What doe cylinder 8 mean when running a key on engine running test?
 

Just bought another 90 f150. 5.0 5 speed. The transmission on mine went out. Found this one down the street with 83k original miles. Noticed the check engine light comes on after you drive for a little bit. Took it to to O'Reilly's so they could read the codes so I didnt have to count flashes. There was a code for the egr valve. The power steering pressure switch I think. Does anyone know what that is? Then it just said cylinder 8. Flipping through the codes there was the egr and pressure switch then just cylinder 8. What does that mean? It runs really smooth. I wouldn't think it would be a missfire code. Thanks.

Buy an Inova code reader from Amazon only about $35, comes with a helpful instruction booklet. Key on engine off is the way to check for codes on these old OBD1 systems.

It means scanners don't work reliably on these old EEC-IVs, and that parts-store employees know less about your truck than you do. Learn to count flashes - a jumper wire will never show spurious codes, and you'll understand better what's happening. Click this & read the caption:

https://www.supermotors.net/getfile/.../dlc-eeciv.jpg
(phone app link)

I've never really understood why some members get so stuck on counting the check engine flashes for code reading when a reliable reader is so inexpensive. The paper clip flash count is a hack to be used when that's all that's available.

Back to the original problem, most likely seeing an EGR code but the truck is running fine would point to a minor vacuum leak.

Simple fix
 

Check the plug has correct gap/ check wire or coil whichever u might be running to see if it is cracked and possibly that u just have bad gas

The paperclip (jumper wire) is what the Ford service manual says to do if you don't have a T-handle or other Ford scanner. That's where all those instructions came from, so it's not a "hack". It's what Ford designed the EEC to respond to.

And based on all the members reporting spurious, incorrect, and useless codes from inexpensive aftermarket scanners, they've never seemed reliable to me.

When doing the key on engine running test it does a cylinder balance test. I was thinking it saying cylinder 8 means its low on power or something. So the egr code could just be a vacuum leak? When the egr went bad on my other truck it ran like crap. Where is the power steering pressure switch? What does that do? I read only manuals have it.

The guy I bought it from says he changed the spark plugs. I dont think he did the wires or cap and rotor. He said he flushed and cleaned the rear tank and that's the only one he was using.

No, these EECs don't do that. The EEC doesn't actually know which cylinder is firing, or what happens when each cylinder fires, so it can't measure their balance. Other EECs on other vehicles can do that test, which is why it's mentioned in the KOER explanation.Yes, or several other possible causes.That's one of many symptoms of EGR failure.On the output hose from the PS pump.Tells the EEC when to bump the idle. Otherwise, it's ignored.

I'll check for vacuum leaks and I'll probably swap the egr out anyway. I have a bunch of new parts I just put on my other truck before the tranny went out. I think the power steering pressure switch might be ok. I read your supposed to crank the steering wheel after it flashes for a v8 engine. I never did that. So that's probably why it threw that code.