Exact same code on two different PCM's, is highly unlikely to be a PCM problem. If you actually are getting 5 volts TO the various sensors, are you getting return signal FROM those sensors to the PCM?

 

That make sense. I don't think I'll be getting this PCM apart anyway Haha

Okay - so on the MAP, Crank and Cam sensor I've tested for voltage at both the 5V power wire and the return signal wire with the sensor itself unplugged and key on - so I'm testing on the harness side. All three of those connectors are getting a constant 5V at two of the pins and then have 0 at the ground pin.

I've only tested the MAP sensor return signal wire (green/red) by cutting the wire close to the PCM - I didn't think it was necessary to do the same for the cam and crank return signal wires if I was getting an internal 5V short.
When I pulled apart the connector everything looked perfect and I cant see a way that a short was happening in there since every pin is separated and there wasn't any melted plastic or melted/damaged wires.

Also I went to live data on my scan tool and it showed the MAP reading at "10" - not sure what it's supposed to be but that was just sitting with the key on.

 

Is that with engine off??? If so, its really low. (unless you are at altitude??) Theoretically, its rated in PSI.... but, it *should* mention that somewhere. (depending on scanner?) at sea level should be 14.7, give or take.

 

Yeah - that's engine off. I'm at about 1100ft for altitude.

I noticed that if I check the live data with the sensor unplugged it shows 104. And 10 when plugged in. I just pulled the MAP sensor and cleaned it - there was a bunch of carbon on it...? But when I plugged it back in and checked the live data again it still reads 10.

Additional observations:
Live data also shows the ECT at 2°C which is somewhere around 35°F and it is 35°F in the shop right now so that seems accurate. Tach moves when cranking to the PCM is seeing a signal from there.


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So I did a test and I think that the MAP sensor itself is the problem?
I got to thinking that maybe the MAP sensor was possibly breaking that 5V signal or something when it was put under pressure? I got my scan tool where I could see the live data and then I tried shaking it, tapping and blowing on it to see if I could maybe get something to change or maybe get a loss of signal to happen somewhere - couldn't tell.

As another test - since it was already out - I tried cranking the engine with the MAP sensor hole plugged - but the sensor hooked up but just sitting on the intake manifold. Cranked for about 10 sec - no code. Waited for a few minutes and then did it again. I repeated this 5 times and never got a code to pop up. Then I installed the MAP sensor and cranked again. Now that the MAP was clean it kept wanting to start but wouldn't and then after about 7 seconds the check engine light came on and it never tried to fire again. Checked codes and the "No 5V to MAP" had came back.

That still raises the question though - is there supposed to be 5V on two wires of the sensors though? Where's this coming from? Ive read posts where you, yourself had said there's only supposed to be power to one wire at the connector.

 

sorry deleted because I made a duplicatepost...

 

Yeah, there is a 5 volt sensor feed, the sensor alters the voltage, relative to manifold pressure, and feeds it back to the PCM. If you are seeing 5 volts on both wires with the sensor unplugged, there is a short somewhere. If you only see that with the sensor plugged in, that's a bad sensor.

 

Hmm... That totally makes sense and was how I understood it to be...
But that definitely means something is being weird.. Because I see 5V on two wires/pins at the connectors - unplugged - on the MAP, Crank and CAM sensors. I haven't checked others... And thats the same with both PCMs. I looked up pinouts on all of them and used the ground wire to check but also hooked up directly to battery ground to check them as well - still 5V (well, ranging from 5-5.2V) on two wires.

I ordered a MAP sensor to try and swap out - I know throwing parts at it isnt the right way to go about things but I figured based on my test that I'd give it a try and see if the thing will at least run.

I'm also confused how I could get it to run - though badly- enough to get it in to the shop, get it to run perfectly in the shop by unplugging the MAP, and now cant get it to run at all without changing really anything... Maybe this is the plague the PO was meaning..?

I wonder if something is going on in the wiring that is causing the PCM to short out on the 5V return/signal..? I've read people have had sensors shot out and cause the 5v on the return lines - but I think that only applied to the individual sensor?
Though looking at the diagrams all of the returns are on individual pins so it makes me wonder how 5V is being sent OUT on at least 3 different return pins on 2 different PCMs... Doesn't make sense... Maybe the next step while I wait for the MAP and NEW PCM is to test all the sensors that use a 5v power/return from/to the PCM?

I've already taken apart the entire engine bay wiring harness to check for a short and couldnt find any sign of a burnt/melted wire.... Let me tell you getting to the part where the main harness meets the driver side injector/MAP/TPS/Cam harness was terrible! Haha! Even worse to get back together!

Another thought is maybe he was on to something and he really messed up something in the dash wiring somehow some way that s effecting these things... I just done know what/how that could've happened.

Something I've noticed when checking the Cam sensor is they must've busted off the Cam sensor bolt because it's JB welded into place... So hopefully that never goes bad! Haha!

Final question - is there supposed to be a ground strap or something from the body of the PCM?

 

Did you test the connectors one at a time? If so, might try unplugging ALL of them, see if you still have five volts across them all.....

The feed wire is a common wire. They all get power from the same place, the sensor returns though, are individual...... having them ALL show the same symptom is really weird.

 

Sorry, didn't have time to get in the shop yesterday. Well, I did but spent the time cleaning and organizing the house to finish a project and to try and make sure things were nice as they could be when the wife got home tomorrow. Going to do a little more tonight too. So I left work "early" today - only got 11 hrs instead of 12-13 to try and get into the shop to try some things out before I finished the house.

How many sensors are we talking about unplugging? I tried unplugging the crank, cam and MAP and still have the 5V on signal wires with all of them unplugged at the same time already. There's quite a few sensors on that same plug on the PCM - though could something else on a different plug be causing the issue as well? Another thing I noticed that hadn't thought about checking for some reason was the ground. I notice there was about .02ish volts on the grounds when tested to battery ground. Not sure if that's enough to effect anything or not but.... Had me wondering if anyone's added a ground of some wort from the PCM ground wires to battery ground? Is that a bad idea? How does the PCM get grounded anyway? I didn't really look into that in particular when I was looking at wiring diagrams. Certainly not through it's body because its gets bolted to a plastic/rubber mat on the firewall...

I checked continuity on all three plugs for each wire to ground and itself and found that the ground to 5V SOURCE to ground always had continuity but not the signal wires. When I unplugged the plug from the PCM there wasn't continuity anywhere. Something I didn't think about that I thought of just now was to check continuity between wires on different plugs...? Wanted to get something to eat but might jump back out there and check that....

Noticed that the RPM gauge doesn't ALWAYS move when starting cranking - about about 50+% of the time that it does it wants to fire. When it does I can blip the gas pedal and she starts right up. The first time she ran rough - and then I realized I accidentally left the MAP sensor unplugged... Plugged it back in and she fired up on her own and ran actually pretty nicely for about 15 seconds and then went back to a low loppy idle so I shut her down and called it a day - for now.

Another question - How important is having all the vacuum lines hooked up on these trucks? I've noticed at least two in my digging around that aren't attacked to anything and can't really tell where they are actually supposed to connect to... I know on my old Jeep they were pretty easy to bypass/get rid of - but that was a carb'd engine - not EFI... Maybe time to look into vac diagrams as well.....