T5 stutter

[Niles]

got me a stutter in 1st & 2nd when i bury the accelerator, seems to shudder/stutter the as the revs get to appx 3500 it kicks in & WHOOOOOOOOOOSH!!!!........ the turbos been turned up via the wastegate actuator, iv got an FSE presure regulator which is capable of over fueling on request, so is it the computer thinking 'to much air, cut the boost'? Ive checked all my vacuum pipes from the turbo etc. Me thinks the ECU reprogram is the only way to boost the power (ie Electronical upgrade rather than basic mechanical) or is there a known boost problem with an 850?

[racer]

I think it's your FSE pressure regulator overfueling the engine. These things work by increasing the fuel pressure when the engine is under load. They look at the manifold vacuum and the more vacuum they see the more the fuel pressure goes up. Of course the ECU knows nothing about this, so it will decide how much fuel the engine wants and open the injectors for a given time to deliver the required amount of fuel at a fixed fuel pressure.

My theory is that at full throttle, your ECU isn't looking at the Lamda sensor. It's trying to fuel the engine for max power, but there's too much fuel getting in there as your regulator has upped the pressure. On part throttle, the fuel pressure is near normal (less vacuum) so there's no problem.

This being a turbo engine, when your revs get up, Mr Turbo will force enough air into the inlet manifold to see off the vaccum and move the other way to a positive manifold pressure. Your fuel pressure reg sees the vacuum go away and drops the fuel pressure back to normal levels. At this point the ECU gets the fuel it's asking for and Whosh!

Simple test for this is to remove the vacuum pipe from the fuel regulator, block the end of it and see if the problem goes away.

I'm not convinced these are a good idea on a turbo engine. I run one on the race car, but I don't have the vacuum line attached. It's just there to give me the ability to run a higher than stock, but constant, fuel pressure. The ECU takes care of the fueling.

Well, that's my theory. Adam and or Hamish will know more. Guys?

[blackbooty]

hi niles, i have run a saab 9000 turbo for 3 years with an fse , an 854 t5 for 4 months and my bro had one on my old 620 ti for a year without any of the probs youve just mentioned. (racer is plainly a man that knows much more than me about this product and its effects tho) .
have you touched the adjustment screw under the silver nut ?
anti clock turns weaken the mixture, clockwise richens.
this is only a "thought" incase you bought it second hand... if youve adjusted anti clock to far, maybee shes stuttering due to a very weak mixture at lowish revs,and when the fse gets going (overfueling i think racer called it) it feeds the engine at the correct (or close to it) ratio ??
as i say , just a thought!!! i dont know if weak mixture would cause her to stutter.
ive always had the vac pipe connected without a prob.
if you dont have the instructions and bumf that comes with the fse, pm me and ill scan n send it to you.
wayne.

[blackbooty]

oh yeah, on all 3 motors i know of using them, all have been wound up on the wastegate 9000 15 psi, 854 14 psi and 620 11 psi. all with foam replacement air filters also.

[Niles]

I got it new, when i fitted it I left it at its standard settings, fiddled a little with it, turned the nut about 90 degrees, didnt seem to make much difrence other than leaving black soot on my exhaust exit. duno if its a fule thing, ignition or just maybe the timings out a little. I'll give the 'remove the vacuum pipe' trick & see wot happens. Keep you posted. Thanks.

[Niles]

i removed the vacuum pipe to the fse, took it out for a spin & the shudders gone, performance seemed a little down & during the test thrash killed a water pipe lol (yet another weekend of greasy hands eh?

[blackbooty]

glad to hear the stutter has gone mate. what year is your t5 ? ive only run an fse on a 94 m phase 1, im wondering if ill have probs if i put it on my 96 n phase 2.
wayne

[racer]

Glad you nailed the problem. Bugger about the coolant hose though. :(

Might be worth getting your fuel pressure checked, just to be sure it's not way off.

[Niles]

mines also a'94 M. thanks people. (next tech question coming soon lol)