Resolved 1g ECU wont power up

[Bricktop]

91 talon I have spark, CAS is working, the tach is jumping on crank, no injector pulse, and the logger is inactive. MPI relay is clicking, what else would keep and ECU from firing up and the ECU is good.

 

[steve]

The MPI relay clicks/chatters when the coil can't hold the contacts in. That's usually due to low voltage to the relay, bad ground from the ECU, or damaged relay, or wiring problems.

Without the MPI relay on solid the ECU isn't going to run and talk to the logger.

So measure the voltage going to the relay, check continuity between the relay and ECU, try grounding pin 63 to activate the relay. If you have a solid 12+ volts at the relay, check that pin 63 goes from battery voltage to about 0v when you turn the ignition on.

 

[mrfister11]

If you have spark then the ECU is on...

 

[Bricktop]

Hey guys, I put this in the engine management section on accident at first.

I have an 1991 Talon TSi Automatic. Car ran great until I miswired a O2 sensor and popped a driver in my ECU. I wired in the 02 right, and switched ECU's to a known working ECU, and it won't start.

So far, I have spark and no injector pulse.

I grabbed a tester and with info from the other thread, I found I had 12v from the ignition switch on pin # 110 with the key on. Nothing at pin 103. Nothing at pins 66 and 63 with the key off.

I have 12v to the MPI relay and the fuel side clicks.

Any Ideas?

 

[steve]

Pin 103 comes from Junction Box fuse #19 sometimes referred to as the "room" fuse. It also provides power to the radio to maintain the setting and to the cabin lights. Without power to 103 I don't usually see the ECU able to power IC110 that controls the MPI relay.

ECU pins 63 and 66 should read battery voltage due to there being battery voltage on the MPI relay pin 10 to which the relay coil is connected and the other side is pin 8 which runs to 63 and 66. When the ECU isn't actively pulling these pins to ground to turn on the MPI relay they should float at battery voltage. There is a transistor on IC110 that pulls them to ground causing current to flow and triggering the MPI relay.

There are two different circuits being switched my the MPI relay. The "MPI" circuit to the ECU and sensors, powered from the MPI fuse on the battery going to pin 10 on the MPI relay (91-94 cars) and the "Fuel" circuit from the ignition fuse on the battery going to pin 3 on the MPI relay.

You should not be seeing the "Fuel" side of the MPI relay activate unless the ignition switch is in the start position or the ECU is seeing the CAS pulse and it's activating the pump. You mentioned on The DSMECU forum that your fuel pump has a toggle switch for activation so that may be causing it.

 

[steve]

if you have spark then the ecu is on...

Depends on what you consider on. IIRC, there is a limp mode build into the IC that drives the power transistor.

If the CPU isn't running inside the ECU you might still get spark.

 

[Bricktop]

Steve, What do I need at the bare minimum to get the ecu to turn on? My wiring is hacked.

 

[steve]

How hacked?