PCM Fuse
1997 Ford F150 6 cyl Four Wheel Drive Manual 100000 miles

I have recently tried to get my truck running again. I have went through and replaced and diagnosed some things and now I am stuck with a PCM 30amp fuse that blows every time i try to start the truck. It did start the first time and ran for 5 mins and blew the fuse. Since then i havent been able to even start it before the fuse blows. It even blows a 40amp fuse. I am not sure how the PCM works or what could be causing it to blow.

I just pulled my spark plugs and they were in bad shape I had 2 broken plugs and they all had a 100 thousand gap(double what they were suposed to have). I heard that if my coil pack was bad it could blow my PCM fuse. Could this be the problem?
Any help is appreciated
Thank You

 

Which PCM fuse ?

cab fuse panel fuse #30, Ignition coils and PCM relay
or
Engine fuse panel Fuse #24 PCM power

If it is cab fuse panel #30, then I would double check in the 1997 -2003 forum or the correct engine forum, but I would say yes bad coil packs.

 

Its the PCM fuse #24

I have looked at 2 things that could be the problem. 1) a fuel pump short that is causing my PCM fuse #24 to blow. 2) My coil pack causing it to blow the fuse. I isolated the PCM fuse#24 by taking out the fuse for the fuel pump#19 (under hood) and the fuse for ignition coil and pcm relay#30 (under dash). I then tried to start, PCM fuse was still good. I then returned the fuel pump fuse#19 and tried to start, PCM fuse was still good. Then I returned the ignition coil and pcm relay fuse#30 and tried to start, the PCM fuse blew imediatly!! I know this narrows it down but does it pin point the problem? Is my next step to replace the coil pack?
Thanks for your input
Also any links for Diagrams very helpful


Maybe i will move this thread to the appropriate fourm

 

Fuses # 19 and #24 are fed from the same source, one is not tied to the other.

Fuse #30 feeds the ignition coils, radio cap, and the coil on the PCM power relay ( through the PCM diode ).

The normally open contacts on the PCM relay is what Fuse #24 is feeding, as well as engine fuse #1.

Now if my memory ( just having been jogged a bit ) is correct, this is also the same circuit to the heated O2 Sensors.

Might want to check H02S #11 and #12 wiring harness for chaffing. Usually caused by the wire falling against the pipe.

Hope this is it.

Good luck.

 

Thanks for the feedback....... I am not exactlly sure what harnesses you are refering too..... But I gave it a good look over and couldnt visually see any wire damage.. if you could specify where I should look that would be helpful.
As for the fuses I put good fuses in #19 and #24(engine) and #30 (cab) and just diconected the wire harness for the coil pack and tried starting...... PCM Fuse #24 didnt blow. I reconected the wire harness and the fuse blew immediately. So i am on my way to get a new coil pack. Please let me know if there is anything else that could be the problem or if there is anything that I am overlooking. Thanks for the help

 

Could then be a wire to the coil pack that is has a short to the manifold or the coil pack itself.

You could pull the coil pack and check the primary and secondary resistance on it, before doing a R&R on it.

All the threads I could find on the topic are mostly related to the HO2S wiring.
https://www.f150online.com/forums/el...-fuse-f24.html

https://www.f150online.com/forums/el...-pcm-fuse.html

https://www.f150online.com/forums/el...use-blown.html

https://www.f150online.com/forums/el...not-start.html

https://www.f150online.com/forums/el...help-here.html

Take a close look at the coil pack connector back to the engine fuse panel for chaffed insulation. Could be where the harness runs around the engine, and might be in a wirign loom that looks ok ( need to run the complete harness with your hand, and get a visual on it ).

 

Hey thanks alot sscully that gives me plenty of material to look over. And since I swapped out coil packs and am still blowing fuses........ It looks like I am going short hunting..... Hey once again thanks and Ill let you know what I find.

 

Hey well I just wanted to let you all know that I found my problem..... It only took me a couple of mins once i knew what to look for. There is a cluster of wires running from a harness next to the battery and it runs down to the transmission and transfer case. And well that cluster was just sitting on the exhaust. It had exposed who knows how many wires. Im working on getting the harness disconected so i can get it to where i can fix it. I just want to say thanks and it sure saved me some time knowing what to look for thanks sscully

 

If you can, take some pictures of it. Even if it is after you repair it, just take a picture with the area that was touching the manifold, and put a circle on it via mspaint.

This would be invaluable for the next member with a similar problem

 

Fuse F24 faults are most commonly due to wiring on an exhaust manifold.

The O2 sensor harnesses are particularly prone to this.

 

Yeah I havent got to it yet Im working on getting other projects out of the garage, so I can get it in. Before I fix it I will take some pictures and post them. I was wondering if I need speacial wire to splice in there or if similar gauge will be fine? Also does anyone know how to get the wiring harness loose? ( Grey harness, Into grey rectangle, On a Black mount to the right of the battery, the wires go to the tranny and T-case) I have pulled and pulled and broke a couple clips but in Alaska its still 10* so it think once i get it warmed up in my shop it should come right off. Also the passenger side O2 senor wires outer rubber was also melted but the wires weren't comprimised. Hey thanks guys

 

The formal answer on the topic of wire under the hood is yes, there is a specific type.

Ford's answer on the topic :

My Opinion
This has to do with how the wire reacts to heat, and the amp drop at a given temp. I have never used anything but 105* temp wire myself ( not the 90* temp wire from HD for your house ) in general, but I have a tendency to oversize wire.

If you can find it, this would be the best thing to use, if you can only find 105* wire, step up a AWG size to compensate for the load characteristic change when the temp is out of bounds.

 

These pictures are from under the truck right next to the front passenger wheel well.

 

I hung my repaired harness up to what I think is my AC and there is no reason that it needs to be even close to the exhaust. So all fixed, thanks for saving me time and money!!

 

You saved yourself the money. I don't recall any dirt under my fingernails from searching that harness

Glad you got it take care of, sorry you bought the coil pack, but you have an extra now.

Thank you again for posting pictures.

The next member to search for the similar symptoms of PCM fuse, F24, Fuse 24 will be thankful for the pictures you posted.