. Again DO NOT use a test light connected to 12v positive to test K4 20BK/LB or you are extremely likely to damage the PCM.

That really sucks... sorry for any bad ideas. Gauges generally run on 5 volts like the MAP sensor (there should be a regulator in your dash), but it still wasn't the best idea since it wasn't the 5 volts from the PCM.

It may be possible it is still good, but due to internal filtering it's not showing continuity if I understand things right... unless I missed something. If the ground itself is bad I would think you would have many more codes than before. Have you checked them lately?

 

https://forums.neons.org/viewtopic.php?f=1&t=420568&start=40
This is how you can test the circuit to the sensor With the connector disconnected from the map sensor or you can use a poke probe through the insulation and leave it connected. Use a Digital Multimeter set to Volts DC put the black lead on the black with light blue stripe wire then touch the red lead of the DMM to battery positive. If you see 11-12 volts you know you have a ground all the way thru the ECM. If it does not show 11-12 volts on the DMM then there is an open fault in either the wiring to Pin 43, a problem with the connector and that pin, or an open fault internally in the ECM.

Instead of poking holes in wire insulation you can stick some paper clips or stiff wire in the back side of harness connectors as probes. The silicone seals are hard to tear up. Just push it along side the wire and it will go into the seal make a connection. Most times there's just a little clip on protector to snap off for better access.

 

I'll agree it is strange. Have you tried using your sensor ground as a ground for your test light? I know it doesn't make sense, but sometimes who knows. It pegged the temp gauge which is essentially the same thing.

Let me try that today.
EDIT: actually i am too scared to try that, as any voltage on that wire will damage the PCM.

Did you get 8 volts yet? I checked your pin charts and found an orange wire (#72) that goes to the vapor canister pump switch driver which I'm thinking would correlate with the evap code I saw earlier. Have you looked into that at all? It doesn't specify a voltage in the chart, but I'm hoping since it's also orange that it's also supposed to be 8 volts and unplugging the pump will cure it... or it may just be something else not getting power.

no not yet, my multimeter died & my new one just arrived. Wish i had checked with the engine running last weekend.

see two uploaded files named vapor canister pump & photo. The schematic shows that orange wire (#72) goes direct from the PCM to the vapor canister pump. But that wire does not exist on my vehicle, & my photo, taken today, of the connector to the PCM shows the absence of that wire. Just an empty slot.
Now i need to locate the vapor canister pump.

I lost track... does the fuel pump relay turn on when you turn on the key? I remember the ASD not working still, but I'm thinking that won't turn on until you sort out the other problems first. It is a shut down relay which would normally shut the engine power off in the event of a problem if needed.

No, the fuel pump relay does not turn on when I turn on the key. The fault, wherever it is, is intermittent.

Now I am looking to purchase a replacement wire harness. hope this guy delivers.
https://forums.neons.org/viewtopic.php?f=45&t=420536

 

No disrespect meant by this comment, but, this must be one tricked out Neon to spend this much time or money on.

 

No disrespect meant by this comment, but, this must be one tricked out Neon to spend this much time or money on.

this is my winter car, i need to go to work in ice & snow. My bike won't do

 

That really sucks... sorry for any bad ideas. Gauges generally run on 5 volts like the MAP sensor (there should be a regulator in your dash), but it still wasn't the best idea since it wasn't the 5 volts from the PCM.

It may be possible it is still good, but due to internal filtering it's not showing continuity if I understand things right... unless I missed something. If the ground itself is bad I would think you would have many more codes than before. Have you checked them lately?

my code reader is giving me "linking error" again.

 

Did you get 8 volts yet? .

see three uploaded pics. Performed voltage drop test on connectors to three sensor--cam, crank, & vehicle speed.
Each test has orange wire probed, with other probe to chassis ground. Result is about 2.4 volts each time.

 

I was hoping for quick and easy with the vapor canister... the diagram says I would have been wrong anyways even if it did have one.

Now I am looking to purchase a replacement wire harness. hope this guy delivers.https://forums.neons.org/viewtopic.php?f=45&t=420536

Hope so too. The way things come and go it may be in the harness and you're just moving it the right way to make it work from time to time. Good luck

 

Something just sank in after checking over diagrams again...

Are you getting power to fuse going to your DG/WT that feeds your fuel pump relay? I'm guessing it would come off your ignition and only have power at the fuse with the key on. A failing ignition switch is just another thing that can make it only work when it wants to.

 

Good news! all systems are a Go. the wire harness was replaced with one that I extracted a junkyard '96 Neon.
this includes the PDC relay box. the old wire harness is scrapped. it was hard, as the wire harness runs under the entire dashboard,
to three big connectors.

now the fuel pump is humming. spark is alive.

really wish i could have figured out the problem. but the temps are in the 30s now,
and cold rain falls every day, and my dad has the garage stuffed full of useless crap.

Thanks for the help everyone.

 

and my dad has the garage stuffed full of useless crap.

Add the old harness to his stash.