1990 tbi ecm shorting

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Schurkey

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One illustration calls for a 5-amp fuse, the other says 10-amp, to power the two fuel injectors. But I don't know the source for the second illustration.

The 10-amp fuel injector fuse in his truck didn't pop, but there's enough current on that circuit to melt solder in the ECM. But not enough to discolor/melt/burn the wire insulation leading to D16. Doesn't seem reasonable.

He said there were two wires connected to D16, but that's not the case. He says there's no power to "the fuel system" but the ECM doesn't control the power side, it controls the ground side of the injectors, and only powers the fuel pump relay control coil. Which would be bypassed by the oil pressure switch, so it's not really essential. IF (big IF) there's truly no power on D16, it's not the fault of the ECM (and he says the fuse is good.) Go figure.

I'm about out of ideas. The only thing I have is "Do we know what the melted circuit-board trace actually connects to?" Maybe that trace connects to something OTHER than D16. C16 is straight battery power at all times (not switched.) If the internal circuit of the ECM were faulty/grounded, that wire would carry massive current; perhaps that circuit trace is acting as a fuse, being smaller than the C16 wires and fusible link.

Or--hell--maybe that circuit trace connects to something entirely different.

I've been all over the map on this. For now, and until I get more info on symptoms and test results, I'm back to Post 5: Faulty ECM.
 
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BennyPorras

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There's only one wire connected to D16. The blue wire that's supposed to be there.

One of the illustrations above says "5-amp", the other says "10-amp" fuse for the injectors. I missed that before. And D16 is the ground for only one injector, not both.

I guess it's time to find the schematics and circuit description for YOUR vehicle.
These are the schematics I have been basing off of. I just do not know what would cause a ground to fail in the ecm. I have checked the injector wires for that particular injector there seems to be no short or exposed wires. The fusible link is good as will as the oil pressure switch. And fuel pump relay wires. When I go to start the truck all it does is crank. It will start if you pour a little fuel in the throttle body. Just won’t stay running. all other electrical components all seem good. Yes I was off on the two wires going to d16. I know that the injector wire is d16 and the oil pressure switch is c16. Since I’m away for the week at college I won’t have time to check the truck again till this weekend. How would you guys go about checking.

Also When I bought the truck the injector connectors were melted and burned. I put in new connectors and replaced all the burned up wiring. It seems that previous owner was having a issue with the fuel system. They had replaced the fuel pump, and injectors on the old throttle body. The fuel pump wires were poked from being tested. Im not sure if the ecm had already melted this ground before or after the fire. But there is no power going to the a1 wire, d16 and d14. But c16 does have power.
 

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Schurkey

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Where are you checking for power on D16 and D14?

***Disconnect that plastic connector from the computer.***

Test for voltage at the "Injector A" fuse, test at the two-socket injector connector, (unplug from injector, re-connect after testing One of the two at each injector (Red on one injector, and White on the other, according to your latest schematic) should have voltage) then test the terminals for the green and blue wires at the plastic connector that plugs into the computer, AFTER you've plugged the injectors back in. You should have voltage at all five places.

Might have been nice if you'd mentioned the prior burnt wiring and repairs before now.

A1 is the power for the fuel pump relay. There's not going to be any power there except when the engine is running, or for the first two seconds after turning the key from "Off" to "Run".
 
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BennyPorras

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Where are you checking for power on D16 and D14?

***Disconnect that plastic connector from the computer.***

Test for voltage at the "Injector A" fuse, test at the two-socket injector connector, (unplug from injector, re-connect after testing One of the two at each injector (Red on one injector, and White on the other, according to your latest schematic) should have voltage) then test the terminals for the green and blue wires at the plastic connector that plugs into the computer, AFTER you've plugged the injectors back in. You should have voltage at all five places.

Might have been nice if you'd mentioned the prior burnt wiring and repairs before now.

A1 is the power for the fuel pump relay. There's not going to be any power there except when the engine is running, or for the first two seconds after turning the key from "Off" to "Run".
I’m checking from the injector connectors and from the ecm connectors. Okay so what I did was unplugged the ecm, injectors, and with the key off I tested for power on all four wires red, blue, green, and white as well at the fuse. No power as it should. Then with the ignition on I did it again with the Ecm and injector connectors unplugged. Only power to the red and white wires. None to the blue and green.
 

Schurkey

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You have voltage at red and white. Therefore you also have power at the fuse. All as it should be.

Now plug the injectors in, check for voltage at the blue and green wires at the disconnected ECM connector. That should be D16 and D14.
 

BennyPorras

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You have voltage at red and white. Therefore you also have power at the fuse. All as it should be.

Now plug the injectors in, check for voltage at the blue and green wires at the disconnected ECM connector. That should be D16 and D14.
so I’m getting nothing going to both d16 and d14 how much exactly should be going through these wires?
 

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Battery voltage. Same voltage you got on the white and red wires.

Find out where the voltage stops.

[Later Edit] ...and if there's "nothing going to both D16 and D14", clearly neither one of those is melting the solder trace. THAT problem is somewhere else. [/Later Edit]
 
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Mathies

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I have no idea about A1. Not on the schematic or circuit descriptions posted above, although there's a dark green/white stripe wire from the ECM to the fuel pump relay is. But that's at C2, not A1.

D16 is a ground for the fuel injectors. The injectors get power via the injector fuse, they're "hot" any time the key is in "Run" or "Start".

If there's too much current for the ECM to handle...so that it's melting solder...I'd think that injector windings would have to be shorted. If the insulation on the wires melted, the resistance would go way down, and the current would go way up. But that SHOULD pop the 5-amp injector fuse. That brings us back to why there's an orange wire connected to D16 when that's not on the schematic.

Did someone slap a higher-value fuse into the injector fuse position? Is your '90 wired differently than that '88 schematic? Did someone cram an orange wire where it doesn't belong? According to the schematic, there's an orange wire like you describe connected to C16, but not D16.
Hye shurkey im having the exact same problem here with my truck i also aplied fuses on the orange wire unplugged the injectors so the injector cant be the problem. I measured ohm between c16 and d16 and read OL so thats good right?

Could it be the ecm has failed? Or still a grounded wire in the wire harness?
 

BuiltToWork

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Hye shurkey im having the exact same problem here with my truck i also aplied fuses on the orange wire unplugged the injectors so the injector cant be the problem. I measured ohm between c16 and d16 and read OL so thats good right?

Could it be the ecm has failed? Or still a grounded wire in the wire harness?
My ECM Failed/similar issues as listed in OP. Water leaked in on it because I'm a dumb a. OP photo looks like my old ECU. Bought a new one and swapped the chip - ran just fine after that.

1990 454 K3500

ECM EM8747 - for the TH400

New ECM from Rock Auto cost me $138.34
Would have cost me $88.79 if I sent the core back (I did not)

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