variable boost with IHI

[stewbie55]

I've noticed for a little while now that I seem to get inconsistent levels of boost when holding max (or near max throttle).

On a good day it will spike to 1.55 bar and pretty much hold that steady to near the rev limiter (well maybe drop to just under 1.5bar). At other times it will spike to 1.5ish but then almost instantly drop to 1.3bar and wont rise again even if the throttle is buried. Othertimes I get somewhere in between these two states.

There doesn't seem to be any obvious reason for this and it can do either of these things on consecutive pulls it would seem so I don't think it's a boost leak.

My car has the Jabbasport boost controller fitted and I was wondering if it's likely to be the cause of the problem.

I know I could take it to Jabba to look at but was wondering if anyone had any ideas first?

 

[cupra_matt]

Maybe a cracked exhaust housing, common problem, does feel any laggier?

 

[stewbie55]

ooh I hope not but now you mention it it does seem laggier sometimes.
If it is cracked is it in a common place and am I likely to be able to see it without taking everything apart?

 

[ibizacupra]

nope

 

[ryan_s3]

If it's cracked it will be laggy all the time mate.

 

[phil_m]

This is what mine was like when i removed it last year.

 

[dan-ish]

This is what mine was like when i removed it last year.

How come the waste gate hole isn't ported? did Jabba fit it?

 

[phil_m]

No Jabba didn't fit it, why do you say that is it meant to be?

 

[stewbie55]

If it's cracked it will be laggy all the time mate.

In which case I reckon I'm alright then

My thoughts are still that it's a boost control problem - cananyone explain to me how the Jabba Manual boost controller actually operates?

As far as I'm aware I still have the N75 valve fitted and I'm wondering if this could be causing the issue or conflicting with the MBC in some way?

 

[dan-ish]

No Jabba didn't fit it, why do you say that is it meant to be?

Jabba port the wastegate opening and radoius of the inside.

The boost fault sounds more like the N75 to me comon failer

 

[stewbie55]

Well just to update, I eventually got round to fitting a new N75 valve this morning.

Went out for a decent blast and it looks like its fixed
It's holding 1.5 bar now absolutely rock steady, in fact I've never seen it this good since I fitted the boost gauge.

Let's hope it lasts now - I know it seems to be a common failure but should I expect the N75 to be a consumable item and only last x thousand miles??

 

[ibizacupra]

a few of these cropped up as faulty components lately.

 

[stewbie55]

I may have spoken too soon about fixing my problem - or in fact I think I have a second problem

The N75 has definitely improved things and there's no surging now, if I hit 1.5 bar boost then it holds it smoothly. But on a couple of occasions the engine has felt a bit hesistant and in this case will only hit 1.2 or 1.3 bar. It seems to me that the hesitation is either a slight misfire or ignition timing pulled right back, if it does this then it lasts for the duration of my journey but is normally OK next time I use the car.

As I'm still on my original plugs I'm going to change these anyway (probably go for denso IK22's) and I'll check the coilpacks look OK when I do this. If it's not this then any other ideas???

 

[h17och]

you cant tell if a coil pak is ok by looking at it, unless its snapped in half like ive seen before.

as for the problem, i would do some logs as see what goin on

 

[ibizacupra]

plugs possibly.. more likely misfire related issues with these than variable boost.

boost controller? N75?

worst case considering VF34 is exhaust housing damage from overheat/lean conditions

 

[stewbie55]

Thanks for the replies, I'm still hoping it's not the exhaust housing.

I've ordered the plugs so hopefully will get to fit them at the weekend, I'm hoping when I remove the old plugs I might be able to see if one cylinder has been misfiring, though if its only slight I guess it wont look much different?
The odd thing is that since changing the N75 its generally been spot on, but driving home last night it was holding back.

I have sometimes had some jerkiness after starting on cold/damp mornings which has been noticeable again with the cold weather the last couple of days. I'm guessing this could be a coilpack on its last legs.

 

[stewbie55]

Just thinking whilst I'm waiting for my plugs...

If it's my exhasust housing that is cracked, can this part replaced separately from the turbo core, as Jabba list it as two separate items? If so then it won't be too expensive.

Presumably it is relatively straightforward to remove the down pipe to check with the turbo in situ?

 

[pj1985]

Dont know about leon but removing the dp from the ibiza is a pita. Being able to see a crack in the exhaust housing with the turbo still on the car is not ideal either as you will not be able to see properly and taking the turbo off the mani is even more of a pita! Exhaust housing can be changed but at what cost as new IHI can be had for about £500 and what else has been stressed ie bearings. If it is exhaust housing then you are fixing the problem only for it to happen again unless you find out why it has cracked and remedy that aswell.

 

[Balf2k]

I have Jabba stage 3 IHI conversion LCR also and have had the same problem mate, it has been underperforming for a while, intermittently gives me full boost, sometimes only around 1.1 - 1.2 bar, I finally got to the bottom of it....
The turbo intake pipe (From MAF to turbo) has been modified by Jabba and cut far too short to allow a good overlap of the fabricated metal part that the IHI turbo uses, the hose had come away a little bit at the back (side nearest bulk head), I removed the jubilee clip and the whole TIP, there is absolutely no way I can get it to fight right over the metal pipe fron the turbo the way I would like it to, I just had to push down on the hose as tight as I could (bloody tight) and really crank up the jubilee clip but I basically need to buy a new Forge TIP and cut it longer to allow for a more secure fit as i'm sure this will only work lose again and I hate bodge jobs anyway. Nice one Jabba!
Anyway, once I had the hose back on I have just been out in her and it's fookin' flying, really really fast compared to before, I thought I was just used to the power before and thats why it felt slower but seriously, spool up is quicker / less lag, and it holds boost perfectly, no tailing off like before, I forgot just how hard it tries for traction in 3rd gear. I actually can't wait for the 30 mile drive to work in a few hours. If you haven't done so already then have a look at this area mate, worth a try. hope this helps.

 

[ibizacupra]

good info there Balf