1997 Taurus GL Runs Rough/Sputters/Backfires only when hot

[LouNaTech]

1997 Ford Taurus GL Sedan
3.0L V6 12-Valve DOHC Vulcan Engine
Automatic Trans
178,000 Miles

The vehicle has recently (last 2 weeks) started running rough, sputtering, backfiring, and idling hard in the afternoons when I drive home from work.

In the mornings when it's cool, it runs perfectly...nice and steady. The same goes for cooler days when the outside temp is below 75 degrees or so. The problem doesn't happen after the car warms up, as much as it does when it hasn't been running for a while.

This afternoon, it really started backfiring & sputtering hard (much worse then ever before). I'm assuming that this might be a sensor issue of some sort, because of the fact that it's affected only when the ambient temperature outside is above 75 degrees or so, but I'm not sure where to start looking.

Any ideas would be greatly appreciated.

Thanks,

Lou

[shorod]

You may want to start by swinging by a local chain auto parts store and having them read the diagnostic codes (usually at no cost to you). If there are not any codes that would point to a DPFE sensor, then consider replacing the coolant temperature sensor.

You '97 will have two coolant temperature devices, a sensor and a sender. The sender provides the signal to the instrument panel guage. The sensor provides the coolant temperature voltage to the PCM, and the PCM uses that information to adjust timing, air/fuel ratio, idle speed, etc. So, even if the guage seems to read accurately, the Coolant Temperature Sensor could be out of specification and causing your issues.

You should also check the fuel pressure when the car is running fine (below 75 degrees ambient) and when it is running rough. Compare the pressures. The fuel pump in the fuel tank is an electric motor that relies on the fuel to help keep it cool. Electric motors can become temperature sensitive as the brushes wear or the windings start to open at the commutator.

-Rod

[LouNaTech]

Rod,

Thanks for the great ideas. I've actually got a simple OBDII code reader that I've connected, but there's no codes being displayed...when the vehicle's running good or when it starts running rough.

The temperature gage on the instrument panel isn't reacting at all when the car starts running rough, either...so I'm going to try locating & replacing the Coolant Temperature Sensor, as you suggested, first.

I've got a CD maintenance manual that I downloaded from this forum earlier, when I was t-shooting an emissions problem that was keeping me from getting my vehicle smogged (you assisted me with that issue too...thanks!)

If you've got any quick guidance as to where I might look for the Coolant Temperature Sensor, I'd appreciate it...otherwise, I'll load the manual in the AM and start trying to find the sensor...

Thanks again!!

- Lou

[shorod]

I'd expect the sensor to be mounted very near the thermostat housing, but I'm not positive on that. Plus, you'll want the manual to show you which deally bobber is the sensor and which is the sender. You want to start with the sensor, at least I would.

Good luck!

-Rod

[LouNaTech]

I replaced the ECT sensor (only $18) but that didn't fix the issue. It's still hesitating & missing when I accelerate...still no codes when I connect a OBDII reader either.

I've got a friend who's going to help me do a compression check on the fuel system.

Any other ideas?

- Lou

[shorod]

Hmmm, I guess Intake Air Temperature (IAT) sensor would be a good one to make sure is plugged in. Also, consider cleaning the Mass Air Flow (MAF) sensor. There is a cleaner made especially for this that some folks have been having good luck with. I've found the CRC brand MAF sensor cleaner at Advance Auto Parts.

-Rod