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Overboosting Problem

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I've been getting an overboost problem when on high boost with my RB26. Max boost should be 1.5 bar but its going over this up to 1.8bar and then the map pressure limit cuts the engine.

Not sure what is causing it, it never used to do this so something has changed. The duty cycle should be correct because it used to work fine and I've not altered anything, the Mac valve I assume is still working fine because when on low boost setting it has no problems holding 1 bar. It also does not seem to do this every time but it has been getting more frequent making me think its wiring, but wiring is all brand new Tefzel wiring and all properly crimped and I can find no issues with it.

Running RB26 in 260Z with Link G4+ Xtreme ECU. I have attached my map and a short datalog showing the issue. If you follow the MAP trace you can see where its reaching above 1.5 bar before the ECU cuts the power.

Any ideas?

Attached Files
  • 260Z-RB26-MapFinal-September-2015.pclr
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  • Log-2015-10-16-20528-pm-High-Boost-problem.llg
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

Hi Ian,

Was the map only done in September?

Your boost control is only controlled in open loop and with the colder weather we're having in the UK it's a lot denser meaning that a fixed duty cycle will produce more boost, it'll be able to control the low setting as the turbo isn't 'running away'.

It'll need either calibrated into closed loop to allow the ECU to correct for boost errors or a correction added in the IAT table to pull the boost back when it's so cold, 20oC is a massive difference from the temperature it would have been reaching in September as it was so mild.

if ur afrs are correct its very lean too on boost , as said the cold weather will affect bost levels u need to get ur iat compensation table ajusted

Just looked over your log/map again Chris is right, the fuelling is running lean on high boost, it is mapped in 4D (check the webinar below) your main fuel control is done via throttle position, the fact that you are likely going beyond the mapped area with colder charge temps means it'll likely not have the fuel consideration to cover it


Thanks for the replys.

It wasn't mapped in September (I just re saved it then after altering the cold rpm limit) It was mapped in March and it was late at night so was pretty cold. Therfore I don't believe temp differences are to blame.

Thanks for pointing out the AFR's, I hadn't actually noticed before but thats not good, Was tuned by Greg @ ProTuner so I'm sure it would have been set right, he knows what he is doing. Also didn't realise it was only set with open loop until now, I'll have to ask Greg why. Even though it was mapped in March I work offshore so I've only had it on the road about 6 weeks since then otherwise I'd have it more sorted.

I'm aware of the 4D Table, I set up the base map for this but thats as far as my skill goes.

Unfortunately it will be along time before my car is out again due to work and training next year but I prefer to work out solutions before I get it out so I limit the amount of driving time I loose.

I'm pretty sure ur not a million miles from me Ian if u want a hand or want me to get a look over it with you I would be happy to help out ,

Iive never mapped in 4d but the 4d table looks odd to me as there's very little going on in it , but if it works it works

So you're in NI?

Thanks for the offer, unfortunately I won't have the car out again until around August and September time as on my next leave will be spent training and studying (it sucks, but it has to be done) If I'm still stuck at that point then I'd certainly appreciate someone to look over it.

The fuelling should be easy to sort, just need to check the accuracy of my wideband first to confirm figures are all correct. I guess since its on boost its running lean then its going to have to be the 4D table that the adjustment is made from.

I also think the 4D table looks a little empty and unless I'm reading it wrong it seems to be taking fuel out at high boost?

Yeah man I'm from co down (ballygowan) I'm happy to help at some point if needed man , yeah that was my thoughts too on the 4d map , edit once u watch the webanar it becomes clear why the 4d table is pretty empty .

Once you watch the webinar you'll understand. you'll need to expand your open loop AFR axis and your 4D table axis to cover the extra boost.

If it's not map related I'd look at a punctured actuator hose, it won't be a big split as you've still got boost control on low boost

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