Alright guys I'm clueless. About a couple days ago I was cruising at about 65 to 70 mph in 3rd gear so about 2600-2700 rpms and the engine light started flashing. I was close to home so I put it back in drive and the engine light went away. When I got home I threw the laptop on and pulled P0300 - Random Missfire which is nothing new since the cam seems to trip it when I let it idle for a while. So I ran a log showing the current missfires in each cylinder and as expected at idle it was picking up a few on every cylinder. I took it for a drive and it wasn't picking anything up normal driving, agressive, WOT or anything. It pulled strong, AFR was right where it should be, injectors went maxing out, nothing. Then I set the cruise at 67, shifted into 3rd, and cylinder 1 went crazy, cylinder 6 a little less so, and all the others were picking up missfire here and there. Thing is I don't think it was bucking, (road was not the best so I had a few bumps), seemed to hold fine and still had lots of power when I got on it. The weird thing is, anywhere less than 2500 it doesn't do it, and anywhere over 3000 it doesn't either, and anywhere in between there if I am accelerating even slightly it wont either. The whole time the AFR stays normal.

As a process of elimination I have moved the spark plug (looks fine) from #1 to #3, the wire to #5, the coil to #3, and the injector to #3 (all one at a time of course). The missfire didn't follow any of the parts. I think it is a faulty crank or cam sensor just because I can't think of anything else. Any ideas?

The truck is a 2000 ECSB with a 5.3. It has a K&N 77 series intake, Stainless works LTs with ORY, 220/220 .581/.581 112 LSA cam, and I switched to an 02 OS about a week and a half ago but all of the missfire tables are the same. The only thing I did notice was the injector tables were different but it seems to be running fine other than this.

The only other thing is I picked up my enclosed V-nose tonight (heading out on a trip with it tomorrow afternoon unfortunately) and I couldn't get it to missfire while I was cruising at 65-70 in 3rd. The only time it would do it was under light throttle coming down from 70 to 60.

Sorry for the long post but I am clueless. Anything else I could check?

Thanks in advance.

 

It sounds like what you are saying is that this started after a cam swap??? Is that correct???? Are you using the vehicals Original PCM??? Did this start before you upgraded the OS???? I am new to tunning but can you see the cam and crank sensor signals with what ever tunning software you are using???

Are you haveing any trouble with any thing else? Hard starts? Does your Fuel pressure look ok? Did you try swaping injectors?

 

Did you retorque your rocker arms?

Mine loosened up and caused misfire probs.

 

Hey guys sorry for no reply but I just got back from my trip. I did about 600 miles pulling 24' V-nose enclosed in 3rd and the truck didn't blow up so that's good (or bad, I do kind of want a 6.0).

Still though when I unhooked the trailer and tried cruising at the same rpm I was just pulling the trailer at it started flashing again but like normal, it wasn't bucking or acting funny.

To answer your questions, the cam swap was done almost exactly a year ago along with springs, lifters, pushrods etc. The rockers are stock and I have had them off since (about a month and a half ago) but I may try to torque them down again just in case. The PCM itself is stock but I just flashed over the 02 OS two weeks ago or thereabouts. The problem started about a week after the OS swap so that leads me to believe they aren't related. The only issue I had before this was a fair amount of false knock which the 02 OS cured. I haven't swapped in new parts yet but I have moved around plugs, wires, coils, and injectors and the problem always stayed at the same cylinders according to the scanner. I don't have a fuel pressure gauge but since the problem seems to be isolated between 2500 and 3000 rpms at light load I'm can't see it being a fuel pressure issue. Tomorrow I guess I will throw in a new crank and cam sensor and see if that helps.

Thanks for the help guys

 

It sounds like its related to your OS or possibly the ECU it self. What are you tunning with??? I have EFI LIve and I also have an 00 excab with a 5.3L I have the factory original os and the new update os. If your using EFI I can send you both. I have never had any knock issues.

 

Was just re reading your post what was the difference between new and old injector tables??? That could be related to your issue.

 

+1 The Injector Flow Rate table definitely needs to be the same as the original tune.

Other than that, did you try doing a crank relearn?

I have a fuel pressure gauge if you need to borrow one.