Engine misfiring when I hit 2nd hard

[soldave]

Wonder if I can get your thoughts on this little problem I encountered at a drag tournament today. Got an Ostrich real-time emulator in my car and have tuned an Evo 2 map to my specs. Today I must have had about 8 runs in total. 6 of them were fine but on 2 of them (and one in particular) I had a strange problem.

I launched at 5200rpm and after a little wheel spin I hooked up fine. Went up the rpm range to my shifting point at about 7,300rpm. Then when I dropped into 2nd the car felt like it was misfiring and not pulling nearly as hard as it should. Did it through 2nd and into 3rd. Then from about 4,000rpm in 3rd it went back to normal and pulled really hard again. But then the next run I could go straight away again and it would pull fine. Also, if I go from a roll all the way up 2nd and 3rd gear, there's no misfiring.

Any thoughts what it could be? Have just got some new Iridium plugs in there so I sincerely doubt it's that. If you need any more info for diagnosis purposes, let me know.

 

[MrBoxx]

As a safe experiment, try replacing those iridium plugs with a normal NGK copper plug and see if the problem goes away. I'm not a big fan of the exotic metal plugs in our cars; some people say they work fine, others notice horrible problems. One of those problems is misfires, hesitation, sluggishness, loss of power, loss of fuel economy, etc. from running platinum or iridium plugs.

 

[soldave]

I will try that over the next week or so. Is there any reason though why the misfire would only occur when I'm launching and shifting into 2nd; and when I gently roll into 2nd and then hit WOT it doesn't?

 

[Twistaye]

Picky plugs They only do it to you when they know it'll piss you off the most. I say just try the NGK's, might work, might not, but it's a good place to start. I don't see why it would target one gear, unless maybe it's the way your air/fuel is set up and a certain point in your 2nd gear it triggers the hesitation (possibly ?). Just a guess though, try the NGK's and let us know if that helps it out.

 

[soldave]

Just a thought - could it be a fuel cut?

 

[MrBoxx]

Fuel cut generally presents itself when you feel like you've hit a brick wall and your teeth embed in the steering wheel. Do you have any datalogs from the times it does this?

 

[soldave]

Doesn't sound like it's that then. Sorry but I don't have any data logged from those runs

 

[soldave]

Went out last night for some testing and it looks like taking the spark plug gap down to about 0.6mm from 0.65mm has worked. Did plenty of runs through the gears and not a single misfire. I also managed to log my first 400m (or 1/4 mile) runs. Not too bad times as you can see below, and a nice benchmark for when I make future mods to my car.

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[soldave]

Well, I changed the spark plugs to NGK copper ones and... it did exactly the same thing when I launched. Even did it in 3rd gear on one run today. Am not sure where to go from here. Am going to change spark plug leads as a long shot, as well as decrease the spark plug gap. We'll also look at the fuelling map to see if it needs leaning out between 3000 and 4500rpm.

Any other ideas folks?

A little more info on this persistent problem I'm having. Did some more tuning on Saturday and found it was still misfiring when I hit 2nd and sometimes into 3rd. The misfire usually stayed for a few seconds, but sometimes it was momentary and sometimes until about 6,000rpm. At one point I let off into neutral when it was misfiring and even at idle the car was misfiring and died. When it did that i tried to start the engine again and it didn't want to start a couple of times before it fired into life again.

Got home and as a last resort I decided to put the stock Evo 1 chip back in there and see if it was the Ostrich chip emulator that was causing the problem. The results were interesting. With the stock chip in the only misfiring came when I was at 6,000-7,000rpm, and I assume that was because of overfuelling as I was running AFRs of 10.0 or under all the way up from about 3,500rpm. Tried it with the boost turned down and then all the way up to 1.34 bar and it was boosting fine. Got the Ostrich chip emulator in and it was misfiring again on boost when I hit 2nd gear.

Am wondering if the Ostrich is somehow to blame so I'm getting a new chip burned based on my current maps to see if that sorts things out. I'm praying it does as then it will be a relatively simple solution. If not I'm gonna have to be going for even more long shots.

You can hear me misfiring here

 

[soldave]

I may have finally found out what is causing my misfiring, and I don't think it's the ECU (directly), the ignition system or anything like that. I think the misfiring occurs whenever I shift after pinging off the rev limiter. Don't ask me why it's doing that (something to do with the rev-limiter causing a fuel cut rather than an ignition cut or something; I don't know completely what I'm talking about) but if I don't hit my 7,600rpm rev limiter then I seem to be shifting cleanly.

It got worse over time as I was pushing my car a little more and when the wheels spin in 1st my timing has to be spot on letting off the gas just before the limiter. I know you're probably thinking "Well how hard can that be?" but you really have to experience racing here at Nago in Okinawa to understand! I really hope it is that as that means it's not a huge problem in the end. And I have spoken to another guy who had an Evo 1 with exactly the same problem.

If the weather's good this weekend I'll do more testing but I think I'm onto something.

 

[Laser-Fist]

I also run an ostrich, I use tunerpro rt. The only time I have experienced this is when I overran my maf, per readings I was not even close however switching to a 2g maf made the car rock and roll again. For ignition woes it is rather simple, make sure your colipacks are within resistence specs, create excellent grounds for all sensors especially the coilpacks, side gap bpr7es plugs, and run Taylor thundervolt 50 ignition wires.

 

[soldave]

You experienced in when you shifted gears ano not before? And it went away after about 5,500-6,000rpm?

 

[soldave]

Just a thought about this one. Could it be possible that it's not the rev limiter I'm hitting and some other sort of limit or threshold that I hit at about 7400-7500rpm then causes the misfiring? This thought just came into my head when I was doing a bit of testing this evening.