Urgent Bad WOT Misfire

[pboxfun]

As the title states I’m having a pretty bad WOT misfire. This problem happens when I WOT from a dead stop it’ll immediately start missing and won’t stop till I let off the gas, and it’ll also happen if I’m moving and I hit the gas it’ll work fine until I get above 5k and it’ll start missing and breaking up bad until I let off the gas. Other than those times the car will drive normally. It’s only under WOT I have a problem. I replaced the opti, plugs, wires, and tps less than a year ago. But for all I know one of those things might have gone bad. I’m also not throwing any codes as well. Does anyone have any idea what the problem might be? I’m planning on checking the wires, coil, icm, plugs, and opti. Is there anything else I can check or I’m missing? Everything that’s done to my car is in my signature. Any help would be great.

[steveo]

WOT ignores a bunch of sensors... so.. you probably have an issue that's being severly compensated for by your oxygen sensors or whatever in closed loop

can you datalog?

if not, how about forcing open loop operation (unplug an o2 sensor or something), does it suddenly run like crap all across the board?

[bobdec]

You have a tune so this probably does not apply.. stock setup cuts injectors at 5805 back on at 5795. Bucks and pops until you let off throttle.. At what RPM does the problem start, did it run OK w/tune befor it started having problems. Could be just plain 'old school' HV ignition failure under load. Coil, coil HV wire to opti, plug wires, cross fire, opti rotor, burnt plug wires, plug cutting off-on under load.

[pboxfun]

Yes I can datalog. When I do what should I be looking for or at?

It's been fine with the tune until yesterday. It happens at WOT from a stop or if i'm moving WOT at above 5k.

[steveo]

do a run and post it up, lets have a look..

i'd be more focused on part throttle at first to see if you're getting really heavy trim because of another problem.

closed loop is really good at concealing an issue, but it would stick out on a log like a sore thumb.. and as soon as you're in wot, those compensations are thrown out the window.

it'd be weird for an ignition thing to show up at WOT but not right before (say 3/4 throttle from a roll or whatever)

[pboxfun]

What is the best way for me to datalog my car? Like should I do it from a stop or from a roll or both? Also should I do it in open or closed loop?

[davesLT1]

First off did you replace the opti with a GM unit? Had same type of issue when i first got my whip, anytime i went WOT it would buck and pop, and wouldnt shift until i let out of it... Turned out to be my optispark.. Always buy a GM unit, never a ebay or any other one..

[pboxfun]

Due to the nice weather today I’ve finally been able to datalog my car. The car was in closed loop during these runs. The first file labeled misfire 1 is from a dead stop. I had a little trouble getting traction at first but once it hooked you can see it immediately started missing really bad, I had to let off the gas because it wasn’t going anywhere. The second file labeled misfire 2 was from a roll. I had the car manually in 2nd gear from the beginning of the roll. The car took off fine but as soon as it got around 5k it started breaking up bad and wouldn’t shift into 3rd. Once again I had to let off the gas because it wasn’t going anywhere. Also I checked my electronic fuel pressure gauge I have in my car during these runs and it was fine. Does anyone have any ideas or can see something I’m missing????? Any help would be greatly appreciated.

Missfire 1
misfire1.xlsx
Missfire 2
misfire2.xlsx

[pboxfun]

Anyone???

[pboxfun]

I changed the coil and ICM and it didn’t fix the problem. I also used a millimeter to check the fuel injectors and the wires going to them to make sure they were getting power and functioning properly, which they were. The reason I checked for that is because in my datalog my left o2 senor was reading very lean compared to my right one when the car starts acting up. So I thought it might be a fuel problem. But according to my fuel pressure gauge and testing out the injectors and wires it seems like everything is working right. I can also hear the fuel pump kick on when I turn the key. I also looked under the hood at night to see if I could see any arching but I didn’t. I’m going to take the wires off to get a better look. Anyone else have an idea what might be going on or what I should check for next? What could be causing my left o2 to be reading so lean? I also replaced the o2 sensors about a year and a half ago. Is this a fuel or electrical problem???

[USMC]

What type of wires did you use on your tune up?

[pboxfun]

I used JEGS 8.5mm Yellow Ultra Pow'r Wires

[steveo]

what would cause one bank to read much leaner than the other?

- an exhaust leak before the o2 on that side (smoke test)
- a sizeable vacuum leak that you missed (test all vacuum accessories with hand vac pump, and use propane instead of spray fluid)
- a sizeable injector flow mismatch (swap injectors from left bank to right bank)
- a poisoned/fouled o2 sensor (swap o2 sensors left to right)
- damaged o2 wiring or corroded connections (inspect visually and test with multimeter)
- an injector miss on that bank or a spark miss on the oppisite bank (... good luck with that one, unless you have a 'scope)

[USMC]

Originally Posted by pboxfun

I used JEGS 8.5mm Yellow Ultra Pow'r Wires

I bet its your WIRES. I used JEGs too and they are junk. The reason I asked this question is because the same thing happened to me after a tune up and it ended up being my brand new JEGs wires. I put MSD on and had no issues what so ever. Try pouring or spraying water on those wires and see what happens. I tried the make it dark and see if there is a light show technique and well there was no light show. When water or in my case oil got sprayed on the wires it did ot want to drive and going up a hill was a joke. JEG wires are junk. Good luck!

[pboxfun]

I finally had time to work on my car a bit yesterday. So I decided to go through all the plugs and wires. All the plugs looked good and didn't show any signs of running too rich or lean. But I did fine one of plug wires on the driver side to be cracked and arching. I had to look at the wire at weird angle which is why I must have missed it the other night. Hopefully this has been the cause of my misfire. I'm going to be changing all the wires to MSD and route them OTVC. I'll let everyone know if this fixes the problem or not after I change them.