1998 Mercury Mountaineer Runs Rough/Dies At Times

[mlochala]

I have a 1998 Mercury Mountaineer with the 5.0, approx. 225,000 miles. Has, for the most part, always been very dependable.

Sometimes, however, particularly on a hot day, it begins to run very rough. This mostly happens after it is left idling for a while, such as waiting in line at school to pick the children up or if I run into a store for just a minute while the wife waits outside with the motor running and the air conditioning on. This also happens when we go to town and are in a lot of stop and go traffic.

What happens is, it begins to run rough and seems to bog down at first. Then, it either clears up or then it gets worse and dies. The other day it died while leaving the grocery store and I basically had to let it sit for a minute or two before it would crank back up. It will seem to start missing and then acts like its flooded and then sometimes lets out a little backfire when it gets going.

Anyone experienced this or have any knowledge of what could be going on here?

 

[gatzdon]

Does it start just fine after sitting overnight? If so, your likely culprit is the Engine Coolant Temp Sensor.

Either way, I recommend using Forscan to pull the extended codes from the PCM (not the OBD codes). Hopefully you will have pending codes that point you in the right direction.

If there isn't a pending code for the engine temp (failing to warm up quick enough), you can also check the PID values to see what temp the PCM is reporting (should be 190F or higher) and verify that the engine is going to closed loop for fuel management (open loop will throw too much fuel into the engine causing issues you described).

 

[mlochala]

Oh yes, it starts fine after overnight. Also, we don't notice this problem when we go longer distances down the highway. Just mostly after idling or stop and go traffic, especially on a hot day.

Does it start just fine after sitting overnight? If so, your likely culprit is the Engine Coolant Temp Sensor.

Either way, I recommend using Forscan to pull the extended codes from the PCM (not the OBD codes). Hopefully you will have pending codes that point you in the right direction.

If there isn't a pending code for the engine temp (failing to warm up quick enough), you can also check the PID values to see what temp the PCM is reporting (should be 190F or higher) and verify that the engine is going to closed loop for fuel management (open loop will throw too much fuel into the engine causing issues you described).

 

[gatzdon]

Here's a little write up I did on how to check out your Engine Coolant Temp Sensor.

http://www.explorerforum.com/forums...ng-when-hot-but-starts-fine-when-cold.435965/

 

[Harpua216]

when any of my cars start doing this, my first 4 checks are fluids, vacuum lines, fuel filter and plugs and wires. i also think about the last gas i bought and where.

after that. some diagnostics can be very helpful

 

[Turdle]

Silly questions, but

Does the check engine light turn on when you switch the key on? Does it turn off once the engine is running, or does it still display while driving around?

 

[gatzdon]

when any of my cars start doing this, my first 4 checks are fluids, vacuum lines, fuel filter and plugs and wires. i also think about the last gas i bought and where.

after that. some diagnostics can be very helpful

When the engine runs rough after warming up, but starts fine when it's cold, that's indicative of the fuel control loop staying in open mode.

There are PCM codes that indicate that the fuel control loop didn't close after x number of minutes, but these require certain conditions to be met before they set the MIL including several repetitions of the failure. Going into closed loop once may reset the count preventing the MIL from being illuminated.