My Mom's Car an Antique???

[Dandy Dave]

My elderly old mother bought a new Mercury Grand Marquis in the spring of 1985. Hard to believe the car is now 25 years old and among the survivors. The old Merc. was not feeling well and would stall at a stop sign. I pulled it out of the garage yesterday and pulled the exhuast re-circulating valve off of the back of the manifold and it was stuck open with some chunks of carbon around it. I cleaned it, and blew it out, and put it back on. The car idles fine now. Goes down the road fairly good still, but seems to have a hesitation on a slight grade in overdrive. The transmission kicks into drive and will pull with plenty of power. Kicks back into overdrive and has a miss. Anyone out there know which sensor or control I should look at next?

Anyone out there want to see photos of the next generation of Antique cars? Dandy Dave!

[Ben Bruce aka First Born]

Catalitic converter??

Yes, Lets see some pics.

Ben

[Dandy Dave]

Usually if the cat is plugged you will have no power when you rev the engine. The car has plenty of power in drive climbing a hill. It is just when it pulls along at a fast idle in overdrive. That is why I am leaning toward a control, or sensor. Will take, and post, some photos later then. Dave!

[mastertech]

If the egr valve was ful of carbon then i would start at the begining check the plugs and wires cap and rotor in other words i would do a complete tune up then take it for a long drive to get it good and hot to burn off the carbon on the valves and maybe put in some combustion chamber cleaner

[impala]

Possibly the lock up function of the torque converter? Try to determine if there's a subtle shift after the trans goes into O.D. This is the converter locking up. Some people actually disabled the locking function or installed a switch rather than install a new converter.

impala

[Marty Roth]

Mercury and Ford Models of that era frequently need replacement Spark Plug Wires replaced at about that mileage. I've had to change mine ,and it made all the difference.

Acceleration,even if mild under load resulted in engine miss.

Go ahead and change plugs at the same time because it is expedient, convenient, and inexpensive. You'll love the difference, make better gas mileage, and help the environment at the same time.

Let me know the results, please.

[Larry Schramm]

Put a vacuum gauge on it and drive it. You should see some value of vacuum at maybe 25 & 35 mph and going up should not change too much unless you go wide open throttle. The vacuum will drop off some slowly. If the catalytic converter is plugged, you will see a significant drop above 35 mph and the transmission will not shift correctly because of the increased back pressure.

[Guest ZondaC12]

Another thing is you just DONT try and accelerate up a "mild grade" in overdrive. At least if the car has the typical 2.73 gears out back. That's what my '87 Crown Vic daily driver has. Worthless. In all honesty for them being called "highway" gears, they aren't great on the highway. Id like to know why Ford didnt make an EFI 351 standard for those cars. The S.O. (standard output) 150 horse 5.0 Liter was bad enough in say a cougar or tbird, but throw another 400-500 lbs on to about 2 tons with one of these boats....the poor thing can't move it along to save its life.

Now a friend used to have an 89 grand marq and that got around no problem...he must have had 3.08s or 3.27s in it. I think I see a rear-axle teardown in my future!!

[cutlasguy]

I had the same problem in my 89 Caprice Classic. Whenever I would back off from accelerating the car would hesitate, somewhat like a miss.When driven at low speed nothing was apparent. Just when you tried to cruise at 50 would you notice the miss. I took it to the Chevy dealers where they replaced the distributor and shaft. Cost me $650.00 and didn't solve the problem. Since I already replaced the plugs and had the injectors cleaned I knew it wasn't them. Just when I was ready to yank the fuel pump someone suggested the transmission. The local trans man took it for a ride and came back with the proper diagnosis...Lock Up Solenoid in the Transmission. He dropped the pan, replaced it, cleaned the screen and put in new fluid. Problem solved!

[Dandy Dave]

Hey, been gone over the Easter holiday. Will try some of the suggestions and get photos up soon. Thanks, Dandy Dave!

[Guest ZondaC12]

Good point about the lock-up function, although in this case that wouldnt be an issue...with Ford AOD trannies, lockup is actually engaged before OD even hits! 3rd gear is when lockup occurs, and it does not engage or disengage based on throttle input (TV-kickdown cable input).