I have a 1986 2.9 and it is running overly rich. The only things I’ve done to it since I got it are a new inline fuel pump to replace the one that wasn’t working, new spark plugs, and new fuel injectors. I know it is running rich because of excessive black smoke out of the exhaust and every spark plug is soaked in fuel. Also there is fuel getting into the oil. It will occasionally misfire in the low rpm range. The truck was running rich before I did the injectors and plugs, what is going on here?

 

Welcome to the forum

Check the vacuum line on the FPR(fuel pump regulator), its on the engine and has the Fuel Return hose attached, also has a vacuum hose, if that vacuum line has gasoline in it then you found the problem
Replace FPR

1986 Ranger uses Batch fire injection, so there are only 2 ground wires from computer for the 6 injectors, each one opens 3 injectors when grounded by computer

IF(big if) one of those wires got grounded in the harness..............then 3 injectors would be open with KEY ON, unlikely since I doubt engine would start that way

FPR is best bet

 

So I pulled the vacuum line off the regulator and there’s no fuel. Just to verify, I put a gauge on the fuel rail and I get 40psi. As for the ground wires, are you talking about the ones that ground out to the upper manifold?

 

40psi is too high, not a problem but not normal reading

Was that with engine running?

Should be 30-35psi engine running

Engine off and cycling key on and off a few times can get pressure up to 43psi or so, that's the FPRs spring rating
With engine running Vacuum at FPR pulls it down to 30-35psi, this causes fuel pressure to be more stable with the different loads the engine has

With engine off fuel pressure should hold above 20psi for months and months
If fuel pressure drops to 0 after engine running and key off, then you could have a stuck or leaking injector
If fuel pressure holds at 20psi or higher you don't

No, the ground wires for the injectors come from computer
All the fuel injectors get 12volts with key on, on their common Red wire
The other wire on each injector is its Ground wire, the computer grounds that wire to open the injector for a few micro-seconds to let in a calculated amount of fuel

If one of these injector ground wires was damaged and grounded to metal then that injector would open when key was on, and fuel pressure would drop to 0psi

And at 34 years old your 1986 computer could be failing, not calculating fuel flow correctly, no way to test for that
Best you can do is test everything else that could cause rich running, and if that all looks good then its down to the computer

You have ECT sensor and MAP sensor that can cause rich running

 

Yes my reading was 40 psi with the engine running. I replaced the fpr anyway and it brought it down to 35 psi. Also replaced the ect sensor. It is definitely running better and not as rich but when you rev it, it puffs out black smoke. I am also going to replace the o2 sensor tomorrow.

 

Also the fuel pressure holds on the gauge, so as far as I can tell, there are no fuel leaks

 

Good testing

The rich running may be O2 related although they do tend to go Lean when they wear out, not rich

And you don't think the smoke might be oil from worn valve guide seals?

 

That’s possible that it’s contributing to the smoke but there is an obvious black smoke that smells like unburied fuel. Also it only smokes at idle and very light acceleration