#5 misfiring again, now also under acceleration.

[DenaliHD66]

Out of the blue today, stop at a red light, misfiring pretty hard, causing a decent amount of shimmy in the truck. Under throttle it persisted, with the engine power bogging down a bit and the exhaust note giving evidence as well. The coil pack was replaced the last time it misfired (within the last year), and diagnostic shows that #5 was the only one misfiring. It also had a crank sensor code in the history.

Taking it in tomorrow to have compression checked, any thoughts on what else it could be? Its been a recurring issue with #5, so is it time to check injector and valves?

 

[DenaliHD66]

Didn't get the full analysis yet, I haven't picked it up yet, but over the phone they said that oil is leaking through the cam phaser and that is causing the misfire. I have had a new CPAS, so I think its finally time to put that on. They were going to give me a list of parts to order on Monday. They said its good to drive in the meantime though.

 

[DenaliHD66]

SOLVED


Oil was leaking into the CPAS, and the wiring harness. Fortunately I've had my CPAS that I bought a while back just sitting around, so just ordered the wiring harness from a local dealer.

 

[DenaliHD66]

Well scratch that, still misfiring. Then I noticed....

This is the camshaft position sensor, right?

 

[CaptainXL]

Well scratch that, still misfiring. Then I noticed....

This is the camshaft position sensor, right?

Lol. Looks like half of the CPAS or camshaft sensor. If you look down where that went you will see a holddown bolt for either and it comes out.

This is the CPAS
View attachment 31385

 

[DenaliHD66]

I replaced the CPAS... it has its own wiring harness that I replaced too. This follows towards the front of the engine, and hooks in at the corner going to the front.


So, right above your finger, follow that black tube to the right, and that leads into the sensor I pulled out. I think the very right side of your picture shows it, it pulls out towards you and slanted down slightly.

 

[CaptainXL]

Ok, then what you are holding is half of the camshaft position sensor. There is a holddown bolt for it. It doesnt just twist out.

 

[DenaliHD66]

Yeah the other part is stuck into the engine still. It basically just slid right out, soo yeah.

 

[kkoether]

Word to the wise. Stick with the Stock GM part. #12615873. GM Parts Direct: Your direct source for Genuine GM Parts usually has very good pricing. I read quite a few horror stories about using the aftermarket replacements for the CPAS. Good Luck!

 

[gmcman]

I agree, definitely go with AC for the sensors. Those cam position sensors can get stressed if you aren't careful changing or removing the serpentine belt, they are right in the way and I always remove the connector to gain a little clearance to reduce the risk of breakage. Not saying this is what happened but just a FYI.

 

[CaptainXL]

I agree, definitely go with AC for the sensors.

Normally I would agree with ya gmcman. I have been using a Duralast camshaft sensor for a couple years with no problems. Go figure.

 

[DenaliHD66]

I agree, definitely go with AC for the sensors. Those cam position sensors can get stressed if you aren't careful changing or removing the serpentine belt, they are right in the way and I always remove the connector to gain a little clearance to reduce the risk of breakage. Not saying this is what happened but just a FYI.

Mine came right out, but I did have to loosen up some slack in the wiring harness to be able to plug it in. It was under a lot of stress, which caused it to break apart in the first place, so I re-routed the wire in front of one of the [engine components] and it allowed for more room.

Normally I would agree with ya gmcman. I have been using a Duralast camshaft sensor for a couple years with no problems. Go figure.

I bought the Duralast one. I didn't want to wait to order the Delco one from amazon, even though it'd be cheaper too.

 

[CaptainXL]

My guess is that even though you have a bad camshaft position sensor we will still need to address the misfire as there should be little correlation.

Your next step should be a coil and spark plug swap and then a dry+wet compression test. This should tell you if your #5 is exhibiting valve/ injector problems or not.

From a technical standpoint reading your short and long term fuel trims should tell you one of two possibilities. Either you have a bad fuel injector on #5 that isn't firing all the time or there is an intake leak in the #5 intake runner.

Have you used any fuel injector cleaner lately? If you get around to using it and the misfires stop for a while then the problem is the injector.

 

[DenaliHD66]

My guess is that even though you have a bad camshaft position sensor we will still need to address the misfire as there should be little correlation.

Your next step should be a coil and spark plug swap and then a dry+wet compression test. This should tell you if your #5 is exhibiting valve/ injector problems or not.

From a technical standpoint reading your short and long term fuel trims should tell you one of two possibilities. Either you have a bad fuel injector on #5 that isn't firing all the time or there is an intake leak in the #5 intake runner.

Have you used any fuel injector cleaner lately? If you get around to using it and the misfires stop for a while then the problem is the injector.

I think this WAS the exact cause. I am very adamant about running cleaners through it periodically. So far, the engine has been running smooth as silk and idling smoother than it has in recent memory after I replaced the sensor. Like I said, the previous one was literally hanging by a thread, so it wasn't even working at all. If the misfire comes up again, then it'll be onto injector and valves.

In the research I did about how the camshaft sensor works, it was directly correlated to malfunctioning and causing misfires. It functions like a magnet and goes by the position of the exhaust cam gear. It is kinda strange that I've ONLY ever had a misfire on cylinder #5, and not all of them, so I guess we'll wait and see.

 

[gmcman]

Like I said, the previous one was literally hanging by a thread, so it wasn't even working at all.

When you state this, was the wire broken? Good chance if the wire was still intact, that the sensor was still sending a signal to the PCM...even though the housing was broken.

 

[DenaliHD66]

When you state this, was the wire broken? Good chance if the wire was still intact, that the sensor was still sending a signal to the PCM...even though the housing was broken.

Wire was good, likely it WAS sending a signal, but most likely very inconsistent. No exaggeration it runs super smooth now. Startup has absolutely no rumble or roughness to it, even in the cold weather now.

 

[CaptainXL]

It is kinda strange that I've ONLY ever had a misfire on cylinder #5, and not all of them, so I guess we'll wait and see.

That is strange. The camshaft position sensor feeds a signal to the PCM telling it where the exhaust camshaft is in relation to the crankshaft position sensor. This position is needed by the PCM to control exhaust camshaft position via the Camshaft Position Actuator Solenoid (CPAS). If the signal is intermittent then the exhaust camshaft will not move correctly or be in the correct position. This is just a theory but it could be that if you have any other variables such as an intake runner leak or slightly leaking injector or valve issue in conjunction with the faulty cam sensor...those may be enough to trip the misfire counter. Maybe. Again just a theory.

 

[DenaliHD66]

Compression was tested twice, no leaks. Its been running smooth as a top ever since the CPAS and CPS were replaced. Wide open throttle is throaty and absolutely no "gurgling" sensation upon startup.

 

[DenaliHD66]

Aaaaaand the SES light is back on.

 

[CaptainXL]

Aaaaaand the SES light is back on.

Read the codes and see what you got.

 

[CaptainXL]

Got an update? You should have immediately got the codes read a couple days ago. Sometimes after a few drive cycles the code erases and then you are left scratching your head. Just trying to help you out is all. Good luck.

 

[DenaliHD66]

Yeah figures the light didn't come on Monday, so no codes. Maybe it was just getting used to the new sensor? Did have an issue with a 4WD sensor that i got fixed though.