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Assuming that you have 12v on the 5v ref, I would unplug the connector at the engine control module. If you still have 12 v, I would say that the 5v ref is shorted to power. If the 12v is gone once unplugged, I would look for bent pins and bad ecu grounds. If you have good powers and grounds, you may be dealing with a bad control module.
Thanks for the reply Monde. I'm completely new to the diagnostics world, so forgive me if I ask what would seem to be the obvious, but can you elaborate a bit more on the bent pins, and ECU grounds? Specifically how to check them?
Powertrain control modules have pins that the connectors plug into. Sometimes, they get bent and touch each other. If a 12v feed touches the 5v ref, you will get 12v on the 5v ref.
Oh, ok. Yeah, so the pins are straight. I looked at the ECU earlier when I had it out, and they are definitely straight. So, do I unplug the ECU harness next, then check for 5v again on the TPS?
I don't have a wiring diagram to post. If you have a diagram, try to locate the connector with the 5v ref. back probe it and see what kind of voltage you get. If 12v, unplug that connector and see if you lose that 12v. I would turn the key off before unplugging the connector just out of precaution. By the way. are you getting the save 12 v at the sensors that you have checked?
The only 12v I'm getting is at the TPS. The other sensors that share the 5v are getting less than one volt. I have a wiring diagram now (since I checked some things earlier today), and it looks like the 5v ref is an orange white wire. Also, the diagram looks like this same wire is jumpered between the TPS and the MAF. I need to look at that closer though. The MAF is less than a volt.
The MAF may have a 12v feed, 2 grounds and 1 signal, The DPFE if equipped may share the 5v ref with the TPS. See if you also have 12v at the Delta Pressure Feedback (EGR) (DPFE)
Do you have any drivability problems? Any codes? Can you share your wiring diagram? I had the time to glance at a wiring diagram for that truck. It looks like the 5v ref wire color is Brown/ White. Did you put the black lead of the multimeter on the ground post or a good ground and the red lead to each wire of the TPS sensor?
This truck is a no start. Turns over great, but not hitting at all. No spark confirmed. Been using known good grounds, and verifying the ground each time I do a check. I basically been back-probing all the wires in the sensors for a reading. So, does it look like that TPS is supposed to be 12v constant? Or is it on the 5v circuit?
5v ref. What color are the TPS wires? According to the diagram I glanced at, one of the wires was brown/white.
If you could share your diagram with us, I would appreciate it.
If I have time tomorrow. I will try to look at the diagram again. By the way, does the check engine light go out upon cranking?
Hey man, before we go any further I wanted to say I really appreciate your help. I will try to post the diagram I've been looking at. There is NO check engine light, at all. From the moment the switch is turned to the on position, there is NO CEL.
The Orange-White is the 5v ref. Manifold Absolute Pressure( MAP), Throttle Position Sensor( TPS), and EGR position Sensor (DPFE) share the 5v Ref.
Do you have injection pulse? TPS issues are not going to cause a no-spark condition. If you have injection pulse, you may need to start looking for the cause of the no spark. Does the RPM needle bounce when the truck is crank?
I don't understand why you get 12 v on the Ref at the TPS and not at the MAP and DPFE as they share the same circuit.
Just going to throw this out there, it's definitely 12.00v with the meter set to volts DC.
The meter isn't auto ranging and showing 12mV? (otherwise displayed as 0.012v with the meter set to VDC)
you may want to go after the no start , may be disconnect the sensor then check your ignition module by the driver side fender for power firing the coil wire . I think mr S Danner has a vid on that or on U tube there is two that i know on 94 @ 95 crank no start good LUCK .
I watched those videos, and after creating a spark he commented on how this confirmed there was communication with the ECU. I have no communication, and couldn't get spark by using a test light at the PIP wire. I confirmed power going to the ECU, but it isn't sending anything out. The only thing I didn't check was the ground going in the ECU harness. Anyone refresh me on how to check the ground there?
