Violent jerk around 4500rpm

[V8HAHA]

My and my buddy just finished installing a FMIC and MAFT, the previous problem had been fixed, but a new one has come up. At WOT it jerks really bad at around 4500 RPM. It feels like if you were in 1st gear and was flooring it and letting off repeatedly. We don't know where to go from here, where do we start? Any input would be great.

 

[FrostBite]

that happened in my 1st turbo dsm and it was the spark plugs, how high does the psi go when this happens?

 

[halik008]

My and my buddy just finished installing a FMIC and MAFT, the previous problem had been fixed, but a new one has come up. At WOT it jerks really bad at around 4500 RPM. It feels like if you were in 1st gear and was flooring it and letting off repeatedly. We don't know where to go from here, where do we start? Any input would be great.

does he run on MBC or BCS???

halik

 

[FusionTalon]

actually my talon did this untill i found a hole in my intake pipe ...thats after the sensor, this means the sensor was telling the engine that a certian amount of air was going into the engine when a shit load more was actually going in, and this makes the bucking at high rpm, the engine is tryin g to shut off becasue not enuf fuel is going into the engine with the air, but at high rpm it really cant do it that easy so it bucks.

 

[4G63 GST]

fuel cut possibly? .. what other mods has he done .. ?


Luke

 

[TurnUpTheBoost8]

yea my buds evo did that and it was a fuel cut cause of high boost... if it kicks back really hard ...then fuel cut is prob it

[Fuel cut is not caused by boost level.]

 

[I-luv-em-all]

i dont think its fuel cut, i think V8haha knows what that feels like. is their any CEL's, any smoke, does ur friend have a logger. i knew of a guy that had some jerking when accelerating and he changed his fuel filter plugs and wires and he was good to go, id start their.

 

[V8HAHA]

Ok. Yes he has a MBC hooked up, however it is turned all the way down so we could test everything without high boost. His upgrades are all hard pipes, HKS SSQV, 450cc injectors, stock turbo, FMIC, 3" cat back and MAFT. Before anyone say anything, yes a FMIC is overkill for a 14b, however he got it for christmas because it was one of the more expensive things, and this way he wont have to buy it. We took out the boost control solenoid (is this what you mean by BCS?)

It kicks at 4500-5000 rpm, and I am thinking its not fuel cut, becuase while hes running stock injectors, its at around 11 psi when it happens. I checked the spark plug gap with a .025 (all we had) and the gap was a tiny bigger than that on each plug. I guess we'll have to swap out the plug and filter and go from there.

What is really confusing me is that it didn't do this before we installed the FMIC and BOV. We did swap the coil pack while eliminating possibilties why it wouldn't start, so maybe I didn't push the plugs back on it very well.

The reason it wouldn't start turned out to be the CAS, we have NO clue what made it go bad, maybe we touched it wrong while installing the UICP? Are these really sensitive?

 

[Sic95gst]

i had the same problem at WOT in my car so I upgraded my plugs to NGK bpr7es's and magnacore wires and the problem stopped and i can run WOT all day long with no bucking or jerking

 

[I-luv-em-all]

I checked the spark plug gap with a .025 (all we had)

u should try 0.28 gap at the least not 0.25, although it shouldnt make too much difference.
what plugs are u using?

 

[xcelr8n]

what are the maft settings, as soon as I hooked mine up, my car broke up around 4000 at wot..
all I did was lean the wot trim 5% each time until the car pulled like a monster til redline.
I say try that out, im assuming you have a logger as well...

 

[V8HAHA]

u should try 0.28 gap at the least not 0.25, although it shouldnt make too much difference.
what plugs are u using?

To be honest, I don't know. I figured the gap was close to .028, because there was a little space left.

I don't understand why spark plugs/wires would cause this, does someone know the actual reason? Everything worked great before the FMIC and MAFT, why would this change anything? Maybe because the intake temps are lower?

what are the maft settings, as soon as I hooked mine up, my car broke up around 4000 at wot..
all I did was lean the wot trim 5% each time until the car pulled like a monster til redline.
I say try that out, im assuming you have a logger as well...

The MAFT is all zero'd out because he has an AFC. He does have a logger, but of course, the palm is broken .

 

[RedRain]

To be honest, I don't know. I figured the gap was close to .028, because there was a little space left.

I don't understand why spark plugs/wires would cause this, does someone know the actual reason? Everything worked great before the FMIC and MAFT, why would this change anything? Maybe because the intake temps are lower?

"Always check that the spark plug gap is compatible with the engine manufacturers specification. A gap that is too small means that the spark duration will be very quick and the spark will be thin and weak. The consequences of this may be bad starting and high exhaust emission levels. This will result in an increase in fuel consumption. If the gap is set too large, the ignition system will not be able to cope with the demands and a misfire situation will occur..."

-NGK(http://www.ngkntk.co.uk/technicaltips/sparkpluggap.asp)

 

[GsX-666]

We did swap the coil pack while eliminating possibilties why it wouldn't start, so maybe I didn't push the plugs back on it very well.

btw it wasnt the wires I tried =) did the same thing..yes sir although one wasnt in all the way.

 

[V8HAHA]

Well, then it looks like its time to buy some new plugs. I think the wires you have are upgraded ones... magncore I believe... check them. Also, try putting more gap in the spark plugs... maybe that will help.

I am guessing the gap is like .027. Anyone think this would this make a difference? The fecotry spec is .028.. correct?

 

[xcelr8n]

... lean it out =)
I guess first though make sure theres no boost leaks or spark issues which would hinder the car similarly.

 

[GsX-666]

I dont see why it would matter it's not like i changed my plugs before i swapped the fmic and piping so i doubt thats it. And no the plug wires are NGK, the plugs are bosch platinum or somthing cant quite remember

 

[Defiant]

I figured the gap was close to .028, because there was a little space left.

Please tell us you're kidding.

 

[karbon]

There is NO such thing as "pre-gapped" plugs. It's garbage. The boost could be blowing your spark out, it could be fuel filter-related, it could be the plugs themselves, wires, etc. My car is doing this right now because it's got a huge leak in the intake that I haven't had time to diagnose and fix yet. Yes, boost leaks will cause what feels like fuel cut.

 

[V8HAHA]

Would it have to be a fairly major boost leak to cause it? This is the only thing that makes sense to me, as this is the only thing we changed.

 

[CyberEye]

I'm really surprised nobody has said this yet. He's said a few times that it didnt start doing this untill they installed the front mount. Check all your piping and couplers, sounds you have a leak.

 

[97GS-TSpyder]

anyone think maybe a MAF that is going bad? i had this problem on another car and thats what it wasadn taht RPM something was messing around with it and it would give a bad reading....just my experience

 

[V8HAHA]

We'll check all the couplers, although I think we did it pretty well. One thing I thought odd, is that we are able to twist the hks bov around. So we could say have it pointing towrds the front of the car, and very easily just turn it around to the rear.

 

[karbon]

We'll check all the couplers, although I think we did it pretty well. One thing I thought odd, is that we are able to twist the hks bov around. So we could say have it pointing towrds the front of the car, and very easily just turn it around to the rear.

You should be able to do that, but it shouldn't be easy. It mounts on an o-ring using a big ass C-clip, doesn't it? It should be really tight. The person that sold me the HKS > 1g adapters said this sealing technique has been tested to 40+ psi.

 

[V8HAHA]

Yes, thats how you do it (P A I N I N T H E A S S). I just didn't think you should be able to move it around.