1988 Ford Mustang GT 5.0L V8 Misfire - Replaced many components.

From one Fox Body fan to another, glad it's running good again!
I have to ask though, what is a fuel pump solenoid?

I meant to say Fuel Pump Relay. Thanks.

And from what I saw online this is a common weak point in Ford’s of this era, even if the car starts and seems to run fine. I did not test it under higher current load. Mine was original to the car so it just seemed worth replacing.

The old timer remark I would always here when faced with a problem like this for an older 5.0L when I worked at Fords was: well is it fuel or is it spark? Which for me the answer was if I knew I would fix the problem. Although the crass statement makes a lot of sense, but you have to formulate a plan based on what you know.

The EEC-IV will support blink codes, and I think it is also compatible with a Super Star II tester (the high tech scanner of its day), where you are essentially just getting what are called blink codes which are either two or three digit codes blinked out by looking at a voltage on a pin.

But if we get back to your list of the work that has been done the one item I do not see is the in-tank fuel pump. The issue with these older cars is the pump could be working but there is a leak in the flexible plastic hose.

So how do you test for fuel pressure, not easy because what you really want is to measure the pressure across the injectors which would use a differential pressure measuring device. But, you can use a simple gauge on the fuel rail tap reference to atmosphere and see what the pressure does at idle and at WOT (wide open throttle). If there is a flow problem the pressure will die at WOT.

As a matter of old Ford repair 101, the lesson learned is with any older car project when starting out, drain, dry and inspect the tank, if okay, replace the fuel pump, sender and fuel filter. Put fresh gas in the tank and then move on to the next problem.