car jerking

[bnaliang8]

any rotary sifu can explain to me why whenever i up the boost the car will jerk like it not enough fuel going to the engine by the way i on fc mark 4 engine with stock ecu thanks

 

[SideWaysGrey]

Possible that the fuel pump is not working fully and not enough fuel is delivered. Checked the injectors?

 

[Alchemis]

it's either not enough fuel or u hitting a boost cut on the stock ECU...
i'm not 100% sure on FC... but on FD's case... there's a limit set on the ECU.. so.. if u up the boost.. it might high chance hit the boost cut. and the engine will automatically cut the boost and once i got lower than the threshold, you'll have the boost again... so.. it's like jerking feel.. but it should be a mild one when u're flooring it..

2nd possible is there are too much air and fuel inside.. ur spark plugs are not strong enough to ignite the mixture.... either a ignition booster or better spark plugs will help in the situation.

 

[theseira]

Are you running a boost controller with your stock ecu?? If so, then maybe you're boosting too high and the stock ecu is hitting its boost cut. What boost you're running at?? If you're running stock boost then maybe it's not the ecu problem:regular_smile: .

 

[jasonlel]

I had this problem before. On boost, car jerk.

Check this out.

1. Check feul pressure (get your model std. feul pressure)
2. Check feul pump voltage. If voltage is not good, try to tap directly from 12v batt.

Good luck.

Copy and paste from my previous posting from other forum.

>>>
Do you guys mean 38psi at idle? I thought it is about 31-32 psi....
Please advice...
>>>

>>>
Initially I'm running 24psi at idle, after I have install a walbro fuel pump, I'm getting 30/31psi on idle.

But I'm still experiencing jerks during positive boost. (maybe around 0.1-0.3) I'm very sure is not the ON boost jerk coz it jerk a few times. What could be the reason? Fuel filter just change few mths back.

Some extra information
Exhaust temp, degree celsius
On idle: 400
Normal driving:500-600
Hard Drive:>600 ~ >>>

>>>
At last, my problem solved.

Did a check at fuel pump wiring voltage. Everything is oke. Last resort was to look at the fuel pump resistor. We are not sure how to check if the resistor is in perfect working condition, so we switch to another resistor. But it didn't solve the problem. So out of curiosity, I did a voltage check on the wire connecting to the resistor. I'm getting about 10v+/-. So I guess this is the culprit. It is not powering enought voltage to the fuel pump resistor.

So I by pass the fuel pump resistor and rewire the fuel pump to get 12v from batt source with a relay.

Violaaaaa, problem solved!!!!
>>>

 

[bnaliang8]

thanks guy the quick respond manage found the culprit seen that the stock boost sensor was faulty have it remove walau eh now can boost all way to 1bar without jerking.anyway guy thanks again......

 

[Alchemis]

beware of boosting so high with stock ECU... they generally does not provide enough fuel at that range of boost... use a AFC to add extra fuel.. do a dyno... we dun like to hear people saying engine blow...

really becareful... go for a dyno before you continue whacking at 1 BAr. make sure ur AFR is at below 12... at high boost region.. if it's 13... u're very close to death

 

[theseira]

Good to hear that you got the problem fixed. Btw fit a boost controller in and do not boost more than 0.9 bar especially with running a stock ecu. Iam running RE ecu with extra injector and controller and Iam boosting at only 0.8 bar. Your engine must be strengthened internally first before attempting anything above 0.9bar. My engine is stock internally.:regular_smile:

 

[bnaliang8]

thanks guy for the valuable advise just play around only n now back to 0.6bar n play safe n enjoy the rotary ride. oh by the way i on knight sport turbo. what guy think this turbo ?is it good ?thank guy.........

 

[SideWaysGrey]

haih...when am i gona get my RE out :(