2G violent shutdown

[CARBON GST]

Got a question for you guys about my 97 Gst. Recently every time I get on any kind of significant boost (13 pounds and up). I am getting a VIOLENT miss or shutdown . . . or something. Its like I lose all power for a half second. If I stay on the power, it will go through this cycle about every 2 or 3 seconds. I noticed (at night) that when it happens, I get a flame out of the exhaust . . . so I'm guessing that its not a fuel issue?? Maybe mass air sensor???? I had hollowed ALL of the honeycomb things out of it, and later was told that was a bad idea. But that was three years ago and no problams until now. Anyway, heres a few mods that may help you guys diagose.
Big 16G turbo/Greddy profec b boost controller/walbro 255 fuel pump/(otherwise stock fuel components) . . . . any ideas?

[KoukiDrftr]

check for boost leaks

[Spyder]

is the car turning off, like you lose all power or just the motor does for a second?

[SpecV_Scott]

Might need a colder heat range of spark plugs. Plus, it's cold out lately, so you might be running a little lean, causing some knock, which will trigger the ECU to pull timing. Hence the hesitation/backfiring issue. Might want to richen up a little bit.

[YokotaS13]

or could be fuel cut, bad injector, bost leak, turbo is blowing, bad wastegate
The list could go on. Change your plug to a range colder, Check yoru TB for leaks, performa a leakdown, tighten all your clamps, get a datalooger

[YokotaS13]

adn hte fact you have no fuel management, might also have a fact to do with it

Does no one follow supporting mod paths anymore?

[CARBON GST]

yeah . . . the mod path is "fix it as it breaks with better stuff, and just hope that you can afford to keep it on the road."

[SleepingTalon]

The setup on that car is so simplistic, it doesnt "need" fuel control to run properly. Of course, it would help, and obviously make the car run faster and smoother, but it's not a neccesity at the level of upgrades he's at. Is the Profec setup properly? Check the WG duty on the boost controller and make sure the numbers for those settings are right.

[eclipsemonkey]

Hey Jonothan, it's Mike. I'm gonna upgrade in the next month or so, so if you my safc or injectors just give me a call.

George! Where have you been? I tried to get in touch with you last week, but your phone is not accepting calls. Anyway, give me a call sometime.

[SleepingTalon]

Oh, lol. I have a new number, sorry! 404-518-1122, hit me up Mike! BTW, upgrading eh...? So I guess it's time for me to retune...

[SilverJester]

Yeah taking the honey combs out is a horrible idea. Yeah your problem could be a number of different things, did you do anything to the car lately or did it just start up? btw how much boost are you running on the stock injectors? And with a 255 you really should get a fpr. You really would have a decent setup if you just got the rest of your supporting mods (which aren't much) to complete it then you could turn boost up safely. Just get injectors (550cc would be fine), a fuel pressure regulator, some sort of fuel management (safc is just fine).

[SilverJester]

Hey Jonothan, it's Mike. I'm gonna upgrade in the next month or so, so if you my safc or injectors just give me a call.

George! Where have you been? I tried to get in touch with you last week, but your phone is not accepting calls. Anyway, give me a call sometime.

what size injectors do you have? My 550cc aren't cutting it anymore, I need something around 650-700cc.

[SleepingTalon]

what size injectors do you have? My 550cc aren't cutting it anymore, I need something around 650-700cc.

He's got 550's in there. It's enough for 400whp or so, and he's at 330whp. I have no idea what he's thinking of upgrading to, since he's making 330whp right now on a 16g, and still has plenty of injector, but whatever works. Anyway, a AFPR, OR some sort of fuel control is a good idea, but you dont need both with that setup, just one or the other.

[CARBON GST]

Yeah, it just kind of started up on its own (and progressively became more and more frequent). For some reason I have a hunch it could be that mass air sensor. Lately, its been dying every so often when at idle (or falling to idle) and runs like complete poo until it gets well up to temperature.
(I normally run it at about 16 pounds)

[SleepingTalon]

I've tuned cars with all the honeycombs out of the MAF, and the airflow signal is unsteady, and the recovery is sometimes bad, but other than that, it's normally not that big of an issue. Of course, these cars also have fuel control, and I've dynotuned them all, but a few of them were setups very similair to yours. Again, I think when you take the big honeycomb out, it's pretty much hit or miss, cause I've seen it go both ways. Have you checked the plugs yet?

[SilverJester]

He's got 550's in there. It's enough for 400whp or so, and he's at 330whp. I have no idea what he's thinking of upgrading to, since he's making 330whp right now on a 16g, and still has plenty of injector, but whatever works. Anyway, a AFPR, OR some sort of fuel control is a good idea, but you dont need both with that setup, just one or the other.

That's about where I estimate my hp at too. My injector duty cycle too high for comfort and is kinda a limiting factor right now, it's at around 95%. So I can see why he wants to upgrde his injectors. And about the afpr, if he has a 255 fuel pump, it is overflowing his stock fpr. It's not so bad on stock injectors because they can only dump so much fuel in there being 450cc. But if he upgrades his injectors (as he should) then it could cause a little more problems. But that shouldn't replace fuel management.

[SleepingTalon]

Well, fpr overrun is actually likely, although only at idle, not WOT. Anyway, it can be a helluva problem because of the closed loop problem it causes. At any rate, it's not "necessary" to have both, but it is optimal. Infact, most of the time, I dont worry about the afpr until about the 400whp mark. I get an EMS in the car first, and offset everything through that. Of course, if all you've got is an SAFC, well, then things become more difficult. I would say that if you're gonna use something to change MAF voltage, then use the afpr as well, but if you have something to control both fuel (via maf voltage, or actual pw) and timing, then I wouldn't worry about it. That's why I say one or the other. It really just depends on the setup. In his case, the setup is pretty simple, and doesn't require a whole lot to get it where it needs to be, so just an afpr would make things, although not perfect, "driveable" for him. I was merely speaking on the bare minimum to get the car driving ok.

[aznevo8]

ok you guys are forgetting. correct me if im wrong. i dont think its fuel. but i do think its the ratio. i say its not fuel because yeah hes pumping 255 lph out of his tank but its not being shot into the motor anyfaster with stock injectors and rail. so i dont think the pump is hardly doing anything for him. but everyone is right he has no engine management and u cannot correct the a/f. ur throwing in a lot of air and your running almost stock fuel if its not stock period. so he would be detonating. hense the choking. and i was the same as u, run it til it breaks and replace it with better parts. that will not work the way you did it. whatever breaks and you replace with better parts will put stress on other parts your not replacing. SUPPORTING MODS is a must. esp in dsm's.

[SleepingTalon]

ok you guys are forgetting. correct me if im wrong. i dont think its fuel. but i do think its the ratio. i say its not fuel because yeah hes pumping 255 lph out of his tank but its not being shot into the motor anyfaster with stock injectors and rail. so i dont think the pump is hardly doing anything for him. but everyone is right he has no engine management and u cannot correct the a/f. ur throwing in a lot of air and your running almost stock fuel if its not stock period. so he would be detonating. hense the choking. and i was the same as u, run it til it breaks and replace it with better parts. that will not work the way you did it. whatever breaks and you replace with better parts will put stress on other parts your not replacing. SUPPORTING MODS is a must. esp in dsm's.

No, he's not running lean, infact, he's probably running rich. I'd say he'd probably fuel foul the plugs if anything. The high flow pump will bump his base fuel pressure up, effectively "increasing" the size of the injectors loosely speaking. There are a number of things wrong with his setup that I've already discussed with him, all of which I'll address within the next week or so. If you log the stock injectors with a 255 pump, at the boost level he's talking about, you'd see that the injector on time is probably well within its limitations, as they are good for well past the 230whp he's making right now. As far as the rail, well I've got the stock fuel rail in my 650hp race car, so that's not an issue either. The way the DSM fuel system works is when you increase fuel pressure, there's a "drop" as the fuel moves from cylinder 4 to cylinder 1 (#1 being the leanest). There is actual data from a liquid flow bench I can post if you're interested to see, but this is one of the reasons I "trim" each cylinder when I tune stock fuel system cars. The DSM fuel system does have it's limits, but to be honest, it's one of the best stock running fuel setups I've seen. I've made well over 600whp with just a walbro, afpr, ems, and some larger injectors. Infact, the 580whp in my sig was made with 650cc injectors, and stock fuel sytem, which leads me to believe that his problem exists somewhere else.

[Xrated O.G.]

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