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4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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  #1  
Old 02-20-2015
Lammchop1993's Avatar
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Help me diagnose my problem (maybe transmission)

I've had my ranger for about a year. Bought it with 99,000 miles. Just hit 110,000. I noticed when I bought it last year, I could get this weird vibration feeling in the gas pedal. It seems to be more noticeable now. Paying attention to my gauges when I get this vibration feeling, my RPM's seems to be "stuck" at the lower range of the gear. If I mash on the gas pedal, my RPM's stay constant and I get this vibration feeling in the gas. If I let off the pedal completely, and then step on it, my RPM's shoot up, and I do not feel the vibration.


Is this my transmission getting stuck and not shifting? Any ideas?
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Old 02-21-2015
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It reads more like computer is not responding correctly when you open the throttle plate to increase engine RPMs, so you feel engine struggling(vibration) in response to more air and not enough fuel because computer isn't opening injectors more.

Computer uses two devices to manage air for the fuel system.
MAF(mass air flow) sensor tells computer the volume of air coming in to the engine, these need to be cleaned every now and then with a spray cleaner.
They use a heated wire to detect air volume, the faster the wire cools the more air is being pulled in, pretty simple, but if the wire gets dirty it acts like an insulation so air flow/volume data is incorrect, this is often the cause bogging and hesitation, and in some cases of Lean codes being set.

Next thing to check would the the TPS(throttle position sensor), this allows computer to respond faster to driver input rather than the delay you would have in the MAF sensors detection of air flow increase when throttle plate is opened more.
TPS is on the upper intake opposite of where the gas pedal cable attaches to the throttle plate, it will have a 3 wire connector.
TPS is attached to the bar that moves with the throttle plate, this sensor tells the computer "what you want to do" as far as engine RPMs.
It is a fairly simple device, similar to a volume control or light dimmer, a variable resistor.
Computer sends the TPS 5volts
If throttle is closed resistance in sensor is high so computer gets back under 1volt(.6-.9v).
If throttle is wide open(foot to the floor) resistance is low so computer gets back 4.9volts(above 4.6v)
And just like a volume control or dimmer anywhere in between closed and wide open will be a specific voltage between .9v and 4.6v.

It is an easy part to test with a volt meter.
Key on, engine off
Use sewing pin to pierce the wires to test.
In general the upper wire is the 5volts, middle is "return voltage" and lower is ground.
set voltage meter to DC volts, 20vDC if available
Ground the meters black probe, to engine or battery is fine.
Pierce the upper wire and test for 5volts, 4.8v or higher is fine.
remove needle and pierce center wire, throttle is closed so you should see under 1volt(.6-.9v is expected).
Now slowly open throttle manually and watch voltage increase, it should be steady, no jumping up or down(dead spot), when you get to wide open you should have above 4.6volts.
If all is OK then have someone push the gas pedal all the way to the floor, you should see the same "wide open" voltage you had when you did it manually.
If not then your throttle cable has stretched, Google: Ranger throttle cable mod
An easy fix for a stretched cable.

If your TPS voltage is not reading as describe then replace TPS.
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Old 02-21-2015
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Quote:
Originally Posted by RonD View Post
It reads more like computer is not responding correctly when you open the throttle plate to increase engine RPMs, so you feel engine struggling(vibration) in response to more air and not enough fuel because computer isn't opening injectors more.

Computer uses two devices to manage air for the fuel system.
MAF(mass air flow) sensor tells computer the volume of air coming in to the engine, these need to be cleaned every now and then with a spray cleaner.
They use a heated wire to detect air volume, the faster the wire cools the more air is being pulled in, pretty simple, but if the wire gets dirty it acts like an insulation so air flow/volume data is incorrect, this is often the cause bogging and hesitation, and in some cases of Lean codes being set.

Next thing to check would the the TPS(throttle position sensor), this allows computer to respond faster to driver input rather than the delay you would have in the MAF sensors detection of air flow increase when throttle plate is opened more.
TPS is on the upper intake opposite of where the gas pedal cable attaches to the throttle plate, it will have a 3 wire connector.
TPS is attached to the bar that moves with the throttle plate, this sensor tells the computer "what you want to do" as far as engine RPMs.
It is a fairly simple device, similar to a volume control or light dimmer, a variable resistor.
Computer sends the TPS 5volts
If throttle is closed resistance in sensor is high so computer gets back under 1volt(.6-.9v).
If throttle is wide open(foot to the floor) resistance is low so computer gets back 4.9volts(above 4.6v)
And just like a volume control or dimmer anywhere in between closed and wide open will be a specific voltage between .9v and 4.6v.

It is an easy part to test with a volt meter.
Key on, engine off
Use sewing pin to pierce the wires to test.
In general the upper wire is the 5volts, middle is "return voltage" and lower is ground.
set voltage meter to DC volts, 20vDC if available
Ground the meters black probe, to engine or battery is fine.
Pierce the upper wire and test for 5volts, 4.8v or higher is fine.
remove needle and pierce center wire, throttle is closed so you should see under 1volt(.6-.9v is expected).
Now slowly open throttle manually and watch voltage increase, it should be steady, no jumping up or down(dead spot), when you get to wide open you should have above 4.6volts.
If all is OK then have someone push the gas pedal all the way to the floor, you should see the same "wide open" voltage you had when you did it manually.
If not then your throttle cable has stretched, Google: Ranger throttle cable mod
An easy fix for a stretched cable.

If your TPS voltage is not reading as describe then replace TPS.
That is a huge help! Thank you. I do have a OBD-II scanner where I could read the codes. But I have no idea how to tell if it's running lean.

I will clean the MAF and check the TPS this afternoon.
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Old 02-21-2015
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STFT(short term fuel trims) will show Lean by having "+" numbers.
STFT numbers are only valid after engine warms up because computer runs the engine rich in Choke Mode, until engine temp is above 160degF, and O2 sensors can start working.

STFT and LTFT(long term) numbers show the open time for the fuel injectors, the Pulse Width time.
LTFT numbers are only used when engine is cold or if there is a main sensor failure, as an engine and vehicle gets older parameters change, i.e. fuel pressure may drop a few PSI, the LTFT compensates for these changes, by giving the computer a long term reference to bias fuel trims.

0 is set by the MAF sensor data and the computer calculation of the optimum 14:1 air:fuel ratio.
So if MAF says 14 units of air are coming in, then 0 means 1 unit of fuel is being added
"-" means the injectors are being opened for less time, so .9 units of fuel added
"+" means the injectors are being opened for longer time, so 1.1 units of fuel added

O2 sensors read the Oxygen in the exhaust not the fuel
The oxygen content for a good 14:1 ratio burn is known.
If there is too much oxygen in exhaust not enough fuel was added, a Lean exhaust, so computer opens injectors longer, a + number
If there is too little oxygen in the exhaust then too much fuel was added, so rich exhaust, computer reduces injector open time, a - number.

STFT should switch very fast as computer "hovers" around the 0, -5 to +5 is normal when cruising.
Idle needs to be richer mix so +5 to +10 is not unusual

If MAF is reading less air than is actually coming in, or there is an air leak(vacuum leak) then the 0 is wrong and trim numbers will get above +10, engine will run fine because O2 sensors are correcting for the extra air.
If trims get above +20(or -20) computer will usually set a code and turn on the CEL(check engine light) to notify the driver of a problem, engine will still run fine and have the correct 14:1 ratio, the computer is just letting you know that something isn't reading correctly.

Just for future reference, codes hardly ever mean a sensor is bad, it usually means sensors and computer are working GREAT, they detected a problem and are letting you know.
So never "shoot the messenger", lol.

Last edited by RonD; 02-22-2015 at 09:49 PM.
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  #5  
Old 02-23-2015
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I'm having trouble puncturing the middle while to get a solid read on it. Gonna wait till it gets above freezing outside so I can feel my fingers and work on it.
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