Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

2000 Mercury Mountaineer "missing" when temp over 92 Degrees

For 2 years when the temperature outside is 92 degrees or above the RPM’s will drop. Only once has it completely died. Typcally it will stall for a couple of seconds and re-engage. Only a problem when I am pulling out in traffic. Just had the “mass air control sensor” cleaned and it helped, but after 2 days the problem is back, however not as bad. Also added STP to my most recent tank of gas. Any ideas of what the heck it is? Not sure if it matters, but I have about 145,000 miles on the truck. Thank you in advance for any help! PS: Ford thinks it “could be” the fuel pump and/or regulator. I’m just not ready to spend $1000.00 on a guess!

Don’t spend $1000 on a guess. Pay $70-$100 for a diagnosis which if is incorrect you don’t have to pay for the bad repair. If the dealer is unwilling to do a diagnosis they are willing to stand behind then go to an independent shop that is.

They will do that?! Thanks!

No they won’t do that, nor should they. Auto repair is not quite that simple and nothing is etched in stone. Forty years ago a half decent mechanic could go over a car and within 10 minutes tell you why it won’t run.

Now a vehicle that acts up may be acting up due to half a dozen things at once. There is a perception that a mechanic can scan the car, get the code, replace a part, and problem solved. Not. There are too many things that can act up for which there is no code at all and for which there really is no valid test.
In some factory service manuals you will find procedures that state (paraphrased) “if all tests show blah, blah, blah, to be good, etc. then try replacing this that or the other to see if it fixes the problem”.

First off, get the vehicle scanned. AutoZone, Checkers, etc. will do this for you free.
Since the MAF has recently been considered what should be done is to go over every inch of the intake tract between the throttle body and the air filter. Any air leak due to a vacuum or breather hose crack, loose intake boot or air filter housing, etc. will affect the MAF.
The symptom may mimic a MAF but it’s not the MAF doing it.

It could also be the fuel pump acting up; especially if the vehicle has not had the fuel filter changed on a regular basis. A semi-clogged filter can kill a fuel pump but at this point examine the intake tract for leaks, no matter how small.

This truck does have a fuel pressure test port. When it is acting up, a fuel pressure gauge can be attached in a matter of minutes and give you a reading of the fuel pressure system to determine if it is the problem. No need to spend $1000 on a new fuel pump and regulator on a guess. Replacing the fuel filter every 60,000 miles is a good idea. The filter is about $20-30, and takes almost no time to change. The only tool required is a disconnect tool to release the quick connections on both sides of the fuel line.

Thank YOU so much for taking the time to respond! Awesome!!!

Hmmm…Where I work we get paid 1.2 hours to do a diagnosis. If our diagnosis is wrong, we get to try again, only we don’t get paid a second time. So yes, there are shops that stand behind their diagnosis. I can’t believe there are shops that wouldn’t stand behind their work, that’s pathetic.