Full boost studdering

[99 gst spyder]

MODS are in profile.

I can slowly gas it all the way to redline but as soon as high boost kicks in at anytime after 4-5k rpm, then it spudders with some jerk in there. It sputter different from a foul uneven gap spark plugs which I know how that's like. Its more like a soft popping exhaust sputtering anytime of WOT. I've change my wire to a COP setup and still same results. Plugs are gap at .028. Last done to the car is FIAV block off, TB shaft seal replace, biss #5 O-ring, and 160* thermostat, convert 93 pump to E-85 with base idle tune, new filter, and idles great and regular driving except in boost and WOT.

Will perform another leak test but I doubt there is any since I run very short pipings and everything is sealed up with rtv in most area, but my only question about leaks is that I have a magnus smim, and there seems to be a loud hissing sound either from under the smim or might it just be air hissing inside the smim to the motor, this I'm not sure and cant seem to detect the hissing sound and if anyone has a smim can chime in on this loud hissing sound?

 

[c2ypt1c]

convert 93 pump to E-85 with base idle tune

If you just tuned the idle, you'll be running way too rich at wot on e85, which will cause a studder. Have you tried switching back to pump gas to see if it studders?

 

[93AWDDSM]

another BLT for shits and giggles would be good. might have recently started a leak while in full boost around the intake around maybe intake mani gasket?
-what lbs of boost are you running?

 

[99 gst spyder]

If you just tuned the idle, you'll be running way too rich at wot on e85, which will cause a studder. Have you tried switching back to pump gas to see if it studders?

I'm still on E-85 and still have half a tank left in there. I can try to switch back but I'm not sure if that's the reason why it's causing the studdering.

another BLT for shits and giggles would be good. might have recently started a leak while in full boost around the intake around maybe intake mani gasket?
-what lbs of boost are you running?

I have a brand new intake manifold gasket in and it's not even about 500 miles yet on the motor. Would leaking gasket from o2 housing to turbo cause this? I'm on stock 14 lbs wastegate spring. Tru boost setting A and B are zeroed out. If I remember before E-85, Wot was good and hold at 14 psi but now it seems to stutter and my aem tru boost will give red light flashing at wot meaning over boosting.

 

[93AWDDSM]

what is your wide band at when wot and the studder occurs? the o2 to turbo might cause a slight exhaust leak and cause it to read slightly lean if its a big enough leak.

 

[99 gst spyder]

what is your wide band at when wot and the studder occurs? the o2 to turbo might cause a slight exhaust leak and cause it to read slightly lean if its a big enough leak.

As far as I remember on e85 at wot was like around 12ish for air fuel according to link. The exhaust leak is very minor so that can be out of the way. I'll try to post up a log when I get home later the afternoon.

 

[93AWDDSM]

any records of getting the 1000cc injectors flow tested and cleaned?

 

[Colt4G63 also]

I find that when you start running higher boost, the plugs wear out a lot. When I feel that miss at full boost, I just slap in a new set, and I'm good for around 60-80 more 1/4 mile passes at 30+ psi.

At 20 psi the plugs just work fine indefinitely.

 

[c2ypt1c]

I'm not sure if that's the reason why it's causing the studdering.

I'm betting it is. Same exact thing happened to me. I was chasing plugs, wires, coilpack,, injectors, fuel pump, filter...everything. As soon as I mixed in gasoline, the studdering went away. Apparently, my dsm didn't like anything richer than 12.5 afr on full e85.

Before you spend any money on replacement parts, try switching back to pump gas to rule it out. Also, don't be afraid to mix gas with e85.

 

[99 gst spyder]

any records of getting the 1000cc injectors flow tested and cleaned?

No record....

I'm betting it is. Same exact thing happened to me. I was chasing plugs, wires, coilpack,, injectors, fuel pump, filter...everything. As soon as I mixed in gasoline, the studdering went away. Apparently, my dsm didn't like anything richer than 12.5 afr on full e85.

Before you spend any money on replacement parts, try switching back to pump gas to rule it out. Also, don't be afraid to mix gas with e85.

So what you are saying is that I can add regular 93 pump gas into the half tank of e85 and it'll be alright? I'm trying to get some answers from one of the local tuners and see what he got also. I would love to go back to pump gas to see the results.

 

[c2ypt1c]

So what you are saying is that I can add regular 93 pump gas into the half tank of e85 and it'll be alright?

Yes, you can. E85 itself has 15% gasoline already mixed into it. However, you'll need to adjust your global fuel to account for the new stoichiometric point of the mixture. What I do is warm the car up completely, add gasoline, anticipate a lower global fuel (more negative. roughly midway between your 93 and e85 setting), start the car, lock the ecu in open loop and adjust global fuel until wbfactor reaches zero.

If you're running speed density, you can verify a correct global fuel if your VE table is within a reasonable range at wot.

EDIT: Forgot to mention, before going wot on a mix, you may need to richen up your afr map as well, depending on how lean you set it for full e85. The same applies for timing advance. Just because you ran 22* timing up top on e85, doesn't mean you can with a 50/50 mix. As always, watch for knock...

 

[99 gst spyder]

A local reputable tuner said it shouldn't matter on e85 much and with e85, gap should be .024 and could just be something else like plugs, coil, ignition might be a factor.

 

[WES_393]

Before you go messing around with changing fuel and whatnot, run a boost leak test using soapy water to find leaks. Especially since you just replaced a bunch of intake parts. Don't just assume your boost leak free.

After that, activate the fuel pump in Link and try raising the fuel pressure with the AFPR. Go 5-10psi higher than you plan to run. If the fuel pressure won't go higher, or the needle on the gauge bounces back and forth, then your losing pressure at some point in the fuel system.

 

[99 gst spyder]

Before you go messing around with changing fuel and whatnot, run a boost leak test using soapy water to find leaks. Especially since you just replaced a bunch of intake parts. Don't just assume your boost leak free.

After that, activate the fuel pump in Link and try raising the fuel pressure with the AFPR. Go 5-10psi higher than you plan to run. If the fuel pressure won't go higher, or the needle on the gauge bounces back and forth, then your losing pressure at some point in the fuel system.

Thanks. I will give that a try and still going to perform a boost leak test. I'm going to gap it at .024 first and see what happens.

One other thing to add, my launch control is set at 4.5 and it feels weak, slow and stuttering. It's not fast like normal like how it was. Half the slowness.

 

[kevingmorales]

I would check your gap on the spark plugs, that happen to me too, it ended being for me the gap was to wide on it, so I bought new plugs and checked the gap before install.

 

[99 gst spyder]

I would check your gap on the spark plugs, that happen to me too, it ended being for me the gap was to wide on it, so I bought new plugs and checked the gap before install.

Problems solved. Thanks. Plug gap are too wide. Gapped it down to .023ish and that fixed the stuttering problems. Guess I have to run smaller gap with e-85. It was gapp at .028 on pump and no problem and now on e-85 at .023 works. Pull strong to red line without any stuttering problems now. Thanks to all for the helpful info.