Misfire problem

Might as well make my first new thread here... :biggrin: This post assumes you have been following my odd problems, but there may be some interesting info so I'll put it up here too. I went to LVD in new york saturday since NED was closed for rain friday night. Plus the GF was being a douchebag so I figured I'd go to the track... Best run was a 12.5 at 115 I think. I'm going up wednesday to NED to dial in the car on pump gas and 25 psi for the shootout...


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So yesterday was another waste of an otherwise good track day. But first let me say the import event sucks there. There was supposed to be a quick 16 qualifyer, but I dont know why, since its all POS bracket racing either way. And there are some hardcore bracket racers there. No way an inconsistent 11 second car has a chance against these stock auto tranny Hyundias that are running a few hundreths off thier dialins ;o) There was a 7 second toyota there, tons of starlets, tons of fast RX7s, and plenty of very fast rednecks. The track has WAY too much traction. My clutch was slipping all day. When I finally forced my brain to try to spin the tires instead (a no brainer at NED ;o) I got a 1.64 and 1.65, and the clutch held up for the rest of each run. But then, the misfiring continues...

Same as before at NED for those of you that have seen/heard the problem.. I ran more 17 second slips yesterday than I have in the last 3 years combined. I swapped back to my trusty stock wires, no change. On one run, out of pure hatred for the car, when its started misfiring in 3rd, I just kept it at WOT hoping something would blow up or give in. Well, it cleared up and started to pull again. So I said HMMM... Maybe its a fuel issue. I was leaned out 15% over stock settings, on race gas. No timing added, 28 psi. So I leaned out another 10%. Then in the lanes I got nervous and dropped boost to 25 psi. No stumbling, but it ran a lousy 113 trap, so I know its too lean. AF ratio was 13.x on DSMlink, which is at least one number too low, so its more like 14.x to one, lol. So it was lean (supposedly, more on that later). No knock though. So on the next run I cranked boost back up, stumbled to a 17.1 at 27 mph. ;o)

Now on pump gas I've been running 25 psi, 5% leaner than stock, no timing added, and there isnt a hint of knock or stumble and it pulls harder than I have ever felt this car pull before. Its all over the road in second gear. Everytime I say I am going to run pump gas though, I get greedy and change it out and crank up the boost, only to run 17s. There is almost no lag, while on Race Piss it takes forever to get boost back, even when its not stumbling.

So my latest theory is a boost leak that isnt an issue at only 25 psi, and/or isnt an issue until aggrevated by the fact that Race Piss runs richer than pump. Its a pain in the ass because if its too rich from this leak/race piss, the ECU senses the misfire and cuts fuel, so I cant get a decent log of O2 voltage, or calculated AF ratio while its actually doing it. And to further complicate the issue, my car has always run in the .90s even leaned way out (30%), depsite the fact that it will be .92 on pump. So I have no way to measure AF ratio without relying on the DSMlink calculated AF ratio, which wont account for boost leaks or other air/fuel issues.... Which is why I can supposedly run 14:1 at 25 psi and not blow up.

While the a$$ ramming donkey f*ckers at VP were kind enough to get me my FMIC in 4 months, I would have gladly waited another month if it would have meant getting the TB flange welded on the right way, not friggin backwards. I have been fighting a leak there since the day I installed this kit. That steel is so damn hard after a half hour with the grinder/carbide burs, which barely scratch the surface, I give up an work on it more another time. Finally yesterday after round 7 I gave up and just made a cork gasket for it. That spaces it out 1/8th inch so it clears the protrusion for the throttle closed switch (which I also ground down when I installed the kit). The flange is no longer flat as well, so the cork is good. I didnt have time for a pressure test, but my airflow dropped 2 lbs/min over what it was an hour before. So that was a decent leak. I'm now only getting 43 lbs/min at 25 psi, and still zero knock on pump.

I'm hoping this fixed the rich condition that I am hoping was casuing my misfiring. I'm going to leak test it and try it out wednesday. If the car still wont run I'll be running pump gas from now on. ;o)

Kevin

Kevin,

First off I would say leak test for sure all the way up to 30 psi to be safe. It sounds just like rich misfire, if it were wires the misfire would show up at lower boost, even cruise conditions. (At least mine did). Anyway, if its not a boost leak, check your plugs to make sure they are gapped correctly, might even be worth it to gap them a little closer. Sometimes when you run real high boost/compression you can extinguish the spark if the gap is too large. (If thats the case its an MSD for you:)) If you tried leaning it out then its not a fuel problem and that just leaves a boost leak or spark problem.

Also, since pump gas ignites easier than race gas, you might be able to burn your full charge of pump gas, but can't ignite all the race gas. Hopefully that gives you one more thing to look at.

Best of luck,
-Jacob

I did check the gap at the track. I have to gap to 26 to avoid misfire detection/fuel cut. After a couple weeks it can blow out to over 30 with the airflow I get. But it was fine. The plugs looked fine, but rich as usual. :) What you said about the pump gas burning esier is the key. Now its just a matter of verifying that I fixed the leak, the one at the TB elbow. I could barely get it up to 30 psi last itme I checked it. But from 10 to 0 it dropped very slow, almost a minute probably. Could be all the RTV I had in that gap... It looks like rain for wed night, but I'm hoping I can get to NED and see if its fixed. I need to get the car dialed in too for the SO dammit... :biggrin: