loss of power and check engine light on. - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #1  
Old 09-07-2014
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loss of power and check engine light on.

my ranger(1994 4.0l) has recently began to lose power. it starts every time but it has been idling rough and slowly losing power and surging a little. the exhuast smells rich and the check engine light came on today. i looked around to see what it might be and i saw that it was possibly a egr problem. i cant find an egr valve( i also didnt have much time to look). what else might be causing this?
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Old 09-07-2014
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get the code scanned
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Old 09-07-2014
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will do
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Old 09-07-2014
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Not all '94 4.0l's had EGRs, mine doesn't.

If it runs good cold then starts crapping out as it warms up, and the CEL comes on at that time then ECT sensor could be the issue.
Computer reads engine temp and then runs engine rich when it is cold(choke mode) then leans it out as it warms up, computer has a timer for the ECT, if it doesn't change after 5-8 minutes of running CEL comes on.
ECT sensor is used ONLY by the computer to see if engine is warm or cold, it has TWO wires.
Dash board temp gauge uses a ONE wire Sender, not a sensor.

Dirty Fuel Filter, but wouldn't smell rich
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Old 09-08-2014
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it runs rough all the time and the check engine light turns on when its warmed up.
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Old 09-08-2014
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Check the exhaust flow.
Have some one rev the engine while you have your hand over the tail pipe.
Exhaust blockage(collapsed cat or muffler) can cause your described symptoms.
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Old 09-08-2014
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i did that yesterday to see if i had a stuck valve. it seemed to be flowing fine
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Old 09-09-2014
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when i drove it yesterday i paid more attention to how it was acting. it did get much worse after it was warmed up.
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Old 09-10-2014
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Old 09-10-2014
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this is the closest thing that looks like a egr valve. I dont think it is though.
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  #11  
Old 09-10-2014
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just got a code. po113. IAT sensor.
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Old 09-11-2014
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IAT(intake air temp) sensor is on the upper intake drivers side near to the Vacuum manifold.
It has a two wire connector.

Never really ran into one that failed, check connector, could just be loose connection.
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Old 09-11-2014
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i replaced the iat sensor and put in a new coil wires and plugs. i cleaned the maf sensor and the throttle body and the truck seems to only run worse. it has no egr valve so thats not an option.
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Old 09-11-2014
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thowing a 137 code and a coolant temp sensor code.
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Old 09-12-2014
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As RonD pointed out in thread #4, have you done anything with the ECU coolant temp sensor? This sure sounds to me like the culprit. When the engine is cold, the ECU (engine Control Unit) uses a fixed set of parameters (called a "map") to run the engine rich (for startup) for the injectors, much like how a choke on a carborator for a cold engine did. The ECU monitors the engine temp sensor (the one with two wires), and when it detects that the engine is warm based on this coolant temperature sensor, it switches the fuel mapping off of the rich pre-setting, and adjusts the fuel pressure to the fuel rails that feed the injectors by way of several other sensors that feed information to the ECU. If this ECU coolant sensor is not providing a correct reading to the ECU, then as RonD points out, a timer expires if the coolant temp does not provide a warmed engine reading within 5 minutes (engine thermostat should be opened at this point and engine warmed up), and a CEL (Check Engine Light) is illuminated on the dash cluster, with code set. My guess is that the ECU is now confused with how warm the engine is, so the fuel pressure is not going to be regulated correctly, and you are still in an overly rich condition, even though the engine is warmed up. If this continues, you can do catalitic damage, so you want to correct this ASAP.

Remember, the ECU coolant sensor is seperate from the dash coolant sensor. The dash guage can be reading just fine, but the ECU's coolant sensor may be faulty, and this is the one that the ECU is going to react to in the way of initial fuel pressure, and engine warmed up fuel pressure. Your rich smell, this new code (coolant temp sensor) is pointing in this direction.

About 12 bucks for the coolant sensor.

Last edited by bucko; 09-12-2014 at 06:14 AM.
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Old 09-12-2014
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the coolant sensor has been ordered and so have two new O2 sensors for good measure. this should work. illkeep yall up to date
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  #17  
Old 09-12-2014
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put in a new coolant sensor. started and idled better than ever. once i tried to move it still had a large lack of power and it was almost like it wouldnt do more than 10% throttle. im stumped. i did go looking under the truck and found an exhuast leak but i dont think thats the problem. im trying not to throw parts at it but i cant find many clues.
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Old 09-12-2014
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Warm up engine, turn it off

Unplug MAF sensor and start engine, see how it runs, CEL will come on that's OK.
This checks if MAF is giving computer the wrong information, computer runs preset air/fuel mixes based on RPM and TPS data when MAF is unplugged, so engine will run OK but not great if MAF fails outright, this state of computer operation is called "limp home mode", so owners/drivers are not stranded.


Turn off warmed up engine
Turn on key but don't crank engine
Press gas pedal to the floor and hold it down, all the way down
Crank engine, it should NOT start, fuel injectors should be shut off.

If it starts then TPS could be the problem.
TPS(throttle position sensor) has 3 wires, it gets 5 volts from computer on one wire, and sends back under 1 volt(.6-.9v) when throttle is closed and above 4.5 volts(4.6-4.9v) when throttle is open all the way.
Voltages in between are how the computer tells if you want to go faster or slower.

With key on/engine off the computer sees .9v from TPS, if foot is off the gas pedal
If you press the gas pedal to the floor the computer sees 4.6v from TPS, then computer checks the RPMs, if it is 0 then computer starts "clear flooded engine routine", this turns off fuel injectors but leaves spark working while cranking engine.
If you let off the gas pedal while cranking fuel injectors will start again.

A $25 volt/ohm meter is easy to use and can save you hundreds of dollars on replacing perfectly good sensors, with the exception of O2 sensors all other sensors can be tested with either volt reading or ohm reading.

Last edited by RonD; 09-12-2014 at 09:29 PM.
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  #19  
Old 09-12-2014
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once i get the time ill get out the volt meter and check this out.
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Old 09-13-2014
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well i warmed it up, i unplugged the MAF sensor and cranked with the pedal to the floor. it didnt start. i lifted off the gas a bit and it started right up. just like it was supposed to. next steps???
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Old 09-13-2014
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once i changed out the IAT sensor the CEL went out. i forgot to mention that.
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Old 09-13-2014
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i did a throttle body cleaner check for vacuum leaks. nothing. i did find a disconnected vacuum line that had a bad hose that ended by what looked like charcoal canisters by the battery. reconnecting it with some new hose didnt change anything.
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Old 09-13-2014
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Did it run better or worse without MAF connected(drive it), and did CEL light come on with it disconnected?
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  #24  
Old 09-13-2014
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It drove worse without the MAF connected and the CEL did come on.
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