I've had trouble with my '91 LX 5.0 for some time. It started running very rich and progressed to the point where it barely ran. Think it was the computer, I took the car to a local shop owned by a guy that is into Fox bodies. He loaned me a spare computer he had, and it seemed to run fine. I sent my first computer in for repair, and it was too far gone. I bought another A9L on eBay and installed it. I returned his loaner to him and headed home. I live about eight miles from the shop and made it about halfway home when the same problem happened. I sent the second one in and it did have a few issues, but it was repaired and returned with a lifetime warranty. When I installed this computer, it seemed to run fine. I drove it five miles, shut the car off for an hour. When I was ready to go home, I made it about 100 yards, and it died. It restarted but died four times on the way home. I bought a third A9L and same problem. It ran for about two miles and died. I pulled the spout connector out and it runs fine. I have no idea where to go from here.
I used to hear about this same story a dozen times a year......Usually the seller will say computer was tested or came from a running vehicle but without a readout or a video who can say the seller is honest and not trying to sell the ecu quickly then sometimes its the fault of the guy just changing parts instead iof doing proper diagnostics and its not at all an issue as we cant all be rocket scientists and to say many moons I was where you are as far as being able to diagnose issues and figue out problems by knowing where to look...
Ive had an issue that was caused by a failing tachometer wire grounding out behind the cluster................
When I buy ECU's off of ebay I instantly send them right to ECU exchange for a diagnostic also repairs also being beefed up...
ECU exchange doesnt only fix and repair ECU's too they also tell you where to look for possible issues if the problems found arent the run of the mill issues like leaky capacitors so if you used them to repair your ECU and they neglected to tell you where possible problem areas are Im gonna be perplexed..
Usually 80% of issues develop in the salt and pepper shaker type connections and some develop in the ignition switch attached to the steerng column under the dashboard..
If you pulled the spout and it runs fine means that youre running on limp mode and your timing is locked where the distributor is set to manually with zero advance/retard going on and that usually points to a failing TFI module / or a failing internal distributor pickup module thats mounted under the rotor vane going back to wiring issues and possible problems with the way the ECU gets its signal .........
One of the biggest problem areas to cause a failing TFI module are the grounds and the relays for the ECU and fuelpump and should be upgraded to relays with built-in diodes..
Advancing the ignition too far without making changes in the ECU cause the timing between the injectors and the spark events to be off causing the ECU to constantly make corrections causing the ECU and TFI module to run hotter.If you look at the third to last picture of the A9L computer settings you can see the spot where you can advance the timing the safe way where it keeps the timing and spark events happening at the proper times..
If you look at the second to last picture you'll see that Ford was actually supposed to set Mustang 5.0 engines with MT at 4 degrees BTDC but in order to utilize any other setting that would require them to change the module type settings fron NON-CCD to CCD also remove the 22k resistor and install a CCD TFI module so its a crapshoot on really how to get one to run flawlessly based off of this newfound information......LOL
If you look at the diagram the fuelpump relay feeds off of the ECU relay trigger wire and it controls the power thats supplied for the fuel injectors too as each injector is triggered by the ground wire so if the injector harness wires are getting baren and can touch metal thats bad.........
Another thing to do is a resistance test on the fuelpump and see if the inertia switch isnt raising the resistance and lowering the voltage. plus do a vacuum test on the fuelpump relay and do a fuelpump output reading using a gauge on the schrader valve coming from the fuel injector rail... On my injector rail I have a liquid filled gauge also a schader valve plus I also monitor my fuel pressure while Im driving so theres a fuel pressure sender switch that goes to a gauge on the dash too.....
If I was you I'd go back to the basics and remove the ECU from the plug and go pin by pin to each corresponding plug doing resistance and continuity checks on all pins and plugs to eliminate any melted together wires or bad grounds then I'd find and clean all grounding connections especially the ones coming off of pins #40,49 and 60 and clean them up..
On pin #4 (IDM circuit) on the ECU plug going to pin #2 (coil -) on the TFI module should read atleast 22kohms if the car is a 5 speed manual and the TFI module should be the NON-Computer Controlled Dwell type TFI module..
If its an automatic conversion car there will be zero resistance between pin #4 and pin #2 but should have a 22kohm resistor installed in-line and the TFI module...
You'll notice in the illustration I got online about TFI modules youll notice theyre identified as Black or Gray which is misleading as you can see from my pictures the CCD and NON CCD can come either black or gray and the way to tell is by weight as one weighs considerably more than the other or simply pry off the dust cover and look.......
Good Luck
