I have a 1999 Ranger 4.0 L vin code X engine - 2 wheel drive - AOD transmission
with 107K miles on it. The truck is new to me. No history.

The system sets 172 and 175 codes, rich left and right bank. The o2 sensors are working properly - in the .3 to .8 range. The fuel pressure is 65 psi and all other inputs seem operating properly. Or at least the scanner shows the proper information. I replaced the fuel modulator (the old one was good)

My problem is
a. Can't find information on the 65 psi fuel pressure - I think it's correct for flex fuel, but this is NOT a flex fuel engine.
b. There is NOT a return line from the engine to the fuel tank.
c. There is something that looks like it's from outer spact above the spare tire. I know it's part of the evap system. But I can't find any info on this plumbing.
d. Don't have a clue as to the location of the fuel pressure regulator. It's NOT on the engine. I may be above the spare tire.

Hope you have some ideas.

 

All your questions are related to the same thing. 1998+ Rangers use a "returnless" fuel system. Returnless fuel systems have the following characteristics:

(1) there is no return line running back to the fuel tank from the fuel rail;

(2) designed to operate at higher fuel pressure - 65psi is dead on correct;

(2) the fuel pressure regulator is now in the fuel tank with the pump, not on the fuel rail.

Have you check out the MAF? Tried cleaning it?

 

Thanks
I hope this is the correct way to reply?? If not let me know.

The MAF was very dirty. I cleaned it along with the intake hose and the throttle body. The voltage and resistance readings are OK now. I replaced the IAC when I got the truck, it was dead.

One additional NOTE - If I reset the codes when driving, I can drive 300 miles or a tank full (on the interstate) and not set codes. (Truck is from Arkansas and I drove it to Arizona)

 

Possible causes of a rich condition:

Fuel System:
·Excessive fuel pressure
·Leaking/contaminated fuel injectors
·Vapor recovery system concern

Base Engine:
·Oil overfill
·Cam timing concern
·Low cylinder compression
·Excessive engine wear

Powertrain Control System:
·PCM concern

Induction System:
·MAF contamination

 

Thanks for the info.
I have been working through the list and have eliminated most. More work to do.

Thanks Chuck-AZ

 

Another thing to consider (IMO) is the ECT sensor. If the ECT is telling the PCM that the engine is colder than it really is, then that may cause the PCM to command too much fuel than what conditions actually require.

 

Welcome to FTE

You've done some good troubleshooting & given the results obtained so far, I like the engine coolant temp sending unit idea Rockledge tosed out.

The computers temp sending unit has two wires & is separate from the instrument panel temp sending unit, which has only one wire.

You could pull it's electrical connector & check it's resistance with the engine cold & hot, to check it out. at 45-60 deg F, it should be about 40K ohms & at 180-220 F it should be about 3K ohms.

You should also pull the battery B- cable after cleaning the MAF sensor, to reset the computers KAM, so it can begin to relearn it's fuel trim, with the cleaned MAF sensor.

If you'll turn something electrical on after disconnecting the battery, it'll help drain & clear the computers KAM back up & reset the computer faster. Leave a door open, switch a light on, push the cigar lighter in, ect.

Just some more things to ponder.
Let us know how it goes.

 

Thank you !
I'm starting to get the hang of this (as a first time fourm user)
You all are a great group and I appreciate the response to my question.
I agree the IAT (intake air temp) is a good starting point. Now that I know the 65 psi fuel pressure is not a problem, I can go forward.

Thanks again

 

Rockledge & I were saying to check the Engine Coolant Temperature (ECT) sensors resistance.

If it's fibbing to the computer about true engine temp, the computer will think the engine is cold & keep the air/fuel mixture richer than needed & that could cause your rich codes fo both cylinder banks.

 

Correct - It was getting late last night. I plan to check both ECT and IAT, when it stopps raining. Today I hope.

 

More questions
Since CHILTON is not clear as to the locations of sensors and senders, I have this question. I tested (cold) the ETC - or I think it is. It's located to the left and above the steel water outlet pipe. It tested about 40K lower than the chart inticated it should for that temp. This device has only one wire connected to it, the sensor has two flat pins. One pin is at ground potential. I have ordered a replacement.

CHILTON also shows a coolant temp sender, that seems like it's under the intake manifold. Is that correct?

One more device is located to the right and under the throttle body and screwed into the front timming cover. CHILTON calls it a oil pressure switch, it has two wires.
Any thoughts?

Is the (ECT) a one or two wire sensor?

 

The ECT is the two-wire sensor. It is located to the right of the one-wire temperature sender that you mentioned.



The IAT is mounted in the air intake tube.

 

Thanks for the information. (picture) CHILTON has some limitations.

Not sure if you had seen this link.
http://www.aa1car.com/library/returnless_efi.htm

 

Replaced (IAT) as it was about 25% out of specifications.
Replaced (ECT) it checked close but I replaced it anyway. Scanner shows a more accurate water temperature now (higher-that's good). I disconnected the battery, let the door open to kill KAM when I changed the sensors.

I drove five miles and set 172 and 175 codes within the first two.
The long term is -25

Do you recommend changing the O2 sensors as part of a 100K mile tune up?

I have to take a few days off this project to attend a car show, but will continue next week.

 

Use your scantool to monitor the O2 sensor switching speed & range.

If it's sluggish/slow/lazy, then it's likely gone belly up. Some go before, some after 100K.
Things like sniffing coolant, or silicone spray, or the wrong kind of sealant fumes, will make em sick too!!!!