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Rb25Det Troubleshooting, Lots Of Info And Video, Help Needed

Traah221

By Traah221,
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Traah221

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Here's my information so far, trying to be as thorough as possible. The engine idles fine, and runs perfect until around 2000-2500 rpms only, then, regardless of load on the engine, (video done at idle), it completely cuts power, it feels like all 6 cylinders shut off instantly. Now, the car stays running, the RPMs will drop down past that tiny threshold and the engine will fire once more, kill itself, and repeat. It feels and sounds like a Rev limiter set at 2500 RPMs. That's a guarantee in any gear, but at the higher gears (I have to limp around only for work, try to keep it parked as much as possible), the engine will break up with any load that causes me to hit useable boost.

The major change I had done immediately before, most likely causing this to happen, was I had finally gotten around to fabricating in the VCT solenoid, as I had been running without this whole time. My theory is that, with the ECU now switching my cams for low-end responsiveness, a problem that hasn't been readily apparent is now rearing its ugly head. It's time to start slowly diagnosing, but thankfully I am faily certain the fuel system is not to blame, nor is it my spark, since I have done much work in both areas. This narrows it down to air, but what could possibly be causing this bad of a problem in terms of my air system?

Full list of broken down information:

1994 RB25DET S1 swapped into my 1992 R32 GTS-t Type M.

No modifications to the engine yet, running stock ECU on stock boost, used RB20DET Harness with injector plug swap method.

Troubleshooting steps performed so far:

-New Spark plugs, Gapped to 0.8mm, BCPR6ES
-Taped/sealed coil packs, strong spark on all cylinders
-New Walbro 255 pump, hardwired in via SAU's writeup, No fuel pressure check though, can't find anywhere with gauge immediately
-New fuel filter
-Replaced FPR with one from known running RB25DET

-Took off and cleaned AAC, helped with an idle hunting issue, but not this particular one

-Cleaned MAF, shows signs of wear on the filament though, considering replacing

-Compression checked at 154+ PSI, all cylinders

Link to a video of the described symptoms:

http://www.youtube.com/watch?v=e3IofvhHqsw

The zoom in on the piping by the turbo was because, just for a bit, I thought I could hear a whistling indicating a huge vacuum leak. When the engine is shut off, I can hear a very audible release of air from somewhere near my Turbo. Possible major vacuum leak? Strangest symptoms I've ever seen for one, but I haven't seen it all so I don't know, frankly.

Any tips much appreciated.

Traah221 Contributor

Traah221

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Update:

I forgot to mention that yes, superben, I already tried disconnecting the VCT, but no change. Something tripped when it was turned on, but wasn't being held on by the VCT.

As for my Air systems now, I have checked every vacuum line and my IC Piping all the way through for leaks, and I found two probable causes for an improperly running engine, and after fixing them, she runs beautifully now, aside from the ECU cut. First, my external wastegate was impossible to move by hand, and even when removed, getting a good solid grip and really yanking it, it barely moved, and no air puffed out to indicate the flange working like it should. Replaced with new wastegate, much better. Next problem found was by pulling my turbo, and seeing my gasket in terrible condition. One side was completely separated, as well as one entire corner missing, so replaced with new gasket, and my engine bay is much quieter and smoother than what was heard in the video. Lastly, when putting it all back together, I started it up to find no change in the ECU cut issue, BUT, I also saw my MAF was completely unplugged. So, I plugged it in, and to my surprise, no change. Strange way to find the fault, but I now know, despite my cleaning, my MAF is not functioning at all. Side question, is it possible to wire in an RB25 S2 MAF for my S1? Since the pins are different?

Edited by Traah221
Traah221 Contributor

Traah221

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Here's the public solution in case anyone else stumbles upon this issue.

So, I fixed the issue earlier today and took her for a quick spin. I found a replacement J60 AFM, and it was almost new, plugged it in but there was no change. I checked Voltage with the car running and got 12V, and two grounds, so I knew power wasn't an issue. Ran a continuity check from my AFM signal to the ECU, and got lots of resistance, so I tracked the wire down and found it had fused itself to one of my grounds in that protective sleeve. Bypassed it, ran a signal straight to my ECU, and it runs beautifully. No signal meant ECU in Limp mode.

AFM Wiring for a J60 (RB20 and RB25 S1), here's what you should see:

Black/White - 12V

Black/Silver Tag - Ground

White - Ground

Black - Signal to ECU. Check continuity to Pin 27 of the ECU. If any resistance, fix/replace wire, and voila, Limp Mode problem solved.

gotRICE? Veteran

gotRICE?

Posted
Posted

As soon as i started reading this i was thinking it sounded like an AFM issue.

Well done on tracing the issue! Electrical gremlins are a nightmare to find.

I have a circuit in my R33 thats not outputting the full 12v it should. Had multiple things failing on me untill i figured it out. Boost control, fuelpump, CAS, idle control.. lol.

  • 2 weeks later...
Traah221 Contributor

Traah221

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Haha, I agree completely gotRICE. Electrical gremlins, especially in a wiring job done yourself in your room through a series of wiring diagrams is just a nightmare.

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