loss of power and check engine light on.
#1
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?
#4
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
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
#12
#15
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.
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 05:14 AM.
#17
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.
#18
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.
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 08:29 PM.
#20
#22
Thread
Thread Starter
Forum
Replies
Last Post
sprx26
General Technical & Electrical
1
03-19-2014 11:07 AM
warner.325
SOHC - 2.3L & 2.5L Lima Engines
5
12-09-2009 03:48 AM
Sonic04Edge
2.9L & 3.0L V6 Tech
5
08-17-2008 06:41 PM