What is the backstory on this vehicle?

Something happened along the way. Think carefully, you've owned this for a certain time period - let's say 2 years for the sake of discussion.

Everything was OK, (or at least $300 PCMs weren't scorching off.) What happened?

Either some kind of maintenance was performed, or a stereo was installed, replacement transmission, maybe a flood,

Something.

 

Judging from the markings on the engine and harness it was wrecked from what I can tell it was front driver side and fixed professionally from the wield job on the frame... radio was removed before purchase alot of stripped wires inside radio bezel and some cut slap in half but nothing touching metal...

 

Oh and I've only owned it for 4 weeks...

 

Okay, I just have to ask the dumb question...is your battery connected properly or is it connected backwards?

 

Well, what did you find? I mean what was the measured voltage drop between the starter motor housing and the negative post of the battery?

 

Not sure what it means without the measured voltage drop between the body and the negative POST of the battery. You may have a missing or poorly grounded body and the PCM is some how trying to provide a ground path for the body. Won't know until you measure the drop.

 

I didn't see a drop in fact it didn't even register so it was definitely below a volt... but what about the pcm smoking when the highbeams were cut on... and the radio wiring?

 

What exactly do u mean by drop?

 

Sorry.............I mean 'voltage' drop.


Depending on your DMM, you may have to set it on a lower (DC voltage) scale. Will your meter read tenths of a volt?


If a ground circuit drops 0.0 volts it means you have a "perfect" ground. But nothing is perfect. In the real world if the circuit drops a couple of tenths of a volt that's about as good as it gets.


Now if you have a severely corroded ground wire or very rusty ground wire connection,, the voltage that can't get through the ground circuit because of poor grounds, that voltage will come through your meter and be displayed on the meter when doing a voltage drop test.


Say your ground circuit is dropping 2.3 volts because of a poor or missing ground. Those volts will be looking for a path back to the battery. Back in the day, they sometimes would find a path via the speedometer cable, or the gearshift linkage, etc. and cause all kinds of corrosion in weird places.

 

Drop is .04- .01 starter to battery terminal... other like I said when I turned on the load aka high beams the pcm started to smoke profusely... I'm sure u will say that is a short to ground but the question is where and how would that directly affect the pcm I would assume something like that is too far down the chain to be unfused... correct? My mind is boggled by this 1... also I forgot to say before also if the driver side door is opened and I push on the harness that goes between the door and cab the lights and chime will go on and off but I have dismantled the door and nothing is frayed or short to ground etc...

 

Sorry I don't know y it popped up that way. The drop is .02-.01..

 

While it is true "too many cooks spoil the broth "
I don't think that is the case here. You need to read for content.

Words have meaning (unless one is a politician) so let's define our terms. This is not a "short to ground" problem, as I mentioned this is something that should be grounded but is not.

Maybe you mentioned this already - but has the truck ran correctly since you've owned it, ever?

Or, was this a project of some kind, that would not start, bought cheaply and it was purchased with that in mind?

.02-.01 sounds good. So good, in fact, I don't think you know what you're doing (kidding!) But, it would be tough to see a starter cable below 0.10 on a drop test.

You measured this while actually cranking?

Here is a good link for performing voltage drop tests, read carefully:

http://www.aa1car.com/library/voltage_drop_testing.htm

 

Well, since you think the starter wiring is so different from a '99 to a '05, I just went out and checked my friends '99 Expy 4.6 which is waiting for a new water pump, and it has the same heavy gauge wires going directly down to the starter from both the negative and the positive posts from the battery. There's only two negative wires on it, the heave gauge one to the starter, and another slightly smaller connecting to the body on the firewall. There's a ground strap going from the firewall to the aluminum intake manifold, which I'm guessing the 5.4 doesn't have due to having a plastic manifold. Other than that, there's several ground straps on the firewall, and I'm sure there's more under the car and to the engine, but I didn't crawl under the cars to check those...

 

No the truck has not ran since I bout it u hit the nail on the head the truck was bought cheap as a quick fix and has been the opposite... we got it to fire up a couple of times when we did the last relearn and then fried the pcm again.... I'm going to bring home my other dmm today I left it on the job in my trailer because I need a new attend in it, I think the dmm I used last night was sub quality compared to mine. And the reading was probably .2-.1 a d yes I had my wife crank it while I checked the drop down... it sounds like I was wrong about the engine being that different from the 05 version however there is a ground strap that goes from damn near close to the top center of the fire wall to the top of the intake.... my intake is metal it is the plenum/lower intake that is plastic as far as I know... I haven't changed the intake gaskets on this 1 yet... and as I asked last night when I was told to do the load test and had my wife turn on the headlights qnd they didn't cut on I told her to flip the highbeams on and the pcm started boiling smoke so what would cause this and 2 here should I look for this issue? For some reason this question has been avoided to be answered like wild fire?

 

Oh and as far as the starter wiring goes I also looked at my ford f150 4x4 to see because it is also a 4.6 like your buddies and the fat gauge ground wire you are talking about that goes to the starter also goes to the bolt/stud that holds the starter on, I even looked up a pic of it for a 5.4 and it is wired correctly... the smaller gauge piece of the wire that t's off is attached to a nice shiny piece of the chassis/frame... so unless when I get off work my other dmm says differently I'm sure the starter and it's ground is fine.... we need to check somewhere else (possibly somewhere in the headlight circuit) or related to it, etc...