Sputtering At Boost

[FourWeeks]

Hi, just recently bought a S13 coupe with a blacktop SR20DET. Internals are all stock AFAIK, Walbro 255, stock turbo, recirc bov, ISIS 3" blast pipes with 3" test pipe.

The other day after having filled up my gas tank, I decided to drift around in a parking lot. After I was all done I decided to do a little pull and realized that as soon as I started to build boost around 3500rpm-4000 my motor felt like it was hitting fuel cut and attempting to build back up, kinda like what it feels like when you try to accelerate from a standstill in a high gear. The car won't sputter as bad if I ease into boost but if I go into it at WOT I feel like I'm bogging. Also, idle is a bit sporadic as in sometimes when I approach a stop, RPMs will dip down to 300rpm or lower but will go back up immediately.

I checked and my plugs and coil pack #3 have white residue on them which leads me to believe I'm experiencing lean conditions, so maybe a fuel delivery issue? I've since changed out the plugs and cleaned the coil pack and will be checking my fuel filter. In the meantime, does anyone have any insight? Car will not always start first key turn, but I blame it on the shrunken battery and cold weather. I can definitely hear the fuel pump priming though.

[fliprayzin240sx]

Since you said it happened while you're drifting, check the fender harnesses. Tire might have rubbed them out if they have not been relocated.

If thats good, my guess would be a boost leak.

[EvoVIII808]

sounds like you have a VAC leak of some sort, Fuel pressure or Spark Plugs..

[Driftwire]

check intake manifold gasket. My buddys bolts were loose and it was leaking from the middle.

[aga]

if it was a vacuum leak it would be rich, not lean. coilpack or sparkplug would be my guess. check the gap on your sparkplugs too.

[Thomas0zero]

Originally Posted by aga

if it was a vacuum leak it would be rich, not lean. coilpack or sparkplug would be my guess. check the gap on your sparkplugs too.

im pretty sure a boost leak will cause a lean condition.

[aga]

Originally Posted by Thomas0zero

im pretty sure a boost leak will cause a lean condition.

nope. cause you are losing air that the airflow meter has measured, so you are getting more fuel than you re supposed to.

[Thomas0zero]

Originally Posted by aga

nope. cause you are losing air that the airflow meter has measured, so you are getting more fuel than you re supposed to.

You know, you're right. Im thinking it was a vac leak i had, it was so long ago. But i had cap blow off the port on the TB under 17psi, caused a hellacious lean condition and the car ran like crap. Capped it and never had an issue again. completely stock Redtop SR20DET.

This guy needs to invest in a Wideband. Sure makes your life easy when diagnosing problems, and an extra layer of security.

[DJ 21o3]

Originally Posted by aga

nope. cause you are losing air that the airflow meter has measured, so you are getting more fuel than you re supposed to.

Sorry but that is not correct. Yes your MAF meters the air from the intake and that determines the fuel, but you got the rest backwards. When you have a vacuum leak, the engine is a vacuum pump and sucks air into the engine from the leak giving you more air than what the MAF read causing a lean condition.

No offense, just letting you know and so others don't read that and get confused. The solved problem proves that it was a giant ass vacuum leak. lol

[savages13]

Also check the gap on the plugs. If the car hadnt been romped in much prior to you doing the drifty shenanigans you may have opened up the gap on the plugs causing a spark blowout in boost. Could also be an over boost situation. All the sudden heat could have nuked a vacuum line to the wastegate. Ideally if you have a boost gauge in the car monitor the levels. If boost levels are stock or close to it throw some plugs in it and gap them down to .028-.030. Go from there

[FourWeeks]

Thanks guys. I bought BKR7E's and have them gapped down to .030 right now but a fellow SR owner suggested I get BKR6E's and gap them down to .025 to see if that will make a difference.

[Driftwire]

7E is a colder plug. 6E is going to be hotter.. I would recommend the 7E

[FourWeeks]

Yeah, I'm thinking about getting a wideband. Where would be the best place to put one?

[Thomas0zero]

Originally Posted by FourWeeks

Yeah, I'm thinking about getting a wideband. Where would be the best place to put one?

Modern

They usually have the absolute best prices on genuine AEM stuff.

[FourWeeks]

Originally Posted by Thomas0zero

Modern

They usually have the absolute best prices on genuine AEM stuff.

lol thanks but I can get them pretty cheap as well. I was asking about what the best location on my car would be to put the wideband on

[aga]

Originally Posted by FourWeeks

lol thanks but I can get them pretty cheap as well. I was asking about what the best location on my car would be to put the wideband on

in the downpipe, somewhere near the firewall so you can run the wires to the cabin. it has to be around 2 feet from the head. if you get the AEM, it has specific fitment instructions in the leaflet. (the instructions are also on their website in pdf's)

[Thomas0zero]

Originally Posted by FourWeeks

lol thanks but I can get them pretty cheap as well. I was asking about what the best location on my car would be to put the wideband on

oh my bad. i though you said buy. haha. On the downpipe, for sure. Directions state, 36" from the turbo but honestly, ive had them 1" from the turbo for years without problems. just put it in a location thats convenient for you and wont get knocked off by road debris.

Once you get you a wideband and assuming your setup is stock-ish, get a AEM Tru-Boost controller and crank that boost up! I was running 17-18psi on factory fuel support with 10.9 afrs, all the way to redline. 10.9 is actually still very safe, anything past 11.5 is to lean. The boost controller really brings the car to life. Did the same thing to my buddies SR. The T25 cant flow more than 10psi at 7.5k RPMs. So you can hit 17psi at 3k, the boost falls perfectly and you maintain perfect AFR's.

[EvoVIII808]

Be sure to check you FPR as well. I just replaced one on my friends KA-T. He was having the same exact problems you are.

[FourWeeks]

Turns out the piping that goes down into the SMIC had come off the coupler completely. Don't know how I missed that... But on the bright side I'm able to get sideways again thanks to all that helped!

[aga]

you are wrong. i'll prove it to you :

1. the air coming OUT of the leak, is pressurised. so its coming out, with the force of 1 bar, rather than weakly sucked in by the engine

2. the sputtering was happening under boost, which means again, that the pressurized air was lost, otherwise it would happen on cruising etc. too.

come on, that's basic stuff. also, it's happened to me and i've got a wideband...on cruising the AFR was almost identical to normal, when boosting, the car would hit full rich.

[smoked240]

Originally Posted by aga

you are wrong. i'll prove it to you :

1. the air coming OUT of the leak, is pressurised. so its coming out, with the force of 1 bar, rather than weakly sucked in by the engine

2. the sputtering was happening under boost, which means again, that the pressurized air was lost, otherwise it would happen on cruising etc. too.

come on, that's basic stuff. also, it's happened to me and i've got a wideband...on cruising the AFR was almost identical to normal, when boosting, the car would hit full rich.

Bazingaa!!!

Key word is "under boost"

[curo72]

I'd check your fuel pressure. Longer crank time and a lean condition can both be attributed to a low fuel pressure condition.

[20thbryce]

So this happened to me and ended up being one of the plugs in the intake tube popped out.


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[kat7]

I would check either your fuel pressure(might be your fuel pump) or a vacuum line.