I was checking the coolant gauge on my truck so I was going to ground it and see if it swung to full hot. Well I was thinking about it wrong, and used a positive wire. Got some sparks but the gauge didn't move. Well after that, the truck wouldn't start. It started with some ether but won't keep running unless my foot is on the gas. Think I shorted something out or blew fuse somewhere? Does that wire just connect to the gauge or does it go to the computer too?

 

Sorry, I should have noted that it is a 1985 302 EFI

 

Go over to the starter solenoid and check the small wires leaving the large post that comes from the battery. You will find little rubber pieces in the wiring, these are fusible links. You might have burnt one of those out.

 

Question about the fusible links,

One has a ring terminal then goes to a large rubber overmold that says fusible link, then goes to another rubber overmold and then on to the alternator, I test that one with a pin stuck in the insulation behind the second overmold and it tested fine with continuity.

The other two wires only seem to have one overmold before they disappear into the wiring harness. I stuck the pin in right behind the overmold and it has continuity, is it possible it could still be bad? Is it a bad idea to just try using a regular wire, since I know I'm what caused the short in the first place and then replace it if that's the problem?

Also another question the small ground coming from the battery terminal goes to a connector with two wires coming out of it. I disconnected the connector and push a probe into the two wire side. I then try to get continuity between the two wire connector and anywhere else on the truck. I was thinking I should get continuity between the small ground wires and the large one going to the engine. Does anyone know where those two wires go besides into the main wiring harness?

Also, I hooked up my code reader and it wouldn't give any led flashes, it just said steady on. Which according to the book could either be dead battery in the code reader(I don't have another 9 volt) or a bigger problem. I did also have the battery disconnected last night so that might be why.

Also, the truck would start with starting fluid and kept running but at a very rough idle for about 5 minutes until I turned it off. Really seems like an ecm issue to me.

Thanks for the help!

 

This sounds to me like a problem with the IAC - idle air control (or some such) it's an electric
motor that controls the idle speed and is controlled by the computer. But, I have no idea how
to test it, and the fact that you can't get any codes tells me something is up on the computer
side....

 

Another thought... I have zero experience with computer-controlled truck engines but
my understanding from what I've read here is that there are two sensors for water temperature.
One is for the dash gauge (or light) and has no involvement with the computer whatsoever, the
other is used by the computer for making engine-control decisions.

Assuming a 302 or 351W, I think the dash-gauge sensor is on top of the intake manifold
somewhere and the wire is red with a white stripe; dunno about the other sensor but I *think*
it's on a radiator hose gooseneck (no idea of its colors).

If you fed 12V into the computer in a place where it's not expecting it, you almost assuredly
fried it.

 

That would kind of make sense, it sounds like it's trying to suck air, like a vaccum cleaner. Much louder then normal. I wonder if I could have shorted that out, or if it's because of the computer that it's acting weird.

 

Yea I fed 12 volts into the two wire sensor on the gooseneck. So stupid. So do I order a new computer or cut out the fusible links, even though they have good continuity. Anyone had luck with the autozone computers? Shows $128 for my application/transmission, 302 EFI/Manual

 

Your fusible links are probably fine, you might be able to get a junkyard computer for pretty
cheap but the AZ computer you mentioned isn't horribly expensive and it has supposedly
been tested and is known to be good (in theory, anyway).

 

Here is a pic of the coolant temperature SENDER that has a single red/white stripe wire that
leads directly to the dash gauge (or light), I believe it's located on the driver's side rear on top
of the intake manifold but could also be on the top front somewhere:

The way to test this device and your gauge is to pull off that wire and, with the key in ACC
or RUN, ground it out someplace, the gauge should swing all the way in one direction (prolly
towards the high end).




The two-wire SENSOR hooked to the computer for making engine-control decisions looks
like so:




If you get a junkyard computer, BE SURE YOU GET THE RIGHT ONE/SAME PART
NUMBER as "the right one" depends on the engine's year and Calibration Code.

 

Do yourself a favor, when you're done poking holes in your wiring insulation, plug them up with a dab of liquid electrical tape to prevent moister from attacking the copper and corroding.

I know it's done frequently and has been for many years, I do it at times, however poking holes in insulation is ignorant!

Sometimes, you gotta do what you gotta do, to get what you gotta get done, done!

-Enjoy
fh : )_~

 

Yea, I don't like poking holes either but like you said....

Before I buy a new computer, I wanted to do a complete test of the harness plug and make sure all the wires going to it are good. I have the factory ford manuals for the truck, but they really make no reference to the computer.

Is a Chilton or Haynes manual worth picking up. If people have both which one would help me out more?

 

I know the dealers/authorized Ford repair facilities had an electronic device with
blinkenlights to plug in in between the computer & harness that would do the tests you're
speaking of, wouldn't know how to do it manually.

I have the factory body/chassis, engine, and wiring diagram manuals for my 1981 F350 but
I don't know if *any* 1981 had a computer as mine certainly doesn't. There might be
something listed in the vacuum/emissions troubleshooting manual but I really don't know,
have only heard they're good manuals.

IMHO the Haynes/Chiltons are good for looking up common specs - lug nut torque, for
example - but that's all.