Massive over boost on tuned JTD 16v - Alfa Romeo Forum
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(Post Link) post #1 of 17 Old 15-09-11 Thread Starter
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Cry Like A Baby Massive over boost on tuned JTD 16v

Well I'm going to go through all the options with you guys and see if I can eliminate the components. A while back I mentiond that the JTD used to overboost occasionally while on track. This would put it into safe mode and I'd have to turn it off and on again to sort it. I could only ever replicate the problem on track and so I never got round to seeing if the problem had been fixed. It used to boost to about 1.8 bar when it did this error. Now the mrs has been driving it for a few weeks as she is too lazy to sort out her own car (thats another story which I will probably rant about at some point) and she said that it went into safe mode the other day. It did it once with me the other week too but as I wasn't expecting it I wasn't looking at the boost gauge. Well today I took the JTD to work and it would seem the problem has got massively worse. Got onto the dual carriageway and on it came as I accelerated up to 70. Pulled over in a layby and switched it off. Pulled out and accelerated and it did it again. So pulled over again to pay attention to the gauge. It's a defi electronic gauge which are known for there accuracy and it measures boost pressure at the beginning of the plenum so I'm confident these figues ar correct. Under hard acceleration it goes off the end of the gauge at 2 bar Then you get the light after a second or too. Trying various things I can't use full throttle for more than a second or it spikes the boost and it seems to be running about 1 bar in 6th at 70mph or partial throttle when it used to be running aroun 0.5-0.7 bar so there is definitely a boost issue at all parts of the rev range. If you drive it at high revs (3.5K+) it overboosts even on partial throttle. Also when trying not to get it to spike the boost which used to bleed at 1.6 bar and stay static ish at 1.6 bar is now all over the place between 1.4 and 1.8 bar. It's like it can't bleed it off in a controlled fashion.

So things I have done in the past.
Changed the VNT hoses
Cleaned the MAP sensor which was clogged.

Possible things I think it could be
Need to clean MAP sensor again
MAP sensor is bust
VNT solenoid ( one on the back of the rad) is not functioning properly
Turbo issues with the vains getting stuck.

The car is remapped, has full turbo back exhaust with no cat and one silencer, egr delete, and high flow filter.

Any suggestions would be appreciated

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Alfa 156 GTA, Q2, Super sprint, CF2, EQ, KW coilovers, Eibach rollbars, Powerflex.
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Hey Joss maybe this time I can help. This happened to me last summer, car all of a suddent began overboosting for no reason once I got to a certain speed. 70mph and it was dead, had to stop and turn it off to reset it but as soon as I would get to 70 again limp mode came on.
It sounds like your turbo is on the way out, I think boosting at 1.8bar is too much for the standard turbo unless you changed it for a more powerful one. Also VNT solenoid could be the problem, along with my tubes being cracked (especially the one that connects to the turbo) my solenoid had a crack running through it so bad readings were coming through. Changed the VNT and problem sorted. If your EGR is off then I would also give the MAP a check - dont think it affects limp mode but it can add to the problems.
Hope this helps Joss or im not talking absolute bo33ocks.

Also as new MAPs for the Alfa arent that cheap for a small piece of plastic, I bought a new Fiat Multipla JTD MAP as they are both the same, but that was the 2.4 156 and the Multiplas MAP was a 1.9 - but they are compatible. Worth checking
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I would have though the MAP must be working OK as it is (correctly) leading the ECU to default to safe mode when your boost is excessive. My MAP sensor was a solid lump of carbon and was still working OK. If I remember correctly the VNT is fairly cheap so might be worth changing if the pipes are OK to rule this out? Cleaning sticky turbo vanes would be a lot more hassle but I suspect is quite likely!

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Also Joss as we were talking yesterday about women flooring turbo cars when they are still cold isnt a great thing and I think this could well be another factor to the issues - not saying thats what caused it but it doesnt help.
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(Post Link) post #5 of 17 Old 15-09-11 Thread Starter
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I didn't think it would be the map and yes 1.8 bar is far too high. It should be 1.6 max on the JTD really. It always used to be. The pipes between the VNT and the turbo are all new as I changed them. I will be changing the solenoid first but aty 164,000 mils on the original turbo it may be time to cash it in.
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There are a couple of guides out there I have seen for how to clean the variable turbo vanes on the JTDs. Obviously, you'd have to take the turbo off first but from what I have seen its not a particularly tricky job.

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(Post Link) post #7 of 17 Old 15-09-11 Thread Starter
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Quote:
Originally Posted by gammakeith View Post
There are a couple of guides out there I have seen for how to clean the variable turbo vanes on the JTDs. Obviously, you'd have to take the turbo off first but from what I have seen its not a particularly tricky job.

Keith
Yeah I thought about this. If I can rebuild an engine then why not a turbo
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Can i bring my car to you then Joss
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(Post Link) post #9 of 17 Old 15-09-11 Thread Starter
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Originally Posted by bear1 View Post
Can i bring my car to you then Joss
if you trust me
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Pff more than my previous mechanic
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(Post Link) post #11 of 17 Old 15-09-11 Thread Starter
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that doesn't say much bear
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Considering Ive never met you, I think its a nice compliment for the day
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Considering Ive never met you, I think its a nice compliment for the day
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Does seem like the vanes are sticking.

One thing to try first would be to un-cap the EGR valve and see if it makes any difference to your symptoms. Do you have a working EGR valve you can try on it?
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Originally Posted by Pud237 View Post
Does seem like the vanes are sticking.

One thing to try first would be to un-cap the EGR valve and see if it makes any difference to your symptoms. Do you have a working EGR valve you can try on it?
I can borrow one of a friends. I am going to borrow one of the VNT solenoids too, just to try but surely if the problem has only really just developed and the EGR has been blocked for over a year with no real problems would it really be the cause now.
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Unfortunately the most likely cause is the turbo; you may be lucky and it's just the vanes that are sticking. More likely however is that the turbine wheel and/or the vanes are damaged.
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Managed to fix it tonight. Borrowed a spare solenoid from a mate and plugged it in just to rule it out before i dismantled the turbo. guess what. No overboost. Runs up to about 1.6/7 bar and levels off. Perfect even under hard prolonged load. Thank god for that eh lucky boy eh. Was sure it was going to be the turbo!
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