Blowing Pcm Fuse

[shibby_cbs]

so i have read a few threads on this issue and still havnt found any specific solutions so heres what i have...was driving down the road to work. stopped at a stop light and the truck just shut off. no sputter or or any sign that this was going to happen it just shut off...pushed it into the parking lot. ive checked the fuel pump which is not kicking on and ive also checked for spark which i am not getting. i then checked my fuses and i had a blown 30a pcm fuse. replaces it with an adjacent 30a fuse turned the key on to start and no dice. checked the fuse again and it was blown again. it seems to me that im having a wire issue and ive read in a few places that burnt wires on pipes have caused this issue. i went out and looked over the car as best i could but didnt find anything out of the norm but then again im not exactly shure what i am looking for. another thing that leads me to believe that this is a wire issue is that in the months leading up to this i have had the trans light blinking on and of causing the transmission to kick into limp mode for no aparent reason when i know the transmission is fine. i have herd that this is sometimes caused by a burnt through wire. i have also had the 4x4 hi and low light flashing on the dash causing the 4x4 to kick in at random times. any insight on to where i should start my search would be greatly apreciated... i am at a loss

p.s. sorry for the novel just thought i would give as much info as possable

 

[robertoa1a]

Usually grounding problems. A bad ground somewhere.

 

[shibby_cbs]

well there are a lot of grounds...where should i start

 

[robertoa1a]

Do you have a friend who reads schematics? A geek! I want to explain a trouble shooting procedure that I would understand in my garage but without the benifit of pictures and other stuff I am afraid that the wrong move may fry your PCM. All I can say is that It sounds like a hot wire is rubbed bare to ground or there isnt a ground where should be. The ground wires are braided strips in every part of the vehicle and thier connections get corrotion sometimes causing problems.

 

[shibby_cbs]

alright i guess i could give that a try...an update i stuck another fuse in there and noticed it dosnt blow right away but about 3 to 4 seconds after turning on the ignition...also i hooked a volt meter up to the port and it reads exactly 25.1...it never spikes or changes unless cranking the engine so i dont see why it blows after 3 seconds...dosnt make sense...also i notice alot of corrosion around the positive battery terminal below where the positive wire connects

 

[shibby_cbs]

well i dont know about reading schematics but im pretty good at following directions...give it your best shot...im pretty desperate at this point

 

[robertoa1a]

I would run diagnostics on it at Autto Zone.

 

[shibby_cbs]

i already tried that and it wouldnt read because of an error...which makes sense because the computer isnt turning on

 

[budwich]

alright i guess i could give that a try...an update i stuck another fuse in there and noticed it dosnt blow right away but about 3 to 4 seconds after turning on the ignition...also i hooked a volt meter up to the port and it reads exactly 25.1...it never spikes or changes unless cranking the engine so i dont see why it blows after 3 seconds...dosnt make sense...also i notice alot of corrosion around the positive battery terminal below where the positive wire connects

.....???? what's 25.1 ???? mamps???? Hopefully.... anyways, not many meters will out respond a current spike.... by the time it will "read" something, the fuse will blow... not very useful.

Anyways, try just turning your key to "ON" and leaving it there. IF the fuse doesn't ever blow, you then have eliminated a "few circuits" from the power circuits for that fuse. From there, you might be able to start unplugging other circuits that are enabled during "START" to find your problem.

 

[BrooklynBay]

According to other member's posts over the years on this site, it appears that you have 2 possibilities. Check the wiring to the O2 sensors near the exhaust. They sometimes get melted insulation from the heat. The other thing to check is the internal wiring harness in the transmission. One of the wires could short against the pan or the inside of the transmission.

 

[shibby_cbs]

the 02 sensor wires seem to be ok from what i can see...im guessing that i have to pull the pan to see those wires.....and thats what i did...i turned the key to the on position and left it there...herd a couple clicks...then about 3 seconds later pop...there she goes

 

[budwich]

OK... that "precision" helps a bit. To save your money on fuses, you don't need to use one for your testing. At the fuse box, with the fuse out, find out which side is the 12v side. The "other side" is the "circuit" side. From here / there, you can attach your meter and MEASURE resistance to a KNOWN GROUND. IF you are "lucky", with your key in "OFF", the readings should be high / very high / to open circuit. When you turn your key to "ON" (not start), you should see some resistance level... lower than before BUT not ZERO.... when it goes to ZERO that is when you are doing the "fuse blow" thing. Once you observe these "activities", you may be able to start further down the road to isolating your problem. Let me / us know if your observations concur with the description provided. Actually, I suspect that you might not see a "ZERO" at all because since there is no current running (ie. fuse is missing), that your "soft fault" might be relay related (ie. weak / worn winding) which may only show with juice applied. Anyways, keep us posted.

 

[shibby_cbs]

thanks for the advice...ill be shure to check that as soon as i get back home here in about an hour and let you know

 

[stu bag]

Hi
Any luck on fixing your ex as this is the same problem i have.
Thanks
Stu

 

[jiml4075]

blows pcm fuse

Had this intermittent problem with 1995 Explorer. Fuse blown. Replace fuse.
Drive several days. Blows again. Turned out be a bare spot in the harness
by the transmission. The nylon tie that holds the harness to the shift cable
bracket had broken, allowing the bracket to wear a bare spot in the harness.