You do with key on. You can't do anything with key off. Use an analoge volt meter or a light. There are different codes for key on and engine off and key on and engine run. It will give you K.O.E.O. and K.O.E.R. codes. Thats key on engine run and key on engine off. The electonics on a car can take a lot of abuse. Within reason. Your car has E.E.C.
IV 3 digit codes. Buy a code reader. What are you going to do when you get 3 - 6 different codes ? Are you getting a check engine light or are you just playing around ? If you get a R.C. 172 code which is O2 sensor lean doesn't mean
the o2 sensor is at fault. Your engine is lean on the right side and you figure it out. Good luck.

Thanks for the info. I know there's more to it than pull the codes and replace a componant. I'm just looking for a place to start. There should be a couple of codes in it at least. The check engine light has come on while driving for years. Not much, just once every couple months, and just for a few minutes. Always ran ok so I didn't care. My daughter drives it now. She says lately first thing in the morning, it runs poorly and dies after start up. She says it's fine after that. Of coarse I went out to try it this morning and it worked fine that time.

Erase the codes and start fresh. Then see what codes you have. Do both. K.O.E.O. and K.O.E.R. Disconnecting the
battery will not erase the codes.

Information I read said disconnecting the battery for 10 minutes is supposed to clear codes. Haven't done that yet. Can't remember the numbers I had now but it was MAF sensor and something about injector pulse longer than expected. I dumped some injector cleaner in it today for starters. Worked on my dodge. It had a dead cylinder, this ford doesn't. Too many projects. Daughter keeps wanting to take off with the car 5 minutes after I pop the hood.

For what it's worth. Disconnecting the battery for a month
will not erase the codes. Read your code manual. It will
tell how to clear the codes. Sorry but every time we say
something, 20 people say 40 of us are wrong. I'll tell you
how to clear the codes if you don't get the info from the proper source. Disconnecting your battery will do nothing
but screw up your clock and radio.

Not really a dumb question Gary.

Your 93 has EECIV. Which means on top of being able to display trouble codes, known as continuous, or history codes. You can perform the KOEO, (Key, On, Engine, Off) test, as well as the KOER, (Key On, Engine, Running). These tests are very handy for the technician because Ford programmed the system to test itself for active problems under the conditions that the test occurs. With a scan tool you can also get scanned data from the PCM which can save a lot of steps trying to set up and pin into each sensor, especially when you could inadvertently restore the connection accidently as you attempt to get a measurement.

I don't know of any way to run these tests without a scan tool, mostly because with three scan tools capable of doing so I have no reason to even think about doing it any other way. But the most important thing is when the testing is being run by the computer, the technician needs to manaually watch the test occur and be positive of why the code sets. Which means running the test several times.

As an example, (This does not apply to your car this is a demonstration of how the test is used effectively). I had an F-150 setting a poor EGR flow code. Early 90's, 4.9l 6cyl. Code would set when driving. However bringing the truck in the service bay it would pass the KOER test. Part of the KOER test demands the EGR open, and since the EGR valave has a positive feedback system, the computer knows if it opens or not. Complete testing for the cause of this trouble included: Measuring the vacuum applied to the valve at idle during the KOER test, and again when driving the truck when the valve is commanded open by driving conditions. There was not enough vacuum at cruise when driving. That simple check showed that the trouble was either with the vacuum source, and resevior or the EGRV (EGR Vavuum Regulator Valve). Simple testing from that point confirmed that the vacuum resevoir was leaking.

The whole thing here is codes alone don't tell the story. Proper complete testing is the only way to solve these problems without driving yourself crazy. Proper testing means using a full function scan tool, not just a "code puller", let alone attempting to read volt meter sweeps.

On EEC-IV systems disconnecting the battery WILL erase the codes, as will (when codes are being output) removing the jumper wire you used to connect the self-test output to the self-test input.

EEC-V is a little different, but you won't be getting codes out of that one with a test light and a jumper wire, nor will you find it in a 93 model.

URL

Here is a link that might be useful: EEC Test handbook

Thank you for all the info guys. I'll see where it leads me armed with a volt meter and a test light. If that's not enough, I'll take it to someone with the knowlege and proper test equipment. I just like to take a wack at it myself first and learn something along the way. Thanks!