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gsracer
09-10-2004, 02:28 PM
Im posting this on here for a freind who is desperate, this problem has been goning on for months already, anyway this is what he has

His car
s14 with s14 sr engine
z32 maf
nismo 550cc
Stock t28
Greddy FMIC
Walboro
SAFC II
HKS SSQ
and exhaust

The problem he has been having is this , the car will backfire or stutter for 2 or 3 hundred RPM as your accelerating in any gear. At first it would do it at around 5000-5500, then it started around 4600-5000, then 4000-4500 and now its 3600-4000. It will only do this for like 2 or 3 hundred rpm and then once it passes that point it will accelerate perfectly fine.

We have changed and swapped parts from my car that runs perfect to his to see if it will fix it ,and nothing so far. here is what we have done

BRand New SR harness from nissan converterted by nostalgic hero on FA
REdid all the SAFC connections
Swapped out all the coil packs from my car
IGnitor from my car
300zx MAFS from my car
Verified 15 degrees w/valve cover removed
checked and checked and checked again for boost/ vacum leaks

Its worth noting that this car has done this ever since the headgasket was changed. to 1.2MM. And antoher thing to note was that his car makes 17in/hg of vavum at idle and mine makes 20-22 inches at idle .

Kookz
09-10-2004, 02:44 PM
Spark plugs aren't on the list of changed items.

beetlejuice
09-10-2004, 02:44 PM
Have you looked at the settings on the AFC? Were they changed after swapping the head gasket?

I would try messing with the AFC at the specific rpm settings your friend is having problems. Maybe lean or richen the air/fuel mixture to see if that cures the stumbling.

Hugh
09-10-2004, 02:45 PM
How do the SAFC settings look? Its been the culprit for many people I've seen with wacky problems. Excuse me if you've already fully investigated this.

EDIT: Damn, you beat me to it!

gsracer
09-10-2004, 02:50 PM
the safc settings nevver changed it started doing it at high rpm , then the weird part it kept doingit it at a lower and lower RPM like first it would do it at 5000-5500, then it would do it at 4000-4500 etc, after it does it , it will accelerate fine and strong till redline

gsracer
09-10-2004, 02:51 PM
Spark plugs aren't on the list of changed items.



i will be putting my plugs into it today, i know those are good.

Nikeboy355
09-10-2004, 03:11 PM
what about pulling the 550s out, putting the stock 370s in and trying it like that?... That way you are ruling out bad injectors or a mistake in the SAFC...

gsracer
09-10-2004, 04:10 PM
we tried that to 370's and stock ecu settings, just out of curiosity if the air filter is dirty or clogged could it cause turbulence to disrupt the mafs momentarily. Were gonna go for a drive with me monitoring the MAFS with the voltmeter to see what it is doing when it happens.

Best i could describe it , is like the car is having a hiccup momentarily the exhaust pops and then it goes. It is also down on power , it doesnt throw black smoke just pops. Like its hitting a fuel cut. Then it runs fine.

thanks for the replies so far

masterbunta
09-10-2004, 04:24 PM
check your in/out settings on the SAFC, if you mess around changing stuff it can change. That happenend to me just yesterday, drove me crazy for about 10 minuites.

Ovrated
09-10-2004, 04:37 PM
i would try to find someone locally that can check all the s-afc settings..

and then im guessing its running rich before full boost... get a wideband and check all of it

Hugh
09-10-2004, 04:53 PM
The SAFC displays the MAF voltage in the sensor check menu. No need to hook up a multimeter to it. http://forums.freshalloy.com/images/graemlins/wink.gif

Kookz
09-10-2004, 05:25 PM
I don't know why everyone is pointing to SAFC settings, the problem wouldn't change where it occurs if it was electronic. It's most likely spark plugs, air filter, or fuel filter.

EDIT: Also, check the walbro...you may need to wire up your own relay and run thicker wire to power it.

MATT_BACK_VASS
09-10-2004, 05:57 PM
have you checked the TPS?

try disconnecting it and see if the car still stutters..

gsracer
09-10-2004, 06:53 PM
ok pulled the plugs first was gone rest were fine. But the car ran great except for the hiccup. put new plugs in it and it ran ok at 9 psi but when you turn up the boost it [censored] up again. Thinking faulty injector all ready tested the coil packs and the were ok

Barney_240
09-10-2004, 07:08 PM
have you checked the TPS?

try disconnecting it and see if the car still stutters..





i've mention that to the desperate person too .. Finn Finn..

Hey Jerry ( gsracer ) .. try Matt's opinion.. i hvae somethign similar on my car and still messing around with my TPS ...

btw, what size dress ? LoL

Hugh
09-10-2004, 07:35 PM
The SAFC can tell you if the TPS is good.

If it reads zero% at zero throttle, and 100% at full throttle, then its fine.

You see, the SAFC can do a lot for you. http://forums.freshalloy.com/images/graemlins/wink.gif

Barney_240
09-10-2004, 07:37 PM
The SAFC can tell you if the TPS is good.

If it reads zero% at zero throttle, and 100% at full throttle, then its fine.

You see, the SAFC can do a lot for you. http://forums.freshalloy.com/images/graemlins/wink.gif



even if the voltage of the TPS isn't set right ?

Hugh
09-10-2004, 07:59 PM
To read the TPS voltage, go into the sensor check screen. It's constantly reading it.

If the percentages are accurate, then how could it be wrong?

asad
09-10-2004, 09:13 PM
To read the TPS voltage, go into the sensor check screen. It's constantly reading it.

If the percentages are accurate, then how could it be wrong?



The sensor check screen actually reads the TPS voltage, not just a percentage. But as you say...it's equivalent to putting a multimeter on the TPS itself, except that you're also checking through the wire harness as well (a neglible additional resistance).

Asad

gsracer
09-11-2004, 12:12 AM
ok guys this is what we found First spark plug was completely demolished, i dont know how it ran as well as it did ceramic was missing tip burnt etc. ALL THE REST of the plugs were ok. We put a set of ngk iridiums i had laying around and it ran perfect at 9 psi .When you turn up the boost it still hits that brick wall.

So we figure the first cylinder is leaning out and causing that cylinder to detonate. We switched all the the coil packs, coil harnssess and it still did it so we suspect a faulty injector. Tomorow we will be pulling the manifold to swap injectors with the ones in my car that we know work. Hopefully it will be that fingers crossed.. http://forums.freshalloy.com/images/graemlins/grin.gif http://forums.freshalloy.com/images/graemlins/grin.gif http://forums.freshalloy.com/images/graemlins/confused.gif http://forums.freshalloy.com/images/graemlins/confused.gif http://forums.freshalloy.com/images/graemlins/rolleyes1.gif http://forums.freshalloy.com/images/graemlins/rolleyes1.gif

Oh and we did a compression check and had all cylinders including lean number 1 at 135 +or- 5 psi. So the engine is still good. He has a 1.2mm gasket, and the same gauge read 155 psi on my sr with stock gasket so its not so bad

Hugh
09-11-2004, 09:08 AM
Thats not bad at all. 135psi with that headgasket... as long as its consistent from one cylinder to the next is fine.

You may be right about the injector there, but its easy to test an injector without having to pull it. Just hotwire two wires to the battery. Unplug the connector on the faulty injector. Now tap the two wires to the socket on the injector itself and listen for a click. It doesn't matter which side is positive and which is negative.

If you don't hear a click, try the next injector to make sure your test is correct. No click = stuck injector. Replace it.

Email me if you need a set of stock 370's.

Vapor
09-11-2004, 09:27 AM
Everything written here says LEAN CONDITION all over it. Put this thing on a wideband yet? I saw no mention of that anywhere.

gsracer
09-11-2004, 11:11 AM
Everything written here says LEAN CONDITION all over it. Put this thing on a wideband yet? I saw no mention of that anywhere.



john we put it on a dyno and it was running a/f in the 13's. Were not thinking stuck injector were thinking partially clogged because it runs ok at low boost its when you turn it up that it misfires, will be doing this as well as fuel pump check today.

gsracer
09-11-2004, 06:58 PM
ok we changed the injectorsand put the ones From my car, we changed the CAS from my car, we put a long line and guage outside the car and puts 41 psi at idle 64 psi under boost. We took off the knock sensor,and the water temp sensor.

IT STILL DID IT!!!

The only thing left to do this is the ECU, or something with VTC, which i know nothing about.

Im at a loss for words, here guys.

body80
09-12-2004, 03:46 AM
What's the gapping on the plugs. Don't try gapping the iridiums. Buy some reguler NGK copper plugs with a heat range of 7. Then from personal dealings as you turn up the boost you'll need to gap the plug less. Try .028 if you're boosting more then 9 PSI.

If you haven't adjusted the gap I'll beat this will fix your problem.

gsracer
09-12-2004, 01:10 PM
the plugs are gapped to .28 ,and are irridium, and are the same plugs im my car running 19.5 psi making 300+whp

gsracer
09-13-2004, 09:05 AM
Any one have any other thoughts

Vapor
09-13-2004, 10:26 AM
if your a/f is in the 13s, you have misfiring problems, and you've eaten a plug, 1+1+1 = 3. Your a/f needs to be in the lower 12s or mid/high 11s in order for it to be safe. You are misfiring because of the lean condition most likely.