Sputter at high RPM

[againstdawall06]

ok basically in first at high rpms my 87 turbo supra sputters.its not like a vilent one, it just makes a sputter sound and loses power. i have exhaust and a filter. im boosting about 9-10 pounds. it only does it in 1st and 5th sometimes. no boost leaks. when i up the boost to about 12-13 it does it really bad in all gears. im affriad it could be leaning out. would that cause something like that? could it be the stock plugs-wires? any help or info would be nice.. and i searched, but i couldnt find anything. atleast links to threads that i missed during my search would be nice.

thanks for any help

andrew

 

[IJ.]

Andrew: What are the plug gaps?

 

[jkbmkiii]

thats what Iam saying, PLUG GAP!

 

[againstdawall06]

thats what Iam saying, PLUG GAP!

no idea. i havent changed the plugs since iv owned it. i have NGK plugs sitting on my dresser though. im waiting for my next paycheck so i can get NGK wires. would that prolly be it? what is the gap i should run? just spec gap or something different?

 

[IJ.]

Stock gap is something like .040" but once you bump the boost you need to pull it back a bit.

Each motor is different try it at .028" and see how it goes.

 

[againstdawall06]

alright thanks for the reply, it seems like no one ever replys to my threads :cry:

 

[IJ.]

Better getting 1 or 2 good replies then 20>30 bad ones

 

[SupraDreamPDR]

i had the same type of problem... here is my old thread on it. hope this helps out some. good luck
http://www.supramania.com/forums/showthread.php?t=16999&highlight=stutters+at+high+rpm

 

[jdub]

The stock plug gap spec is .031 for a turbo motor and should be fine if you are running stock boost. If you run boost above stock, gapping the plugs down a bit like IJ suggested will usually stop the studder. New plug wires like you're planning to do is a good idea, especially if your stockers are old

 

[djordan97]

there is always the possibility that you are hitting boost cut. that starts at like 11.5 psi but can be adjusted up to I think it's 13.5 psi by turning the screw in the afm.

 

[againstdawall06]

no its not fuel cut. iv hit that before. totaly different. its not like a rough cut out of the engine, it just makes a sputery sound and get real weak. my timing is also at 12-13 degrees. if it just the ignition it not a big deal but i im just really hoping im not leaning out already. i would buy a wide band but thats WAY out of my price range.

 

[againstdawall06]

i had the same type of problem... here is my old thread on it. hope this helps out some. good luck
http://www.supramania.com/forums/showthread.php?t=16999&highlight=stutters+at+high+rpm

did you ever fix that?

 

[aljordan]

If the car feels like it's missing under boost, it's most likelyl your plug gap. I couldn't run 18 psi on the stock gap. I now run a gap of .028. I can (and have) run 30 pounds with that.

 

[SupraDreamPDR]

did you ever fix that?

well, funny thing, i was in the process of fixing it and then i blew my HG at the drag strip. :nono:

 

[againstdawall06]

ouch.

 

[SupraDreamPDR]

ouch.

eh, it comes with the territory.

 

[gilberjj]

hey guys, my car is doing the same kind of thing, it pulls real good up to about 5k-5.5k and then slightly sputters and stumbles. when i have a passenger they can't hardly feel it, but i can. i know i have a slightly bhg. i ordered my mhg and arp head studs last tuesday, so im acctually taking my car apart tomorrow. im pretty sure that the very small amount of liquid that is getting in the combustion chamber is what is causeing the stumble. anything that throws off the air-fuel mixture will mess with your car and it won't run right. as for stumbleing cause of a lean mixture, it can't be that. your car will pull real hard if it is lean, but it will eventually explode. it is more likely to fall on its face when its rich, which is what 7m's are known for. when i get my car back together ill let you all know if the new hg fixed the problem

 

[againstdawall06]

it shouldnt be a BHG since my hole motor only has about 6k since its last rebuild. and its not showing any signs of it. i hope its just the plugs/wires.

 

[IJ.]

There is a point in the power curve at maximum cylinder pressure that spark blowout can be an issue.

At 30 psi for me with a .025" plug gap it happens around the 5300 point (max Tq) I've bumped the timing up a touch at this point to tune around this but normally you'd either raise the spark energy (new ignition parts) or back the plug gap down more.

Against: Just try knocking the gaps down before you start suspecting BHG's or anything mechanical, diagnose it one step at a time.

 

[againstdawall06]

o ya i know its not that. it prolly will be a week or so till i get a chance to change the plugs and wires out . is it bad for the motor at all? even at about 6lb it does it at the top of first.