Car Jerks Violently

[Kumarz34]

hi guys i have a 98 r34 gt auto 2 dr and it has started to play up recently so just wondering if someone can pinpoint the problem.

the car works fine yet when i accelerate hard (floor it or go up a hill) the revs go crazy and start jumping going back and forth and the car starts jerking around violently. It seems fine when driving normally (taking it easy) and there are no issues with the idle. It recently started to get worse after i serviced it (changed oil, fuel filter, oil filter, air filter and soon to change plugs) yet it did happen occasionally before that. Iv already changed my coil packs and everthing else in the car seems to run fine. Im thinking its either the ecu, injectors or fuel pump yet after reading around seems lik it could be the o2 sensor aswell?

any feedback would be much appreciated.

ps if in wrong section pls move or if there is another topic similar jus direct me to that one as i couldnt find it using search.

thanks

[Benzino33]

try cleaning your AFM..i think the o2 sensor would mostly affect idle and fuel consumption(correct me f i'm wrong)..but might as well get it changed.

also just check for any intake leaks..hope that helps

cheers

Ben

[mad082]

just to clarify, when you say the revs go crazy, do you mean the revs are jumping up and down, or it is just missfiring and losing power?

if the issue is the revs actually jumping up and down, it may be a gearbox issue.

[Kumarz34]

sorry shouldve clarified i mean loose power, lik the car is trying to accelerate but it can't. Yet it works fine when driving normally this only occurs when u push the car. i'l clean the afm 2m and see if that makes any difference but after driving again from work im guessing its either a fuel pump issue or ecu jus not sure which one

thanks

[3LGODZILA]

sounds like its hitting boost cut aka rich and retard.

R&R works off the knock sensor so it may be faulty,

hows your boost control? if its making too much boost then it will hit R&R so u may be getting boost creep or if your running more then 11-12psi

BTW when u hit boost cut it feels like you hit a brick wall until your boost/revs drop and if u hold full throttle it will keep repeating this making a the car jerk violently

[Kumarz34]

lol its an n/a so dnt think im hitting boost cut unless something similar happens to an n/a

correct me if im wrong tho thanks anyway jimmys-33T

[mad082]

sounds like its hitting boost cut aka rich and retard.

R&R works off the knock sensor so it may be faulty,

hows your boost control? if its making too much boost then it will hit R&R so u may be getting boost creep or if your running more then 11-12psi

BTW when u hit boost cut it feels like you hit a brick wall until your boost/revs drop and if u hold full throttle it will keep repeating this making a the car jerk violently

that is the first time i have ever heard that. i (and pretty much every other person on SAU) thought it was when the AFM was reading too high a voltage for a set rpm and load and the ecu registered this and would back things off.

[fib]

I had a similar problem with jerky acceleration, but normal driving when taking it easy.

It was the knock sensor wiring in my case causing the timing to go bad, once replaced by the workshop car ran beaut!

[Kumarz34]

hey guys so i went for a drive quick to pick up my plugs before i cleaned my afm and the car felt ALOT better it ddnt skip nearly as much and the car actually started to go. Im thinking instead of something big could a really bad batch of fuel do the same? i mite drive around abit and see if it improves and let u guys know

thanks heaps anyway for the quick responses. i mite clean the afm and change the o2 sensor anyway since its probably needed anyway.

[mad082]

just so you know, the o2 sensor won't affect anything at wide throttle. the ecu ignores it then. the ecu only reads from it at light throttle for better fuel economy. once you give it the beans (basically anything over about 1/3 throttle, but also depends on rpm) the ecu goes from closed loop (where it alters the air fuel ratio according to what the o2 sensor is reading) to open loop (what the mapping in the ecu says).