2000 Vortec misfire help

[Static]

Re: 2000 Vortec misfire help

If you swapped those out, you'll need to do a CASE relearn, IIRC. Takes about 10 seconds with a Tech2 or similar scanner. A Snap-On Modus can do it, so can the newest one, the Verus.

Yes, does require a case relearn. Need to find someone in town that has a scanner that can do it. Just read up on this and it makes alot of sense about the issues Ive had with this random misfire. When the swap was originally done the original pcm was not used due to the vats programming. I used a 96-97 pcm and relearn was never performed. Learn something new every day...

 

[Static]

Re: 2000 Vortec misfire help

New problem. Misfire #4 cylinder. Spark is there but no fuel. I pulled the plug and started it but no gas comes out. I can put power to the terminals and I can hear the injector. I have 12.x volts at the wire going to that injector. So either something in the spider assembly or bad injector?

 

[Static]

Re: 2000 Vortec misfire help

Ok took the upper manifold off and reconnected fuel lines. crank it and i get spray out of the other injectors but not #4. I pull the plug from the injector and jump it to the battery and I get good spray. So injector functions. Where do I look next???

 

[midnightbluS10]

Re: 2000 Vortec misfire help

Is this the CSFI engine? with the big central plug on top for the injector that fires 6 poppet nozzles? Start checking the pins on that plug. Make sure none are bent down and that none of the female sockets are too loose and not making a good connection.

 

[Static]

Re: 2000 Vortec misfire help

CSFI with the updated MPFI kit. Im thinking I have a valvetrain issue, something not allowing the intake valve to open. Pulling the valve cover tomorrow when I get off work.

 

[Static]

Re: 2000 Vortec misfire help

ok double checked everything again, tearing out my hair on this one. Valvetrain looks good, cranked it by hand and the valves go up and down, have spark. Pulled the spider out and fired it with the rail hooked up and i can watch it spray consistently when cranking. Swapped the injector with #2. Put it all back together and misses on #4 still. Looked at the wire harness found a pin that wasnt fully seated, was sure that was the issue. Repaired. Still misfires on #4. continuity from the injector ground to the ECM is good. I can ground pink/black and it fires the injector full time, can smell gas out the tailpipe. Bad ECM????

 

[Static]

Re: 2000 Vortec misfire help

Ok so I cut the wire that runs #4 injector and used the wire that runs back to the ecm and used it to one side of a bulb and ran 12v to the other. I have pulse. So ECM is telling injector to fire. What am I missing?:rant:

 

[Static]

Re: 2000 Vortec misfire help

I drove the car over the weekend mostly because I had to move it out of the way to access the lift. I reset the P0304 code and drove. Car runs awesome until you stop at a light. Then you feel the rough idle and then the p0304 code comes up again. I drove 15 minutes on the freeway, got off got back on the freeway headed home, idled in the driveway and bam light came on. So its only misfiring at idle. It does not smell rich compared to when I pull the plug wire on either #2 or #6.

So:
Intake valve not opening due to bad lifter or bent pushrod? I would think it would be noisy tho.
Can I eliminate the case relearn not being done as an issue? I would think that I would have misfires on other cylinders if crank/cam correlation was off too much. Both shops Ive taken it to say the relearn cant be performed if it has a misfire and is setting codes.

 

[Static]

Re: 2000 Vortec misfire help

Ok I am working on this again. Had it in a shop for a quick diagnostic and they called and said it has low compression on #4. I picked it up and brought it home and sure enough it struggles to make 120 psi. #2 and #6 make 160ish on the first stroke. Dunno how I missed that the first time. Regardless, Ive got the head off and the piston out expecting to see an issue with the cylinder wall or the rings but Im really not seeing anything. Anyone live close to me that can look at this?

 

[Static]

Re: 2000 Vortec misfire help

Spotted the issue today in a better frame of mind and some better light. Exhaust valve is bent on #4. Looked in the exhaust port and could see light all the way round and when you spin it in the seat it really shows up.