Hi folks, has anyone got any ideas from experience why the following is happening to my car?

It pulls cleanly for first 2/3 runs up to 7k then after that it stutters at different revs 3 or more times in quick succession (feels a bit like overboosting). It seems to do it from .5 bar boost onward up to 1.5bar. Once it got through the stutter phase it pulls and boosts cleanly.

Its a V5 Sti with a new Simtek mapped by JGM, Simon has checked the map and "its perfect" and is not overboosting. Mind you im getting a fair bit of soot out of the exhaust. This is a recent development and did not happen prior to these upgrades. Soot is bepositing on the rear bumper and boot! Simon mentioned this is not uncommon on cars running higher HP (380 on mine). Im not overly convinced by this though. But Simon has been very helpfull and really knows his stuff.

It has Lateral flow matched injectors, SC40 turbo, from mount and walbro FP plus decat.

Before you ask yes I have changed the HT leads for genuine new ones and tried a different working coil pack plus checked and cleaned the NGK 7b spark plugs which are gapped to .6mm, these are only a few months old. But it still does it

Any ideas before I break the car after 7 years of ownership ?? Your thoughts opinions would be appreciated.

 

Have you tried a fresh set of plugs just to eliminate them?Or maybe a crank or cam sensor giving intermittent problem.
As regards the "soot" or unburned fuel deposits that is normal especially with high boost and keeping the engine safe

 

Thanks at least the soot issue is not uncommon, car gets dirty very quickly. The plugs looked fine and why would they fail after a few successfull initial boosts? It pulls fine initially its just when you give is some gas repeatedly. I have a spare set of plugs so may change them.

Thanks

 

Ok well the plugs was not the only suggestion so maybe time to look else where than spark related issue.

 

I think you may be right eliminate the simple things first. Unfortunately the hastle and costs rise alot from here! Its the intermitant nature of the fault that confuses me

 

Is it possible that a boost pipe is weakening and sucking closed?

 

The car correct me if I am wrong Kirk, does a lot of short off boost journeys, the exhaust is flowing a lot of exhaust gas on boost and its cleaning out the exhaust.
If it were overly rich it would be using more fuel which I dont believe it is?

The misfire to me appears spark related and got worse with heat hence my thought of coilpack. The only other thought is cam or crank sensor or teeth as they get hotter the clearances alter etc and the sensors get hotter.

Steve at simtek when I discussed it with him yesterday (check it wasnt something he had seen on the new simtek before) almost seemed eager to get his hands on it, and see if it might be something that can be dialed out.

So as suggested via txt earlier Steve and I would like to try and organise taking a look together.

Simon

 

Hmm. . .sounds similar like my v5/7 . . .but t'was aftr g.change and frm low rey eg. 2k

 

Have you changed your spark plugs for colder ones? I believe that for every 75bhp you add you should select a spark plug that is one range cooler.

- Someone correct me if i'm wrong, I will do some research now...

 

First google link I found...

'With modified engines (those engines that have increased their compression) more heat is a by-product of the added power that normally comes with increased compression. In short, select one heat range colder for every 75-100 hp you add, or when you significantly raise compression. Also remember to retard the timing a little and to increase fuel enrichment and octane. These tips are critical when adding forced induction (turbos, superchargers or nitrous kits), and failure to address ALL of these areas will virtually guarantee engine damage

Found HERE:
http://www.ngksparkplugs.com/techinf...stallation.asp

Again, I have never tuned an Impreza... this was all pen on paper stuff at university, so don't jump ahead and do this, Talk to your tuner and he should be able to advise you.

 

FUel pressure?

 

Just had a similar problem with my 2006 wrx, it's being doing my head in for months.

Then I cleaned the crank sensor and the MAF / IAT and now it's running like a dream again.

Worth a try for a 10 min job.

 

Bro, how did you do them?

 

You can buy this cleaner http://answers.halfords.com/answers/.../questions.htm

And give the maf a good spray. I also used a cotton bud to clean the IAT.

For the crank sensor I just wiped the pickup with my finger.

There's plenty all over the Internet about cleaning mafs, some people do it every oil change.

 

Mine is mafless but cleaing the crank sensor is an idea especially if its an easy job. Will look into it. Cheers bud.

Whats the IAT?