Resolved 2g turbo. 5v reference grounded at ECU

[Diamond Star Werks]

I am just putting this car together. It's a shell I bought almost two years ago. I have the motor in and everything hooked up. 2.4 setup with custom evo turbo kit.

I had to fix the wiring from the PO ripping out the turbo timer and gauges. As far as I can see wiring is good right now. Engine cranks but has no spark or fuel.

Cam and crank sensors do not give any signal. They are not receiving a 5v reference. There is no continuity between ECU pin 81 and the cam/crank (95 style) sensor harness connector pins. There is continuity to the green/yellow wires at the TPS and MAP sensor connectors.
Coming out of the ECU pin 81 is grounded, key on/off. When cranking it switches to 1.4v-1.6v. Other than then, it's a ground but (tricky part) it doesn't have continuity to the battery ground or ECU sensor ground pin.

The engine harness is out of my old GST that I used to drive everyday. Only thing I changed was I wired the white wire for the lc1 into the ECU sensor ground wire and the blue wire from the lc1 into the O2 sensor heater ground.

I have no clue what else to check. Same result on two known good ECUs.
@steve @snowborder714 @luv2rallye

 

[luv2rallye]

Cam and crank sensors do not use the +5v from pin 81. They use +12v from MPI relay and their outputs are to pins 88 and 89 (which are ECU internally pulled up to +5v). Pin 81 is +5v for BARO, TPS, Mani Diff Pressure sensor, and fuel tank diff pressure sensor. Pin 81 should not be connected to ground.

 

[steve]

And it sounds like 81 isn't directly grounded.

Pull the matching pin at the harness and measure the ECU output. If it's not about 5v then the ECU is damaged. If it is then you need to find out what's pulling the voltage down.

 

[Diamond Star Werks]

Okay I'm headed back to the garage now to check on a few other things before work again.

@luv2rallye thanks for that info. I had checked a couple diagrams but didn't find that info yet. Anyways at the harness connector there is no voltage of any kind with key on.

Before I left yesterday I checked pins 12 & 25 and neither had B+ on them. So I don't think the ECU is even powering up.

There are some wires at the drivers left foot that are cut but IDK what they are for though. The PO must have had something spliced in I guess. I tried to upload a photo but it was too large I'll try to take a smaller one when I get back there. Edit; pic added. The wires run up to and plug in the side of the fuse block

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[Diamond Star Werks]

@steve I checked the ECU output at pin 81& it's 0v, but I'm thinking now it's because the ECU isn't getting power from 12 & 25. Would that make sense?

Ok so pin 82 supplies power when the switch is turned on. Checked that and it's good.

Pin 80 back-up power supply, supplies constant 12v. Checked that and it's good.

Pins 13 & 26 are grounds. Checked those and that are good.

Pins 12 & 25 are ECU power supply wires from the MPI relay. Checked those and they are dead. They also carry no continuity with any wire at the MPI relay and the relay beside it which I think is just the fuel pump relay anyways. (I have a later model AWD harness that I checked and the 12/25 pins at ECU connector had continuity to the wire at the MPI relay connector)

Pin 38 @steve I read in anther thread you said it should have 12v with switch off and next to 0v when switch is on. Checked that and get nothing at all with the switch off and a grounded .02v with the switch turned on.

That's as far as I got today.

 

[Diamond Star Werks]

Fixed. MPI relay connector wasn't fully seated.

 

[joshuah]

Reviving this old thread to work my ECU issues.

Cam and crank sensors do not use the +5v from pin 81. They use +12v from MPI relay and their outputs are to pins 88 and 89 (which are ECU internally pulled up to +5v). Pin 81 is +5v for BARO, TPS, Mani Diff Pressure sensor, and fuel tank diff pressure sensor. Pin 81 should not be connected to ground.

So seeing 12v on my crank and cam sensor is normal voltage ? Also get 5v on the other wire on my can which I assume is correct for signal to ECU

 

[luv2rallye]

Yes. 12v (power) on the crank and cam red wires is normal. 5v (signal) on crank blue-white and cam blue-red is normal.

 

[joshuah]

Yes. 12v (power) on the crank and cam red wires is normal. 5v (signal) on crank blue-white and cam blue-red is normal.

Thank God saves me another