I mentioned this in my other thread, but I've got a problem. The car drives perfectly fine until it starts to boost, then I get power loss and the exhaust note changes as if its running on 5 cylinders. I believe its an injector going out, but it only does it under boost (like the extra pressure is causing it to lock up). I'm not getting any codes whatsoever, so pinpointing which injector is going is impossible, unless someone knows how to check them.

This all started when the car randomly downshifted (was giving it moderate gas then it suddenly downshifted from 3kish in second to near redline in 1st). The exhaust note changed as soon as it went back into second and I immediately let off the gas. The exhaust note is normal up until boost hits.

Any thoughts would be appreciated.

 

do a compression test?

 

Why jump to doing a compression test already? (thats not the solution for everything)


You dont have stock injectors that you can put in and test them out? What does your wideband say when this happens?

 

Its not a solution to anything. But it helps diagnose the problem,also if the issue is under boost it will say if its mech or elec. He can always check the plugs while there out. But its all just a suggestion

 

What does your fuel pressure look like and WB02?
I had a similar problem, mine would only act up under a heavy load ie. under boost.
I too thought it was maybe an injector on its way out. Pulled the MEVI off and noticed the upper manifold gasket had a decent sized rip in it.
Something to consider.

 

I'm still using my stock injectors (figured they would be fine for the 8psi I'm seeing at redline). I haven't gotten on it really since it happened. I'll see what happens with the AFR on my way home; just makes me nervous getting on it when i know there's a problem.

 

I have pulling that thing off to a science now, i'll take a look at that gasket. As far as fuel pressure goes; I have it set to 43psi at idle and it maxed out at 75ish at redline (seeing roughly 8psi of boost and afr around 11.5-12.2) I haven't really payed much attention to it since the incident (mostly watching afr). It just seems odd that it really sounds like it's dropping a cylinder under load. I thought about using some fuel injector cleaner since I just replaced my stock fuel filter before the supercharger install (and god only knows how many miles were on it when I did). Although with it running as well as it did for a couple weeks, i doubt that would just now cause an issue.

I'm going to check my spark plugs anyway this afternoon and see if I see anything (going to go under load/boost till the noise happens, shut off the car and check the plugs.) They're stock heat/gapped plugs anyway, prolly should just go ahead and replace them. Maybe i'm getting spark blowout though I wouldn't expect that to be an issue in the lower revs.

 

I would start by checking for leaks with some starter fuild/w40 everything after the maf.

Next I would make sure the coils plugs pushed all the way in and the plugs are tight. Next pull the plugs after a run and check for a odd ball and smell the cylinder. If you have a heat gun you can also check the temp on each header after you make a pass looking for the coolest one.

To me it sounds like one of your coils can not keep up under a load and the sprak is blowing out. BTW what is your plugs gapped at and did you change them recently

 

You must have been typing before i posted my last post, but i have stock gapped/heat plugs right now - was hoping to swap and re-gap my roomates since he's not running nitrous anymore (he has 2 step colder plugs at stock gap).

 

the sound and behavior you describe sounds much like spark blowout, but I wouldn't think you'd be flowing enough air to cause that though with an SC @ 3000rpm. it's possible though, with degraded enough spark plugs at stock gap.

 

So i took it out for a quick spin around the block. The onset is around 3700-4k in first (noticed it was lower in second - little over 3k). Going to check my plugs.

 

Plugs look fine from what i can tell, though i can't find my damn gap tool to check for disparity, and none of them had a strong odor of gas or anything. I will say that the car was stumbling a bit when i got back to the house. It was definitely misfiring though not at any type of real interval. It only did it in drive and reverse at a stop. When the car was put into park, the stumbling went away.

AFR actually looked a bit leaner (was in the low 13's), I was expecting it to be richer (injector locked open or something) and fuel pressure didn't really go up as fast as usual under what little boost i was able to get (1-3psi ish - happens quickly).

Edit: I might try to get a video of it, but I really don't want to risk the motor getting on it again. It still runs perfectly fine under normal driving at mild throttle levels without any stumbling. I'm going to go ahead and get some colder plugs and regap them to 0.034-0.036ish just to completely negate that part of the equation.

 

I agree. When i was experiencing blow out the exhuast tone made a very distinct audible tone. Mine occured right a 4500, and only at WOT. Cruising and just going under normal throttle car performed just fine. After closing the gap the car pulled really well all the way up to 6500

 

Gap your plugs small like .030 to start off. Dont keep flooring it, retune or increase your fuel pressure a bit, to get to the 11's a/f.

 

Well it was the spark plugs. Got some 1 step colder plugs and gapped them to .035 and no more issues AFR is back where it was before (though I really thought it would be running richer during the blow out).

Thanks for the help guys!

 

glad to see the problem was resolved so easy and cheap

although 1-3 psi should not blow out the plugs at stock gap, I think either your plugs were gapped beyond stock, your coils are going or the plugs were really really beat.

 

Glad you found an easy fix. I always check the very simple stuff first, even if it does not make sense. In this case your symptoms were exactly from when you get spark blowout. You probably had a big gap in there like t6378tp(whats your name dude?) said.

 

as the electrode and ground strap wear away the gap of a spark plug will increase. if your plugs were old and worn enough you could have had a really really big gap in there, much larger than stock and obviously way beyond what you'd want for an FI car.

 

Tom

 

the iridium plugs i had in there were at about a .044-.046 gap. Now i cant remember what the electrodes originally looked like on the iridiums, but when i got the copper replacements, they made the electrodes look eaten away as hell. they were almost pointed but stuck up alot higher than the coppers. I could have swore i replaced them about 20k ago and iridiums should last more than that, or so i thought.

 

I have always used copper, I really suggest you doing the same. They are way cheaper, and some say are better for our application (I dont have much say on that, but I havent had issues with them).

BKR7ES-11 2step colder
BKR6ES-11 1step colder

 

Iridium plugs are pointed when compared to copper plugs. The plugs most likely are not bad, willing to bet if you clean them and drop the gap to.35-.38 they'll work fine

 

Good to hear you figured it out. I'm not boosted but mine did something similar the other day after a quick first gear to second gear pull.

Would you describe the sound as similar to that of a WRX impreza with an aftermarket exhaust? Thats what mine sounded like. Just trying to diagnose mine too.

 

That's exactly what it sounded like, had a problem like that NA and it was a bad injector.

 

Mine sounded like that. It was a dead coil pack.

 

Mine did too, i had a blown headgasket....wait....


coilpacks did that for me thou.

 

I'm jumping on the bandwagon. Sometimes when I nail it, the sound is higher pitched and the car doesn't accelerate as fast. There's no stutter or anything except rarely at idle, but the power delivery isn't there. This usually happens when the engine isn't fully warmed. Although, from owning 3 maxis and 4 engines lol, I know that a cold VQ puts down the power. I've always dismissed it as the ECU being a POS (is any other time for me haha), but the tone change mentioned has intrigued me.

Last summer I swapped in iridium 1 step colder plugs (I'm still N/A) and the issue wasn't present (or noticeable anyway) until winter season. Any thoughts? Sorry for the wall of text and thread jacking. The car does have 167k on it and I'm not sure if coils/injectors have ever been replaced (doubting it).

 

my first injector went out at about 150k, my first coil went out at 160k. I dont think it's too uncommon (with the mileage you have - assuming no prior replacements) that you might run into the issue of either going out with your mileage.

 

I was just thinking about the plug change...the injectors had some small plastic things on the ends (nozzle sat on top of it or something). Most of them were broken. Store gave me the wrong replacement part, so I just removed those useless things and threw them back in haha. I wonder if that has anything to do with it. I guess it would make more sense if I mentioned that I put on NWP spacers at the same time.

Nvm, just found out what those things do.

 

mine did the same thing. dead coilpack - except mine was misfiring around 5000 rpm (8 psi or so)