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Rpm / Load Cut At 3000 - 4000 On Rb25Det

guricha

By guricha,
in Engines & Forced Induction

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guricha

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Hi guys

I have really strange problem on my car, was searching for answers through Google but found only questions.

Here is the deal:

I bought R34 with RB20DE and manual gear box,

engine was swapped with RB25DET from R33 series one

wiring i didnot change coz i had no wiring loom from r33 with ABS so i decide to adapt R34 wiring to R33 engine, was needed some adaptation especially with cas and few more sensors

ecu is used from R34 gtt with nistune board inside

Car has the problem, during the acceleration with load it has fuel or load cut at 3000-4000 rpm, cut mostly looks like RPM limit

Dont know where to find problem, change everything few sensors maf even fuel pump, took the car on dyno to measure boost and its standard, i mean car cuts at 5 psi of boost, boost leaks, spark plugs, gap and timing, all this procedure i have done but no success

Maybe anyone had similar problem during the swapping rb?

only thing i have left is change cas, they are different type on r34 and r33 s1, that will be hard and easiest is to change wiring to r33 and run on Z32 ECU, but am not sure that this can help, found over the net same problems and nobody writes how they fix the problem or what was the reason

Ah and yes cuts at different rpm depending how the ignition is set

thanks in advanced and looking for some help

GTSBoy Grand Master

GTSBoy

Posted
Posted

If you are running more than standard boost then it is possible that you are bumping up against a funny problem caused by not having ABS/TCS stuff installed. What the Nistune guys have worked out is that when the R34 ECu does no see the TCS equipment, it causes a strange cut, exactly as you describe. Not at stock boost levels, but definitely happens once you wind it up a bit.

They have tried changing to Stagea bin files to get around the problem, because Stageas do not have TCS, and that solves the problem. But it is not a good solution, because Stageas are all auto, and the auto images do not run a manual car very well. I have tried it. Even after changing every map and switch in the Stagea auto image to be the same as the manual R34 image, my car had drivability issues. The trouble is that Nistune only gives you access to about 1/3 of all the stuff inside the ECU, and we simply do not know what the majority of the rest of it does. There must be differences between the autos and manuals hiding inside the dark matter part of the ECU that you can't change.

My suggested solution is to go into the DTC flags section of Nistune, I think what you want is in DTC Flags 1 and DTC Flags 4, and switch off the TCS flags. There are 3 of them. I do not know if this will actually solve your problem, because it is really just masking the fault code, not fixing the problem, but it is worth a try.

If that fails, you could always try getting the ECU reprogrammed with the Stagea image and see if you can live with the little drivability problems.

guricha Collaborator

guricha

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Posted (edited)

I already change maf to Z32 and fuel pump is 044, as i mentioned boost is the standard and dyno showed somewhere 5 psi at the moment of cutting

DTC flags i already play with :) i think disable or enable them is only giving that errors not comes up and that is all

Really strange thing is that car runs at really lean unless i dont play with Constant , it should not be! after changing the Maf constant goes from 3xx to 560 and that value is terrible lean unless i dont go to 640 to make at idle close to 14.1 -5

Also as soon i will go from neutral to any gear car goes to knock Map

what about cas? if its wired right should it have this issue anyway ? maybe the signal is different voltage ?

On S1 is mitsubishi cas system and on later one is Hitachi, i have checked cas discos and there is almost no difference, anyway some guys have succeed same swaps with no issue, but looking at google i found threads where people got this issue on stock car but couldn't find reason

Edited by guricha

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