94 Splash with a 4.0L, could my Computer be out?

[ThatGuy1988]

Been chasing an issue. Truck just stopped starting. Fuel pump wasn't running, figured it failed. It didn't. Figured the wiring was bad, it wasn't. Went through the grounds. Fuel pump runs when I ground the Fuel Pump pin in the diagnostic harness. Ok, Progress. Still doesn't start. Good fuel pressure (45+). Check the injector wiring, 12v on both pins but none of the ones I can access (Would check all six, but 3 are buried under the darn intake plenum) pulse when cranking. I've gone through the distribution box, checked all the fuses, basically short of replacing and rebuilding the box. I am increasingly suspecting the computer as a failure would explain why the fuel pump doesn't run and why the injectors don't pulse. Also, I can't get the check engine light to blink codes. I can't find my OBD1 reader, so yea. Banging my head against the wall.

 

[franklin2]

Normally I would say no, the computer failing is rare. But here lately I have been running into a lot of failures with the older computers of any brand of car or truck. It seems it's mainly the capacitors are failing. You can get capacitor kits for your computer and replace them if you are handy, but doing that I still failed and found out later the gook from the capacitor can attack the traces on the circuit board.

Don't do what I did and buy a used one on ebay. I bought it, stuck it in, and had the exact same problems. I said to myself, "what are the chances that this computer has the exact same problem as my computer?" Well after to many months of fighting it, I finally spent the money and bought a reman computer from Bluestreak. Stuck it in, problem solved.

 

[Curious Hound]

Lets back up and look at this some more. You make 3 statements that don't go well together. 1. Fuel pump runs when you test it. 2. Good fuel pressure - 45psi. 3. Fuel pump doesn't run.

The fuel pump obviously runs if you have 45psi of pressure. So, why do you then ask why it doesn't run? The fuel pump should come on a run for a few seconds when you first turn the key on. That is to build pressure for starting. It then remains off until engine rpm rises sufficiently to demonstrate that the engine has started running. So, check distributor and crank sensor if you have one to make sure the pcm sees engine rpm.

What test are you performing to see if the injectors are pulsing? Are you using a noid light?

And, double check your fuses. Don't just look at them. Pull them out and test with an ohm meter. Sometimes they blow but don't "look" obviously blown.

 

[Shran]

Does it start & run if you leave the fuel pump test jumper hooked up? It should. If it doesn't, and you have verified that the injectors are firing during that process with a test light, then there is another issue (spark?) I agree with Hound in any case, there are some conflicting statements that we need clarity on.

I have seen a couple trucks of that vintage with corroded under hood fuse panels. One had tin foil shoved in with some fuses, not to bypass them but I assume to make a better connection? Check all that over really well... those fuses and the terminals did not look bad to me but they were oxidized just enough to be a problem.

 

[ThatGuy1988]

The fuel pump does not run unless the fuel pump pin on the diagnostic port is grounded. When it's grounded, it keeps running. Otherwise, it doesn't run at all or prime.

The engine fires with ether, so there is spark

I did check the injector wires, 12v on both wires, but they don't pulse when cranking. The PCM is supposed to ground one of the wires to get the injector to fire. I tried an amazon noid light kit and it didn't work, returned it. But I have a multimeter.

I did confirm continuity on the fuses.

 

[Shran]

Do you have a 2nd small wire that comes off the negative battery terminal? If there is one (think there still was in '94...) it is the ground for your fuel pump relay and other things. Make sure that hasn't come apart, it commonly does and will cause issues like this.

IIRC the ignition module needs to see a signal from the crank sensor before it will fire the spark plugs. So if it's firing on starting fluid, the ECU and ignition module are at least partially working. I feel like you are dealing with a loss of ground issue.