Hesitation/Popping in upper RPM range under WOT

[MarkEmark]

Haven't posted about a technical problem in a while, but here goes...

First off, the setup...370cc SR injectors, JWT ECU, walbro 255 lph fuel pump, aeromotive adjustable FPR, 93 octane, alcohol injection, large intercooler, T3 super 60 B turbo @ 9 psi

I took the car out the other night (it was nice and cool, 59 degrees is what I like...) to do some tests using G-Tech, such as 0-60 and 1/4 mile and the like. When I was doing these tests, however, the car in first, second, and third gear past 5000 RPM or so under WOT would start hesitating noticeably (and not accelerate very quickly) and then would start making these really loud, scary sounding popping sounds, a bunch all at once and overlapping eachother, like backfiring....it would do it most noticeably in 1st gear, then not as much in 2nd, and not as much in third.

My fuel pressure was 32 psi @ idle (lower than stock to accomodate the pig-rich JWT ECU fuel program), so I bumped it up to 34 psi because I figured it was running lean in the upper RPM Range. It's noteworthy to mention that I'm not at a full 9 psi past 5000 rpm either, I'm at more like 7.5 psi around then (gotta love the tiny turbo). Anyway, at 34 psi it would still make the same incredibly loud popping sounds in first, second and third, and the tach needle would jump erratically (not smoothly) past 5000 rpm either. It did the same thing at 32 psi as well. I thought maybe I was misfiring, but I haven't thrown a code and this was 2 days ago. So I bumped the fuel pressure up to 36 psi, and it still does the same annoying popping sounds, but only in first gear now (or so it seems), so i bumped it all the way up to 39 psi and haven't taken it out yet. My question is, how could I be running lean, even at 36 psi, with a small turbo that's only at around 7.5 psi when the hesitation starts ocurring, especially considering the JWT program runs notoriously rich and conservative at stock fuel pressure (34 psi @ idle)?

My second question is: Are the symptoms I described due to running lean, or is it some other (worse) problem?

My third question is: why would it only do it now in first gear, and not second or third like it used to...is it because there's more stress on the engine in that gear?

I don't see how I could be running lean with the fuel system I'm running...and I previously have not noticed this problem, and it has ran very well at around 32 psi of fuel pressure for a while, but come to think of it, I rarely bring my car up past 5000 or 5500 which is when the hesitation starts...but if I need to run 40 psi of fuel pressure just to cure whatever this problem is, I think I'll be losing substantial power because the fuel pressure SHOULD be fine at the stock 34 psi.

I'm definitely going to invest in an air-fuel ratio monitor in the near future so i can see what the hell it's doing--anyone have any suggestions for what's a good monitor/kit that's ACCURATE and economical and isn't that much of a PIA to install? (It doesn't even need to be a permanent install)..I was thinking of a split-second air fuel monitor which uses a bunch of lights--my dad has it installed on his car and it seems pretety accurate.

Any help/suggestions is greatly appreciated.

BTW, for anyone wondering, my best 1/4 mile time (with all that hesitation and a crappy launch) was 14.28 @ 106.1 mph. (2930 pounds with driver and 5 gallons of gas)

The trap speed is pretty impressively high, but the ET seems very h igh for this speed--anyone know why this could be? 14.28 usually corresponds to around 100 mph...and 106.1 mph usually corresponds to a 13.5 or so ET.

[klattr1]

gap your plugs lower. Try .028" or lower.

[ftrs13]

sounds like you may have a boost leak, which would cause you to run really rich especially at higher RPMs. this would explain why your boost goes down considerably.

you may be running lean when at idle or no boost, but would then make a drastic switch to rich when the air starts flowing out the leak. also that would explain the popping, backfiring.

another idea is the knock sensor, if you are getting knock/detonation up top the ecu would pull timing, causing you to run excessively rich, and backfire like mad.just 2 ideas that I haveSteve

[MarkEmark]

gap your plugs lower. Try .028" or lower.

Would it really make a difference? The plugs I'm running are Iridium IXs, BKR7EIX-11, recommended for t/c engines, and I put them in as they came in the box...I'm unfamiliar with gapping techniques, I believe I have a gapping tool here but I thought you could only use that to make the gap bigger... maybe i'll swap my platinum + 4's in (don't need to be gapped)... they never gave me trouble.

The thing about a possible boost leak is that all the way up to 5500 rpm it runs fine and is at 9 psi...if it had a boost leak it wouldn't build boost and hold it for that long I don't think.

There's no way I'm getting knock/detonation...not with an intercooler, alcohol injection, 93 octane, and conservative boost...

If I were running excessively rich would it backfire under full throttle?

I took th car out and at 39 psi @ idle it still has the same problem, but only in first gear...

[C-Kwik]

Spark plug gap makes a huge difference. Given the same overall available spark energy, you are now forcing a denser mixture of furl and air. This means there si more resistance between the center electrode and the ground. The plug gap that you would normally run is with consideration to the highest density of air it will see and to allow some room for wear.

Secondly, Gapping Bosch +4's may prove difficult. Though supposedly, the +4's are supposed to have less resistance for a given gap as a portion of the spark will travel along the surface of the insulator. At least if I remember what Bosch claimed correctly. But I wouldn't rely too heavily on that. I found the +4's to make my old S13 run worse so I have my biases of course.

I say just shorten the gap and call it a day. What is yours at anyways?

[MarkEmark]

I was reading some previous posts regarding spark plug gapping and perhaps this is the reason why my car's hesitating..it is kind of like a "rev limiter..."

Still confused as to why it only does it in first gear now though...

I just checked the iridium ix's gap, and they appear to be about .041 or .042, which is substantially more than the .028 that I hear recommended. So I definitely want to "de-gap" them, but I've never done this and have no idea how to...

I know that I have a spark plug gapper, (see pic below) but can anyone explain to me how to use this thing to de-gap it? (sorry, it sounds very n00b-ish)

http://www.nissaninfiniticlub....2.JPG

Thanks guys

BTW--My plugs look to be in pretty good shape

http://www.nissaninfiniticlub....1.JPG

[WDRacing]

Use a thickness gauge and simply tap the ground strap on a non metalic surface lightly till the gap is closed to the correct size. I insert a .030 piece of shim stock then tap my plugs on a table top...done. You want to run the most gap possible without any stutter. I'd try .032 for starters, then decrease to a max of .028. If .028 isn't fixing it then you either have another problem or simply need more juice to your plug.

WD

[Drift]

Hey, don't mean to point you in a different direction, but all the problems your describing were exactly similar to mine N/A - that is stumbling, loss of acceleration, the popping noise from exhaust, and lastly the jumping tach needle. My problem was the crank angle sensor, but it was never detected by the ECU because it was an on/off problem. It started off as a mild problem such as yours (again on N/A though), but then eventually started stalling the car until it no longer start. Then when it started stalling, the ECU finally detected it. Replaced the distributor, and the car ran like a charm. Just another possible suggestion to your problem.

[MarkEmark]

There's no .032 on the gauge so I'll go straight to .030....I could go to .034 because mine is gapped at like .042 right now, but I'm getting real sick of this problem and want it gone so I don't want to be f**ing around with spark plug gaps---.030 seems like a good place to start.

Hmm...crank angle sensor? Thanks for the input Drift...I'll keep that in mind. The last time I had my distributor off it looked to be in perfect condition, and indeed it's working well as far as I know...If the gapping of the plugs doesn't work then I'll start investigating the possible sources of error from the ignition, etc..

Thanks for the input guys, I'll keep you posted.

[MarkEmark]

Just gapped all the plugs to 0.030, took it out, and it doesn't hesitate anymore...for now (knock on wood). Amazing to think that something that minute, and that simple (.010") would make that big of a difference.

So now I can back the fuel pressure down to what it was before...around 32 psi (34 psi runs pretty rich).

Did a quick/crappy 0-60 run with the fuel pressure @ 36 psi and I got 5.41 seconds. now I gotta see what 1/4 mile times I'll get, but I feel so guilty for thrashing my car these past couple of nights...I should have fixed the problem first and then thrashed...Oh well.

[mean green s14]

.10 is a lot man , i have to gap mine at .026-.028 anything over or under and mine does the same thing your describing.

im looking into a msd 6abtm

to drastically improve spark power and also retard the timing to whatever setting you dial in.

then i could probly gap my plugs back up to about .34

[Structure240sx]

i was having the exact same problema s you when i first put my turbo on. i was running .035 gap at 9psi jsut fine. are you adjusting the fuel pressure without any kind of air'fuel ratio moniter (personal wideband/dyno)? stock fuel pressure at idle is 40psi with the vaccuum line on and 43.5psi with it off. the jwt isnt that insanley rich. its also programmed to be used with the stock fuel pressure. i would get a wideband on that before messing with the fuel pressure

[MarkEmark]

.10 is a lot man , i have to gap mine at .026-.028 anything over or under and mine does the same thing your describing.

im looking into a msd 6abtm

to drastically improve spark power and also retard the timing to whatever setting you dial in.

then i could probly gap my plugs back up to about .34

It's not .10, it's .010...An improved ignition system is a good idea but so long as it's running fine with my plugs gapped at .030 i'm going to keep it...you know, if it ain't broke, don't fix it.

I'm not using any air/fuel ratio monitor when adjusting the FPR, but I'm also not adjusting it very much....an a/f ratio monitor is next on my list of things to do. Stock fuel pressure at idle is 34 psi according to the FSM (not 40); 43.5 psi is the pressure you get when you turn the key to the "on" switch. The JWT program is rich @ stock fuel pressure (34 psi), so 32 psi just leans it out marginally. Again, never once had a detonation problem.

[C-Kwik]

Use a thickness gauge and simply tap the ground strap on a non metalic surface lightly till the gap is closed to the correct size. I insert a .030 piece of shim stock then tap my plugs on a table top...done. You want to run the most gap possible without any stutter. I'd try .032 for starters, then decrease to a max of .028. If .028 isn't fixing it then you either have another problem or simply need more juice to your plug.

WD

I'd avoid using this procedure to gap a plug with iridium plugs. The small piece of iridium that is used can get imprinted into the gapping tool and fall off as you try to remove the tool. A feeler or wire gauge is a better optin along with a proper spark plug gapping tool.

[WDRacing]

Thickness gauge = feeler gauge buddy, I didn't think you civilians called them feeler gauges...lol. So I went with other terminology.

Good deal on the plugs Mark, you have to love when somthing simple fixes the problem.

[MarkEmark]

Yeah I love how it was a simple thing to do and made a huge difference....

OT-With my fuel pressure down @ 33 psi @ idle, I did some tests yesterday for a 1/4 mile...I got 13.86 @ 108.9 mph...I hate how high the ET is but I love how impressive the trap speed is...I was shifting at 7000 rpm for these runs, but I'm starting to think that's not the best idea, because my car definitely isn't accelerating as fast in the 5500-7000 rpm range as the 4000-5500 RPM range (due to boost drop off, etc)...If I shifted at around 6000 instead of 7000 i'd be in a chunkier part of the RPM band and therefore it'd be accelerating quicker...I could do this in first and second gear, anyway.

Likewise with the 0-60 run...I should shift earlier in first gear so that 2nd gear comes in a nice part of the RPM band...it may even be faster to shift into third once 6000 in second approaches instead of holding out 2nd gear till 7000 rpm (so I can actually hit 60 in second instead of losing time on the third gear shift---Gotta love tiny wheels). Anyway, i'm just a ramblin' fool

[Structure240sx]

your using the gtech for these tests correct? will be getting to a quater mile track sometime to compare the results? it would be good to know just how accurate the gtech is. i definitly think with your all around steup these numbers are very close.

[WDRacing]

I used to use the Gtech, its pretty close believe it or not. I never had more then a .5 difference.

[MarkEmark]

your using the gtech for these tests correct? will be getting to a quater mile track sometime to compare the results? it would be good to know just how accurate the gtech is. i definitly think with your all around steup these numbers are very close.

Nahh, I don't care enough about times to ever take it to a 1/4 mile track (I'm more interested in how much power it's actually making, which can be estimated via 1/4 mile ET or trap speed). Plus, I'm not a big fan of really abusing it like I did. I just did those tests for the hell of it to see how it stacked up to other cars. I know it's substantially faster than an S2000, 350Z, Porsche Boxter S, standard WRX, etc etc.

I know I could decrease that 1/4 mile et, probably by shifting at 6000 rpm instead of 7000 rpm so I stayed in the meat of the powerband...I'm pretty terrible at launches too.

But the G-tech quotes +/- 0.1 second margin of error for ET and +/- 1 mph for elapsed time. If the G-tech is set up correctly (perfectly level), you find a perfectly level road, and you know the weight of the car/driver, it's pretty hard to fudge the 1/4 mile numbers. The only thing it doesn't take into account is reaction time...

[huguetpj]

and you know the weight of the car/driver, it's pretty hard to fudge the 1/4 mile numbers.

The G-tech does not need the weight to calculate 1/4 mile... it uses it to calculate power... just as my Power Meter. Just for clarifying purposes...

[skatanic28]

congrats man....sounds like a nice setup. how do you like the aero afpr and whered you get it from?

you guys really think the g-tech is that accurate?i used it last year while i was at school for 0-60, and i got from a 6.6 low up to 7.2. just seems like thats a bit quick for what i have done, not that i would be complaining or anything.

[C-Kwik]

Thickness gauge = feeler gauge buddy, I didn't think you civilians called them feeler gauges...lol. So I went with other terminology.

Good deal on the plugs Mark, you have to love when somthing simple fixes the problem.

I should have been more clear in saying that you should not tap the electrode to butt up against the feeler gauge. There are also tools that push the electrode down against a sized shim to bring the gap to the desired gap. This should also be avoided with irridium plugs. And by proper tool, I am referring to the tool that hooks around the base of the ground electrodes and you use it to bend the electrode to the desired gap. Sorry if it was unclear.

[MarkEmark]

congrats man....sounds like a nice setup. how do you like the aero afpr and whered you get it from?

you guys really think the g-tech is that accurate?i used it last year while i was at school for 0-60, and i got from a 6.6 low up to 7.2. just seems like thats a bit quick for what i have done, not that i would be complaining or anything.

It's not that I "think" it's that accurate; I know it's that accurate. It's tried and true...it's a precision accelerometer and GTech boasts it's, for all intents and purposes, as accurate as the testing equipment car magazines use...the internal accuracy for the 1/4 mile ET is 1/100th of a second, and for the trap speed it's .1 mph...the real life accuracy they list is +/- 1/10th of a second and +/- 1 mph, which they quote as the worst case scenario to be expected in the measurements, with variables like temperature, vibration, etc. The discrepancy you got for your 0-60 times are normal--it's extremely hard to launch the same way and do the exact same thing every time.

I basically just did these tests to see how it stacked up against the sports cars available right now...the 0-60 and 1/4 mile tests that all car magazines publish do not take into account reaction time, and neither does the G-Tech, so it allows for valid comparisons.

I like the aeromotive adjustable FPR...it's an extremely well-made device...heavy duty, anodized aluminum, gorgeous finish, the works. Plus, it has a built in pressure gauge port and is adjustable, so it's very easy to adjust the fuel pressure...just pop the hood and watch the gauge as you turn the adjustment key. I forget where I got it but it was somewhere around $140--it will not install on the stock fuel rail at all...I made a custom 90 degree elbow that bolted into the stock fuel rail and allowed me to mount the FPR wherever convenient.

C-Kwik==

Why should tools that push (not tap) the electrode down against a sized shim to gap the plug not good for iridium plugs but good for other plugs? IIRC, iridium (not the ground electrode) is an extremely dense metal...would butting it or tapping it to a shim really destroy the iridium tip?

[C-Kwik]

[quote=" MarkEmark

C-Kwik==

Why should tools that push (not tap) the electrode down against a sized shim to gap the plug not good for iridium plugs but good for other plugs? IIRC, iridium (not the ground electrode) is an extremely dense metal...would butting it or tapping it to a shim really destroy the iridium tip? [/quote]

From what I've read, the amount of iridium used in a plug is small. A small "button" of iridium is used in the areas where the spark occurs. Iridium is a rather hard metal. When pushed into the softer gapping tool, the "button" can be loosened or get stuck as you try and pull the tool out and the "button" of iridium can fall off the electrode.