2psi stutter

[ftrs13]

for a while after having my KAT together it ran beautifully, but recently under part throttle and about 2psi of boost, the car all of a sudden starts bucking.it only happens when its warmed up, and doesnt occur at all when boost is 0 or at 5psi, which is my max boost right now.

Im thinking that its my plugs, because Im still using stock. if anyone could shed some insight that would be greatly appreciated.

KAet

Thanks,Steve

[Structure240sx]

when i first put on my turbo kit it sputtered at higher rpms because the boost was blowing out the spark. the fix- close the gap on the plugs

[ftrs13]

the thing that has me confused, is that it runs fine at WOT all the way up to 4500+rpm

[Structure240sx]

does the sputter start after 4500? cuz thats when mine would start to sputter. it was fine upto that point

[ftrs13]

no its really confusing, It starts as soon as a little boost is generated, about 2500, in any gear, at partial throttle. full throttle is fine, no stutter, its only really cruising that is the problem

[Structure240sx]

whats your setup? mainly your fuel/timing/tuning?

[smokey86678667]

hey, just a thought, but it sounds to me like it could be one of two things, I have had problems out of the blow off valve leaking at partial throttle before, or it could be a fuel problem. If your running an s-afc, it may not be adjusting fuel right at part throttle. What does the a/f gauge read when it does it?Thanks, Ben

[:: orion ::]

I'd guess it's compressor surge...

No, not due to blow-off stuff, but due to the turbo spooling too fast...then engine can't ingest the volume of air the turbo's putting out.

What turbo is it? Does it spool to the left of the surge line on a KA...have you checked the maps?

Can't be spark, fuel, or timing if only at part throttle...mine does this only in 5th gear, and I knew it could - The compresspor map told me before I bought the turbo.

Let us know - Brian

[LongIsland240]

for a while after having my KAT together it ran beautifully, but recently under part throttle and about 2psi of boost, the car all of a sudden starts bucking.it only happens when its warmed up, and doesnt occur at all when boost is 0 or at 5psi, which is my max boost right now.

Im thinking that its my plugs, because Im still using stock. if anyone could shed some insight that would be greatly appreciated.

KAet

Thanks,Steve

I'm having a simialr problem right now, i'll let you know what i find out tomorrow...hopefullly. First thing i'm going to try is closing the gap some as it seems to only have started since the plug and injector swap.

[Structure240sx]

::orion: im more than sure that its a z31 turbo

[huguetpj]

I'd guess it's compressor surge...

No, not due to blow-off stuff, but due to the turbo spooling too fast...then engine can't ingest the volume of air the turbo's putting out.

Can the turbo reach surge at part throttle?

[ftrs13]

yes its the z31 turbo. If it is compressor surge than I would think that it would have been happening since I put the car together, or even on a regular basis now. the biggest thing thats got me confused is that it only happens after the engine reaches temp. it runs fine until the engine temp comes up to middle on the stock gauge, then it starts going crazy

Steve

[Structure240sx]

could it be once the o2 sensor is warmed up and is on its open or closed loop? i forget exactly how it works but i know it needs to warm up

[LongIsland240]

I checked into my similar problem today and fixed it, i'm also using a z31 turbo btw. first off i closed the spark plug gap to .025 on a fresh set of NGKs (bkr7e), and also cleaned up the dist. cap since it had become slightly corroded from sitting in my driveway since october when she came off the road. The coil wire was making a pretty poor connection as well....anyways, no more miss/backfire under load!

You only experience it when the car warms up, right? Check into the ign. module and the O2...you did put in a fresh one with the turbo didn't you? There is a possibility if you re-used the old one that it got damaged in the swap and is now reading incorrectly, they are VERY fragile! They can take tons of heat, but one drop and it's all over.

[ftrs13]

ok, I didnt swap out the O2 sensor, or the ign.

I am going to do this as soon as I get back, maybe not the O2. the thing is that it has been running fine, and all of a sudden ran into this problem.

the thing about the 02 sensor, is that its a 3 wire, and the origenal was 1.

but that sounds like another good option, once the O2 warms up, then it goes bad

Steve

[smokey86678667]

Yea, I would definately check the o2 sensor out. those f*%$^*! can be a pain. Let us knowThanks, Ben

[Structure240sx]

what? i dont know on hardbody's but on 240's o2 sensors are as easy to change and spark plugs if not easier. they jsut cost a lil bit more

[smokey86678667]

what? i dont know on hardbody's but on 240's o2 sensors are as easy to change and spark plugs if not easier. they jsut cost a lil bit more

Hey,No, that wasnt what I meant. What I was trying to say was that the leasyt little thing will make them go bad. A good example is if the car sits for a good while and they dont get used they go bad or if you run 110 octane leaded fuel, because the lead coats the sensor and ruins it. As far as changing them on a 240 ive never had to change one. Sorry I wasnt very clear on that one.

Thanks, Ben

[Structure240sx]

ooo i see what your saying now

[ftrs13]

my car sits quite a lot while Im at school right now, so that may be something to look into.

3 months at a time, or so

[smokey86678667]

Theres a way that you can test the sensor, but I cant remember how you do it right off. Let me know if you need to know how to test it and I will find the procedure.Thanks, Ben

[ftrs13]

ive got a while till I get back home.