Hey everybody. I recently bought a 1999 Mercury grand marquis LS with a measly 48k miles on it! It needed a new intake manifold. I replaced the old one with a new ford racing intake manifold meant for the 2003 and up models. A few heater hose changes and it’s running great!
I never drive the car before I bought it but now that it’s running it is SO SLOW TO ACCELERATE!! I think it’s starting out in 2nd gear. My friends do too. And I have a check engine light on..throwing code po750 which basically says speed sense out of range or something like that. Maybe it’s a solenoid issue? I don’t think I left any wiring disconnected or even damaged anything. The fluid is at the correct level and looks to be a good color. This is just so strange to me. If anybody has experienced this or has heard of this issue let me know!!

 

Hello, Dustin, and welcome to the Mercury Forums --
Regarding your Tranny problems --
Most important: DON'T DRIVE THE CAR 'TIL IT'S FIXED !! Further damage will happen !
Your po750 code indicates a bad shift solenoid.
At 48,000 miles, there's a good chance that the Transmission Filter and Fluid were never changed. If the fluid and filter WERE changed, we don't know if the job was done properly, or if top-quality parts/materials were used.
In any case, change the filter and fluid (Motorcraft Filter, MERCON V Fluid only) -- Re-Use ORIGINAL pan gasket, with NO RTV sealer.
Check the fluid -- if it's not a brilliant red color, drain the Torque Converter, too. It will take 12 quarts to replace the tranny and torque converter fluid.
Drop the trans pan and clean the pan and internal ceramic magnet.
Locate, remove, and replace the solenoid.
There are two (2) types of solenoids listed for the '99 Marquis -- match your old one to a new one.
RockAuto.com has info on the 2 types, with pictures -- easy match-up.
I HOPE that you are doing the work yourself -- it's the ONLY way to know for sure what is going into your tranny. Parts/Materials for this job should be around 125 bucks. If you have the work done professionally, it will be around 400 dollars, depending on where you live.
While doing a Filter/Fluid change several years ago, I installed a "B&M Shift Improver Kit" in The 95 MERC -- tighter shifts, and a VERY slight gas mileage improvement. A B&M Trans Cooler keeps the tranny cool here in the desert heat.
I use and recommend Sears Craftsman "Clicker" Torque Wrenches, in both inch/lbs. and foot/lbs. models.
Lemme know how you make out.


95 MERC Engine Bay

 

Sorry I took so long to respond! I’m an hvac tech and have been busy as hell lately. I took the car to a trans guy in my neighborhood that does honest work. He looked it over for free. He said when he dropped the pan there were some clutch material in there but nothing out of the ordinary. He said he removed the 1-2 shift solenoid and tested it(?) and it was working fine. Replaced the filter and only the fluid that was drained. I got the car back and i have first gear again!! I’m guessing the accumulator was maybe plugged up or the shift solenoid was stuck. Either way the car is running great after the trans tune up and all new ignition coils. I want to drain the fluid and replace the filter again When it gets cooler outside. It’s no fun laying on your back on an asphalt driveway in august. Thank you so much for your insight. I’m happy I didn’t have to replace any parts (yet). Next project on this ride is the front end. Boy is it sloppy! But that’s gonna cost a few bucks so it’ll have to wait. even with the front end needing a rebuild it still drives smoother than any car I’ve owned!

 

You might want to invest in a new oil pan which has a drain plug for future drains between filter changes and it makes pan drops far less messy..