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GTB Boost issues?


GravelBen

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So after 1.5 years trouble free the GTB (standard 2002 Rev-D E-tune, manual) seems to have started misbehaving this weekend. Basic symptoms for diagnosis:

Secondary turbo doesn't seem to be doing much at all - you can't feel it kick in until ~5500 rpm (after huuuge vod when its usually vod-free) and when it does its much weaker than usual.

Primary turbo still seems to be boosting but feels a bit laggy, much less responsive than usual.

Net result = bugger all torque and feels really flat above ~4k rpm. In other words, no fun.

I did fill it with 95 recently (no 98), had been just pottering round town and cruising open road for half tank then a quick squirt passing was when I first noticed it felt flat. Back to 98 in it now tho and no change, it really feels like a boost problem rather than retarded timing.

Had a quick look for loose vacuum hoses etc but couldn't see anything obvious. Actuator on secondary is quite oily so possibly gunged up? Otherwise not really sure where to look first, I obviously don't know the sequential system well enough!

Any ideas or suggestions for things to check?

PS if anyone tells me to go single they get a virtual slap around the ear, I like the twins!

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 boostin said:

Sounds like a failing AFM to me.

Interesting, had a MAF go on old BG5 TSR with completely different symptoms but I guess they can be strange things at times. Is there a way to check fault codes on the denso ECU? I heard the old black plug technique is only for the older ones.

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Guest boostin

The black plug trick still works, but it tells you which number fault code it is in a list, and I don't know what the list is. When Spotme's air/fuel ratio sensor went it gave 13 flashes, meaning the 13th code on the list. The actual fault code using the Select Monitor was P0031. So in short they work differently. You'll need to get it scanned, but most probably there won't be a fault code.

Do you know anyone else with a Rev D turbo?? See if you can borrow their AFM to try.

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Further testing:

Wiggled and poked a few things, tightened hose clamps, unplugged and replugged AFM.

Took it for a squirt and it was back to full beans at first, but following that one out of every ~3 or 4 'exercises' seems to reproduce the symptoms.

The inconsistency makes me inclined to think you're right about AFM, though it could possibly just be one of its wires or connections? Car often spends plenty of time on gravel for things to get shaken around.

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Tightened hoses (and spent a lot of time retrieving the spanner I dropped down between turbo and IC doh), replaced dirty air filter, no improvement. Maybe it is the AFM :( Anyone in southland have one I can swap in briefly to check it?

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sames as what i had. Sometimes it would boost hard, and sometimes nothing on the secondary at all. Tracked it down to a loose hose clamp. Might be a split in some of the intake hosing somewhere?

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  • 4 weeks later...

Got a mechanic who knows Subarus pretty well (builds and races them) to have a look at it. He reckons it won't be MAF or an air leak as it still idles and runs smooth as anything. Is only giving 7psi boost which apparently is spring pressure so he reckons the boost control isn't working. Even tried swapping in a different ECU which didn't fix it.

Quite puzzling really, his advice was to install an aftermarket boost controller.

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Was just wondering about that actually, will try it tomorrow. Can you properly reset a denso just by disconnecting the battery for 20min? I remember reading something about having to use the green plugs under the dash, must be time for some googling...

Hmm this article says it has to be done via OBD:

http://www.scoobypedia.co.uk/index.php/Knowledge/ECUReset#toc2

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Thinking some more, if swapping in a different ECU didn't solve the problem then I doubt resetting it would either (assuming I'm correct in thinking boost control is handled by the ECU not a separate module), and it may point toward a faulty sensor of some sort - so what sensor would cause it to cut boost without messing up mixtures etc - MAP maybe?

I think what I might have to do is track down an OBD cable and software to have a look into the ECU, no codes flash via the check engine light but the more I read about the newage ECUs the less I think that means. :-X

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Guest boostin

AFAIK it has to be reset via the OBDII port. The battery method definitely doesn't work. Not sure about the green plugs.

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  • 3 weeks later...

Got ECU scanned today, no codes (as I thought) and no sensors showing any obviously unusual signals. Bloke there thought another possibility could be a turbo on the way out, but they're not making any unusual noise and I don't know how likely that is on a regularly serviced, well treated car with 82k on the clock.

So the puzzle continues...

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 GravelBen said:

Black plugs just give constant flashing so no codes I guess.

Long flashes have a numbers value of ten

Short flashes have a numbers value of one.

eg,if it flashes TWO long then TWO short then its a fault code 22,which is faulty AFM.

Hope this helps...

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