I can’t seem to figure out why my ranger is running rich and causing rough idle. At startup it runs smooth until the motor warms up, and then the smell of gas fumes is STRONG and the motor bogs down. Otherwise the truck runs fine down the road, and has plenty of power. Mileage seems low at 21mpg, expected 25-30 when I purchased the truck. (Only owned for 6 months)

The only codes I pulled off the OBD1 were running rich, and EGR sensor voltage out of range. I replaced EGR sensor and checked EGR (appeared to be in working order). I have also replaced MAP sensor, O2 sensor, checked for vacuum leaks, cleaned throttle bottle, sea foamed fuel system, and checked TPS voltage (.8 at idle to 4.5 wide open).

At this point I have no idea, since it runs fine until the motor warms up. I will continue looking at the fuel system, injectors, and temp sensors but any help or insight would be greatly appreciated.

 

Welcome to the forum

On the engine is a Fuel Pressure Regulator(FPR)
You will see two fuel lines coming up from the drivers side frame rail going over to the engine
One is the IN from the fuel pump and fuel filter
The other is the OUT, Return line back to gas tank

The OUT is connected to the FPR, small can, on the FPR is also a Vacuum hose
If FPR leaks, then raw fuel can be sucked into the engine via this vacuum hose
Find the FPR and check the vacuum hose for fuel
If found replace FPR

A cold engine needs extra fuel to run, after warm up it would stumble with this extra fuel, also lower MPG and show Rich codes


Its possible you have a leaking injector, but FPR leak is more likely, check that first and post back results

 

RonD,

Thanks for the response! I found the FPR, and after running the truck for some time, I found the corresponding vacuum hose to be dry. I believe the FPR to be in working order after breaking down the throttle body and finding raw fuel in the intake manifold. Possibly pulled in through the EGR once operating temp was reached? (Also found fuel out of tailpipe)

At this point I was sure an injector was stuck open, so I pulled the wiring and tested resistance with voltmeter. All 4 showed 17 with little variance. I have no experience with injectors, but to my understanding this means they are not stuck open or clogged?

What other failed components could cause this? TPS is my best guess but I tested again today. Reading from green wire to negative terminal, .9 volt at idle and 4.8 wide open (with engine warm). I would suspect the temp sensor; however, after the warmup period the rpms drop as if the computer sees the temp increase. My only other guess is the timing belt jumping a tooth? What do you think? Thanks again

 

No, OHM reading just tests if the Coil inside injector is OK
A Fuel Injector is a valve with a spring, it is pulled open by passing voltage thru the Coil, works like a solenoid or relay, an electro-magnetic device

But there is a test you can do to test for leaking injector

All fuel fuel injection computers have a "Clear Flooded Engine" routine, most use this one including Ford
Turn key on, and off 3 times, this is not technically part of the routine but if injector is leaking it will pump more fuel into the engine

Turn key on
Press gas pedal down to the floor all the way and hold it down, at 0 RPMs and WOT(wide open throttle), this tells computer to shut off the injectors to "Clear Flooded Engine"
But spark is still on
Now with gas pedal down all the way crank the engine over
If should NOT fire, so should not start, should be no gasoline in the engine

If it fires then there is gasoline getting in, and no on the EGR, thats exhaust only coming in

If it fires you can ID which injector it is thats leaking

Unhook the coil wire from distributor, so no spark
Repeat the test, including key on and off
Crank it a few times
Now pull out the spark plugs, the one with the WET tip has the leaking injector


The computer controls the injectors by GROUNDING
All 4 injectors get 12volts with key on
In 1987 you have Batch Fire injection, this means computer opens(grounds) 2 injectors at the same time, 1 and 3 or 2 and 4, they alternate
So there are two ground wires that run back to the computer, each connected to 2 injectors
So if...............one of these wires was chaffed, and was shorting to a Ground, then 2 injectors would open when key was on

You can test the injector wires for short to ground with OHM meter
Red wire is the 12volt wire so test the other one, all 4 injectors must be unplugged to test, and key on or off doesn't matter

 

Not sure what to think. The truck fired up with gas pedal mashed, so I followed the rest of the test with spark disengaged...could not find a plug wet with gas. I performed the test 5+ times, and finally found a plug that looked slightly damp.

I proceeded to pull off the fuel rail, inspect injectors, and swap suspect injector with another cylinder. Performed test again and could not find a wet plug with another 5 tests. I cycled off\on 15+ times and turned the motor over for 10ish secs on the last attempt.

I also ohmed injector wires while I had the fuel rail off, and no short found.

At at this point I don’t believe it to be an injector. Surely one is not leaking enough to cause it to run this rich. Possibly a fuel pressure gauge could verify? Also might try to find vacuum gauge incase I missed a leak. (Any idea what the corresponding values are for these?)

Not sure what else to look for at this point

 

Test if the gas pedal is opening up the throttle all the way
Put a stick on gas pedal and against the seat to hold it down then go to engine and see if you can open up the throttle more

If so you have a stretched throttle cable, so computer is not getting the WOT(wide open throttle) signal from TPS, 4.5-4.8volts, so it is not turning off injectors

Goggle: Ranger throttle cable mod
Just a couple of Zap Straps above gas pedal

Then try test again, engine should NOT fire or start


I used this "clear flooded engine" every morning on my high mile 4.0l engine, I want to pump oil thru the engine BEFORE it fires up, so crank it for 5 seconds or so and then release gas pedal for start up


But if yours started but spark plugs are not WET, how did it start?
Kind of a chicken and egg thing
Can't start without fuel
But spark plugs show no fuel

 

Exactly why I’m stumped at the moment. I tied throttle wide open with steel wire and check TPS at 4.8v. Cranks right up, even without cycling the key. Tried the same process without spark and plugs are dry.. Maybe I will try again tomorrow.

 

Since my results were inconclusive yesterday, I attacked this from a different angle. I pulled the fuel rail, tied injectors to rail with tie wire, attached fuel pressure gauge, and began to build fuel pressure by cycling the key on/off. (Anybody know what this rangers spec on fuel pressure? I guessed 35-40 psi)

With this approach I hoped to visually identify the leaky injector. After building the pressure to 40psi I could not find a leak. However, I did notice the the pressure gauge slowly drop. I placed a paper towel under the fuel rail assembly and could not find a wet spot from injector or o-ring. After 5 minutes or so, when the psi dropped to 35 psi, I cycled the key again and popped an injector loose.

At this point I’m willing to buy all new injectors if it will solve my problem, but I am not convinced. Anything else I could look for before spending the money?