car feels jerky in 5 and 6

[Tcman2006]

hey i just installed my cobb sri its amazing but now when im at wot in fith and six gear the car feels kinda jerky has anyone else experienced this and if so what could be causing it

[wassup61]

Yeah, you are getting fuel cut. You need a fuel pump upgrade, and it helps to get new plugs too.

PM me for a package deal and Ill hook it up for a great price.

Jeff at PG

[Tcman2006]

the cars brand new and all i have it cobb sri

[wassup61]

Stock cars can get fuel cut. Its a faulty pump design that isnt up to snuff. Some get it with no mods, some dont even get it fully bolted.

Its a safety "feature" that closes the Throttleplate which is the jerkyness that you feel to save the motor from death by knock. (super lean condition)

1 step colder plugs also help smooth out the powerband and keep knock down.

[glocK23]

Originally Posted by Tcman2006 the cars brand new and all i have it cobb sri

was this after the ecu reset? because it will take a couple miles and a few WOT runs to get the fuel trims adjusted. does it happen every time? how many miles since you reset the ecu??

you definitely do not need an upgraded fuel pump with just a cobb sri, dont waste your $$ on plugs too.

[Tcman2006]

i put it on yesterday so its only got about 75 miles on it should i resest and try again

[glocK23]

Originally Posted by Tcman2006 i put it on yesterday so its only got about 75 miles on it should i resest and try again

once should be sufficient. does it continue to jerk in 5th and 6th after 75 miles?

[wassup61]

Originally Posted by glocK23 was this after the ecu reset? because it will take a couple miles and a few WOT runs to get the fuel trims adjusted. does it happen every time? how many miles since you reset the ecu?? you definitely do not need an upgraded fuel pump with just a cobb sri, dont waste your $$ on plugs too.

I cut stock (08.5 so no TSB for me) and stuttered in gears with higher load such as 4-5-6. As it got colder, the stutter got worse. I have gone through every issue with this car and then some and worked them out one mod at a time.

And yes, if he is cutting and this is causing knock retard, colder plugs will help too

But hell, since he doesn't have a dash hawk to datalog, we dont know. Speaking of that, its an excellent data monitoring device that can datalog so we can diagnose problems on here and I would gladly provide one of those too at a great price

-Jeff at PG

ETA:


LONG TERM FUEL TRIMS are not influenced by wide open throttle runs since the PCM switches to open loop calculations. You should let the PCM learn fuel trims for 50-100 miles at low boost/ part throttle only so that it can reference these values in open loop.

[fbpem1]

if your getting fuel/boost cut, i don't ever recall it being jerky, i equate it to more a of karate kick its very very very violent, i'm sure others can atest to that i know Darksun can as well. He coined the phrase to me as the karate kick.

[wassup61]

boost cut is VERY jerky like the car hit a wall (fuel cut induced by overboost)

fuel cut is light jerks, stuttering, or power loss during a pull (induced by insufficient fuel pressure to support commanded AFR at a given RPM, so the throttle plate closes as the fuel pressure decreases.) This is more noticeable in higher load gears because more stress is being put on the fuel system in 4-5-6 than in 1-2-3.

-Jeff at PG

[Tcman2006]

ok so tonight i noticed that this stutter doesnt happen all the time and when it does you can kinda hear a difference in the sound of the turbo is there a chance that this is all being caused by a leaky bpv when its under a full load

[wassup61]

Do you have a way of documenting this stutter? Post a datalog.

[FCmaniac]

what RPM are you going WOT in these gears?

[Tcman2006]

I mainly only see it in sixth at about 4 4500 on the interst when I go to pass

[Tcman2006]

i checked again this morning and it is actually about 3200 to 3500 when im in sixth

[wassup61]

KR or fuel cut, definately. Pick up a Dash Hawk to datalog this cut.

Shoot me an email msfprotegegarage@gmail.com and I can work a great deal for you.

-Jeff at PG

[Tcman2006]

Ok ill pm u for a price

[Tcman2006]

What plugs do u guys recommend

[kingpin748]

Could be boost cut. You should probably check that out first before you buy a fuel pump.

[wassup61]

Originally Posted by kingpin748 Could be boost cut. You should probably check that out first before you buy a fuel pump.

Its really difficult to diagnose without a Dash Hawk log. However, with just an intake, it would be damn near impossible to induce boost based fuel cut (2.5 psi above commanded boost for 1 second) since the pressure drop across the stock intercooler is 3.5 psi. He needs a DashHawk before anything else and I will make sure he gets hooked up with one.

-Jeff at PG

[Tcman2006]

ok guys Dashhawk is on the way so hopefully i can fix this problem

[Tcman2006]

OK so i got the dashhawk last night what do i need to log when i do this run

[FCmaniac]

Log boost, KR, DI fuel pressure, RPM and spark advance

[Tcman2006]

ok would it be best to log it in fith and sixth since thats where i can feel the stutter

[FCmaniac]

I think you'll have enough time to log the whole run... start the log and go WOT through the gears including 5/6

[Tcman2006]

So tonight on the interstate I noticed that in sixth gear at wot I noticed that boost will spike fro around 15 to 19 or 20 and then back to 15 and them back up over and over till I let off. What could be the cause. Fuel press is fine

[FCmaniac]

I can understand one spike when you first floor it but it shouldn't be going back up repeatedly like that. Do you have a catless DP? Sounds like your car is having problems controlling boost.

[kingpin748]

Post the log.

[Tcman2006]

the first run is from second throuhg sixth the second is only in sixth..slowing down and going wot over a few times. sumin is messed up so purple is acctually boost



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[wassup61]

I am seeing alot of Knock retard towards the top of every loaded gear. Check your inlet hose clamps/ other clamps, 4.9 degrees of knock retard at WOT is

A)bad juju
B)can be felt

Since your car is fairly new and lightly modded, I dont blame your stock plugs. Upgraded 1 step colder Denso ITV22s can help, we stock them, but you don't need them right now.

-Jeff at PG

[Trader]

What are your LTFT showing? And are your STFT stable?