I finished my rebuild and got the engine reinstalled in the 1986 F150 5.0 2WD w/AT. After two minor uh-ohs, it fired right up and ran great. Tweaked the timing to spec. Then, as it warmed, it began to run rough. At operating temperature it ran much worse. Pulled three of the brand new plugs (3,5,6) to find them coal black with soot. First thought was engine coolant temperature sensor. Sensor tested good. Wiring good but pin 7 voltage was low at 2.5v. At his point, the book says replace ECM. Pulled out the ECM and did a visual looking for a burned component. One burnt capacitor evident so I replaced all three on the board. Still low voltage. Out of curiosity, I checked all the 12v inputs into the ECM. All good.

My thought: Was the ECM showing low volts before the project began and I just didn't know it? Will the low voltage manifest itself as a bad signal from ECT to ECM fooling ECM into thinking the engine is cold? I didn't feel like the ECM should suddenly crap out hanging under the dash with the battery disconnected for three months. But I had pulled the dash out for painting and reinstalled it. Maybe the slight jostling during this procedure had jarred the bad capacitor as the + leg was probably already nearly or indeed burned through. If so, then why didn't replacing it solve the issue?

Time to look for another ECM?

Related issue? Of course I had to test the fuel pressure. It pumps up to a good 40 psi with engine off. But it dropped off, quickly at first then more slowly until 0 psi. Ah ha! But no, the fuel flow regulator diaphragm does not leak. Pulled the return line and pumped it up again with the return flowing into a cup. As soon as I cut off the pump, the return line flow stopped as it should. Conclusion: Since there are no external rail leaks, one or more of my just professionally refurbished fuel injectors is leaking. Is there a check on the fuel pump that could be faulty? EDIT: There are check valves at the tank pumps. Still researching if a check is present at the high pressure pump.

 

Black soot on the plugs do indicate very rich condition. I'm guessing injectors 3,5, and 6 may be leaking.

Those 3 capacitors in the EEC-IV are known to fail as they age. They are part of local voltage requlators, so their failure will mess up sensor voltages. They puke their corrosive guts out, which can burn up traces around them. You might check circuits around them to look for traces that may have been eaten away, and repair if possible.

 

FWIW: The MAP, TPS and EGR position sensor all have the requisite 5v.

 

Since all eight fuel injectors were just refurbished at The Injector Shop by Scott Fleenor, I would like to think none leak. It is possible.

Haven't nailed it down yet but the check on the pressure side may be on the in tank pumps. I had both tanks out during the project. Had both pump/sender units out. Rear tank is bone dry or I would have just switched tanks to see if the leak down problem resolved. Both tank pumps got new strainers.

 

Didn't like the looks of one solder joint on the first capacitor I replaced. Pulled it out, cleaned up the holes and installed a new capacitor. Got 4.54v backprobing at the ECM and at the CTS. Won't know if this solves the rich problem until after I figure out the pressure bleed down.

 

With a CTS that tests 22,000 ohms at 75* degrees and 3200 at 160*, good voltage AND A NEW O2 SENSOR the truck ran better but is still not at all good. I pulled the O2 sensor to see if it had the same black, fluffy deposits as the plugs. It did. But it also has a loose piece of ceramic rattling around in it. Replaced the O2 sensor and drove to the gas station to put gas in the empty tank. After having run gas through both tank pumps, it still bleeds off fuel pressure too quickly. I pulled all the plugs to see if one or more would show signs of uncharacteristic richness. They all looked exactly the same. They all were, however, "cleaning" themselves up. Fluffy black giving way to brown.

I was able to get in a KOER test. All tests came back 11. Since my fears of raw gas in the newly rebuilt engine have been allayed, I'm focusing on the near closed and closed throttle running (or not running)

I've asked over at the Bricks Forum about IACs. Referred to as a normally closed valve, how closed is it when un-powered? Allows some air? Allows no air? I have done some lab (garage) research on the question. I removed my truck's IAC valve and blew air through the un-powered valve. Allowed plenty of air to pass. After a cleaning attempt it seemed to pass less air. After an aggressive cleaning attempt, it was nearly air tight. But when I reattach the solenoid, it allowed more air to pass. I concluded the perhaps it can shut off positively if clean but needs help from the solenoid. With the solenoid installed in the un-powered position, it holds the valve open slightly. Since my truck's IAC is now thirty-five years old, I ordered a replacement. I'll have a new Motorcraft IAC in the coming days. Can't wait to compare.