I already searched P0300 and Misfire. All info found is about miss & lack of power at high RPM's...Mine is the OPPOSITE!! Can someone gimme a hand with some ideas?

Car is 2002 TA, M6. Professionally tuned for a 224/224 .581 112LSA and longtubes. Car ran great.

Just finished installing Stage II heads and it fired up on 1st try. Idles OK, oil press at 40 psi at idle, no ticking, looks good. I also changed the injectors to Racetronix 37# which are like 43 lbs at 58psi. So, I bumped up my IFR table by 150% with LSEdit and nothing else. Added a set of Yella Terras and Comp Lifters (bolted them up to 24 ft/lbs).

I've already seen my LTFT's out of whack. Bank1 is at +23 and Bank 2 is at +15. So I guess i've messed up the O2's with coolant that ran down the header pipes when we popped off the heads. Will change those immediately.

Here's what's wierd. It drives like it's on 7 cylinders (chug..chug..chug) until it hits 3500 RPM. Between 3000 - 3500 you feel that extra cylinder intermittently kicking in, after 3500 ~ 4000 it all cyls fire perfect and the car goes like a bat outa hell.

Logged with EFILive and have:

Cyl 1 Misfire History - 438 <------ yikes!
Cyl 2 Misfire History - 27
Cyl 3 Misfire History - 2837 <------ big yikes!
Cyl 4 Misfire History - 70 <------ smaller yikes!
Cyl 5 Misfire History - 23
Cyl 6 Misfire History - 9
Cyl 7 Misfire History - 9
Cyl 8 Misfire History - 11

Checked wires, plugs and replaced O2's. All OK. By reading everything I could find on Misfire's and injectors, I reached the conclusion that what will cause LOW RPM misfires and be OK at higher RPM's is the Injector Offset. The way I understand it, is that the Racetronix being much larger than stock, the computer is telling the injectors to open and close for so little time, that they sometimes actually never have time to open at all, because the amount of time commanded is smaller that the actual time it takes for them to open and close. This has the effect of starving the cyl of gas often enough that it is detected as a misfire.

So, I think that by increasing the Offset, it allowed more time to allow the injectors to open and spray gas before closing. Now the question is how much more? I tried guessing...with three values derived from the stock values, here's what happened:

1) Multiplied Inj Offset table by 110% - Misfire numbers came down SIGNIFICANTLY, but #3 is still high 1,230 misfires counted, all others are around 10 -20. NO backfires.

2) Multiplied Inj Offset table by 115% - All came down to zero except #3, which did some 70 misfires. But now I have backfiring (LOUD) when coming off the accelerator and any RPMs.

3) Multiplied Inj Offset table by 113% - #3 went to 430 misfires, and backfires are less but still there and LOUD.

Now, I'm really gonna need help from someone who's done these before. Or maybe, the folks at RACETRONIX can use some of the money I forked over for these injectors kindly have someone reply with some information or suggestions.

I'm not trying to become an expert or a tuner or anything like that. But I've put my honest effort into this and basically I just want the car to run sufficiently well to drive 130 miles to Tampa and have it professionally tuned again...

 

thats a lot to read can you sum it up for me lol, im about to go out but i have 38# injectors from them i was having a damn hard time tuning but i have it figured out. do you know what the pulse width is at idle in ms? if you can get me that ill help you out when i get back in tonight

 

also the injector offset tables? im not firmiliar with this...can you explain?

 

Not being a smartass, on the contrary. Thanks for the offer to help, but what I posted IS the summary. I did however, include sufficient detail so anyone out there who's tuned these might recognize what is going on...

Believe me, I spent hard earned money to buy these and one way or another they are going to work! Lemme see if I can figure out the Pulse Width and get back to you.

Inj Offset. Right below the IFR button there is another labeled Injector Offset. It's scaled by Volts @ Load. This is in LSEdit v1.3.

 

if your fuel rail pressure is actually 58 PSI, then you should have about 5.38 for your IFR value. leave the offset alone. sounds like you have a low value for your IFR and you fouled a plug or two.

 

yeah i got ya, sometimes you cant just sum it up. have you messed with proportional fueling at all?

 

edit : missed some of the post, sounds odd...let me think

 

try to turn off proportional idle if you can, but i assume u dont have tuning stuff? if you can do this and it helps it must be in prop fueling. bigger injectors need less fuel shot to make o2s oscillate. if you can get a log of the o2s and see if they are railing or not that would help out. this was where my problems were. plus i was getting about 1.7-1.8 ms on the pulse width, the range of injector misfire.

 

clean the maf sensor off too, a faulty maf sensor could max out fuel trims and cause misfire. happened on my friends 98. then he broek a pushrod after we fixed that.

 

You should figure out what's the deal with #3
first. Maybe mismatched injector, maybe
something else. Don't forget the old school
stuff like a compression test, plugs & wires,
etc. But you're also over-lean, 3000+ is
where you are running more on MAF airflow
numbers and rely less on the speed density
tune (4000 is all-MAF). You improved airflow
with the heads, maybe you didn't tell the VE
table. None of that matters to #3 uniquely.
But something does.

 

check all the part numbers on the injectors, and lot numbers let us know what they are if they are the same or not

 

You're not gonna believe this. For the Nth time I had checked MSD wires and they looked fine. Then I took plugs out and although #3 looked a little blacker I attributed it to the fact that #3 IS misfiring so it was expected, put them all back in. Tested again and same misfire in #3. So, I finally decided to take the coil packs off to check wires and possibly start swaping things around, to see if the misfire moved to another cylinder.

I go to pull the wire boot off #3 and on the 1st tug, The plug snapped in two. Half still attached on the wire boot and the other half on the cylinder head. The plug snapped just below the metal lip where the creamic insulation goes under the body of the plug. Apparently it was far enough under the lip that it stayed all together the 1st time I took the boot off, or was just cracked. The second time I pulled on it and it finally just broke off.

Anyway, put al old TR-55IX I had left from a few months back, and fired right up.

Thanks guys. Damn thing ate two days of my life, chasing a ghost. I guess it's live and learn...

 

damn dont you hate that? its nice if something breaks and it really breaks enough to tell what it is. glad you got it fixed man