86 Bronco II Running Rich

SO here is the back story. Bronco would intermittently cut out while driving like it was starving for fuel, the would start running fine in about 20 seconds. Changed the fuel pump relay, and installed a new harness. Wired the harness incorrectly and popped a fuse-able link. Rewired harness, and replaced link.

Now when I start the truck it is running really rich, so I swapped out the computer with a new one thinking I may have smoked it when I wired the relay incorrectly. New computer, still doing the same thing. Has to be something in the fuel pump relay circuit, I just cannot figure out what.

Sorry for the long explanation, just wanted to inform that it was running fine other than the intermittent stalling out, until I screwed it up some how lol.

Thanks for the help in advance.

are you positive it was starving for fuel and not running rich the entire time? Too much fuel and not enough air will cause the engine to stall out as well. Then when the truck is off, the fuel pressure stabilizes and you can start it again.

Have you checked for leaky injectors? Vacuum leaks? All these can cause rich conditions. Plugged exhaust can cause these issues too. Remember, a rich condition is the ECM compensating for too much air, its trying to keep the engine from stalling. You need to have an even amount of fuel/air mixture.

Keep me posted.

This is a fuel injected engine correct?

Engine is running Rich because....
you see blackish smoke from tail pipe?

MPG is in the toilet?

Spark plugs are blackish color?


Fuel pressure is set by Fuel Pressure regulator(FPR) located on the fuel rail with injectors.
Computer just turns the fuel pump on when engine RPMs are above 400 and then it stays on until key is shut off or engine drops below 400rpm.
So fuel pump itself is either on or off, can't really cause Rich running, could cause Lean if it couldn't pump enough fuel, but not Rich.

FPR is connected to the Fuel Return line, and has a Vacuum hose, if FPR's rubber diaphragm should crack then fuel can be sucked into the intake via that vacuum hose, causing Rich running, check that vacuum hose for fuel.

Fuel pressure should be 30-40psi if you want to test it.

Fuel injectors get 12volts when key is turned on, the computer Grounds each injector to open it to add fuel to the engine.
If a fuel injector wire was shorted to ground then that injector would be open when key was turned on.
Look at each injector, there will be a red wire, that's the 12v wire, and it is just daisy chained from one injector to the next.
On an '86 2.9l you will have Batch fire injection, that means computer opens 3 injectors at the same time, so for the 6 injectors you will see only 2 different colored wires at the injectors, one color goes to 3 injectors the other color goes to the other 3 injectors.
With key off pull off one injectors wires and test the non-Red wire for Ground, OHM or Volt test.
Then test the other color injector wire for ground as well.
If one IS grounded then you will have to find out where it is damaged


O2 sensors set the fuel mix but ONLY after engine warms up, O2 sensors can't work when under 600degF so computer ignores them on startup and uses pre-set Ford air/fuel mix based on engine size and RPMs, until O2s are warmed up, 4 to 5 minutes.
If Rich running is on cold start then it can't be O2s.
If it only starts running Rich after warm up then could be O2s OR.....the wiring for the O2s.

OK so I changed the FPR just in case. I pulled codes finally, got 87/95 for KOEO. Which points me to the inertia switch, which makes sense, since there is no switch installed in this vehicle, so need to correct that error eventually as well.

I was unable to pull codes running because the engine hydro-locked on me. Guessing that is from fuel being injected into the cylinders, so I will test the injectors tonight for grounding issues. I thought I was hearing the high pressure pump continuing to run with the KOEO, but could be hearing the injectors I guess. Even if the fuel pump did continue to run, shouldn't the fuel just return to the tank? and the injectors should only pump fuel if the engine is running correct?

Apologize for the long delay in messages, been busy with work and this is only a project vehicle so not my daily driver. Been in storage for a bit until I got some time to work on it again.