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died while driving, electrical smoke from dash

 
  #1  
Old 06-22-2019, 11:48 AM
gobabcock
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died while driving, electrical smoke from dash

Hi -

I'm new to the forum and I'm a stumped (I've poked around the existed forums to see if anyone's had this problem, but nothing seemed to come up). I've got a '92 F150 with a 4.9, 5 speed with a billion miles on it. I started it up the yesterday, started down the road and then it suddenly died. It rolled to a stop and I noticed smoke coming from the driver's side of the dash and the smell of electrical wires. Tried starting it again, it turns, but won't start. The only thing I'd noticed about it recently was that my blinkers stopped clicking - the turn signals turned on the lights, but they didn't blink. Didn't worry much about it as it's basically a back country road truck that doesn't have much need of blinkers. I pulled the dash cover, but I can't find any obvious signs of melted wires, etc. Any ideas of what I should look for and begin to diagnosis this? It would be great to get this thing solved as the truck's sitting in a buddies driveway. Thanks!!
 
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Old 06-22-2019, 12:45 PM
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Really your only choice is to look closely for burned wires in the area you saw the smoke. I suppose you instead could do continuity testing on every wire, but that could take you years and years......
 
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Old 06-22-2019, 01:48 PM
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Thanks - alas, that was what I feared. If anyone thinks there's anything else worth doing beside digging through the wiring, let me know!
 
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Old 06-22-2019, 01:57 PM
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I don't know where the smoke came from but examine your headlight switch. Apparently they are noted for starting fires. Mine still works but I can definitely see heat charring on it.
 
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Old 06-22-2019, 04:42 PM
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I checked it and it does look charred, though it's still functional. I'll pick up a new one, though I don't see how that would create a short that would keep the truck from starting.
 
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Old 06-23-2019, 09:08 AM
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It's kinda odd that you would have a "crank but no start" condition caused by anything shorting under the dash. If it was a "no crank" condition I tell you to investigate the wiring from the ignition switch. Might as well do that regardless.

Have you confirmed a "no spark" condition?
 
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Old 06-23-2019, 09:53 AM
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Does the CEL come on when you turn the key to Start?
Can you pull codes?

Usually smoke or smell of burning is from the Headlight switch harness shorting out/burning or the PCM has MAJOR problems. Both are on the same side.
 
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Old 06-23-2019, 10:36 AM
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No CEL when the key is on. I'll try swapping in a PCM - though in the past I remember having a hell of a time figuring out which PCM is right for this truck (I didn't swap it out for that reason). Anyone have the PCM part number for a 92 F150 4.9 4x4 w/5 speed?
 
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Old 06-23-2019, 10:49 AM
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Here is the Catch code. I lost the actual number for the PCM, but mine is exactly as yours. '92, 4wd, 4.9

Use that Alpha-numerical value in Google.
 
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Old 06-23-2019, 10:51 AM
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Thanks man! I really appreciate it - I'll report back when I swap one in. Again, can't thank you all enough.
 
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Old 06-23-2019, 11:03 AM
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I had a chance to Google that number.

F2TF-12A650-ASB

Also, mine is a 5 speed. Forgot to mention that in my last post.

Be sure to pull your PCM and open it. Look for any electrical damage.
 
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Old 06-23-2019, 11:49 AM
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Originally Posted by gobabcock View Post
I checked it and it does look charred, though it's still functional. I'll pick up a new one, though I don't see how that would create a short that would keep the truck from starting.
Oftentimes what people call a "short" is really loose, missing, or corroded ground points, cables, and connections. A toasted lightswitch falls into that category, and so does the turn signal symptom you describe. Those cables are approaching 30 years old. I would doubt any of the main connections and grounds have been cracked open and cleaned in all those years? If the cables are original, or even just old, they should be replaced. Low voltage, high current wiring doesn't like any resistance. Even an invisible, paper thin layer of corrosion at a connection is enough to cause major trouble.
 
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Old 06-23-2019, 03:07 PM
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Originally Posted by Tedster9 View Post
Oftentimes what people call a "short" is really loose, missing, or corroded ground points, cables, and connections. A toasted lightswitch falls into that category, and so does the turn signal symptom you describe. Those cables are approaching 30 years old. I would doubt any of the main connections and grounds have been cracked open and cleaned in all those years? If the cables are original, or even just old, they should be replaced. Low voltage, high current wiring doesn't like any resistance. Even an invisible, paper thin layer of corrosion at a connection is enough to cause major trouble.
That's kinda what I was thinking... which, of course, is a bummer. However, I'm hopeful about the PCU. I pulled it and right when I disconnected the wiring harness there was a pronounced burnt smell. I open the PCU up and it looks fried. I'm hoping (fingers crossed) that that's the issue. Once I get a new PCU in I'll let you know what happens. Again, thanks for all the replies - I'd be swearing up a storm looking through wiring right now, never thinking to have looked at the PCU without the help.
 
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Old 06-23-2019, 06:14 PM
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OK, but is the fried "PCU" a cause, or a symptom? Roasted light switches, dash wiring? See where I'm goin with that?

If you leave those defective parts installed, that's the bummer, because stuff will just keep roasting.
 
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Old 06-24-2019, 07:16 AM
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Absolutely - don't get wrong, I'm putting in a new headlight switch and, once I can get the thing started, track down the blinker issue too. Having pulled the dash and looked at some of the dash wiring, the only thing I found the really looked obviously fried was the light switch. I checked the ground by the battery, which was fine - the ground to by the starter was a touch loose. I cleaned that and tighten it up too, just for good measure.
 

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