i bought a parts truck last week that was not running. The PO reports that the truck was running down the highway and just stopped. He towed it home and it only cranks now.
I started with electrical. I tested the crank sensor. I have 8 volts to the sensor. Good ground. 5 volts on/off when engine is turned. I swapped out the ASD relay with a new relay I had on hand. I have checked the power at both wires of the coil both at crank and when first switched to ON. I have no power when switched to ON. No power at the signal wire. Only small needle move on positive wire to coil during cranking.

How can I check the cam sensor?
What should I check next?

 

You should have 12 volts to the coil for a least a few seconds when you first turn the key on. What about the injectors? Do you see power there for a few seconds when first turned on? Are you getting spark? Fuel pump prime?

 

I am not getting any spark. I expected the coil to get power for a few seconds, but I get nothing. I don't have a noid light, so I haven't checked for power to the injectors. There is no relief valve on the fuel rail like my 96, so I haven't checked for fuel pressure. I know that I can disconnect the fuel supply, and test pressure that way, but I haven't brought home a fuel pressure gauge yet.

Maybe I am all wet, but if I don't have power to the coil, it doesn't matter if I have power to the injectors, I still wont be able to excite the distributor, and cause spark for the fuel. I do not hear the fuel pump prime when I turn on the key.

I have checked, and I do get power to the ASD relay. I have switched relays around, and tried brand new relays. I have checked every fuse under the hood. Wish I new how to check the cam position sensor. Where can I check to see if power from the ASD relay is getting back to the PCM?

 

PCM should see 12 volts on Dark Green/Orange wire, connector 137, cavity 12. (grey connector at PCM.)

If you don't have one already, grab the service manual from this thread.

Are you getting power to the fuel pump relay?

 

I am getting power to the fuel system relay.

I am not getting 12 volts on C12 at the PCM. Instead I see ground. I also checked and see ground at the power wire on the coil. I think I will have to look for a short. Are there any common places I should start?

Looks like the o2 sensors are on that circuit as well as the injectors.

I do have the service manual, but it refers me to the Powertrain Diagnosis Manual every time I read something that looks promising.

 

Yeah, I see those references, but, I have never seen any other reference to the Diag Manual..... I think its mythical.

C12 is just a sense circuit, I am not surprised it simply goes to ground. Coil circuit should normally be grounded as well, as the PCM OPENS the circuit to fire the coil. If you aren't getting power TO the coil, nothing that happens after it is going to matter.

If you bypass the ASD relay, will the engine fire?

 

I see you posted this same question on DT. Last two responses...

Not sure if terminal 30 is the input side or output(not looking at the diagram). If you don't have positive power to the coil it's not working. It's direct from the asd relay to the coil 02's etc. The pcm should energize the asd rely when the key is on. Put a small wire in the relay terminal(output) when you install the asd relay. You then can see with a meter if it is coming on or not.

 

I have power on two of the terminals in the ASD relay when the relay is out.

Thanks HeyYou and Moparite for your help so far. I've read a ton of posts by you two, and respect your collected experience. Thanks for what you both give to the forum communities.

I'm going to set this problem aside for a day or so. I'll post results as I find them.

 

You may want to check and see if you have power on the injectors/02's. Might be a rodent chewed the wire going to the coil. Stranger things have happened.

 

Here is my progress to date.
I have ground to the entire A142 circuit instead of 12v power. This DG/OR wire connects the ASD relay to the alternator, 02 sensors, injectors, and coil.
I traced the wire from the back of the ASD relay plug-in to the connection (C127) on the firewall where the wires join the main harness. When I unplug C127, the main harness is grounded, and the other side is neither grounded or powered. I unplugged the grey (C) connector at the PCM. I can still measure a ground at any DG/OR wire in the A142 circuit.

I removed the electrical connection to each component in the A142 circuit. No change.

Expecting a short or frayed wires, I opened the main harness, and found the splice that takes circuit A142 to the fuel injectors, coil and alternator and the splice that leads down to the transmission harness and the o2 sensors. I first clipped the splice on the passenger side. I still had ground on both sides of the cut wire. I cut the driver's side splice and still had ground on both wires. I decided that the ground must be coming from the PCM back through the circuit. I unplugged the white connector and black connector to the PCM. The ground went away.

My guess is that the PCM is grounding back into the A142 circuit. I can trace wires, and test components, but I give up when it comes to the computer.