Fuel cut (maybe)

[BlownCorona]

In my GTti charade (turbo for those unaware)

 

sometimes when i punch it and rev it out at higher boost levels than cruise, maybe between 5 - 10psi (boost is set a roughly factory levels), i will hit what i think is fuel cut, the car looses power, lurches, backfires, and i see a puff of black smoke behind me, all within less then a second and then the car carries on fine. 

 

this doesn't happen regularly, and i probably couldn't replicate it if i tried, its not a certain rev, or a certain gear. 

 

does anybody know what i should do to remedy this? ive read a bit on line and some people say a pod filter can let too much air in and this causes fuel cut, but surely the turbo and boost level control any air that a sensor would see?

 

i dont know too much about turbos, but any help would be appreciated!

[mjrstar]

Generally the "fuel" cut is actually sensing excess air or something untowards and providing protection, the best place to start will be to look for any signs of boost leaks, or problems with the air flow meter.(if the car has AFM) if not you'd need to be looking for the map sensor and checking hoses for any leaks... also check that the car is not overboosting once again excess airflow.

 

If it's not actually hitting the cut check plug gaps and heat range but this should give you a more consistent miss-fire rather than the cut you describe. 

[coldturkey]

I would have thought a backfire was caused by unburnt fuel, not a shortage of it. But I'm probably wrong that's just the logic in my head.

I've had similar issues and it's normally spark related.

[Jase]

mates gtxx charade did this ,

we put it all back to factory and it went way better,

he said the map sens was out of range

[BlownCorona]

it seems to have gotten slightly worse over time. 

 

ie, went from nothing (as far as i know) to doing it sometimes on 1st to now sometimes doing it in 2nd. 

 

i will probably buy a new set of plugs for it since ive not done them since purshace, but its just so sudden and shocking that i dont think its the plugs

[Frosty]

The fuel reg might be getting stuck in the full open position every now and again or the fuel return line my be partially blocked causing an over fueling.

It could also be a faulty injector getting stuck open or not closing fully.

coldturkey could be onto something with his spark related comments to that could be sending unburnt or partially burnt fuel out the back.

[eke_zetec_RWD]

Measure your plug gap and actual boost level and report back

[FuzzayD]

i had a similar problem in my supra to what you described it turned out to be a fault with the egr system i think it was sticking open and causing the motor to suck in too much fart gas at high rpm so it would reach max boost then as boost dropped after about 3-5 sec it would seem to rev limit or stutter like it dropped a cylinder for a second then be fine again . something to look into before you go ripping the motor apart if you have egr.

[BlownCorona]

will do people, im a busy man so bear with me, but im taking all on board! cheers. 

 

for what its worth, i have a nice Autometer boost gauge, and its reading a solid 10psi and nothing more, and as far as i know factory boost cut is about 15psi. is this accurate enough? ie, if there was some sort of leak, would this show on my gauge, this is the main reason for installing to be honest so i hope so haha.

[mjrstar]

^^ Not really... You will only see a boost leak of it's massive and you are failing to make full boost. I had this happen when i split my manifold open it would only make 5-6 psi instead of 20 psi.

[FuzzayD]

^^yeah sometimes you just won't make full boost unless you try go up a hill and really load it up.

[BlownCorona]

when it was doing it more often, the pod filter had fallen off and been removed for a few days ( i hate the fucking thing and would really love a factory air box, but unsure where to get one) and i refitted it yesterday and was giving it a bit of a caining today and it didnt skip a beat. 

 

It HAS done it with the filter on and secure, but not as often, so i thnk its probably as someone above said, and wanting a bit more restriction/factory airbox to run properly. if the filter flows too much air and the afm doesnt like it, it will probably shut the whole show down in a rush. 

 

ill still check all of the above suggestions though. 

[FuzzayD]

Sounds about right what if you disconnect the o2 sensor without filter and see if it still skips? I've seen a few cars that have done this with air intake changes especially when people change the crank case ventilating system as most cars compensate for air being drawn through the rocker and as such bypassing the air meter so if you cancel positive crank case ventilation this compensated portion of air is no longer being received causing it to run rich/lean and lean it self off when noticed by the o2 sensor. Most old fuel injection systems only use the o2 sensor to lean off the fuel mix so by unplugging it you will cause it to run at its richest closed loop mixture unless the ecu can notice its unplugged and switched to some closed loop system that doesn't allow it outside of some parameters but i haven't seen an ecu that does that yet. Running it for too long(weeks and months) unplugged can foul catalytic converters.

If putting a restriction in the intake fixes the problem then i guess that was the problem.

Some cars adapt when the ecu is reset and refine the fuel map to suit the engine and driving conditions perhaps you could reset your ecu and it will detect the correct parameters of running with a different filter on/ not over compensate for adjusting to a restrictive filter