Hey all!

I am here with a problem from my 2000 Chevy camaro z28. The engine is a gen 3 5.3 engine that has been rebuilt with new main bearings, rod bearings, and New piston rings. New cam bearings with stock boring can. Stock pistons and rods. Arp connecting rod bolts and arp head bolts. 862 stock heads.

I’m logging with hp tuners and it’s misfiring randomly on all cylinders. Car breaks up bad when accelerating. The stft start going to +25 and then they go to 0, but ltft goes +25. So it is adding tons of fuel probably for the misfire. Revving the engine helps briefly with the fuel trims, but staying at about 2k rpm the fuel trims stay way lean.

fuel pressure stays at 58 psi. Car has new fuel pump and filter. I’ve put in new spark plugs, plug wires. Changed intake gaskets. Smoke tested for leaks. Checked the timing. Re tuned it with stock tune. Car has long tubes and is an m6 car. Starts up great. Exhaust note sounds flat.

ive also cleaned the injectors. I’ve even changed my valve springs and valve seals. Has new gaskets everywhere. I don’t know what I’m missing here. So posting here hoping someone can save me! Lol

 

 

Hello,

Your engine is virtually identical to mine - a now 156,000 mile LM7 out of a 1999 GMC Sierra. I did everything you mention above trying to solve my misfire situation and in the end, it was a bad PCM. I keep a small stack of a half a dozen or so junk yard P01 / P59 PCM devices loaded and ready to go here for just such small emergencies and diagnostic capabilities. That failing PCM promptly went into the trash.

And no, I don't own stock in the HP Tuners or EFI Live companies nor any financial relationship with them in any fashion, far from it. I have a junk yard wiring harness and I use a set of free flashing tools to keep that small stack of ready-to-go PCM's supplied. Knock on wood, I have only had to jettison that one bad PCM in four and a half years of playing this game. I get my used PCM's out of the yard for $16.00 on Half Price Sale Days or regular price if I see that somebody else has done most of the work to liberate the PCM for me. I use Tuner Pro RT to edit my BIN copies out of the PCM and then use PCM Hammer or LS Droid to read or write the BIN to the junk yard PCM devices. I use either a Bluetooth OBDLink MX device as my interface or a VX DIAG VCX Nano USB-cabled device as my interface. I occasionally have to use a program called "Universal Patcher" to fix my OS BIN checksums when I've done something stupid to my BIN software but another knock on wood . . . I've still never bricked a P01 or a P59 PCM. In a demented way, I'm kinda' looking forward to that eventual bricking to see if I can bring it back from the dead with the "pin grounding on the printed circuit board" trick.

But I digress. Try a different PCM to see if your misfire condition is solved. I've also had STFT and LTFT oddities when I had some different intake tubing than I have now. My theory is that it caused chaotic air to reach the tiny MAF sensor wires but its all good now after I changed things.

Rick

 

I had that sneaking suspicion on it being pcm. I disregarded it because everything seems to work fine on it. Even took it apart and couldn’t find an issue. However at this point I bet you are correct. Thank you for your experience and input! Is there any way I can keep the licensed part of the pcm for hp tuners? I just don’t want to spend another 150 to delete the vats just to try it. Thank again!

 

I'm no expert on HP Tuners, obviously. If you copy the licensed / credits paid operating system BIN out of your possibly failing PCM and then use HP Tuners to write that OS into a different PCM . . . I think . . . that HP Tuners will detect that you are doing this into a different PCM. And then charge you two credits to complete the writing into that new PCM. Maybe somebody will come along here with more HP Tuners experience.

Let's also hope that your current tune is not password protected which is otherwise known as "tuner locked".

Rick

 

thanks a lot! I sent them an email!

 

Hello,

Your existing PCM might only have a little software indigestion / heartburn and only need to have your HP Tuners licensed operating system re-flashed. Its worth a try and costs you nothing if you have access to HP Tuners and the MPV device that wrote your tune. This did not work for me but you have nothing to lose by trying. Hopefully, they either kept a copy or gave you a thumb drive / e-mailed copy of your paid for and flashed OS.

Rick

 

ive reflashed 3 times and no help.

 

Tried a new pcm and new tune and the problem is worse than ever. I’ll insert a picture of hp tuners scanning. It is so far lean now.

 

Why are you in Open Loop with every HP Tuners screen shot? Do you ever go into closed loop? Are you running some kind of a cold air intake?

Rick

 

it will go into closed loop and I can force it too as well. Conditions are the same either way. It has gutted stock air box with a smooth lid.

 

I put the old pcm back in and got it do run better than with the new pcm. I changed the pcv valve to a new one hoping that would help.

here is some screenshots and videos from hp tuners scanner.









The weird thing here is that these code have all been deleted from the ecm with hp tuners. However they keep coming back.

 

Here is one video

 

Here is the other where I simply clear the codes out. These codes have also been tuned out and disabled from the ecm.

 

Just spitballing here, but could I have a hole inside the intake manifold causing and internal vacuum leak? At this point I have no idea what else to even check.

 

If you have misfire codes, it's not burning the fuel, and the O2 is seeing oxygen, and saying it's lean. Make sure you have good ignition on all cylinders first before chasing your tail on "lean" fueling issues.

 

FWIW,, Electrolytic Capacitors are typically good for 10 to 15 years, a lot of these PCM's may be aging out, this was becoming a common problem with Jeep ECU's from the early 90's. to about 2005.

 

What injectors? Did you change the engine size in the tune?

Really the only things that I can think of that would cause this since the fuel pressure has been verified are.

Wrong injector data
Bad MAF, wrong MAF, MAF in backwards
HUGE vacuum leak, like the brake booster line

 

this guys wins! The maf data in tune was for the a truck maf and it had an fbody maf in the car! I found out just by comparing everything. Cheers guys! Hope this helps someone else.