A New Formula In Our Stall

[GTRS Fiero]

Wasn't it stated that the Check Engine light was always on, when the car was still being driven? You may have gotten the car back to its "original" state.

That's what I had thought.

Does the Fiero run any differently, now?

[TopNotch]

I worked on my Ford Escape yesterday, and today it's raining, But i did do a little test. I disconnected the PCM, turned on the key, and checked for voltage at pins WD10, WD11, and WD12. Only WD12, from the AC relay, did not have voltage. Could a bad AC relay cause the trouble light?

[GTRS Fiero]

I do not believe that the AC is "seen" by the ECU at all, do doubtful, but this comment if probably worth every penny you paid for it.

On the other hand, the wiring is an unknown.

[TopNotch]

The ECU has some control over the AC even on a 87-88 duke Fiero. It cuts out the AC if the idle falls below 600 RPM, or at wide open throttle. I imagine a newer car has even more control over it.
Now here's what I did, and what I found out. I stripped a little insulation off the appropriate wires, and connected a 22-ohm resistor between "hot in run" and WD12. The QDM error stays cleared if I clear it, BUT the cooling fan runs. This tells me something is wired up backwards. According to the diagram, the AC relay has 12V on one end all the time the ignition is on, so the other end must be grounded to energize it. But the car must have ground applied at all times, and energizes when 12V is applied.
This makes me wonder what else is backwards. Another thing -- where ever the AC relay is, it's not at the usual Fiero location. There are no relays there (no fuel pump relay either).

[Fierofool]

Isn't there a relay near the accumulator that's part of the ac circuit?

[TopNotch]

Isn't there a relay near the accumulator that's part of the ac circuit?

I'll check that out, but I have some good news. The engine runs smooth now, but was hesitating slightly if I punched the throttle. I ran the trouble shooter on my gizmo, and it gave me a list of symptoms, one of which was hesitation on throttle. I picked that one, and it said the problem could be the mass air flow sensor, which may not set a trouble code. I pulled it out, and sure enough, there was a dust bunny on it. I blew it off, and blew out the passages where it plugs in and replaced it. No hesitation now.

[GTRS Fiero]

That's great!  Good show.

[GTRS Fiero]

The ECU has some control over the AC even on a 87-88 duke Fiero. It cuts out the AC if the idle falls below 600 RPM, or at wide open throttle. I imagine a newer car has even more control over it.

This makes me wonder what else is backwards. Another thing -- where ever the AC relay is, it's not at the usual Fiero location. There are no relays there (no fuel pump relay either).

You can use the old trick of turning on the AC and listening for the click, or turning the key to on, and listening for the FP relay.

In another vehicle, the AC clutch does not engage below a certain RPM.  Not an electronic thing.  Mechanical.  I've always thought that some vehicles cut out the AC on idle and WOT.  I first brought that up on an '86 Chevy Sprint.  Very annoying.

[TopNotch]

While this car does have a new AC compressor on it, because the bearing in the old one was out, and made a racket even with the clutch not engaged, nothing else in the AC is new, and it's not pressurized. So it's not going to run.
I think I'm going to have to take a risk and stick one of my other car's plates on the back and take it for a longer test drive than around the block. You can't really tell how it's doing creeping around the block, and never getting out of first gear (well, once it did get into second gear).

[GTRS Fiero]

Out of curiosity, how do you avoid getting a ticket on a car without plates?  I could park it in my back yard, and still get a ticket.

[Fierofool]

It depends on state and local law.  Georgia doesn't require a plate unless it's being driven on a public road.

Auburn used to require plate and insurance on all cars other than those in a salvage yard or licensed dealership.  Even if it was totaled and on your property.  The unincorporated county doesn't.

When I was in office I rewrote the ordinance and got it passed to remove those requirements so service men and women could park their vehicle at home while deployed, without the added expenses.

[GTRS Fiero]

The ECU has some control over the AC even on a 87-88 duke Fiero. It cuts out the AC if the idle falls below 600 RPM, or at wide open throttle. I imagine a newer car has even more control over it.

You are right.  There is a signal line to the ECU.

[TopNotch]

The SES light is out!
First a little background. There's a test you can do on an automatic transmission car to judge engine performance without driving it. Just push the brake pedal, put it in gear, and give it some gas. This car had sounded OK right after startup, but after a little while, it sounded like like it was struggling when I did that. That means that after closed loop mode started, it was having trouble. My scanner verified that the trouble was in closed loop mode.
You may recall that among the errors I got with my scanner were EST failure and camshaft position sensor failure. Those errors had come back. Well, EST is Electronic Spark Timing, which means the ICM. So I bought both a new ICM and camshaft position sensor. I got the cheapest ones Rock Auto had, just in case they weren't needed. They came today.
First I replaced the ICM. No change. Then I replaced the camshaft position sensor. Bingo! The SES light went out, and performance is normal.
I guess that means that Lee (previous owner) was driving the car around with a bad camshaft position sensor, and reduced performance.

[GTRS Fiero]

Good job.  Glad that's sorted.

[NoMad]

Nice!