99 Grand Marquis Computer

[MarkVI351]

hey everyone. this isint about a marauder, but its a mercury. ok, car kept overheating and burning out fans and a relay. found out that it is the computer. now, here is the question. im going to the junkyard, and will a computer from, say a 97 marquis or vic work on the 99 marquis? your help is greatly appreciated. thanks.

[RoyLPita]

For a little extra pep, you could try for a CVPI PCM. Also, have the wiring harness checked for any shorts. After 8 accidents, that could be a problem, too.

[MarkVI351]

yeah, i check all the wires, and the wires that were cut were the wires by the fan that we had to replace a few times. im just wondering if a computer from a 97 pi will br ok on a 99, cause at the junkyard i go to, i just pick em off and they are about 20 a peice. now wheres the pcm at?

[RoyLPita]

Just to be safe, you should get one for the same year. The PCM is located under the dash on the left side by the e-brake pedal assy. You will need to remove a cover, first. You access the plug in the engine compartment on the firewall behind the cruise control servo . You'll need a 10mm swivel and extensions to loosen the plug.

[MarkVI351]

alright, im gonna be leaving in a half hour. so the somputer is right next to the pcm then, under the dash? so this shouldnt be that hard at all.

[MarkVI351]

ehhh, its raining too hard outside. ill go some other day. im going to get one off a p71, so i dont have to get anything reflashed. that should work out pretty good.

[wchain]

ehhh, its raining too hard outside. ill go some other day. im going to get one off a p71, so i dont have to get anything reflashed. that should work out pretty good.


As long as your Grand Marquis GS has a 3.55 or 3.27 rear end the CVPI computer should be fine. If not, the shift points are going to be SKY HIGH. And the Odometer will be off...99 was the first year that speedos/rear end ratio were computer calibrated.... Also, with a CVPI computer, you lose the PATS feature, i.e. the car will no longer need a PATS key to start properly and run. If you get another PCM from a P73/P74/M74/M75, you will need to program the PATS keys to run with the new PCM.......

[RoyLPita]

This is becoming more of an adventure than previously thought. My apologies for trying to make this easier.

[MarkVI351]

well, we ended up ordering a computer from the stealership. it should be here on wednesday. see, we didnt want to get a new one cause my dad would be trading it in after the winter. but, what the hell, might as well fix it right.

[wchain]

well, we ended up ordering a computer from the stealership. it should be here on wednesday. see, we didnt want to get a new one cause my dad would be trading it in after the winter. but, what the hell, might as well fix it right.


You do realize, if it is a 12A650 the you will have to pay the service department around 1 Hr To Flash it as well, and probably reprogram your PATS keys too...............

[MarkVI351]

we have the car at our mechanic and he will have to take care of everything. as long as we get it done and the car runs, my dad doesnt care. he was left without a car for two weeks already. he had to use the mark vi for a few days, while we had our snowstorm. and now hes just laying around the house. he just wants to get it fixed right so he can get back on the road and make money. thanks anways for your help. im proably going to get a computer from a 96 cvpi, cause when we got the 96 motor installed in our 94 vic, it was from a very low milelage marquis, so i will need to pick up a 96 computer.

[wchain]

we have the car at our mechanic and he will have to take care of everything. as long as we get it done and the car runs, my dad doesnt care. he was left without a car for two weeks already. he had to use the mark vi for a few days, while we had our snowstorm. and now hes just laying around the house. he just wants to get it fixed right so he can get back on the road and make money. thanks anways for your help. im proably going to get a computer from a 96 cvpi, cause when we got the 96 motor installed in our 94 vic, it was from a very low milelage marquis, so i will need to pick up a 96 computer.
Good luck converting your EEC-IV/OBD-I to an EEC-V/OBD II.....why would you want to change the computer? 94 was EEC-IV 95 was a bastard year due to changes towards OBD-II and 96 was the first year for full OBD-II......