I connected the wrong terminals to the battery (reverse polarity).

[ctemme]

i know dumb a** mistake i put in a different battery thinking it was the same setup and it wasnt. i conected the postive to negative and negative to postive on battery. the horn sounded and took it off and thats when i noticed the mess up. know the car started and was able to drive a little bit after i but the battery in teh right way but know it wont start. the brake lights went so i replaced the brake switch then i was told it was the ECU so i just replaced that now it wont start it just cranks and wont kick over does anyone know what it could be?

1999 Ford Explorer Sport 4.0 4X4
All Stock

 

[techieman33]

Did a dealership replace the ecu? If you just pulled one from a junkyard it it probably pats that won't let it start. The ecu and gem have to be a matched pair, and mated to your keys.

 

[ctemme]

the numbers matched i checked that before i got it

 

[ctemme]

could it be the coil

 

[2000StreetRod]

Polarity sensitive

I doubt that the wrong polarity would affect the brake lights or anything else that is just a filament. If the engine started and ran at all after connecting the battery correctly then the PCM may still be good. Many digital devices have diodes to protect them from damage due to incorrect polarity.

I would check all of the fuses - especially the ones associated with the alternator. The voltage regulator may have been damaged but not necessarily. If you find blown fuses and they are associated with the alternator or the PCM I would replace the fuses, reinstall the original PCM and try to restart the engine.

The PATS may have been damaged by the reverse polarity. Check the THEFT light for normal function.

 

[ctemme]

we checked all the fuses and the only one that was blown was the radio. we took the alternator off and had it tested and that was good. it turns over but wont start

 

[fixxxer]

The PATS system disables the starter, if the PATS kicked in, you wouldn't get it to turn over. Did you check for spark? Do you hear the fuel pump kick on when you first turn the key to "on"?

 

[BrooklynBay]

Welcome to this forum! I've renamed your thread, and moved it into the under the hood section.

 

[ctemme]

there is no spark and i cant hear the fuel pump kick on when i turn the key in the on postion. what should i do with the starter? whats PATS?

 

[jrowe6]

maybe this is stupid, but might want to check the inertia switch. i think its on the passenger side on the right corner as far forward as you can get under the carpet

no connection to the no spark tho

 

[2000StreetRod]

Passive Anti-Theft System (PATS)

For normal operation the "THEFT" blinks slowly (every few seconds) with no key in the ignition. With a valid key the "THEFT" should not illuminate when key is in Start. If "THEFT" blinks rapidly with ignition key in Off, On or Start then PATS has determined the key to be invalid. That may be due to the PCM swap or because PATS was damaged from reverse polarity supply.

If you have any abnormal THEFT" indications I suggest that you revert to the original PCM and recheck "THEFT" normalcy. Your engine will not start when "THEFT" is blinking rapidly.

 

[Joe Dirt]

the numbers matched i checked that before i got it

The issue with the PATS isn't that the part numbers match, the ECU, GEM module and your keys have to be mated- there are computer chips in your keys that have to be "ok'd" by the GEM/ECU to start the truck.

If you bought an ECU/GEM that had the same part number as yours, but are still using your old keys, they are not yet mated up. That could be your issue- check the theft light as 2000sr suggested...

 

[ctemme]

if thats the case how would i match the key up with the ECU

 

[Vargas]

if thats the case how would i match the key up with the ECU

Look in 1995-2001 Stock forum. There is a great thread about PATS.

 

[ctemme]

i put the old ECU back in it and the theft light is blinking every 2 secs

 

[2000StreetRod]

Making progress

Does "THEFT" light go out (not illuminate) when key is switched to Start? If so, your PATS issue is resolved and you can start diagnosing why the engine does not start.

Does the starter motor crank the engine?

You may want to read my Engine No Start Procedure