We have a 93 Ranger 4.0 5spd. The problem is the engine is running rough after it goes to closed loop. The CEL comes on with codes 173, 177, and 188. The o2 sensors were replaced. The fuel pressure parameters were good. All other troubleshooting was followed in accordance with the guidelines in the manual but the problem has not been resolved. I need some help.

 

Welcome to FTE!

Bad fuel injectors and/or a bad pressure regulator can also cause too much fuel to get into the combustion chambers.

Or maybe a clogged or kinked vacuum hose somewhere that is choking off the air supply.

You might also try cleaning your MAF sensor and resetting the computer, it couldn't hurt.

Also, your engine will run rich if the computer thinks that it is not up to operating temperature (open loop), so you might also consider the Engine Coolant Temperature (ECT) sensor...

Just a few ideas.

 

Here's some food for thought. I once worked on a late 70's car (thus, non EFI) that was running rich for no apparent reason. In the end, the evaporative emission system was the cause. With the engine running it was continuously drawing a vacuum through the carb via the float bowl and over the gas, thus creating a rich mix. One little sensor was all it took to fix it.

With this though in mind, check your fuel cap for a damaged seal and always make sure it's on tight; turn it 1/4 turn or so after it begins to click. After that you might try crimping off the line leading from the canister to the intake. If this takes care of it, I'd diagnose the evaporative emission system. Hope this helps.

 

"The fuel pressure parameters were good".. Does that mean you *checked* the pressure? The regulator can go nutz, and keep the pressure way too high, at least on the '90 4.0. If your mileage drops about in half, I'd check the regulator with a gauge on the schrader on the injector body. How clean is the air filter? Are the spark plugs fuel-fouled? Coated with carbon? Is the PCV valve clean & functional? Plug wires in good shape? ACT(air charge temp) sensor functional? Just the ?'s I'd ask myself.
tom