93 ranger 4.0 problems

[smokinstroker]

i have a 93 ranger stx 4x4 auto 4.0 i just replaced every gasket and seal in the engine the truck ran like crap when i got it until i unplugged the maf sensor then it ran ok. so i have replaced the maf sensor the temp sensor,coil pack wires,plugs,fuel filter o2 sensors new fuel pump. my problem is that i keep getting code 159 witch is maf sensor is out of range and code 177 is the o2 sensor i have installed 2 brand new maf sensors and o2 sensors and keep getting the cel after about 5 miles. i have unhooked the battery over night to reset the computer also after i start it if i rev it up to lets say 1000rpm for 30 seconds the rpms will jump up to like 1200 like a switch was flipped on for two cylinders it also does this going down the road it will lose power then all of a sudden come back to life the fuel mileage is 9 mpg i am stumped and tired of throwing parts at it. any help will be appreciated thanks

 

[RonD]

Computer codes rarely means a part is bad, so grain of salt.
The point of the code is to narrow down possible problems.
If a code definition mentions a sensor then it usually means that sensor is working or the problem wouldn't be reported

159 means MAF voltage is out of range, so most likely wiring issue

Look here: http://www.therangerstation.com/tech_library/CleanMAF.shtml

Scroll down to TESTING
Have a volt meter set for DC Volts
get a couple a sewing needles to pierce the wires so you can test voltage while they are connected.

Wires A and B(in diagram) should have battery voltage, so a Ground and 12+ volts
Wires C and D are for the computer, its range is .1volt to 4.99volts, so 5 volt range.
MAF would send out close to 5volts at 6,000RPM, just before engine exploded, lol
Around 1 volt at idle
Test A and B with key on
Test C and D with engine running and rev it a few times, to see voltage change.

MAF sensor voltage is also compared to Throttle Position Sensor(TPS) voltage.
As you open the throttle, TPS voltage will increase, and the MAF sensor voltage should as well, more air is flowing.
TPS has 3 wires, top wire has 5volts
Center wire will have under 1 volt when throttle is closed, and above 4.5volts when throttle is wide open, this is what the computer uses.
So test TPS center wire using the sewing pin, key on but engine off
Ground volt meter
test voltage on center wire as you open and then close throttle, should be steady voltage not jumping or dropping out

Code 177 is O2 sensor on passenger side, if you have 2, is at 1volt and is not coming down when computer reduces the fuel on that bank.

O2 sensors only see oxygen, not fuel.
O2 sensor generates it's own voltage, .1v to 1volt
After fuel mix is burned in the engine there should be a known amount of oxygen in the exhaust.
Too much oxygen and O2 will have .1volt, computer calls this Lean
Too little oxygen and O2 will have 1volt, computer calls this Rich, code 177

Computer adjusts fuel mix on the fly and tries to keep O2 sensor voltage at .45 good even burn, not too much oxygen and not to little oxygen.

Computer can only increase or reduce the amount of fuel it adds in a limited range.
When it reaches that limit it sets a code like 177, it has reduces the fuel to its lower limit but O2 sensor voltage is still not going down to .45 volts

This could be an O2 sensor issue if O2 had over 150,000 miles on it
But could also be a wiring problem

But if engine is running rough it could be a leaky injector or Fuel Pressure regulator(FPR)
FPR has a vacuum hose attached, if FPR leaks, extra fuel will be sucked into the engine, causing over rich mix.
Pull off it's vacuum hose and check for fuel.

I would pull out a few spark plugs and see if they are darker brown or black, meaning engine IS running too rich

 

[smokinstroker]

Well the tps voltage is all over the place so I have a new one ordered I will let you know if that fixes my problem thanks for all the help

 

[smokinstroker]

well the new tps didnt fix my problem donig the same thing and now its throwing a tps code i am at my wits end

 

[smokinstroker]

now im getting codes 159 maf sensor out of range 121 tps is out of range and 177 o2 sensor not switching all of these sensors are new i just installed new double platinum plugs and it is still running the same way do you think the pcm is shot?

 

[RonD]

What was the voltage on the top wire of the TPS?

That comes from the computer, should be 5volts, 4.8 to 5.1v is fine

At 9MPG code 177 is correct.

What was the MAF sensor voltage with engine running?
At idle and if held at about 2,500RPM

The fact you are getting codes usually means PCM is OK, not always, but they fail so rarely it can be hard to tell unless they just die out right.
If you want, pull it out and pop the top, have a look at the circuit board.

Good look at one here: http://www.auto-diagnostics.info/ford_eec_iv

You will usually see blacken areas when the capacitors leak and ruin the board

 

[smokinstroker]

the top wire on the tps was only .08 and the bottom wire had 5.20 volts
the maf had 14.23 volts between a-b and 0.76 idling and it went up to 1.25 when i rev it t about 2500 its hard to tell exactly

 

[smokinstroker]

Well I called a Ford dealer today and gave him my vin number and my PCM number and he told me I had the wrong PCM in my truck he gave me the right number and I ordered one from AUTOZONE because the dealer can not get it its obsolete so apparently the guy I got the truck from replaced it with the wrong one

 

[smokinstroker]

Well the PCM fixed my problem

 

[RonD]

Good work

Thank for posting the fix