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Discussion Starter #1
I think after reviewing the advice that members have given me on this forum the most likely cause of the limp mode on my 05 STS 3.0 Di is overboosting. I have not yet fitted a Boost guage or EGT guage, but will down the track. Having read the recent issue of 4WD action it states if it happens occasioinaly its ok, if it happens regularly get it checked by a professional. It happens on mine everytime i accelerate over 80kph up hill, my question is what problems could this have caused internally so far? Having only done 2000kms since i bought it, what if the problem has been there for the last 108,000? If i fix it now and it stops great. But what damage could have already been caused and what can i do to make sure i'm not just throwing a band aid on the problem? I'm happy to take it to a pro, if i can find one in Adelaide!
 

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If it's like an early ZD then it's already got a cracked head and pistons. I'd check the MAF voltage before worrying about overboosting.
 

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Discussion Starter #3
Have been told MAF is fine, had accelerator assembly, throttle position sensor replaced aswell. All signs point to overboosting. Not sure if I'm imagining it but also seems to be lacking some power climbing aswell.
 

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You could check the vane actuator rod on the turbo to see if it's sticking. I replaced a turbo on one once before because it was sticking and not boosting. Yours might be over/ under boosting for the same reason. It might be a good idea to fit a boost gauge just incase you are worrying for nothing as the boost might be fine. Has anyone checked the ECU for codes?
Atleast your ZD runs, so you're one step ahead of mine.
 

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Discussion Starter #5
Going to fit boost guage after Easter break and watch it while problem occurs. On the upside atleast i know i dont have to drive far to have the problem occur............!
 

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I get people coming in from all over the place with the same problem. All the other shops have 'tested' the MAF and determined that its fine etc..

The problem is, how do they test it?
Do they have a flow bench they put an exact amount of air through and measure what voltage its reading?

Nope. They put a multi meter on it and rev the engine a few times... Yep voltage is moving maf is fine.

So the answer is no, you cant test if its reading properly or not. And if you have been charged for this, well shame on them.

The only way to know for sure is to put it on the dyno. Measure the Power/Torque/AFR/Boost the engine is running and compare it against a known good car.
 

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As some have said above, overboost shouldn't cause damage in its self. The fact it goes into limp mode means its self protecting. Overboosting as i understand it is mostly excessively fast spool-up rather than an excessive pressure spike. The ECU thinks its going to see massive boost so cut fuel to generate limp. I've seen my boost gauge occasionally hit 25psi without initiating limp mode or causing damage.

Hope you find the cause soon.

Grogey
 

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As others have said, it’s very unlikely that there will be any damage from over boosting in your case because it’s going into limp mode before boost gets too high. It’s when the ECU doesn’t go into limp and you blow off or split intercooler hoses that you may have done damage. I’m saying 30psi plus could be detrimental, but you’re ECU is cutting power as it should before it gets dangerously high.

Over boosting doesn’t necessarily mean excessively high boost either, but it may just be that your boost is going outside the ECU’s boost parameters at that engine speed and throttle position. I can put my car into limp at 16psi if it’s below 3000rpm at full throttle for more than a few seconds. Above 3000rpm and there’s no problems with higher boost.
 
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