I have recently got myself a STi V5 rally car and on my first event we had a boost problem.

Iam completely new to turbo'd cars so please bare with me!

What happened: From having the car boosting at 1.5 bar (on the guage) on the previous stage when we started the next we had none.

The guage when sitting idling would sit below the 0 mark on the guage, is this because of the vaccum? Then once we discovered we had no boost the guage is now sitting just above zero at idle so obviously there is something wrong.

Things that we have checked:

Changed the turbo and made no difference
Checked the exhaust was flowing freely
Checked all the pipes to the best of our ability and they look ok

So whats left? It seems like possibly an electrical fault as the car is running with a bit of a misfire when trying to drive it.

Any help would be much appreciated and if you need anymore info about it to help please just ask.

Cheers

 

Are you saying that the car no longer boosts or just the gauge always reads 0? Gauge does read negatives at idle due to vacuum and should start to rise with compressor speed. If it's reading 0 at idle then I'd be checking the vacuum hose to it. If it's not boosting at all and reading 0 on the gauge all the time then you may have a pipe blown off somewhere on the inlet.

 

Cheers mate,

It doesn't boost at all and the guage just sits slightly above 0 and doesnt move.

Will check all the pipes thoroughly again.

Any other ideas?

 

None worth bothering with given the amount of information we have to go on. If you want specific help here we're going to need some more information - as some of what you've already said doesn't make sense (or possibly points to a problem in itself).

You haven't told us what engine management your car is running on, and whether it's restricted. As such it's difficult to know whether what you say about the car running 1.5 bar of boost indicates a problem or not. If you're running a standard unmapped STi5 ECU, it shouldn't be running anywhere near 1.5 bar - so how is (or was) it achieving this pressure?

If you're running an aftermarket ECU, we need to know that in order to advise you on how best to diagnose the symptoms. Ditto whether you're running a jacked throttle or similar method of ALS - as this will affect the amount of vacuum (if any) you should be seeing at idle.

Give us more information and we might be able to help you. On the basis of what you've said already about the only thing we can do is suggest you take the car to someone with the appropriate experience to diagnose it - as you'll get a far quicker answer that way than anything we can do over the interweb.

 

Sorry Splitpin I will give some more details, I will be taking the car to a more experienced person at the weekend if I cant get the problem sorted by then. I just though that some of you guys on here might have an idea as there seems to be a great knowledge on this forum!

The ecu in the car is a motec unit, it has ALS but the car was mapped on 95 octane fuel with a 32mm restrictor so the ALS is very mild in comparison to some.

The symptoms in the last stage we completed were a noise like air being drawn when the turbo was boosting and the anti-lag was popping more than normal, nither of which had happened in any of the previous 5 stages.

When we got into service the top of the CAT was glowing red which we are pretty sure wasn't like this after any other stage.

Everything looked ok though so we went back out for the next stage and when we went to pull of the line there was no boost at all and there hasn't been since.

Things we have checked some of which were just precationary and probably not necessary:

Checked compression (fine)
Checked Timing (fine)
Checked Exhaust or CAT wasn't blocked (seems ok)
Checked for any splits in pipes, blockages etc (seem ok)
Changed the Turbo for another spare (made no difference)

Intercooler apears to be in good condition but it hasnt been pressure tested

The only other thing that someone has mentioned to me is the boost controllers on the inner wing, can anyone shed any light on these?

Other than that it leaves the ECU its self

As I say I am very new to turbo'd cars so I have probably missed many things obvious. Again if more information would be required to help daignose please just ask.

Cheers

 

Knowledge can only go so far - especially in this application. Ultimately nothing beats eyes, ears and hands under your bonnet.

Noted, although even mild rally-oriented ALS is likely to be fiercer than most road car implementations.

Are you absolutely sure the exhaust manifold is 100%? Assuming you're running in Group N you should have the standard pre-turbo manifolds and up-pipe fitted. If so double check that the flexi-joints on the front link and up-pipe aren't blowing.

Also, if you're running ALS you should have a brake servo delete. If so have a look at the vac takeoff on the no. 4 branch of the inlet manifold and make sure whatever's been used to bung it hasn't come off.

No reason to think the IC would be leaking, although it's possible so worth checking. Dumpvalve though, are you running a standard one? Either way worth checking that over, but the sudden lack of idle vacuum together with the hissing noise under boost suggests you have an air leak in the inlet manifold or idle speed control valve. Can you hear any hissing from that area of the engine when it's idling, or when you blip the throttle?

If we are to take your boost gauge readings at face value, the boost control solenoid is probably ruled out.

As above it has all the hallmarks of an air leak on the manifold side of the throttle plate, although it could be that you've got a couple of separate problems all rolled into one here, although it could equally also be that you haven't had the car quite long enough to know for sure what the "normal" idle manifold pressure readings should be.

Have a real close look around the exhaust manifold all the way up to the turbo, and closely check the y-pipe between the turbo and IC, and the throttle body/idle speed control valve and the inlet manifold itself for anything that might be causing a leak.

If you can't find anything either visibly wrong (or hissing/sucking under idle) it'd be well worth putting the car in front of someone Motec friendly as it should be the work of a few minutes to track down the problem once there's a laptop connected to the ECU.

 

There is also a lot of crap on here. My opinions are just that, and so may not be anywhere near correct. I made assumptions (which should not be done), with my reply and ignored the fact it was a rally car. I was thinking a major leak on one of the inlet pipes after the compressor because the gauge isn't seeing any vacuum or positive pressure. I assumed that the before situation was normal with the vacuum at idle and 1.5bar on boost. I didn't think about antilag and I don't fully understand how antilag works, but would I be right in thinking it could have no vacuum and even positive manifold pressure at idle?? Also, now that I think about it, on a normal car if the boost gauge was plumbed into the inlet manifold, you would still see vacuum at idle if there was a leaking or blown off inlet hose because the throttle plate would be shut. This was my reason for not saying it was an exhaust leak before the turbo in my first reply as the gauge would still read vacuum. So now the gauge reading zero all the time would make me think the leak was on the inlet manifold somewhere, but then I don't know what effect antilag has on the throttle body, does it keep it open and engine revs are limited by the amount of fuel injected or by severely retarding the spark to when the exhaust valves are open? If so then a leak on the inlet side between compressor and inlet manifold would still be the most obvious cause, but as Splitpin says, without actually looking, it's pretty much guesswork.


Edit: As for the boost solenoid, it is my understanding that all this does is control what pressure the wastegate sees. So if this was not working, then the car would just boost to whatever the wastegate is set to and vacuum would still be present at idle (assuming vacuum at idle is normal). I think anyway, like I said earlier, just my opinion.

 

check the spark plugs allways helps