3.0L Ranger will not Start warm and runs Rich

RangerKid94 · Dec 14, 2014

I've got a 92 Ranger 3.0L that i'm trying to fix for a friend before he comes home from Basic Training. The truck starts and runs fine the first time i start it, but if i shut it off after the engine has reached operating temp the truck will just crank but will not start unless i hold the gas pedal to the floor. I have strong spark at the coil and at the plugs and the spark plugs are brand new. i pulled the #1 plug after trying to start the truck after i had shut it off and it was soaked with fuel. The truck runs and drives well after it starts with the exception of running rich. I'm checking any sensor i believe affects the fuel trim. My guess is that a sensor is giving the ECM a false signal that is then firing the fuel injectors too long.
Any input would be greatly appreciated.

SenorNoob · Dec 18, 2014

I'd consider looking for chafed wiring on the ground for the fuel injectors. Are they staying open whenever the key is on?

The two largest sensors affecting trims should be the MAF/MAP (whichever a '92 3.0 has) and the O2 (which won't have any effect for a few minutes after the engine starts from cold).

Could you be looking at just a severely restricted airflow? Think rat's nest in the airbox...

Just a few ideas. Good luck.

RonD · Dec 18, 2014

Yes, Clean MAF sensor: http://www.therangerstation.com/tech_library/CleanMAF.shtml
That's the Big Kahuna sensor for air/fuel mix

Also check Fuel Pressure Regulator(FPR) on fuel rail, it will have a vacuum hose attached and the fuel return line.
Remove the vacuum hose and check it for fuel or fuel smell, replace FPR is fuel is in there.
FPR's rubber diaphragm can crack and leak, so raw fuel is sucked into the intake via the vacuum hose.
A cold engine needs extra fuel so the fuel leak often isn't noticed until engine warms up a bit.

You can also test for this and a leaking injector by doing a "clear flooded engine" test.
This will also make it easier to start warm until you find the problem.

Turn key on
Press gas pedal to the floor and hold it down all the way(this tells computer to shut off fuel injectors, but spark stays on)
Crank engine

Engine shouldn't fire, there is spark but no fuel since injectors are shut off.
So if engine doesn't fire then issue is not a leaking FPR or Fuel injector, it is a computer/sensor issue

If engine tries to start, fires, then it is getting fuel from somewhere, FPR is easiest to check.

As soon as you release gas pedal injectors will start, so keep your foot down.

Often over looked is an exhaust manifold leak, O2 sensors measure Oxygen in the exhaust not fuel, exhaust manifolds have negative pressure so will suck in air, this extra air shows as Lean exhaust as far as O2 sensor is concerned so computer adds more fuel, runs rich.
You would hear an exhaust leak large enough to effect O2 sensor.

RangerKid94 · Jan 1, 2015

Hi guys, sorry it's taken so long to post what happened with the ranger. The fuel pump had gone bad in the truck which lowered the fuel pressure so the computer adjusted the fuel trim to keep the truck running, after replacing the fuel pump the truck flooded it self out because it though it still needed the extra fuel. After driving the truck and starting it every day the computer adjusted the fuel trim to the appropriate levels and is running perfectly. My friend was able to drive it back to his base with no problems. Thanks for the input.

3.0L Ranger will not Start warm and runs Rich

RangerKid94

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RonD

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