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View Full Version : WTF??? Logic Module is TOAST



85shelbycharger
03-29-2006, 01:23 AM
Ok, here's one for you guys. I swapped back the stock logT1 injectors into my Charger because the 89 T1 injectors I had put in were drinking gas like it was water! haha I went from 25 mpg to 18...so it was time for a change back.
But ok, I changed the injectors and then took it for a drive down the road just to make sure everything was good. Well on my way back up the road I caught a whiff of something that smelled like it was burning, so I shut it down and coasted back into the garage. After parking it, the smell was real strong under the dash and smelled like burning wires or something. But in particular,the smell was real potent over by the logic module. So I pull the module out and took the back cover off of it and sure enough thats what went wrong. One of the wires for the MAP sensor looked as if it had started to burn...
So my question is, what would cause this? And until I get some definite answers, the car won't be getting started or anything. Thanks in advance.

turbovanmanČ
03-29-2006, 02:59 AM
Search my name in this section, I posted how to check for shorts using a headlight, :nod:

Subliminal
03-29-2006, 09:37 AM
I have a spare 85 LM, if you need it. It's out of a 85 600es turbo with an auto.

Let me know if you need it thru PM. ;)

mark
03-29-2006, 10:53 AM
I have an 85 t1 MP comp manual if you need it send me a PM.

turbovanmanČ
03-29-2006, 01:25 PM
Found it for you-DO NOT INSTALL A NEW LM/PM UNTIL YOU FIND THE SHORT!!!!!!!!!!

If you fried 2 in a row, you probably have a short. Check your grounds, make sure there good.
This is how you build a great ground tester, it will find weak ground by actually pulling current whereas multimeters pull like 1/100th of an amp thru. I have find many a bad or weak ground with this simple setup. Grab a old halogen sealed beam headlamp, get the connector-any parts store or wrecker has them. Make sure to use the high beam side-usually the low beam side is blown anyhow-add some lengh of wire-2 ft and some spade terminals. You can grind the terminals down so they fit where the mini plastic fuse goes. This will pull 20 amps or so.

Now, disconnect the PM, find out which wires are ground-hook one side of the lamp to power, now probe all the grounds one by one, the light should glow bright-if its dim-trace and fix the ground, if dead, same-fix, if bright-move on. Check the sensor grounds too. Now when done, hook one wire to ground, check all power wires-they should all be bright. You can also check other wires for grounds and powers that shouldn't be there.

This also works if you keep blowing fuses, simply remove the fuse and insert where fuse went. This lets the circuit work as the filament acts as a resistor. When it glows bright-your short is present-trace, wiggle wiring until it goes out.

CletusJones
03-30-2006, 01:17 PM
Found it for you-DO NOT INSTALL A NEW LM/PM UNTIL YOU FIND THE SHORT!!!!!!!!!!

If you fried 2 in a row, you probably have a short. Check your grounds, make sure there good.
This is how you build a great ground tester, it will find weak ground by actually pulling current whereas multimeters pull like 1/100th of an amp thru. I have find many a bad or weak ground with this simple setup. Grab a old halogen sealed beam headlamp, get the connector-any parts store or wrecker has them. Make sure to use the high beam side-usually the low beam side is blown anyhow-add some lengh of wire-2 ft and some spade terminals. You can grind the terminals down so they fit where the mini plastic fuse goes. This will pull 20 amps or so.

Now, disconnect the PM, find out which wires are ground-hook one side of the lamp to power, now probe all the grounds one by one, the light should glow bright-if its dim-trace and fix the ground, if dead, same-fix, if bright-move on. Check the sensor grounds too. Now when done, hook one wire to ground, check all power wires-they should all be bright. You can also check other wires for grounds and powers that shouldn't be there.

This also works if you keep blowing fuses, simply remove the fuse and insert where fuse went. This lets the circuit work as the filament acts as a resistor. When it glows bright-your short is present-trace, wiggle wiring until it goes out.
that's an awesome tip.

85shelbycharger
03-31-2006, 02:38 PM
Thanks for the help everyone.
What I did was when I went to change the injectors, I swapped a complete rail/injector/harness setup from another motor I had. Well as it turns out, that injector harness was junk. I put the old harness back on, and it's been running good for 2 days now...except now it is SLOW! :mad: That stock computer sure does suck lol.