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I am still trying to revive my 94 Bronco and so far I can only run it with starting fluid: if I keep spraying, it will keep running; if I stop, it will stop.
The fuel pressure is normal (around 40 psi). So the problem seems to point to the fuel injectors.
I checked the power to the fuel injectors: both leads are high (+12V) even when I crank. I also checked with an oscilloscope and found no pulse. So there is no power goes to the injectors.
Could this be the PCM problem? Is there any simple test to verify before I take it out? I did replace the PCM/capacitors once before.
How about a "noid" light test?
What dies the noid light do?
Sure, the processor can be the fault, it controls the timing as well as the injector on time.
How about a "noid" light test?
What dies the noid light do?
Sure, the processor can be the fault, it controls the timing as well as the injector on time.
Yes, oscilloscope can see it even better: no pulse no power to the injectors.
The timer inside the ECM/PCM to shut off the fuel pump is working as designed. There should be power to the injectors and the computer grounds the circuit to “fire” the injectors. I’d say something is wrong with the computer. Hopefully someone will chime in with how to verify that the computer is getting the information it needs to determine when to turn on the injectors.
The timer inside the ECM/PCM to shut off the fuel pump is working as designed. There should be power to the injectors and the computer grounds the circuit to “fire” the injectors. I’d say something is wrong with the computer. Hopefully someone will chime in with how to verify that the computer is getting the information it needs to determine when to turn on the injectors.
There should be some conditions that must be met before the ECM/PCM can pulse the injectors. That's why I think there should be some easy ways to fool the ECM/PCM to think those conditions are met and start pulsing. When it doesn't, we know it's faulty. I think that's how those refurbish shop test them after refurbishment to make sure everything works. The reason I started this thread to see if anybody knows. Thanks!
The signal from the PIP lets the computer know the engine is running. What wire that is at the PCM connector on your truck, I don’t know. I have wiring for my ‘89 but that’s it.
The signal from the PIP lets the computer know the engine is running. What wire that is at the PCM connector on your truck, I don’t know. I have wiring for my ‘89 but that’s it.
It's inside the distributor. I did replace the distributor a while back when the car was still running. I will double check. Thanks!
The PIP signal is pin 56 (Gray/Orange wire) at the PCM for the 1994 Bronco. The OP didn't mention if they have the 5.0L or the 5.8L, but fortunately the PIP signal is the same pin and wire color for both.
Since the OP is getting spark at the correct time since it runs with starting fluid, I don't think the Profile Ignition Pickup from the distributor is likely to be the issue since that also controls the coil via the ignition control module. But, to My4FordTrucks' point, if that signal is not making it to the PCM, it could be a harness issue. If it IS making it to the PCM, then the further supports there may be a PCM issue.
WhyFord, did you replace the capacitors in the PCM or did you send it out to have it done? And to clarify, in your original post you stated that you have 12V on both leads of the fuel injectors, but you also mentioned the injectors are not getting power. Is that what you meant, or do you mean that they are not getting trigger/pulse? If they have 12V, they are getting power. While you're probing at the PCM, you should also check the Tan wire at pin 58 (Injector bank 1) and the white wire at pin 59 (injector bank 2) relative to power to see if you get an active low injector pulse from the PCM.
For reference, here's what the PIP signal looks like on my 1995 Bronco 5.8L.
Thank you very much, shorod! I will check all those and let you know.
Yes, what I meant is the injectors get 12V at both ends so no voltage differential/no power. I probably replaced the PCM before since I saw handwritten numbers/letters on it the last time I replaced the capacitors in it. It's been a long time so I forgot the exact story already.
