Boost drops at 2500 rpm - JTD 8V

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Boost drops at 2500 rpm - JTD 8V

Postby sike_145 » Tue Sep 27, 2016 9:44 pm


I'm struggling with boost dropping problem around 2500 RPM on my remapped 1.9 JTD 8V 115HP on WOT in 4th and 5th gear. Possible there is same problem in 3rd gear, but RPMs rises too quickly to notice that.

When I floor gas pedal around 2000 RPMs, boost rises and cars pulls wery well, for second...but than it feels that acceleration drops and after second or two (when RPMs go over 2500-2600) acceleration is again OK. Above 3000 RPMs is OK.

I have done many logs and fine tuning of N75 maps, because I suspect that maybe my vanes are too closed so boost rises too quickly at 2000 RPMs, so ECU tries to lower it with opening vanes more that is boost drops. But, as I do many corrections, I can see that if I lower N75 values, thing became worse. So I started to going up with values and I'm now reached original value of 44% at 2500 RPM, but problem still exists, however, it is less noticable than when this value is lower.

In remap I request max about 75 mm3 and 2350 mbar boost. I'm wondering, why is this boost drop happening always at 2500RPMs? It looks like around 2500 RPMs turbo needs more pressure to maintain boost than on lower or upper revs.

Here I attach two logs with two different remaps, only difference is few values at last column in N75 eco and sport map, so you can see what is happaning. Logs are made on same road, in 4th gear, less than hour between runs.

Anyone have any ideas what is happening?
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Re: Boost drops at 2500 rpm - JTD 8V

Postby majsterx » Mon Oct 03, 2016 10:23 am

Oh man, leave software... it's not software issue.
100% mechanical or electro mechanical.
Your turbo overboost so after that boost level droping and again back to level higher. That;s case easy, make stock N75 and then check turbo electo-vaccum steering.

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Re: Boost drops at 2500 rpm - JTD 8V

Postby lyecon » Tue Oct 03, 2017 12:04 am

Interesting coincidence is that such drops are preprogrammed in at least two (three, four?) tables in EDC15C7 in a 1.7 CTDi engine. (Isuzu GM Honda 4EE2), but none of them in this way. Also, the standard injection advance is maximum at 2500 RPM.

The reason is clear and plain as a day. Emission testing is done at 2500 RPM.

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Re: Boost drops at 2500 rpm - JTD 8V

Postby andrecu » Sat Nov 04, 2017 2:06 pm

Hello, nice post, i have the same problem with the same maschine,the z19dt from fiat with 165 eds remapped horsepower.

I order now the kess clone because i changed and tested already almost all the hardware Turbo and 3 different brands of the N75, the dpf and everything else and i dont find the problem.
So it could not be the Hardware in my case.

I made also a lot of trace from the parameters N75, boost, mass, rail pressure with the op com.
But i still cannot find out, which thing failed that my boost is going down after reached 1.5 bar to 1.2 bar if i push the gas pedal at 60-100% between 1750 und 2500 rpm in the 4th 5th 6th gear.

maybe the smoke limiter, i dont know, i hope i will find it with the kess and the titanium.

Maybe i can trace the problem with the titanium?

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