Markiii

Got my first code scanners this week and working on my wife's gas sipper and my '94 xlt, 2wd with the fuel injected 302. Truck threw a 118 (engine coolant temperature sensor above maximum voltage, and 121 (closed throttle voltage higher or lower than expected).
Temp gauge seems to be working and reading within normal range. I've had some starting issues that were present before the CEL came on, and replaced the fuel pressure regulator, which didn't help.
I'm wondering if the voltage regulator is bad causing both of these abnormal voltages, possibly causing me to run rich, as gas mileage has steadily decreased from around 15 to around 12. Also, the alternator is putting out around 14.8v at the battery which seems awfully high.
Any ideas on how to proceed, for a guy who's not rich by any means?

sdmartin65

Replace ect sensor located on intake manifold just behind thermostat, about $15. This sensor sends temp info to the computer and a bad one can cause the problems you have. There is a separate temp sensor for the gauge.

Chris_1

iTrader: (1)

Alternator should be putting out that much voltage. If it wasn't that would be a problem.
I agree with changing the temp sensor, a bad one really hurts gas mileage among other things.
The gauge is controlled by a separate sending unit, like sd martin said, it just sends a signal to the gauge.
The sensor sends info to the computer - if the info is wrong, the comp does wrong things.
Get a gauge and check your fuel pressure, you need a min of 30 psi, but you really want to be in the 40 -45 range. If fuel pressure is your starting issue, that'll tell you.

Markiii

Thank you Chris and SD Martin. I ordered the ect sensor this morning and O'Reily should have it in a couple hours. I'll definitely think about getting a fuel pressure gauge.
Now how about the 121, throttle closed voltage higher or lower than expected? Guy at O'Reily said both were because of my voltage regulator, but I trust the wisdom here significantly more. He also was the one who told me 14.8v was too high off the alternator. It made sense since my gas sipper puts out about 13.6v, but that's a much smaller, much lower amperage battery.

Aktech

If the ect is reading under 50 degrees it will send a code.

Markiii

Okay, so I cleared the 118 ECT sensor code. CEL went off but I'm still getting a 121 code, closed throttle voltage higher or lower than expected. Is this definitely gonna be the throttle position sensor? Chilton gives a method to test it by testing the resistance with an ohm meter, which I can do, but the procedure is unclear.

Aktech

The tps can test out OK but can be worn out. Just replace it.

Chris_1

iTrader: (1)

Check the codes using the check engine light. Sticky post at the top of the 87-96 page by Just call me sean. How to read OBD1 codes. You'll need a paper clip or such.

Markiii

Knew about that, but I went ahead and got the scanners anyway. Needed obd2 for my car and got the obd1 for $20, so I went ahead and did it. I'm unclear why you're telling me this, is it more accurate? My problem isn't extracting the codes.

Chris_1

iTrader: (1)

It costs nothing and is a good backup to what your code reader is telling you. Before spending money on parts.
I'd suggest doing the temp sensor, clear the codes, take it for a drive and then recheck codes.
A false signal to the computer can create a false reading somewhere else.