RPM Trigger Fault with Microtech LTX12S and 1JZ

[Danners]

Hi Guys,

I come to you in a last ditch effort in assistance to get my car running and back from the tuning shop.

A very quick overview of my problem is that I had my original 1JZ running and tuned with the Microtech ECU. The engine eventually carked it and i decided to get a 2nd hand engine, swap all the good bits over and took the car down to my local tuner for a tune and start using it again as my daily driver.

The first problem encountered by my tuner ended up being a dud cam sensor on the new engine which was fixed by giving him the sensors from the old motor. Now that the new sensors are in the car starts and idles perfectly until revved to about 2K. At 2K the engine appears to hit a kind of soft rev limit and starts misfiring slightly. The computer throws up an RPM trigger fault when this occurs. You are able to continue revving through this bad spot, the problem goes away and it will continue to rev freely onwards and upwards. Returning to 2K revs and the problem returns instantly.

My tuner is mystified by this error and has done all sorts of things with the ECU, changed leads, tried removing the MAP sensor from the equation and relying completely on TPS. Incidentally I swap the entire plenum from the old engine to the new, so all associated sensors etc are all off the old engine. The old engine died from running lean on 1 cylinder and i'm fairly confident that the sensors in use from the old engine are OK, obviously the new engine sensors are dubious because the cam sensor was DOA, who knows what else.

I took the crank angle sensor off the old engine and gave that to him as well just in case this was the problem, and also gave him the instructions on how to measure the crank sensors effectiveness through a multimeter resistance setting (from the 2JZ engine manual) He hasn't tested this yet.

I'm hoping that there are some Microtech nuts on here that are able to provide some suggestions as we're getting down to replacing some expensive parts on the engine that may or may not be the problem, leaving an even bigger hole in my wallet

Thanks in advance for your comments

[YLD-16L]

Very strange Dan, I had the exact same symptoms of ~2000rpm miss on a 4A with a Microtech, ended up being an ECU issue and had to go back. When returned it worked fine.

Yours is odd though that it was fine on the previous engine and now is an issue.

If the crank and cam sensors come up fine in testing I'd point the finger at the ECU, even though it doesn't make a great deal of sense.

[Danners]

Very strange Dan, I had the exact same symptoms of ~2000rpm miss on a 4A with a Microtech, ended up being an ECU issue and had to go back. When returned it worked fine.

Yours is odd though that it was fine on the previous engine and now is an issue.

If the crank and cam sensors come up fine in testing I'd point the finger at the ECU, even though it doesn't make a great deal of sense.

Its interesting you say that. When I first got the Microtech put in I went to drive it out of the lot and it was borked. ECU was sent away and came back fine. It ran well for about a year before the engine bit the dust.

I wonder if its dead ECU round two? Possibly even the cause of the engine dying... never found out what happened.

[YLD-16L]

Its interesting you say that. When I first got the Microtech put in I went to drive it out of the lot and it was borked. ECU was sent away and came back fine. It ran well for about a year before the engine bit the dust.

I wonder if its dead ECU round two? Possibly even the cause of the engine dying... never found out what happened.

May be worth send it back to be bench tested?

Be very frustrating to kill another engine.

Funnily enough I have an LTX12S with them at the moment off a 1J, second time it's been back. First was because the ignition wouldn't work at all, came back and started first turn of the key. Now it has a few functions not working and a couple of odd issues.

No doubt like the first time it went back it'll be returned with a note stating nothing was wrong with it.

[Danners]

May be worth send it back to be bench tested?

Be very frustrating to kill another engine.

Funnily enough I have an LTX12S with them at the moment off a 1J, second time it's been back. First was because the ignition wouldn't work at all, came back and started first turn of the key. Now it has a few functions not working and a couple of odd issues.

No doubt like the first time it went back it'll be returned with a note stating nothing was wrong with it.

The car has been sitting on its fat arse for the last 6 months, so it certainly wouldn't hurt!

I'm starting to regret getting this computer... everyone i speak to has had a dead one! Someone on Supraforums has told me that his crank angle sensor wiring was in backwards and caused an identical error to mine which is hopefully something else to try!

Thanks again for your comments, keep em rolling! i'm desperate!

[Draven]

Someone on Supraforums has told me that his crank angle sensor wiring was in backwards and caused an identical error to mine which is hopefully something else to try!

I had this issue on my old 1jz ma61 with the LTX12 (old school, not the new one). Turns out their wiring diagrams for the 1jz were wrong. messed around with cam/crank sensor wiring until it worked perfectly... but if you're plug and playing from a known working engine, I can't see how this could be the issue.

And yeah, you chose the wrong ECU bang for buck tho.

[midnight_purple_GA70]

ok sorry to dig up an old thread... but Danners did you end up solving this problem?
mates car ive recently installed an LT16 into is showing the same problem as you describe...

idles fine
2k rpm triggers RPM warning light
beyond 2k rpm seems to rev fine

was it just the crank sensor wires or something?

[CrUZida]

Crank angle sensor is wired backwards.

been there, done that.

[midnight_purple_GA70]

Crank angle sensor is wired backwards.

been there, done that.

hmmm ive had that before and its made the car not wish to rev properly but this example seems to rev fine... but that is on my list of things to try switching round the other way...

Ill be a happy man if thats all

[Draven]

hang on, so the *only* issue is an RPM error at 2k rpm?

no performance symptoms?

[midnight_purple_GA70]

hang on, so the *only* issue is an RPM error at 2k rpm?

no performance symptoms?

well unsure as the car is not yet tuned so not sure if other issues will arise in tuning
in other cars when the cas wires have been wrong it has also thrown home or ref errors with the rpm error.

But it appears to idle fine and rev fine but around 2k the rpm warning is triggered

[CrUZida]

With mine (it happened somewhere between 3500 and 4000, can't remember) you can hear it easily, but the Microtech guages showed nothing wrong (did get the error though)

But you put a timing light on it, and the timing dropped back to the static figure (10deg), from where it should have been (mid 20's) when it reached the critical RPM value.
If you held it at that value you could see it dancing between 10deg and (say) 25deg. Obviously there was a serious performance loss for me (4000rpm @ 10deg = SFA).

With wiring the crank and 2 cam sensors, from memory there was 4 possibilities of wiring them all forwards/backwards, one of each etc etc.
With 2 combinations, she wouldn't start.
With the other 2 she'd start and run fine, but one gave this error, the other was perfect.

[Draven]

and only one of the cam sensors actually needs to be hooked up, hence the 4 possibilities (2x2) - just leave the rear cam sensor disconnected

[midnight_purple_GA70]

was crank sensor wires round the wrong way thanks guys

[CrUZida]

Ah yes, only 1 cam sensor, I knew there was a reason why it was only 4