Slight 'cut out' on boost

[whitie]

Hi there,

I have recently purchased an 82 Starion (JA). I have had it tuned and the machanic increased the boost to 11psi (Im not sure if this is the reason for what is happening, but the more info the better I guess :) I also had new turbo spark plugs installed at the time.

Anyway, Ive noticed that when I get to about 3.5-4 revs that the acceleration kindof 'cut or stutters' out for a moment and then re-engages, it feels like when Ive had a car in the past and it cant get enough fuel for a moment (but since this is boosting and is totally different its probably a whole new ball game so to speak). Does anyone have any ideas as to what is causing the slight lack of 'fluid boosting' ?

Thanks everyone!

[SpidersWeb]

My Starion did the same thing, until it warmed up.

Since I didnt rev the crap out of it when cold anyway, I never actually tracked it down. 11psi isn't that much to cause a problem, but if you have a controller you could always turn it down a few psi, and see if that makes a difference.

The only thing not stock in mine (back when it happened) was the Iridium TX plugs, with a 1.1mm gap instead of the required 0.8mm gap. I also had the EGR system still connected - just thought Id share in case it sparks ideas with somebody else.

[whitie]

The only thing not stock in mine (back when it happened) was the Iridium TX plugs, with a 1.1mm gap instead of the required 0.8mm gap.

Hmm I did have new spark plugs put into the car and I dont think it was having the cut out before hand... It does cut back in almost instantly and only at around the one place on the rpm dial. Could this still be the cause of spark plugs with too far a gap? Do Starions require sparks with a .8mm gap then?

Plus I never let it out until its pretty warm, so I think I can rule that out...

[NachoMan]

There is a factory boost cut at 1.0 bar (15 PSI).
This may be the problem.

[tmz_99]

how has he inreased the boost? (actuator or bleed valve)
did he use factory oost guage to measure it or did he use an aftermarket guage (as if he used the in-car one they can be faulty (20 years old and all) and it may ib fact be the 15psi oostcut nacho speaks of.

[SpidersWeb]

If it was a case of the boost cut - then surely it would keep doing it higher up the rev range.

There is something suspicious about this 3.5-4K zone, people reporting 'flat spots', 'spluttering' etc etc. I wonder what the hell the Starion does at 3.5-4000rpm. Mine ran awesome, except in this little zone, and when cold, it'd almost stall in here. *shrug* I had vacuum leaks, so perhaps it was a case of the vac advance coming on too late? *shrug again*

[whitie]

There is a factory boost cut at 1.0 bar (15 PSI).
This may be the problem.

Thats weird that you pointed this out, because I came on to post that I was boosting during the day and it didnt cut out, but at night it did and noticed also that it was around the 14.5 psi mark (its hard to keep your eyes on the boost guage when you are smoking it at high psi :)

I do have an after market intercooler put on the car, so obviously more cold air comes into the turbo causing to be able to run at a higher psi at night than during the day. It came to me that there might be a cutout at a certain level of boost, when I noticed it didnt really cut out during the day. Thanks for varifying my theory Nacho :P

how has he inreased the boost? (actuator or bleed valve)
did he use factory oost guage to measure it or did he use an aftermarket guage (as if he used the in-car one they can be faulty (20 years old and all) and it may ib fact be the 15psi oostcut nacho speaks of.

... and you to tmz- I did get an after market guage in it.... looks like I might have to chip the ecu, anyone got any pointers on a good chip?

[CussCuss]

its NOT a boost cut, its an injector duty cycle cut, it will cut at 50% duty cycle, thats why its not at a certain psi.

[Chris 83JA]

...which generally happens to be around 14-15psi on a stock setup.

It will cut at around 4k rpm because that's when your car first hits full boost, and due to the bleed valve (or however the boosts raised), it will spike slightly to above your normal boost pressure due to the slight delay induced by the length of the hosing between the turbo and wastegate. If it's possible to shorten the hose, that will help.

[ProZac]

Id say its you knock sensor going off, and your ignitor box retarding the timing suddenly. In the 3.5-4k range your right in the meat of a torque curve, and the engine is under the most load, so its at its most likely spot for detonation.

Check your vacum advance/retard unit aswell. If its not retarding the timing here, as the computer expects it to, then its definatly going to knock around a bit and the ignitor box will retard the timing even more. It does it very suddenly, giving you quite a jolt sometimes.

[tmz_99]

... and you to tmz- I did get an after market guage in it.... looks like I might have to chip the ecu, anyone got any pointers on a good chip?

I think unichip made one at some point, but you may as well get an aftermarket ECU, allows for MPI,etc..check out some of the past posts in this section for a better idea of ECUs.

[Chryzla]

this is interesting... my friends 180sx used to do soem wierd stuff. you'd get into it when its cold and try and hit boost it would launch then instantly loose boost. felt like a bloody rollercoaster. we never found out the problem, we just guessed the ECU did something when the engine is cold to stop it getting damaged, he sold it and to this day we have no idea why it did it....

[Abalistic]

Try looking at the Advance/Retard Diaphram on the Distributor.
If it has a hole in it, then it will cause the surge problem that you have.
A
:)