal.

'A' circuit looks like a white/black wire. But I am guessing a problem in any of the 3 ckp wires may show the same code.
Which it sounds like you checked... made sure to wiggle the wires while checking?


You sound more thorough than me, so I'm hoping I never get a problem like this!
 
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Joseph Garcia

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Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

WOW! You've been through Hell on this issue. Hopefully, we can help get you up and running without errors again.
 
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dshaff45

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check battery & grounds and alternator
add a ground from block to frame
re-check coil/injector harness, particularly when the code appears, use a noid light and also check for open ground while wiggling the wire
check ecm harness (wet or corrosion)
check fuse box (lift it and check for corrosion/wet)
use the tech2 to monitor the misfires it has a long cable you can place it right by you while wiggling wires and watch the screen
if none of that results in a fix report back and we can start looking at other potential issue's
Thank you for welcoming me to the forum! Glad to be here, however wish It was under different circumstances!

So as stated on my most recent reply it did check all grounds replaced ones that were of concern and cleaned the ones that weren’t. Noid lights verified everything that I checked were working as they should, fuse box was dry and zero corrosion. The CKP code is now back and active again also P0335 also with tach not working. From the two replies above I checked all the wires in that videos and we wiggled as we did, we are being as thorough as we can with no prevail.
 
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dshaff45

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If the CKP code and long cranks are related... maybe double check the CKP wiring to ECM or try to datalog that signal.

'A' circuit looks like a white/black wire. But I am guessing a problem in any of the 3 ckp wires may show the same code.
Which it sounds like you checked... made sure to wiggle the wires while checking?


You sound more thorough than me, so I'm hoping I never get a problem like this!
Thank you for the video, we shot the wires wiggling as we went along and no dice. However, when we CKP code came back. P0335. No tach again. Before that fuel pressure balance test was perfect. Noid light confirmed injectors firing as well.
 

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