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RB25DET NEO conversion; limp mode

3900 Views 6 Replies 2 Participants Last post by  Sagaris
Hi guys,

Have been researching for days about this issue, but to no avail. Sorry for the wall of text, it is my attempt at being thorough!

I have recently dropped a RB25DET NEO (Stagea version) in to my R32.

Quick run down:
NEO loom - have had an auto electrician add required plugs for R32 (Window wiper motor, couple of plugs inside car).
Factory NEO ECU
Everything on engine is factory

The problem I am facing is as below:

Got car running great, had it idling and revving fine for a few days in the garage; just letting it run and looking for leaks etc. This was all good.

Decided it was time to test drive the car, took it up the road and was running great. Brought the car back in, idled it down for a good 10 - 15 minutes and turned it off.

Later that day I couldn't resist a second drive, so went and started it up and it wouldn't rev past 2500 (may be higher or lower, tachometer is not calibrated correctly).

This seems to be limp mode.

Usually this would point me at the AFM having issues. Have tested the AFM in all ways imaginable and this seems to be fine. Swapped with known-working AFM, tested AFM in other car, tested voltage on AFM plug, stalls when blocking AFM sensor (not blocking airflow, just the sensor itself), varying airflow over sensor changes idle (i.e. blowing in to it etc); these are all fine.

Have run over intercooler piping and cannot find any leaks. Have had this happen to me on another engine so was a early thing to check.

I think factory recirculation valve is hooked up correctly.

Pulling any coil packs while car running makes a very noticeable difference, so do not think these are an issue.

Gone over all plugs on engine and removed and replugged these.

One curious thing I have noticed is the reference signal wire on the TPS is reading at 2.2v, I would expect this to read 5v? The same pin on the ECU (Pin 48 in this case, "Power supply for TPS, refrigerant pressure sensor and turbo pressure sensor) is also reading 2.2v. Unplugging all sensors on this "line", or pin, does not do anything.

I seem to be unable to check ECU fault codes - ECU LED does not flash, consult port in fuse box on drivers side doesn't seem to be hooked up, and check engine light doesn't seem to flash any codes after bridging RX & TX pins directly on ECU.

If anybody has any further ideas, I would appreciate it!
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Did you check the grounds? I work on Hondas a lot, and a single ground will cause mahoossive problems...
I would get a consult port reader. No point in pulling your hair out, if you can do it the easy way. Or ask any fellow Nissan owner, if he has a computer to test? Maybe at shop down the road?
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