P71 PCM | SuperMotors.net Forums

DE

Member since Nov 2012
17 posts
Minneapolis, MN, USA
1 vehicle in the registry

Sep 17, 2013 at 10:59 AM

I've read a lot of counterdicting information on whether or not I can use a 2005 P71 PCM in my 2005 Mercury Marquis for performance gains. I am way confused so I will ask the question again and PLEASE someone give me the correct advice. If I get a 2005 P71 Police Intercepter PCM and plug it into my 2005 civilian Mercury Marquis will it work and would it be worth my time and money to do so? Lastly my Marquis has 2:73 gears so is that a factor when changing PCMs. thanks......det45

HO

hondaclf

Member since Feb 2009
244 posts
Baldwin, NY, USA
4 vehicles in the registry

Sep 17, 2013 at 2:27 PM

You will also need the correct P71 airbox, the MAF sensor is the same between the 2 cars but the housing is different, your car won't run correctly without the right airbox.
The speedo will be off but not by much since most P71's have 3.27 RAR.

Does your car have cruise?
Does your car have rear air suspension?

DE

det45OP

Member since Nov 2012
17 posts
Minneapolis, MN, USA
1 vehicle in the registry

Sep 17, 2013 at 2:44 PM

Yes I have cruise control but no air suspension.

HO

hondaclf

Member since Feb 2009
244 posts
Baldwin, NY, USA
4 vehicles in the registry

Sep 17, 2013 at 3:07 PM

Make sure the P71 you get the PCM from has cruise.

DB

dbmcd

Member since Oct 2001
69 posts
Los Angeles, CA, USA
16 vehicles in the registry

Sep 25, 2013 at 9:45 PM

You are assuming that a P71 has some secret performance stuff that you car doesn't. To my knowledge it only has a larger air intake tube. I wouldn't mess with the PCM, you'll end up messing with things you don't want to mess with. The ratio in a 2005 P71 is 3.55 (I own one) and yes a lot of stuff would be off beside the speedo, like shift points. Big difference between 2.73 and 3.55!!! P71's idle at a higher speed than a civilian. Bottom line is...your car probably wouldn't perform better but would have a lot of mismatched PCM signals and cause you a headache. Buy a drop in K&N air filter and take your girl out to dinner and you'll be much happier. Dave
http://www.supermotors.net/registry/17956

Quote:

I've read a lot of counterdicting information on whether or not I can use a 2005 P71 PCM in my 2005 Mercury Marquis for performance gains. I am way confused so I will ask the question again and PLEASE someone give me the correct advice. If I get a 2005 P71 Police Intercepter PCM and plug it into my 2005 civilian Mercury Marquis will it work and would it be worth my time and money to do so? Lastly my Marquis has 2:73 gears so is that a factor when changing PCMs. thanks......det45

HO

hondaclf

Member since Feb 2009
244 posts
Baldwin, NY, USA
4 vehicles in the registry

Sep 26, 2013 at 4:36 PM

Quote:

The ratio in a 2005 P71 is 3.55 (I own one) and yes a lot of stuff would be off beside the speedo, like shift points. Big difference between 2.73 and 3.55!!!

You are incorrect, at least partly. Not all P71's have the same rear axle, some are 3.55, some are 3.27, some are open, some are trac-lok.

There is a reason why a P71 has a higher HP rating than a CV Sport and it's not magic, they both have dual exhaust but the P71 has the larger MAF housing and larger airbox inlet.

DB

dbmcd

Member since Oct 2001
69 posts
Los Angeles, CA, USA
16 vehicles in the registry

Sep 26, 2013 at 7:35 PM

I am correct in the fact that he mentioned he has a 2005 which is also the year I have which has a 3.55.

DB

dbmcd

Member since Oct 2001
69 posts
Los Angeles, CA, USA
16 vehicles in the registry

Sep 26, 2013 at 7:38 PM

So you would recommend he change out his PCM to gain performance?

HO

hondaclf

Member since Feb 2009
244 posts
Baldwin, NY, USA
4 vehicles in the registry

Sep 27, 2013 at 12:41 PM

Your exact words were that a 2005 P71 has a 3.55 RAR, for your car that may be correct but it is not a blanket statement. I had a 2005 P71 and it had a 3.27 trac-lok, they can have 3.27 or 3.55 open or trac-lok(pretty sure all ordered with 3.55 would be trac-lok though)

Quote:

So you would recommend he change out his PCM to gain performance?

I would recommend a tune, best bang for the buck but it costs money on top of the mods you use with it.
The power increase from a P71 vs a Grand Marquis or P70/3/4 is because of the MAF and the exhaust, that's it.

DB

dbmcd

Member since Oct 2001
69 posts
Los Angeles, CA, USA
16 vehicles in the registry

Sep 27, 2013 at 1:26 PM

I don't think he's listening to us anymore...