Hello...any/all help would be greatly appreciated for this ongoing issue with my SR motor. I installed this engine in 1999, and still have yet to resolve the issue. Let me first describe this issue, then I will list the mods, and finally continue to beg for help.

What I am experiencing is a hesitation and loss of power from the engine when under a certain load and at a certain point on the throttle. The turbo will spool up just fine, the engine will pull hard, and then all of a sudden it feels like it is running on two or three cylinders. If I press the accelerator down farther it will disappear. I've always been able to "drive around" it, have done numerous tests to try and remedy, and have replaced dozens of parts.

The idle is perfect, and if I step on it off the line, the hesitation will be very mild until i hit a higher gear, then it will hesitate and sputter at a couple specific points in the RPM's, then pull extremely hard after 4800 rpm. The engine has never hesitated after 4800 rpm's and feels like a beast.

It doesn't matter if I am running 8psi or 14psi...it is still there. When on the highway in 5th gear, it is the easiest to force the issue. If i press the gas pedal down just slightly, the hesitation will appear right way, and if I don't let off or press the pedal harder, it will just continue to hesitate and be stuck sputtering. If I press hard to WOT, the motor pulls hard, then will go into sputtering mode while at WOT for a couple seconds until it hits the 4800-4850 mark, where all sputtering/hesitating disappears.

MODS...

JWT ECU upgrade with KA MAFS (stock turbo and fuel injectors)Platinum Plugs gapped to .30HKS SSQL blow-off valve vented to atmosphereFMIC kitWalbro hf fuel pump and 300zx fuel filter

I have replaced with new parts...TPS, O2 sensor, MAFS, wastegate, all hoses. Have swapped coils with friend and no change. Have yet to switch the transister plug?I have checked all my grounds, and everything appears perfect. The ECU gives me code 55.

I have had injector problems in the past, and have needed to replace a few. My first thought was injector stuck open, pissing fuel, and drenching plug??? My other thought is boost leak in intake manifold??? Any ideas?

Help!!!!!!!!!!!!!

pull your plugs and get a vacuum tester to check for leaks

i've run into that same situation and it was MAF related. Also, the other part of the hesitation was my fuel pump. It was a walbro 255lph. Anyhow, i'd start moving into a higher gear and she would do exactly the same then it would come to life and to all the way to red line after the release of the throttle and back on.

Thank you for the suggestions...i will def. pick up a vacuum tester and double check the vacuum pressure. I have a bad feeling i am looking at worn piston rings. Would I see excessive oil consumption or exhaust smoke? I just changed my oil the other day, and it was def. black, but still pulled close to 3.5 quarts out.

I'm fairly certain my fuel pump is functioning properly. I am running the KA MAFS w/ a Jim Wolf reprogram. The MAFS is brand new, but could the use of a KA MAFS, say instead of the Z32, cause hesitation and sputtering?
Modified by bjv240 at 5:24 PM 2/14/2010

did it have this problem before you put that stuff in?

Yup...the stutters always been there. Its never gotten worse, but never improved. I've always wondered if their is a leak in the intercooler system, but upgraded the piping recently, so that's out. The intake manifold or IAV may have a small leak? The other thing that was really strange, my fuel injectors started to go at one point, and i had to replace them. Could be the ECU and MAFS were forcing a very rich mixture...now i'm wondering if the injector isn't causing this problem, but is managing to remain normal at all other times, and not be damaged. I was always told others ran stock 370cc and never had an issue. Thoughts?

So leads me back to leaks, compression, and/or valve issue. The craziest part is the motor runs perfect after 4850 rpms at all boost levels? If it runs perfectly at high rpms, then how could there be compression or valve issues. Maybe a leak?

I'd almost be willing to bet your KA maf is causing it. It's actually a downgrade from the SR maf.

i was thinking the same thing. why did you go with the ka mafs?

hmmm...this was about 10 years ago now, so my best guess would be Jim Wolfe technologies told me no problem when i had the ECU tuned. I had no idea the KA - SR MAFS were that different. Might as well just go to the Z32 at this rate. I noticed enjuku has an OE replacement for $129.99. Now, i've gota get the ECU retuned. Know anyone?

-Bret

send back to jim wolf they have some plug and play rom tunes

Probably good advice...i'll talk to Jim Wolfe soon.

Another piece of info. I neglected to mention...i am having some issue starting the engine when cold...Sometimes she fires right up, although barely catching...and other times I have to wait 5-8 seconds with my foot all the way down on the gas pedal for her to start. When i wait the 5-8 seconds, she starts with a nice cloud of smoke out the exhaust? I'm pretty sure its gasoline smoke, as after it disappears, there is nothing still burning out the tailpipe. Could the cold air influence the KA MAFS like that and give me starting issues?

THAT sounds like a bad CAS sensor or a car out of time. My car did that when my CAS was bad.

The CAS did that? I never considered the CAS might be bad. I know the timing is right on at 15 BTDC, but when the car hesitates, sputters and bucks, it does feel like the timing is off. Chris, Did your car run okay with a bad CAS, but gave you cold starting issues? What else happened with the bad CAS?

The crazy part about the starting issue, is if I head to the food store for a few things, let's say, with the engine nice and warm, when I get back in after letting her sit for 10 or 15 min in the parking lot, ...she starts right away.

I've gota get me a vacuum tester.

LOL My car had a BUSTED cas. She started one time with it and when it did it, it spit a ton of smoke out the exhaust and then it died right after. Try adjusting your cas (it can swivel) and see if the effects are changed. I'm still leaning more toward your ka maf being your big issue.

What's up B?! We need to get rid of this snow and cold so we can tear into your car! We'll get it right this spring. No doubt about it. BTW-I didn't know you were running the KA- maf. Thought you had the sr one. I also heard somewhere that JWT does free retunes. Not sure if that's true...

raw0330 wrote:What's up B?! We need to get rid of this snow and cold so we can tear into your car! We'll get it right this spring. No doubt about it. BTW-I didn't know you were running the KA- maf. Thought you had the sr one. I also heard somewhere that JWT does free retunes. Not sure if that's true...

It's NOT. They charge for a re-tune, but it's not near as much as the initial rom tune.

I'm currently running a KA MAF on my S14 SR and while I might not be having any real problems with it... I defiantly don't have as wide of a power band as I should (I think it tops out at 5k). But it was a temporary fix until I can buy a Z32 MAF, Injectors and a Re-chip. Or a used S14 SR MAF... Anyone have one lying around?

dragonboy, try posting in the WTB section. I'm sure there are plenty of people that have upgraded to a z32 maf that have a s14 one lying around.

EDIT: I checked your website. No love for the hatches?

hmm...depending on the cost of the re-tune, i might as well just up to Z32. Let's hope Jim Wolf goes easy on me.

btw PyRONiak...its "fastback" because its faster...

Rich dude...wtf...call me so we can coordinate this ish.

Are you running any sort of re-tune or ECU upgrade with your KA MAFS? You must have had the ECU tuned for the KA MAFS right? What happens after 5000 RPMS?

thanks for you help bro...this fix is long over due for me.

-B Vas

The reason people run KA MAFs is the SR can run on them WITHOUT a retune. The problem being is it's a downgrade, and even with a retune, your SR isn't going to run like it would with a stock maf or with a Z32 maf and retune.

Knock sensor

Wouldn't a bad knock sensor throw a code? I'm consistantly getting code 55 from my ECU.

Yes, a Knock Sensor would throw a code. 34 if I remember correctly. And it's HATCHBACK. Read the title, and to be honest with you, I'd assume they're a LITTLE slower considering how much that back glass weighs...

Hey I have an Xtrail GT turbo with the exact problem , if you start it and drive it will run well after a bit of driving it srtarts the hesitation and feels very sluggish and lazy , I find that if you drive it hard or run the AC it hapens much faster , If you turn off the engine and start it back , It seemingly resets and runs ok again and after a little while the problem happens again .

Did you ever find the solution to your problem ??