1990 Ford 5.0 diagnostic help...please?

It's an OBD1 vehicle, so you can read the codes pretty simply. Google on how to do it or get a $30 code reader that comes with a pretty book.

Since I don't have the code here, I'm GUESSING you have a lazy O2 sensor.

O2 sensor. I'm glad you mentioned that. BTW, i forgot to mention that the light beginns blinking "usually" after the engine starts to warm up and the thermostat starts to open, that is, from what I can tell by watching the temp guage..

in the colder midwest weather, I'll drive it about 3 miles then the guage starts to rise then the light triggers..

Without the proper diagnostics, is there a way to test the O2 sensor, or just get another one and try it?

O2 sensor. I'm glad you mentioned that. BTW, i forgot to mention that the light beginns blinking "usually" after the engine starts to warm up and the thermostat starts to open, that is, from what I can tell by watching the temp guage..

in the colder midwest weather, I'll drive it about 3 miles then the guage starts to rise then the light triggers..

Without the proper diagnostics, is there a way to test the O2 sensor, or just get another one and try it?

On that car there is not an 'easy' way to test the O2. It sure wouldnt hurt to replace it if its old. I would replace the fuel filter too if its been a while. There are sooooo many things it could be. You really need to get the code(s). Start with a visual inspection (anything obvious like broken vacuum lines......)

Here's a way you can get codes without a reader, though you really should have one if you plan to keep the car. It's cheaper than throwing parts at a problem guessing.

Thanks for the suggestions, guy and also for the links. I haven't had the time to do anything thourough...yet.

But I think I may have multiple problems. first off, I looked down and saw the 02's one on each manifold. I felt around for the wires to find the connectors and the one on the drivers side had quite a long tail which was rubbing against the firewall. Don't know if it had rubbed though but i pulled it away and . Huh? the car seems to be running better and the light hasn't flashed near like what it did. So I'm guessing you all may be right about the 02's.

But the last three days it's been mighty nice weather so I've also run witht he heater off. Well, this morning it's quite chilly so I turned the heat up and put it to floor. No indicator light flash, but the car started to cut out and stagger a little. I do know that if it's on defroster, the AC pump clutch will cycle and cause a very slight and momentary stall. But this isn't the case.

I've never been a fan of the climatic-control system used on these cars. I've always thought them a tinker toy kind of a oke. I don't know what the problem is with the old and very reliabley simple cable system, but the engineers never ask my opinion for some reason. LOL!

And in this past winter the heater never really has worked good. I'm thinking that there is a vacuum problem with the heater system ia not letting the vent door close or operate properly. or something inside the heater controller leaking vacuum. I'm thinking I'm experiencing "old- car syndrom"

I still plan to do the diagnostics on the o2's though.

Get the codes, post them here. We can help. Forget the O2 sensor for now, I might as well tell you it's your spare tire that's causing your engine's hesitation and stumbling. Everyone blames the O2 because it's the messenger for many different problems and parts stores sell tons of them to replace perfectly good ones.

Without the codes I would wager that the EGR system is past due for a complete checkup. With the codes I (we, forum lurkers) might actually be of some help.

Thanks much, I'll work on that....