Part throttle misfire: Any new ideas?!?!?!??

[GraySilvia]

Hello everyone. Well, just last week I installed Enjuku's T3/T4 kit on my 240 after it had been sitting dormant for 3-4 months. Now i've got a hellishly annoying part throttle (usually part throttle, unless high load at very low rpm, say, in 5th gear) that won't clear up despite our best efforts to figure it out and eliminate it. The will NOT idle once the miss has started.

It's a very peculiar problem. If you start the car when it's cold, it will do its usual crappy idle until warm, then if you don't drive it, it will sit and stay idling. But as soon as you drive it and the miss starts, it won't idle at all, you have to keep about 5-10% throttle just to barely keep it running. Actually, it feels more like fuel blowing out the spark, it's not a very clean miss, you know, it's not a complete miss that makes it sound like a subaru. However, i've gone from 53% to 38% fuel correction on the FC with no clearing of the miss, so i don't believe it's purely a fueling problem. So, i was wondering if anyone has any fresh ideas as to what the problem can be cause we've been trying all week and haven't solved a damn thing. Here's what we've tried so far:

-Cleaned + gapped plugs.-Installed new plugs, 7's instead of 6's.-Swapped coilpacks-Installed a genuine TT Z32 maf.-Swapped ignition subharnesses.-Reset TPS voltage-Swapped throttle bodies and TPS's.-Swapped from power FC to JWT and back again.-Pressure tested the intake, no leaks.-Removed Nismo FPR, installed stock FPR.-Resealed Nismo FPR, reinstalled, base FP set to 43 psi.-Checked entire fuel system for blockages, leaks, etc.-Messed wildly with FC fuel corrections.-Reset base timing.-General debauchery under the hood.

Anyone have any new ideas?!? At this point I just want to buy a new wire harness and pull the engine and start from scratch.

[ItzGenX]

I had the same problem a while back ago. It happened when I either did a hard load under low rpm and stopped after it got over a certain rpm (6k under wot). My car always idled after missing cause it idled high all the time anyway (when its cold, missing didn't happen during warm much unless motor just started). Then I figured out the problem after I tried to turn up the boost. When I did, the car would miss after 8+ psi no matter what. So what I got it down to was ignition spark was not strong enough. I also did the same as you, and checked the plugs, got new ones, dif heat range, checked timing, etc, no go. I checked the wiring harness resistance, no go. So I came down to the weak coils. I upgraded to the Splitfire DIS system and I haven't seen a miss since. Running at 12.5psi now.

[ItzGenX]

Say, how's the spool on the Enjuku kit? I was thinking about getting it soon and adding a flex section to the turbo extension. When is "useable" boost achieved at?

[GraySilvia]

Well, i can't really see the coilpacks being the problem because i've tried two different sets and they both did the same thing. Also, I don't understand why it would miss now, when it didn't miss a beat before. Also, under boost it's fine, it doesn't miss when the car is making good power. I just don't get it.

The enjuku kit spools amazingly well considering it's a bushing turbo on a Greddy intake manifolded and semi-nasty cammed motor. It'll get to 17psi by about 3700 rpm, which should be good for 400rwhp if I ever get this miss sorted and get it to secret services so they can tune it and make it nasty. I'm very pleased with this turbo setup. The top end pull is just silly. Also, the AVC-R decided to do it's own thing last night and it went to 33psi momentarily and proceeded to light up the tires in 3rd. Oops. :oy: Well, nothing blew up, so, guess it didn't hurt anything! :ylsuper

[GraySilvia]

OK!! Well, I figured out what is causing the misfire, or whatever it is. I was driving around late last night trying to drive and watch injector duty, airflow, timing and knock on the power FC. Luckily the roads were pretty empty, but, I found out what's happening. At cruise, say, 50mph and ohhh.....10% throttle, the injector duty should be around 6-8%. Well, when this 'miss' occurs, the duty jumps up to 15-17% for some inexplicable reason. I could watch the duty shoot up as the car shuttered from the miss, then when the miss cleared up, the duty would be back down low again.

Now the $20 question: WTF is CAUSING the injector duty to do it's own thing? It can't be purely an ECU issue, because both the JWT computer and the power FC do it. I want to do some more driving and watch TPS voltage as well as airflow and see if I can figure anything out. I doubt either of those is the culprit, since i've changed both of them and the miss has still been present. Anyone know what would cause injectors to act all funny like that? Perhaps the injectors are picking up some electrical noise from somewhere?!? Or maybe they aren't grounded properly? Any thoughts/comments/solutions? Or should I just push my poor car into the lake and be through?

[ItzGenX]

Are you pressing the throttle slightly more for the miss to happen at cruise? If you are, then it is natural due to fuel enrichment for acceleration. If not, then I haven't a clue.

[klattr1]

its gotta be ignition related. I had the same problem but with a ka. My internal coil decided to just go bad. I found this out at the dealership through the help of the CONSULT.

[GraySilvia]

It turns out the MAF was too close to the compressor inlet! All I had was a 30 degree turbonetics silicone coupler and then the MAF. Well, the Enjuku kit came with about a 6" extension for the MAF. I tried that and it got about 80% better. There was still a little part throttle miss and the MAF was doing weird things, so. This got me thinking. I'd seen other people put the MAF in the cold pipe, so, that's exactly what I did. A little Z32 MAF hacking, some cold pipe sawing, and voila! Now I go back to drive it, and WWOOOOWWWW, it drives like a stock SR!!! I'm so excited. I've been messing around with power FC settings today, only problem is they DON'T save when I turn the key off. That's my next thing to fix. It'll run 27 psi without any appreciable knock. Now, I know that's a ton of boost, but it's still completely not tuned, so it's only putting out maybe 370-380 to the wheels at such a pointless boost. But, I just did a 4th gear pull and my JWT clutch wouldn't hold the power! The clutch just started slipping when the boost came in hard! :ylsuper sschhhweett.....secret services, here I come!