1jz intermittant fuel/boost cut, whats the cause?

**Bowlsclubboy** · 28-01-2007, 07:26 PM

Sorry for the essay in advance

Hey guys, had my 1jz cressy out at winton today for the fun day, it went like a freightrain for about 2 laps, after that it would have some strange cut (no power at all) out that only happened at around 2500 and as the car started to boost, after this if i keep driving it off the limiter it will come good within a few corners but then start the same shit in about a half lap.

I have a greddy copy BCC which i set at several different points on the potentiometer to no avail.
I also have a greddy SCC and a defi tacho which is just spliced into the tacho signal near the ECU.

Its hard to explain the entire story but the car was working fine until i decided to strip out the heaterbox and basically everything on the dash except for the cluster itself. When i plugged in all the underdash plugs that i could, i found that even when stationary the car would not rev past 2500rpm and it was like hitting a brick wall. I started removing plugs and playing with my BCC before finding that the only way to make it rev again was to disconnect whatever plug (on the left hand side of the dash near the ECU), makes the digital dash turn on. I read something on the MKIII american forums that 1jzs need an RPM signal to be working properly otherwise they have a 2500rpm cut?
So then after resetting my BCC back to the right spot the car run fine again

My BCC wires are plugged into the ECU using crimps...i know, shoot me but i wanted it to be removable and i tried pushing and prodding the connections to make sure they were working. Should i redo it all to make sure?

Umm, oh and it makes boost in neutral when i rev her up....this isnt normal is it lol...

Thanks in advance to anyone who reads this (and replys for that matter)

Cheers,

Troy

**Wildsupra** · 28-01-2007, 07:33 PM

check that ya map sensor hose hasnt come off.

is it blowing a crap load of black smoke on idle?

Matty

**Bowlsclubboy** · 28-01-2007, 09:01 PM

Checked map hose, seems fine unless its somehow cracked under the factory sheath that it has over it, but its not cracked at either end.

The car has always been fairly smokey (plus i run no cat) so i cant really say if it is blowing any more than usual.

Thanks mate

**Norbie** · 29-01-2007, 11:17 AM

Originally Posted by Bowlsclubboy

Umm, oh and it makes boost in neutral when i rev her up....this isnt normal is it lol...

That's far from normal. It sounds like your ECU is in limp-home mode - have you checked for error codes?

**Bowlsclubboy** · 29-01-2007, 12:04 PM

I would have tried that but the car doesnt agree with me when i plug the dash in lol
Its also an auto ECU so the OD light flashes anyway.

I think i may have to pull all the add on shit off and start from scratch then keep adding them till it happens again. The only problem is that the problem only rears its head when i flog the car for about 2 laps. I seriously suspect it to be my ECU wiring :/

If it was in limp mode that would happen constantly until i reset the ECU wouldnt it? The problem goes away after i get off the gas for a bit...i'm as confused as you

Thanks Norbie

**Bowlsclubboy** · 29-01-2007, 10:24 PM

I read a few topics on here and it threw up the possibility of coil failure due to heat...thats the only way i can explain the intermittant nature of it?

I thought that if maybe 2 coils were failing it wouldnt stop the car from boosting/making a bit of power but my problem feels much like boost cut where i have nothing.

**Soarer_D00D** · 29-01-2007, 11:11 PM

If the coils were failing, that still doesnt explain the whole Boosting in neutral thing.
Check for error codes on the ECU. Try reseting the ECU and see if that helps (Pull power cable off battery for 30secs/reconnect)

**Bowlsclubboy** · 30-01-2007, 09:57 PM

ECU gets reset a fair bit actually

i have a cutoff switch so i dont flatten my piddly little odyssee battery.

Checked over all the wiring of the addon bits, its all as it should be. I plugged in the plug that makes my digital dash turn on (i know that sounds technical) and the TURBO light is constantly on....does this mean the map sensor is confused and thinks boost is being made? As i said before when the dash is plugged in the car will not rev at all, its just a dead cut.

All that this problem can be is something do do with removing the climate control air boxes and everything from the dash except the bare essentials, anyone else experienced this when they were silly enough to strip out their perfectly good cars? I say this because nothing else has changed to make this problem happen.

I know i sound like an absolute newbie here guys and im sorry lol. There is also a grey plug in the drivers side kickpanel which is in the top right of the panel above 2 or 3 white ones, this has nothing going to it, should it have?

Thanks again

**YelloRolla** · 31-01-2007, 12:42 AM

Boosting in neutral sounds like either it is missing spark - causing raw fuel to dump into the exhaust manifold (thus creating boost) or the spark is very retarded - burning the mixture very late and causing excess exhaust heat (again creating boost).
What may cause either condition I am not sure - possibly coils, wiring, but you are looking at these items already.

**Merudo** · 31-01-2007, 12:54 AM

Originally Posted by Soarer_D00D

If the coils were failing, that still doesnt explain the whole Boosting in neutral thing.
Check for error codes on the ECU. Try reseting the ECU and see if that helps (Pull power cable off battery for 30secs/reconnect)

another way is to pull the EFI fuse?? if you don't want to disconnect your battery.

Boosting in neutral eh... just tell people you have an antilag setup?