Help with EJ20R - engine cuts out if there's too much throttle, sensor issue?

[alex-roflcopter]

Hi all,

So based on my reading from this amazing thread (https://sl-i.net/FORUM/showthread.php?20165-So-you-ve-bought-youself-a-JDM-twin-turbo-eh), I've got an EJ20R from a JDM 97 Legacy GTB in my Australian 97 Impreza with (most of) the loom swapped in too. I got it as an incomplete project and it didn't start at all when I got it.

After a lot of work trying to work out what wires needed to be connected where inside the cabin (mainly the cabin fuse box was missing), it starts and runs at idle but if you give it much throttle or give it throttle too quickly, the engine struggles for a second then cuts out.

If you back the throttle off it will splutter back to life.

I thought it might be a fueling issue so I put in a Walbro high-flow fuel pump but that didn't change anything.

I'm wondering if it's an issue with a sensor like the throttle position sensor or something, that isn't sending the necessary data to the ECU...

Also, I have no way to tell if any of the sensors are working at all.

Firstly, I followed a translated ECU pinout to try and check voltages but where the pinout said there should be 12V or ground on a particular pin, I'd check it and find there was like 2.7V or 5.3V or some random voltage.

Secondly, with the multimeter on the throttle position sensor signal pin, I'd expect to see a change in voltage when I adjust the throttle right? Nothing happens, no voltage change.

Thirdly, if I disconnect various sensors in the engine bay (i.e. AFM), it makes no difference whatsoever to how the engine runs.
I would expect it to idle worse or better or at least notice some change right?

The car seems to have the correct ECU for the engine:

https://sl-i.net/FORUM/images/imported/2024/04/20240417123750-1.jpg (https://ibb.co/N1yH89n)

But the cabin fuse box came from an Australian-delivered 1998 Liberty (closest I could find here in Aus).
Looks identical to the BG5 cabin fuse box pics I've found at various JDM parts sites, and everything plugs in, but perhaps the pinout is different and the sensors aren't getting power?

https://sl-i.net/FORUM/images/imported/2024/04/20240417172951-1.jpg (https://ibb.co/H47SGjK)

Any assistance appreciated. I have no idea what to try next :smt088

[duncanm]

Thirdly, if I disconnect various sensors in the engine bay (i.e. AFM), it makes no difference whatsoever to how the engine runs.


Yep - that's what I was guessing. MAF isn't connected to ECU.

Check your engine harness and connections.. maybe buzz them out with a multimeter.

Could also be a dead MAF.

[alex-roflcopter]

Thirdly, if I disconnect various sensors in the engine bay (i.e. AFM), it makes no difference whatsoever to how the engine runs.


Yep - that's what I was guessing. MAF isn't connected to ECU.

Check your engine harness and connections.. maybe buzz them out with a multimeter.

Could also be a dead MAF.

Yeah I really need to track down a "known good" ECU pinout for the 87 ECU / EJ20R.

And ideally a wiring diagram for the complete harness, and ideally in English :razz:

Based on the fact that there are lots of wiring issues, I think that's more likely than a faulty MAF.
But if I can find another one the same while I'm at the wreckers over the weekend, I'll grab it for a spare.

[alex-roflcopter]

Found the ECU pinout (https://sl-i.net/FORUM/showthread.php?20334-ECU-Pinout-Wiring-Diagram-FSM-for-JDM-BD5-RS-BG5-GT-B-Twin-Turbo-EJ20R).

This weekend's project will be to test it all. Worst case I'll wire up every component in the engine bay individually, directly to the ECU.

[LosMan603]

Any luck with this? Curious to learn more about what you found out.

[alex-roflcopter]

Any luck with this? Curious to learn more about what you found out.

Well the MAF is at least getting +12V so theoretically it can work, I've narrowed it down to something like:

1) There is no +5V to the Throttle Position Sensor, in fact there doesn't seem to be +5V coming out of the ECU at all.
There is possibly a short to ground somewhere on that +5V line.

2) This means there's no +5V to the other sensors which run off 5V, so at least the MAP sensor and possibly others.

3) There doesn't seem to be any continuity from the TPS signal pin back to the ECU.

So basically when I open the throttle, the MAF seems to be telling the ECU, hey, here's a bunch of air coming in
But the ECU is like, why? The throttle is closed. And thus not giving the engine proportionally more fuel to match.

My next step is probably going to be pull out the whole Legacy loom (which I need to do anyway to put the Impreza loom in to run the headlights/indicators/power windows etc), cut out all the Legacy's cabin stuff until I'm left with a "standalone" engine loom, and then check continuity from every sensor plug to each corresponding pin on the ECU plug.

[alex-roflcopter]

So got it running today! Turns out there was +5V coming out of the correct pin on the ECU but not at the TPS end.

Fortunately the +5V was working at the MAP sensor and they share the same 5V line so we cut the 5V wire at the TPS (just in case it was shorting to ground somewhere further back) and ran a temporary wire spliced in from the MAP's +5V.

And it runs! And it keeps running when you give it more throttle, all the way to full throttle.

The idle is very rough and there are a few other issues but I'll wire up the CEL straight to the CEL pin on the ECU and see if I can read some codes that way.

Very excited :D