Need help on unknown major problem in 1999 Mercury Mountaineer!

Hey everyone, thanks for the help.

I have a 1999 Mercury Mountaineer (5.0L V8) that has been causing me some major headaches this week.

On Sunday I had driven the vehicle for about 5 miles and encountered the problem for the first time. I was in a parking lot trying to find a place to park and suddenly my car died on me without any warning. Engine just went dead, no jumps or bumps. I was able to recognize the problem and coast it into a parking spot luckily. It would not start immediately, engine just kept turning over. I checked oil, antifreeze, ATF, and made sure that everything was in order - and it was. I went and ran my errands and came back 10 minutes later and it fired right up.

I was able to drive another 5 miles to the grocery store and there, once again as I was finding parking (another low speed situation… hmm) it silently died on me again. Had to get pushed into a parking spot this time. Again, started up after about a 10 minute wait. I went immediately home.

Decided to change fuel filter, which I thought may have worked as I was able to commute the short distance from home to school every day this week… until today.

I went to leave school today and it wouldn’t start up. After disconnecting the negative battery cable and reconnecting it, it started up and I left for home. With a half mile left to make it home, it silently died in flight going about 30 and I had to think quick to get it into a parking lot. Same deal… sat there for ten minutes, fired right up and went on my way home and parked it.

Obviously there is a major system failure somewhere and it is very unsafe to drive a vehicle that will die in flight. I’m just not sure what exactly the problem is. If anybody thinks that they know what is going on, please post! I’ll also check back to answer any clarifying questions.


There are a number of things that could cause something like this and the answer is not always clear cut.
Assuming no Check Engine Light and no diagnostic codes set I would suggest maybe changing the crankshaft position sensor.

Parts guessing is distasteful but crank sensors are a known problem with any car and they’re generally cheap and easy to swap.

I have found the fuel pump as the primary cause in my experience for that era ford. Diagnose it it failure mode.

I have also seen the starter solenoid fail in a certain manner that removes ignition power when the part fails.

Depending upon how this is “dying” will lead to the cause. Crank sensors can do this… sure

Its almost certainly an electronic component…the 5 miles dictates how long the part takes to get “hot” either electrically or from underhood heat. Electric components love to die when they get hot.

Wish the vehicle was nearby because much can be learned from the vehicle in its “dead” phase…this is how I repair most of these issues in vehicles…when its acting up…learn all you can from the vehicle at that time.


Weren’t the electronic ignition modules a major failure point on Ford vehicles of this era when they heated up?

That ignition module problem failure due to heat was on the prior generation. The problem prone TFI modules were for the most part phased out by 1995 or so. I think (but not sure) those modules may have continued to be used on some of the heavy duty Ford platforms such as larger trucks, RV chassis, etc for a few more years.

Gas tank not venting? Just throwing it out there. It might help to know what happens as the engine dies. Does it sort of lose power and then maybe sputter a little before dying or is it sudden like someone turned off the ignition switch?

It is important to know because if it gives you a little warning with some loss of power or some sputtering, then it is most likely a fuel issue where if there is no warning and it just shuts off like someone flipped a switch, then it is likely to be electrical.

ALL good points guys… Nobody has been wrong in their guesses YET.

Did any of you ever see the Ford Starter Solenoids go bad where they would Remove Ignition powe WHILE it was in the crank position? When at rest the ignition has power…then you engage the starter solenoid (Which engages and turns the starter motor) and at the same time…while turning the starter…it REMOVES ignition power… It was the damndest thing when I saw this… I replaced the solenoid…and Voila…she started up immediately… Not sure what fails in the solenoid but hell if it didnt steal the ignition power when it was energized…

We obviously are all after the same thing here… Does the vehicle stall because of Fuel…or Spark… we all know the drill. Problem is…the OP needs to know the difference and the symptoms of each to narrow things down. I guess we need to ask them the right questions… I hate trying to fix things that are SO EASY to repair when the vehicle is in front of you… Just makes me NUTSO


The trouble you are having does seem to be due to an electrical problem, possibly with the ignition or injector circuit, and heat could be involved with the shutdown process. The trouble could be with the fuel system also. A simple way to find out what area you need to look at is have a can of starting fluid with you and spray a small amount into the intake as soon as the trouble happens. If you get no results from that then you have an ignition issue. It could be as simple as a loose power connection.

@"Honda Blackbird"
I very much doubt the starter solenoid caused the trouble you described. About the only way for that happen is for the solenoid to have a dead short to ground when it was activated, and that would have been real obvious. What I suspect happened is you had a bad connection in the main power connection to the battery. The trouble didn’t have enough resistance to have much of a voltage drop while a small amount of current was passing through. But when you tried to START the engine and pull a lot of current you had a lot of voltage drop across the bad connection and accessory power died. Somehow, when you worked in the area you eliminated the bad connection issue, which made it seem like the solenoid was at fault.

Cougar do you really think I wouldnt recognize a directly shorted Starter Solenoid? LOL

No the solenoid was not a dead short…in fact the solenoid worked fine… The only problem was that when the solenoid engaged AND turned the starter over…we lost ignition power.

There is another post here about I think its " F150 Will Not Start Battery Volts Good" That post defines the solenoid failure that i am talking about…its EXACTLY the issue I describe. Got to admit, at the time I first saw this issue…I was shocked. Whenever I have seen the Ford Starter Solenoid issue… it was a concrete failure…it would never run some of the time…it just wouldnt start and run at all.

I agree this issue is some electrical component…when it gets hot…the show is over.


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Or an old ingnition switch. ( the SWITCH, down in the column, not the lock cylinder. )
ALL of these are possibilities and it can also be the switch’s internal contacts that get worn out.

On my truck , you could start the thing right up but the radio and gauges were not on. A wiggle of the key cylinder wiggled the linkage enough to wiggle the switch to engage those cicuits.
It never shut off the engine but it’s happened on others.

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Hey everybody, thanks for all of the help.

After reading everything that has been said I am convinced that it is definitely an electrical problem.

It feels more like someone is “flipping a switch” and it just silently goes dead than it lurching or starving for fuel.

I think that the fact that it happens at low speeds is likely irrelevant. I have paid attention over the last couple of days and it happens after a certain amount of time (usually 10-15 minutes) and it happens sooner if it is really hot out or I park in the sun.

I am going to replace the fuel pump relay today and see if it happens again. I will be back to report on results and ask what to replace next if that is not the answer.

Thank you for helping!!!

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My guess would be electrical but I have been a VW owner :smile: once(enough).

When it dies are all the normal lights on just before you start the car. Eg is the Check Engine light sitting yellow or off? My case a bad ground to computer was cutting the brain off and car would die and crank away.

Bad ignition switches(electrical) cause these things too.

Sometimes just guessing what is causing the problem and replacing it will fix the problem but by using the guessing game you usually end up just buying extra parts before the real cause of the trouble is found. You might get lucky with the relay replacement, it is a pretty good possibility. Before replacing anything I would first find out what area is causing the trouble. It could be an ignition problem and not a fuel issue. Using the starter fluid trick is an easy way to pin down the area of trouble.

Yup…that too… All things to look at. This is what shops cant seem to do these days… Unless the issue is clear cut…like Brakes. They want nothing to do with a job like this. This takes effort and maybe a few wrong guesses to get it right again.


Alright everyone… there has been a new development on this one. I am just going to copy my posting from reddit about this if anyone wants to weigh in.

Hey all,

Still need help on an issue that I posted before with my 1999 Mercury Mountaineer. I included to the original post for some background.

Problem started about 2 weeks ago, car would “die in flight” after roughly 15 minutes of city driving. No lurching, starving for fuel, clunking, just suddenly would lose spark and I’d have to quickly react and find a safe place to coast it to a stop.

I have tried tinkering with things - cleaning battery cables and posts, new fuel filter, installing a new fuel pump relay and a starter relay - with each change running it until it eventually died, thus ruling that problem out. The only thing that seems to fix it is letting it sit for at least 10 minutes.
But wait… there’s more now! Now instead of getting a crank when I turn the key it simply clicks and does nothing. Time does NOT fix the problem anymore. This is a recent development.

  • It has generally started fine from a cold start (first of the day) and I can make my 5 mile commute.

  • When starting from a ‘warm’ start, I do not make it as far before experiencing trouble.

  • Battery was replaced in November, however appears to be volting low based on dashboard reading. I don’t have a volt meter but may go get one today.

  • It runs and drives absolutely fine - until it doesn’t!

In summary, I know that this is almost certainly an electrical problem. In my mind, possible suspects include starter/solenoid, battery and its connections, alternator, fuel pump. My main question: what would cause a vehicle to 1) die in flight [presumably from getting too hot] and 2) not start up at all.

Update: Got volt meter and battery checked out fine, 12.5V.

Judging by your latest post, I think your problem is in or connected to your battery cables. Start with the negative cable. Un do the connections at the block and the frame, clean them and reattach. Make sure they are solid and the terminals are not loose or have corrosion between the terminal and the wire itself. Also check the battery end for corrosion between the terminal and the wire. You may have to peel back some insulation to check.

Check all the ground straps between your engine and the body. There are usually a couple of them now, often between the rear of the engine and the firewall.

Check the Positive cable at the starter, removing and cleaning that end and reattaching (disconnect the battery first) and inspecting the wire to terminal for corrosion. Do that at the battery end of the cable as well.

Sorry you are having this difficulty, frustrating. It’s no fun when you can’t rely on your ride …hmmm… well, mine is admittedly just a wild guess, but I’m thinking either a faulty ignition switch or crankshaft position sensor. Something simple you could try, when you put your key in the ignition, just put the single key in, with nothing else attached to it. See if that helps. Sometimes the junk on the keychain swings around as you go around corners or over bumps and eventually damages the lock. If doing this noticeably improves the situation, well, you know what to do then …

If that doesn’t work, make sure to read out all the active and pending diagnostic codes from the computer memory, that might provide a clue

Beyond that, it is just normal mechanic’s detective work, checking fuel pressure, spark, etc.

OP, why didn’t you replace the crankshaft position sensor like you were told 10 days ago?