1jz wont rev past ~2500rpm *SOLVED*

[Hydra]

Fresh conversion, running on a pallet before it was shipped to me.

I will double check the fuel damper, you never know what might be wrong. The one thing that doesn't make sense is that the duty cycle on the injectors never goes past 4%

Video might be possible - we'll see what I can do.

[woggin]

i know the ISCV can make the 1jz up to 2.5K, when we unplugged my bros ISCV it just revved then dropped, then rose, then dropped, etc. So it sounds like a TPS/MAP sensor problem..

i'd be checking everything is plugged in properly and getting powered.

wog

[Jester]

ok i don't know a whole lot about the injector duty cycle but from what little i learned, 4% is like ultra mega low, depending on the injector pulse width 4% is about what you'd be getting at less than 500 RPM, but my understanding is vague at best. if this were the problem then indeed it would be a sensor not letting the system know that throttle has been opened, like everyone has already said, I'd be checking the TPS setting and getting hold of another if possible for diagnosis purposes and looking at the map sensor, primarily i'd be looking hard at the TPS. but check that damper and then look into TPS, it's gotta be something simple.

If you unplug the TPS while running does anything happen?

[Hydra]

I agree it's going to be something stupid, and simple. I've replaced all 5 capacitors, one was questionable but the rest OK.

Good point about unplugging the TPS - I really should have tried that myself already. I blocked (by kinking the hose) the hose to the map sensor, and the idle improved. While idling without me touching it, it'll pop as if it's missing on one cylinder. When I block up that hose the popping and afterfiring stops.

I'll check the continuity of the TPS wiring, and the function, maybe tonight (sorry neighbours!)

[Hydra]

Oh, the duty cycle on the injectors really suggests to me that 4% is not much more than idle. It's simply what it thinks it needs to continue running. A major thing to consider is that anything more than a little throttle stalls the engine.

woggin - the ISCV is working, it's not an idle problem anyway, it just plain doesn't rev over 2000rpm or so. Thanks for the tip though!

[Hydra]

Unplugging the TPS didn't really affect the way the engine ran - so I checked the wires to the TPS - they are completely normal. with the ignition on (not running) the voltage on the VTA1 pin varies with the throttle position between 0-5v. The IDL pins work correctly too.

I changed out the spark plugs for some spares I had - this also made no difference. The spark plugs that were in there were black - and smelt of fuel too. A sure sign that there is something certainly wrong. I checked the voltage on the PIM pin for the MAP sensor, this varies as you'd expect with pressure/vacuum.

Is there any way to check the CAS with a multimeter (besides making sure the wiring is fine)?

[Gavatron]

If the CAS wasn't working it shouldn't spark of fire the injectors.

[Hydra]

Just thinking this over in my head right now,

If the starter signal wire to the ECU was always getting 12v, would this problem occur? I will test this theory tonight. The other is that the starter signal never reaches the ECU - another possibility.

[Kyosho]

So the MAP sensor changes voltage appropriately with the changes in MAP pressure?
If it does, it NEARLY rules out a hole in the pipe from manifold to sensor.

Have you checked your fuel rail pressure and made sure it changes between when the rail is fully primed, and then when it's idling?

Have you got a wiring diagram for the ECU?

[Hydra]

MAP sensor voltage changes, yes.

Fuel rail pressure - don't have a fuel pressure gauge handy, which sucks.

Wiring diagrams coming out of the wazoo! I've checked it all over, the wires are going where they should be. The starter pin gets it's 12v when cranking and then nothing after that. I'd like to say it's a wiring problem but it seems less and less likely now. I'm starting to think the ECU is borked.

[CrUZida]

Just thinking this over in my head right now,

If the starter signal wire to the ECU was always getting 12v, would this problem occur? I will test this theory tonight. The other is that the starter signal never reaches the ECU - another possibility.

If the starter signal was always 12v to the ecu yes it will run in limp mode but it should still be drive able (what you have isn't limp mode btw). It will also through a code.

No starter signal to ECU just means it will be harder to start.

Limp mode is basically over fuelled and under timed. The car is still very 'driveable' (albeit very doughy) but it will basically not come on boost (or very little very late).



I'd be suspecting the ecu as well, but in the meantime unplug the air temp sensor, the coolant temp sensor, the TPS, the ISCV, and then try it.

[Hydra]

It's certainly over fuelled! I felt dizzy after it was idling for a while It's like a limp mode with limited revs, making it impossible to drive.

So unplug everything, the temp sensors, tps and iscv at the same time? Sure thing! Unplugging the TPS before made no difference to the way it ran, which i thought could be the problem. But having tested the signal going to the ecu, I cannot fault it. It's getting the correct voltage and earth, and the signal is correct compared with the throttle position as far as testing from the ECU pins go anyway.

[MWP]

You say its over fuelled, but the injector duty is never over 4%?
That sounds a little odd... maybe your duty meter (whatever it is) is giving an incorrect reading?

Do 1JZ's use peak and hold injector drivers?
That may cause an incorrect duty reading.

Keep going Chris, must be frustrating as hell, but youll find the problem

[Hydra]

Good point - i'm not 100% sure about that. There are three injector triggers - all have the same duty cycle. I'm using a multimeter to check the duty cycle.

It's bloody frustrating! I'm gonna try another ECU soon, quite possible I think.

[Kyosho]

An idea...

Unplug COMPLETELY the ecu. and then plug it back in. Pushing all wires into there connector...