Help with E38 6.0 210/230 Ls7 cam Random misfires

[Guy With A Chevy]

I have been driving this tune for awhile since Ghuggins help rectify my misfire settings on it and have not changed a thing. In between moving to start school with my GI bill I have not had much time to study this subject..

It's been a while since I've been able to sit down and look over a good log like this one. At first I thought the timing was high but it seems just fine.

Recently the truck has started to have misfires when up to speed and I let of the gas it seems like everything with the engine goes haywire and it says 4 is misfiring just for a moment then sometimes goes away ad sometimes I have to shut it off for it to reset. It has only done this when up to speed and I lightly let off the gas. If I let off the gas entirely it has no problem.

I took off the valve covers today to replace the gaskets and check over push rods and everything seems up to par even though mechanically it seems as there has been a change.

At idle its relatively smooth and not logging any misfires at rpm in neutral or even when I force the rpm down to 600.

Changed oil today and its clean not a spec of nothing. Oil cap loose with an engine rev does not blow it off either.

What direction would you head?

I did get all the leaks sorted out and even installed a 30 row transmission cooler. I have yet to put the fan on as I don't like that it is 1 constant speed. Is there a 6-8in fan I can get to mimic the pwm of the radiator fans?

[gtstorey]

I would treat it as a misfire problem not a tune problem to start with. But that is without looking at the logs.

[LS ROB]

I would treat it as a misfire problem not a tune problem to start with. But that is without looking at the logs.

^^^ Do the simple stuff first. Make sure wires are on good, move the coil to a different cylinder and see if the miss mimics the move if not, try moving the spark plug to a new cylinder.

[Guy With A Chevy]

I just don't understand how I can drive it around town all day long all week and not get on the highway and not have this issue. As soon as I get up to about 60+ mph all I have to do is lightly let off the gas and number four will start misfiring. If I let off the gas entirely or just keep a heavy foot on it has no problem.

[gtstorey]

If it’s always no 4, even more of a reason to look outside the tune. Not really much in a tune to make one cylinder to misfire but not the others.

[Cringer]

Did you remove and inspect spark plug #4 yet?

[Alvin]

I have been driving this tune for awhile since Ghuggins help rectify my misfire settings on it and have not changed a thing. In between moving to start school with my GI bill I have not had much time to study this subject..

It's been a while since I've been able to sit down and look over a good log like this one. At first I thought the timing was high but it seems just fine.

Recently the truck has started to have misfires when up to speed and I let of the gas it seems like everything with the engine goes haywire and it says 4 is misfiring just for a moment then sometimes goes away ad sometimes I have to shut it off for it to reset. It has only done this when up to speed and I lightly let off the gas. If I let off the gas entirely it has no problem.

I took off the valve covers today to replace the gaskets and check over push rods and everything seems up to par even though mechanically it seems as there has been a change.

At idle its relatively smooth and not logging any misfires at rpm in neutral or even when I force the rpm down to 600.

Changed oil today and its clean not a spec of nothing. Oil cap loose with an engine rev does not blow it off either.

What direction would you head?

I did get all the leaks sorted out and even installed a 30 row transmission cooler. I have yet to put the fan on as I don't like that it is 1 constant speed. Is there a 6-8in fan I can get to mimic the pwm of the radiator fans?

It's really hard to get misfire tables to behave in anything other than a completely stock cam.They might be ok for a week, a month, half a year, etc.. but they can come back and bite you. You might just have to raise them until it stops. I assume you aren't feeling a misfire?

I know it is a LS7 stock cam but that cam is still quite a bit more rowdy than what comes in a 6.0 truck.

[gtstorey]

I've been assuming that this is a felt misfire at 60mph. Do "cam misfires" show up at speed?

[Guy With A Chevy]

It is definitely more than a spark plug issue and the misfires being logged are just as P0303 if I remember correctly. There is something mechanically wrong I am certain after today. Seems it has gotten worse even did it accelerating out of my drive today had to restart it rolling. The way it is happening is quite awkward. It was gone all the way across town after that but slowly pulling into the destination on a down rev gave the truck a wierd wobble/shaking until i got back on the gas? Hoping its just an injector. I will report back after some more digging.

Here is the log for the last down rev misfire that gave the truck a horrible wobbling/shake pulling into a drive the bank does go lean during the misfires

[LS ROB]

It is definitely more than a spark plug issue and the misfires being logged are just as P0303 if I remember correctly. There is something mechanically wrong I am certain after today. Seems it has gotten worse even did it accelerating out of my drive today had to restart it rolling. The way it is happening is quite awkward. It was gone all the way across town after that but slowly pulling into the destination on a down rev gave the truck a wierd wobble/shaking until i got back on the gas? Hoping its just an injector. I will report back after some more digging.

Here is the log for the last down rev misfire that gave the truck a horrible wobbling/shake pulling into a drive the bank does go lean during the misfires

I believe p0303 is misfire on cylinder 3. In the scanner its showing misfires on cylinder 4. Bank 1 o2 sensor looks a little lean but your wideband is showing 7.34. Have you checked or swapped the wires, plug and coils around yet?

[Guy With A Chevy]

LS ROB just noticed your post. The wideband is on the driver side not the passenger like most do.

This dreaded misfire has been absent after a week long driving 2 hours daily and came back today with number 2 misfiring right along side it. Next log after that only cylinder #2 shows random misfire. What may be be going on here? I would like opinions before swap coils or injectors. I will be home shortly and will do some diagnosing when it cools off.

Puzzled at the randomness of it running absolutely fine to hard misfires changing cylinders on me?

[GHuggins]

This was really common on earlier 07 to 12ish maybe trucks? What would happen is bits of the rubber fuel line would come apart from ethanol and wind up in the top of the injectors. It would float around in the rails - usually wound up in cylinder 7's injector though. I would drive till it's missing good then pull into where ever your going to work on it and immediately pop the rail with injectors out of the manifold. You can then carry over to a bench and do one injector at a time by popping them out and knocking them onto a clean white paper towel to see if anything comes out.

If it's not that then possibly even a bad ground or driver in the ecm.

[Guy With A Chevy]

Took off the passenger valve cover to check things over, I was in there 2 weeks ago hunting for the #4 culprit. I was leaning towards an injector issue as well with the way #2 started misfiring and number 4 disappearing. About a year ago I reverse flushed them with some carb cleaner not brake cleaner and I'm not afraid to give it another round. I'll report back after swapping a coil pack just incase before cleaning/swapping injectors.

[Guy With A Chevy]

Removed injectors #2 and #4 and gave them a a quick spray with some carb cleaner and swapped them back in and the misfires were cured for one entire drive to my friends house. Upon leaving his house the misfire happened again getting out of the neighborhood but didn't show itself again. Going to rig up a solid way to reverse flush them and pull them all and give them a good cleaning they are only 16 years old!

If I had to where would be the best place for a used tested set of injectors and new fuel lines?

[GHuggins]

If it's something in the system or a line coming apart, unhook it and run it into a clear juice jug or something then have someone cycle the key a few times for you to see if anything comes out. Then remove all of the injectors from the rail, flush the rail and knock the top of the injectors on a towel. If you see specs then the lines are coming apart. You might be better off at that point just to run all new line from the tank. Not sure which would be cheaper.

[Guy With A Chevy]

Thanks for that idea! I will definitely see what I can purge out the main line when I disconnect it again probably Monday. I can figure out the line need be. I see that injectors aren't horribly priced right now, I may free up the money soon.