[LakesKiaGT]

Hi All,

So long story short Ive been experiencing an issue after fitting a Zaustworx silencer delete where only in 3rd or 4th gear at around 2500rpm the engine will stutter. The stuttering may only be once or twice or might last up until around 3500rpm.

I have the new MAF sensor installed which was 1 possibility for this, and previous to this by around a month i had replaced the coil packs down to a misfiring issue with the car under any load above 3000 where misfiring was constant.

Basically my next step is to attempt to refit the exhaust with extra exhaust paste which I believe may be allowing air into / out of the system and messing with the O2 sensor.

My question is, has anyone experienced this type of issue previously, and if so how did you manage to fix it because as far as I can see the list of possible causes are as long as my arm (fuel pump, dirty air filter, fuel filter, spark plugs (checked already), coil packs (changed), injectors, O2 sensor, MAF sensor, leaky head gasket, exhaust fault etc.)

TIA

 

[blaizer]

Replacing the original exhaust or part there of with an after market jobbie,it is most likely to have altered the back pressure in the exhaust system which in turn is likely to alter the fuel trim mapping which normally equates to a weak mixture.When I was a young mechanic some 200 years ago and we wanted to increase the HP of the car the first thing we did was to make up our own exhausts but on every occasion we always had to enrich the mixture to get rid of the issues that you are having now.
The computer factory fitted to your car is not able to self compensate for the loss in calculated back pressure,it might try to alter the timing which is even worse.You need to get the car tuned that will tell you everything you need to know.

 

[Kazza]

When was the fuel filter last changed?
Does the hesitation/stutter happen under normal loads or when you get on it a little?

The reason I ask is I've been having issues on and off for the past year or so with hesitation etc, but boiled down to a nackered fuel pump/filter and guage... the filter had never been changed in 40k for starters and that in turn killed the pump and the float/guage has always been dodgy giving false fuel readings, £373 + £25 surcharge for a whole new fuel pump assembly seems to have sorted it.
The hesitation got gradually worse but only ever under load... it's worth checking the filter if it hasn't already.

I highly doubt the exhaust is the issue unless it's leaking as many have aftermarket exhausts fitted without issues.

 

[Kazza]

And btw I got engine codes related to camshaft sensor PO341 intake bank 1 circuit out of range... after replacing the sensor the code came back, long story short it was my fuel pump causing the issues, something to do with the car being in a lean condition caused the vvt to retard the timing too much giving the code.

 

[LakesKiaGT]

Replacing the original exhaust or part there of with an after market jobbie,it is most likely to have altered the back pressure in the exhaust system which in turn is likely to alter the fuel trim mapping which normally equates to a weak mixture.When I was a young mechanic some 200 years ago and we wanted to increase the HP of the car the first thing we did was to make up our own exhausts but on every occasion we always had to enrich the mixture to get rid of the issues that you are having now.
The computer factory fitted to your car is not able to self compensate for the loss in calculated back pressure,it might try to alter the timing which is even worse.You need to get the car tuned that will tell you everything you need to know.

Thanks for the reply, I had read a couple of weeks ago but I've been sorting out a remap as I can see how the back pressure would be reduced and could possibly affect the fuel trim. However always better safe than sorry so I've told the company about the issue I'm having and they seem to think it could be the option as well (possibly biased opinion I know).

Although the garage also modifies and repairs cars so if this doesn't sort the issue hopefully they have seen something similar and will know where to look for the issue, by the sounds of the noise it does sound fuel related, whether this be by ECU control to alter the fuel trim or a faulty component in the system (low pressure/high pressure pump or the fuel line pressure between the 2).

 

[LakesKiaGT]

When was the fuel filter last changed?
Does the hesitation/stutter happen under normal loads or when you get on it a little?

The reason I ask is I've been having issues on and off for the past year or so with hesitation etc, but boiled down to a nackered fuel pump/filter and guage... the filter had never been changed in 40k for starters and that in turn killed the pump and the float/guage has always been dodgy giving false fuel readings, £373 + £25 surcharge for a whole new fuel pump assembly seems to have sorted it.
The hesitation got gradually worse but only ever under load... it's worth checking the filter if it hasn't already.

I highly doubt the exhaust is the issue unless it's leaking as many have aftermarket exhausts fitted without issues.

Hesitation usually under a wide open throttle or at least getting up there.

I believe the filter was changed about 9 months ago on my last service, its definitely fuel system related whether it be ECU control or fault. My guess would be as Blaizer says above to do with the backpressure altering the fuel trim after reading up over the last couple of weeks, but it could just as easily be a faulty pump or filter which is why I'm opting for a remaper with the modifications side covered.
The main reason I'm going to the remap before the fuel filter is as its just another thing to rule out which they give me a money back guarantee on, that as well as the issues seeming to arise after fitting the exhaust. I'm just slowly ticking off things it could be at this point.