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Ford Crown Victoria/Mercury Grand Marquis Modifications

joe110joe110 Member Posts: 19
Hello to all! Totally new to all this. I own a 2005 Crown Vic P74. I recently had it tuned by SCT (computer flash Excal 2)and it runs really strong. I currently have single exhaust. I want to have duals put on it with Flowmasters. If I do this, does anyone know if it will throw the computer off and make it run like crap. ">


  • euphoniumeuphonium Great Northwest, West of the Cascades.Member Posts: 3,425
    Very likely. Remember your on board computer is programed for one cat sensor and if duals are installed, then what?
  • dekesterdekester Member Posts: 322
    When did they change to a single cat? MY 84 Crown Vic had dual cats and then a "Y" pipe into a single exhaust. When I had the cats replaced under a recall in 1990, I had the dealer put on a dual system. No problems at all with it.

    Haven't gotten underneath my 03 Grand Marquis yet to have a look-see.

  • joe110joe110 Member Posts: 19
    I spoke with SCT today. They said when you install the duals, you have to flash the computer to turn off the sensor. Sometimes you can get by without turning it off.
  • turbo301turbo301 Member Posts: 73
    Don't forget, though, that it's much easier to change stuff like that on the old carbureted cars. With all of the computers and sensors on new cars, some traditional tricks may hurt performance rather than help, if they're not thought through very carefully.

    On that note, though, I could have sworn that my '04 has dual cats, connected through a Y-pipe to the single exhaust. Did this change for '05?
  • joe110joe110 Member Posts: 19
    I spoke to the SCT dealer and he told me if I put duals on my car, he could get me a stock tune for the Excal 2 that would disable the o2 sensor if needed. Its a standard procedure. But for me to see how the car runs first before changing anything.
  • joe110joe110 Member Posts: 19
    My 05 crown has dual cats. I always thought they came with dual cats. I have duals into one pipe.
  • joe110joe110 Member Posts: 19
    I just installed a chrome diff cover. For anyone else who wants one, go to The rear of choice should be a 8.8 10 bolt. There is no listing for a crown vic. You have to match it up as a mustang GT. Looks nice too. Paid 33.98 delivered.
  • marsha7marsha7 Member Posts: 3,703
    It the rear diff cover just flat chrome, or is it cast with heat dispersing fins???
  • joe110joe110 Member Posts: 19
    Its just flat chrome. The ones you are talking about are like 180 bucks or so. Polished aluminum I think.
  • marsha7marsha7 Member Posts: 3,703
    I was pricing one out for my Ram 1500, and it was over $200
  • p100p100 Member Posts: 1,116
    Keep in mind that aluminum dissipates heat three times faster than stamped sheet metal. Therefore, finned aluminum transmission pans and differential covers are the best.
  • dekesterdekester Member Posts: 322
    If I change my 03 to a dual system, would a crossover (or "H" pipe) help? I know this balances the sound and back pressure on other cars. Would I need to "flash" my computer? If so, where would I go to get this done?

    Since I'm younger than the usual Grand Marquis owner demographic (at elast in Florida), I want to have mine stand out from the crowd a little. Looking at some aftermarket wheels; really like the American TorqueThrust "D"( with the dark painted spokes) or the TQ II which are all polished aluminum. A little pricey, so I'm considering the old standby - Cragar S/S, but I can't get anyone to tell me what size/backspacing/offset matches the stock steel rims so I can use the tires on the car now.

    Upgrading to a set of factory LS alloys will run me about $200 per....

  • jsylvesterjsylvester Member Posts: 572
    Get a set of black steelies, and put the chrome center cap, and maybe chrome trim rings. A lot cheaper than alloys, and looks "industrial" to me.
  • joe110joe110 Member Posts: 19
    You should have dual cats already. Take it to a muffler shop or specialty shop and tell them you want true duals put on it. You can choose whatever kind of mufflers you want. Loud or soft. Or buy your own. As far as flashing the computer, some say the car will run rough when the duals are installed and the computer needs to be adjusted. Or some say the car will run fine. At any rate, flashing the computer will give you 12-25 more HP and increased drivability. Go to and go under "products" and click on "ford products." Or speak to the guy I dealt with and ask him anything. I bought my Excal2 from him. He knows his stuff. My 05 kicks butt now. And no, Im not working for him or anything. Im just amazed at what a difference it makes on the car. Go to Just tell him what you want out of your engine. Good luck!
  • dekesterdekester Member Posts: 322
    If I do that, it'll just look more like an unmarked SHeriff's cruiser. Mu GM is Aspen Green with dark tinted windows. I fool people sometimes when they look quick, but once they see the crome grille and rear end reflector, they realize is isn't what they thought it was.

  • jsylvesterjsylvester Member Posts: 572
    Got it. The problem you have is they changed the wheel offset for 2003, so you cannot use any wheels designed for a pre 2003 Grand Marquis; otherwise I'd suggest the lacy spoke wheels on the 95-02 HPP/LX Sport/LSE models.

    They would be fairly easy to find used. New wheels will cost ya.
  • p100p100 Member Posts: 1,116
    More and more rednecks around here (central Florida) are buying old police cars at auctions and driving them everywhere. Boy, does this irritate me! As if we did not have enough real police cars around! Money is tight everywhere, so police is lurking everywhere, trying to give out as many speeding tickets as they can. All we need is these lookalike cop cars to make life more pleasant on the overcrowded roads around here.
    I saw one such car today that still had the police numbers painted on it, including big ones on the roof. It also had the spotlights in the front. Only the civilian license tag and the kid behind the wheel gave it away, as it was a fairly late model car.
  • fatpunkfatpunk Member Posts: 4
    so i am now the proud owner of a 93 GM its got 40k miles on it and its in close to perfect condition 2 owner car. Well my question is simple can anyone on here point me in the direction of any performance enhancements after market or oem, and with those preferably websites where parts can be ordered. i am not looking for anything drastic just maybe a 50 hp gain to get me away from the low baseline of 190....thanks for any help. :) (oh and i am not just being lazy i have actually done a bit of research and am not finding much so i figured i would ask what seems like a good community.)
  • euphoniumeuphonium Great Northwest, West of the Cascades.Member Posts: 3,425
    Maybe a K&N air filter system, but otherwisedue to the, onboard don't mess with, computer you have what you bought.
  • joe110joe110 Member Posts: 19
    I own an 05 CV and I flashed the computer. Go to and Email this guy. Tell him what you have and what you want. He can set you up. My car went from a kinda fast car at 225hp to a real screamer. Not sure of the HP now but it feels like 270 or 280. I am looking to change the air intake because its not getting enough air now at full throttle. The other site is Click on the Ford performance tab. Also look into changing the rear to 323 or 355. I am currently checking the gas mileage and am still getting 300 miles on a tank of gas. This is what I got at the stock setting on the computer. Good luck!
  • marsha7marsha7 Member Posts: 3,703
    Pardon my ignorance, but who did the flashing of the computer, how is it done, and just how does it "improve" the HP and performance??? can't change the compression or the internal engineering of th enginbe, so how does performance improve???...thanks...
  • joe110joe110 Member Posts: 19
    You are not being ignorant. Every car since the 90's are controlled by an ECM. Lets just use Ford for obvious reasons. I was told by SCT that our computers are compatible in more than one car. Its just tuned by the factory with a factory setting. For Ex- my computer can be used in a Excursion or a Lincoln LS. It just needs to be programmed by the factory. The rest you should be able to figure it out. Sure, a bigger cam or higher compression can increase the HP, but you should still tune the ECM to get all you can out of the engine. As far as flashing, you have to buy the flash device. It may be used or new. Mine was new at 425 bucks. Go to He sells new and used Flash devices. Or buy a Fast ford and Mustang mag. Look for flash devices in the mag. There are all kinds. I just plug SCT because I was referred by a Mustang user and tried it. I spoke to him last week and his brother works for a ford dealer. He got a used ECM and was playing with the programs. He was giving it to my buddy with the mustang to try out. Good luck.
  • turbo301turbo301 Member Posts: 73
    "Flashing", or reprogramming, the car's engine control computer adjusts things that are vacuum or mechanically operated in older cars: things like the timing, fuel/air mixture, idle speed, etc. are all adjustable, and all affect engine performance, life and fuel economy. Different vehicles and vehicle types benefit from different values for the various parameters, but using a common, programmable computer in multiple vehicles helps keep the cost down :).
  • abfischabfisch Member Posts: 591
    Have any of you changed the shocks to high performance shocks or changed the bushing to PU??/ Interested in buying a used CV and working on it myself, and wondering if anyone in this forum has done this. I have done this on my 02 Toyota Avalon with dramatic results.

  • rhill7rhill7 Member Posts: 3
    I just bought a left over 2006 GM with the handling, 3.27 rear axle, and dual exhaust package. I am happy with the power, but I would like to change how the transmission shifts and locks up. On my last car with OBDI, I was able to change the start in second gear so that with the shift lever in "2", it would start in first and then shift to second and then stay in second until I moved the shift lever to "D". I was also able to delay the shift to Overdrive and the convertor lockup to what I thought were acceptable speeds to avoid lugging the engine. I know that I can try to train my wife to use the "Overdrive Off" button in the column shift lever, but I'd like to avoid that if possible by reprogramming the transmission shift points.

    Does anyone know who sells a program for editing the transmission shift points and lockup points? Or is that available commercially for this car? I'd like to do my own programming if possible so that I can make adjustments until I get it where I want it without having to send a computer back to a tuning person several times.

    Or, what tuning persons work on our cars?

    Thanks in advance. :) RHill
  • rhill7rhill7 Member Posts: 3
    The Electronic Control Module (ECM or "Computer") typically has a program with instructions like "If the throttle position sensor is greater than X% and the manifold pressure is greater than P, then set ignition advance to A and the fuel flow to F". The values of X, P, A, and F are found in tables which can be edited. Editing the tables can make use of premium fuel and provide more power if you decide to use premium fuel. Editing the shift point tables can also make the car perform more aggressively by keeping the transmission in a lower gear for longer. Other significant improvements to the car's performance will probably involve the traditional increase intake airflow and exhaust flow and cubic inches. Or increase airflow by supercharging and fuel energy with nitrous, etc. Most modifications will involve computer table modifications to get the most out of them.

    To modify the computer tables, typically you copy the program/tables from your car to a laptop or destop computer, edit the tables, and then load them back into your car's computer "Flash the computer".

    For what it's worth and your mileage may vary. :)
  • wearewellablewearewellable Member Posts: 1
    Our 1998 Grand Marquis 4.6 liter V8 has a small crack on top of intake where the thermos goes. Apparently it is plastic and to buy the part is supposed to be over $200. Is there a way to repair the small crack? Husband needs advice.
  • euphoniumeuphonium Great Northwest, West of the Cascades.Member Posts: 3,425
    Check with dealer. That may be the intake manifold that has a factory recall order.
  • chrismiller2chrismiller2 Member Posts: 1
    I have a 1999 Ford Crown Victoria and was wondering if the gauge cluster of a newer model crown victoria such as the 2006 with the tachometer would work in the 1999.

    Thanks for helping, if you can. :confuse:
  • royfroyf Member Posts: 1
    Hi Joe: I own a 04 CV Sport that came with dual exhaust. Each bank on your engine has a cat before it goes into a single pipe. I owned an 04 Cv with a single exhaust & had duals put on it.No problems at all & you will see a marked increase in performance with the duals.
  • greeleygreeley Member Posts: 1
    My manifold is also cracked. Looking for recall info for it but cant find it. Also when i went to the dealer they said that it was past the 7 year warranty period and even if there was a recall they don't fix it. I think that is bull(*&^. Any other advice or stories about intake manifolds?
  • pimpin69pimpin69 Member Posts: 1
  • hyphyhyphy Member Posts: 2
    yes i know its silly. but what mods do i have to do to 97 vic to put these rims on it. spacers? cut wheel well?
  • euphoniumeuphonium Great Northwest, West of the Cascades.Member Posts: 3,425
    Don't know, but submit a photo when installed. :)
  • gearhead11gearhead11 Member Posts: 8
    I have an 84 crown vic 5.0 throttle boddied carb. I just can't seem to get it to idle right. it either idles high or too low and when it idles low it surges. Iv'e replaced dist cap,plugs,upgraded wires and hotter coil. I've checked for bad vacuum lines. Any ideas? Is there any way to bypass the eec-iv computer and run a regular carb? :confuse:
  • dj7tryppdj7trypp Member Posts: 3
    Anyone know how to switch the computer from a manifold air-pressure sensor to a mass air-flow? Do I have to replace the entire induction system? If so, what are some good aftermarket choices?

    Also, the engine likes to cut out when I go around corners... I can''t even find anybody that's had the same problem.
  • ts128ts128 Member Posts: 1
    My Grand Marquis has been doing some strange things lately, it all started late one night when my daughter went out to get something out of the back seat, when she opened the left rear door the car began to turn over like it wanted to start, then it stopped, the next time it did this was when we were driving it, it started grinding like crazy, so the first thing we thought was to replace the starter, didn't help, next was it went to FOMO where they said it was a loose wire under the dash, it didn't happen again for two weeks and then it started doing it even worse, so I inspected the steering column for wires rubbing or loose, found nothing, checked the ignition switch and all looks to be good so I moved on to the starter relay and changed it. I'm hoping this fixes it but just wanted to see if anyone else with one of these cars has experience this.
    Thanks, Tim
  • patsmaleypatsmaley Member Posts: 12
    i have a 98 mercury grand marquise with only has a v-8 4.6 engine.i would like to get at least 300hp or more without ripping my engine completely down. would any one have any suggestions?
  • euphoniumeuphonium Great Northwest, West of the Cascades.Member Posts: 3,425
    Before starting engine modifications, find out if the on board computer is compatible with the proposed changes. I learned a long time ago that should be checked out first when a Crower camshaft replaced the factory part. The computer would not let the new cam do its grind.
  • patsmaleypatsmaley Member Posts: 12
    yes my computer is there anyway i can gain horse power with out tiering down my motor? i'm hpoing to gain at least 150-200hp before april,thats when lebanon valley speedway opens again.ty
  • gunpackergunpacker Member Posts: 2
    Hey everybody,
    I want to change out my 2009 Grand Marquis grill & put in a Chrome Crown vic grill.
    Does anyone know for a fact that the grills are alike ? I don't want to buy one and it not fit...

    Thanks everyone,, :D
  • bushiebushie Member Posts: 1
    Did you ever get an answer to the "engine cut out" problem going around corners? I am having the same problem and haven't a clue. I have been getting a P0420 DTC so I'm wondering if the emissions are getting so rich that somehow the F/A adjustment is leaning it out so much it isn't getting enough fuel.
    As I said, I really haven't a clue. Any help would be much appreciated.
  • gtbinc6gtbinc6 Member Posts: 1
    I have a grand marquis 2000 with blown motor---want to know if I can take front bumper and fenders and put on a slighlty dented 2002 crown vic?
  • blind_daveblind_dave Member Posts: 1
    My 2001 Mercury Grand Marquis is great, and I love it.

    I recently discovered a small crack in the intake, which I've since learned is not unusual.

    I want to replace the intake, but I am wondering if it would make sense to upgrade to a performance intake?

    Does anyone know how much needs to be altered in order to optimize performance with an upgraded intake?

    The 4.6 is ubiquitous these days. Do the Mustang parts work? Are they worth it?

    Any guidance would be most appreciated.
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