I've got a 3.0L SE, 2002. It has an OLD habit of low/stall idle after a hot start on a hot day, but a NEW symptom of after more than an hour on a really hot day at highway speeds, it dies DEAD on the road. After about two hours of cooling off, it'll start and run again just fine. If you try to start it before the cooling-off period, it'll run with poor power for about 30 seconds and die completely again.

I thought it was losing fuel pressure, because everything else seemed good. So I installed a good analog electronic fuel pressure gauge. I got a surprise!

When cold -- key on, not running: 48 psi.
Cold, running: 55psi
HOT running: 58-62 psi
Hot soak parked for a half hour: 68 psi! (huh?)
HOTTER soak parked for another 15 minutes: 72 psi!!!

Now I think (haven't yet confirmed) that the pressure is rising so high that eventually - on a really hot day on a long drive - the high pressure is causing the fairly new 1yr old fuel pump to overheat and shut down. I haven't challenged it yet, because I still haven't found a day when I can waste two hours sitting on the side of the road waiting for it to cool again. But after a tow the last TWO times it did it, it ran fine by the time we got it home, and it continued to on trips under 20 miles. It only dies on long HOT trips. Then it dies almost instantly, like the fuel pressure went to zero.

Anyone seen this before?

Lloyd

 

I have had a similar problem on another ford truck when the engine temp. sensor was telling the computer the engine was overheating. The gauge sensor said the temperature of the engine was just fine. It would start fine after it cooled down. I don't know if the 3.0 has two temp. sensors, but it might.

 

Yes, quite a number of the 1998-2008 3.0L engines had two temperature sensors: One for the dash gauge and one for the PCM -- the ECT... and the Engine Coolant Temperature sensor can read an overheat condition even when the panel gauge is fine. It's supposed to pop a code if it does, but the one time it ever happened to me, it didn't. I monitor both of mine, because I've seen the problem you mentioned. You can't just slap a regular temperature gauge on the rear sensor; you have to monitor the voltage output with a high-impedance amplifier, so reading it won't disturb the value getting to the PCM. The problem I'm having looks like a fuel issue. It just doesn't happen with enough frequency, or soon enough after start-up to easily identify.

The constantly-rising fuel pressure may be a red herring, but it's not normal (at least from what I've seen on other vehicles).

LS

 

Neither the hot low idle/stall problem or the high fuel pressure issue happens if the tank is full! (huh?) With a full tank, the rail pressure stays nailed at 55psi all the time while running, hot or cold.

When the tank level drops below about 3/8 full, the rail pressure rises in hot-soak, all the way to 70+, and the low idle/stall condition on a hot start comes back. That condition goes away after about three miles of driving.

I build hydraulic equipment for a living, but I'm having trouble relating the tank level being low to a higher rail pressure. Huh?

LS