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Mechanics are stumped!

Yesterday while driving my '97 Ford Explorer at 35mph, it lurched forward increasing to 40mph, then suddenly dropped back and stalled out. I was able to start the car again, but this happened three more times on my way home (about 3 miles). No dials show overheating, no Check Engine light is on. After letting the car cool in the driveway overnight I checked all the fluids. The radiator fluid was empty in the reserve tank and low in the radiator. There are no leaks appearing on the pavement. The vehicle has 160,245 miles on it but has been well maintained and showed no sign of any problems over the weekend when I drove to CT and back from ME. The Ford service dept cannot figure out what’s going on, was able to experience the situation on a test drive, but not in the shop. What do you think it might be?

What does your transmission fluid look/smell like? Any rust on the transmission or engine dipstick?

The radiator fluid was empty in the reserve tank and low in the radiator. There are no leaks appearing on the pavement.

Not good. As Caddyman hinted, this might be your problem or you could have multiple problems. Either way, the fact you’re using fluid is a bad sign and will need to be addressed.

Try an independently owned and operated shop. The Ford dealer isn’t that interested.

Since the engine revving pulled the car along with it, and since it stalled after, we can eliminate the tranny as a potential cause.

The engine revved because the fuel supply suddenly increased (high probability) or the spark timing advanced itself (very low probability).

The fuel supply through the injectors probably increased because of a defective fuel pressure regulator. More pressure through the same orafice supplies more fluid. The same defective fuel pressure regulator resulted in the shutdown. Either it flooded the engine or shut the fuel off. Or, perhaps, the oxygen sensor detected way too much fuel and shut the pulsewidth down, which might have occurred at the same time as the engine was revving and starved it.

It’s also possible that you have a flaky sensor such as a manifold absolute pressure sensor or throttle position sensor, but I’d expect a code from one of those.

So, my first area of exploration would be the fuel supply, specifically the pressure regulator.

Good luck. And I mean that sincerely.

Oh, yeah, and TT is right, you need to address that lost fluid cause too. And start keeping better track of your fluids. You can start by checking for a breeched head gasket. Or perhaps by a cooling system pressure test.

There are a number of things it could be but determining this is going to involve a number of tests; and even then it may not be definitive.

First step is scanning for codes followed by a fuel pressure check. You can get the vehicle scanned at AutoZone, Checkers, etc. for free.

How often do you check the fluids under the hood? It’s possible to have a low coolant level and the temp gauge will not show overheating because the temp sender probe is not immersed in hot coolant due it being low.

How often is the fuel filter changed? If seldom or never this could point to a failing fuel pump.
Testing things may also take money. At the Ford dealer did you ask them to perform these for-a-charge tests or was this simply a quick look by a service writer, etc.?

I’m going to guess that you may have a throttle position sensor that’s dirty or out of range—but not enough to set a fault code and turn on the check engine light. I think the coolant is a separate issue—when was the last time it was checked?