1994 Ford Ranger 4.0 Idle & EEC Issues
#1
01-02-2017
Join Date: Jan 2017
Location: Indianapolis Indiana
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1994 Ford Ranger 4.0 Idle & EEC Issues
Hey guys, I am new to the forum, but I have searched and have not found the answers that I need.
Issues:
I just bought a 1994 Ford Ranger 4.0L XLT 4WD, that has an issue of only dying when you put it in park and let it idle for a while.
When you first start it idles great for about one minute, then hunts a few times comes back to a rough idle, hunts harder then dies.
I have replaced the MAF, IAC, TPS, confirmed that the fuel pump is still running as it dies.
I was told that if it was the crank sensor it would not start at all, what else would cause this to happen?
Other issue:
The check engine light comes on when it dies, in an attempt to pull the codes I have bought a code reader for the EEC Tester, as well as tried the jumper method, and neither will present me with any flashing. It is almost as if the tester isn't getting power. I checked all EEC fuses and relays and they are all in working condition.
Why isn't my tester working?
Is it possible I need a new Control Module?
Issues:
I just bought a 1994 Ford Ranger 4.0L XLT 4WD, that has an issue of only dying when you put it in park and let it idle for a while.
When you first start it idles great for about one minute, then hunts a few times comes back to a rough idle, hunts harder then dies.
I have replaced the MAF, IAC, TPS, confirmed that the fuel pump is still running as it dies.
I was told that if it was the crank sensor it would not start at all, what else would cause this to happen?
Other issue:
The check engine light comes on when it dies, in an attempt to pull the codes I have bought a code reader for the EEC Tester, as well as tried the jumper method, and neither will present me with any flashing. It is almost as if the tester isn't getting power. I checked all EEC fuses and relays and they are all in working condition.
Why isn't my tester working?
Is it possible I need a new Control Module?
#2
01-02-2017
Welcome to the forum
On cold start the idle RPM should be 1,100 or higher
EEC runs engine in Choke Mode when cold
Which includes Rich fuel mix, advanced spark timing and high idle.
Cold or warm engine is based solely on the ECT(engine coolant temp) sensor.
ECT sensor is a 2 wire sensor ONLY USED by the EEC
Dash temp gauge uses a 1 wire SENDER for temp.
Both are located just above thermostat housing on lower intake
As engine coolant warms up the EEC will start to close the IAC valve to set lower idle
Automatic trans "target idle" would be about 750
Manual is 625
When you shift an automatic into gear EEC should bump up idle about 50rpm, same if AC is turned on.
That bump in idle won't raise idle RPMs much it is mainly used so it doesn't go down with added engine load.
When engine is fully warmed up and idling
Unplug the wires on the IAC Valve, RPMs should drop to 500, or engine may even stall, either is OK it means no vacuum leaks.
If idle stays high then there IS a vacuum leak.
Air is what controls engine RPMs not gasoline, if you add more gas to idling engine you get a flooded engine.
If you add more air you get higher RPMs
That's the point of the IAC(idle air control) valve
Since a fuel injected engine has no Jets it can't use a Choke plate to suck in extra fuel on cold start, and idle screw won't work for same reason, opening throttle plate without adjusting fuel mix causes Lean burn and engine damage.
So EEC needs to control idle so it can also adjust air/fuel mix at the same time.
IAC Valve is a throttle plate by-pass, EEC adjusts the air flow by opening and closing this valve, and it is VERY accurate, my '94 manual 4.0l idles at 624 to 628 warm.
IAC Valve is a 12volt motor with a coiled spring holding it "closed", IAC Valve gets 12volts with key on and EEC controls its Ground wire.
For starting EEC Grounds the IAC valve so motor turns against spring pressure to open valve all the way, after starting the EEC Pulses the Ground, which in essence lower the voltage and spring pulls motor back and valve closes a bit, the slower or faster the EEC pulses the ground controls the position of the valve.
EEC also "remembers" what pulse count = what RPMs on the engine, this data is stored in the KAM(keep alive memory) in the EEC, and this is the data that you clear if you unhook the battery, like clock or radio preset memory.
After KAM is cleared it can take a few days/drive cycles, before idle will be steady, EEC is relearning pulse counts
EEC's don't often have problems, they can of course, but more likely a wiring issue than EEC.
EEC warranty is long over so you can pop the top and have a look at the circuit board
Look here: Ford EEC-IV
Thats what it should look like inside
Also you can test some of the wiring at EEC from diagram
Since you can't "talk" with EEC it could indeed be faulty, just not as likely as other problems
On cold start the idle RPM should be 1,100 or higher
EEC runs engine in Choke Mode when cold
Which includes Rich fuel mix, advanced spark timing and high idle.
Cold or warm engine is based solely on the ECT(engine coolant temp) sensor.
ECT sensor is a 2 wire sensor ONLY USED by the EEC
Dash temp gauge uses a 1 wire SENDER for temp.
Both are located just above thermostat housing on lower intake
As engine coolant warms up the EEC will start to close the IAC valve to set lower idle
Automatic trans "target idle" would be about 750
Manual is 625
When you shift an automatic into gear EEC should bump up idle about 50rpm, same if AC is turned on.
That bump in idle won't raise idle RPMs much it is mainly used so it doesn't go down with added engine load.
When engine is fully warmed up and idling
Unplug the wires on the IAC Valve, RPMs should drop to 500, or engine may even stall, either is OK it means no vacuum leaks.
If idle stays high then there IS a vacuum leak.
Air is what controls engine RPMs not gasoline, if you add more gas to idling engine you get a flooded engine.
If you add more air you get higher RPMs
That's the point of the IAC(idle air control) valve
Since a fuel injected engine has no Jets it can't use a Choke plate to suck in extra fuel on cold start, and idle screw won't work for same reason, opening throttle plate without adjusting fuel mix causes Lean burn and engine damage.
So EEC needs to control idle so it can also adjust air/fuel mix at the same time.
IAC Valve is a throttle plate by-pass, EEC adjusts the air flow by opening and closing this valve, and it is VERY accurate, my '94 manual 4.0l idles at 624 to 628 warm.
IAC Valve is a 12volt motor with a coiled spring holding it "closed", IAC Valve gets 12volts with key on and EEC controls its Ground wire.
For starting EEC Grounds the IAC valve so motor turns against spring pressure to open valve all the way, after starting the EEC Pulses the Ground, which in essence lower the voltage and spring pulls motor back and valve closes a bit, the slower or faster the EEC pulses the ground controls the position of the valve.
EEC also "remembers" what pulse count = what RPMs on the engine, this data is stored in the KAM(keep alive memory) in the EEC, and this is the data that you clear if you unhook the battery, like clock or radio preset memory.
After KAM is cleared it can take a few days/drive cycles, before idle will be steady, EEC is relearning pulse counts
EEC's don't often have problems, they can of course, but more likely a wiring issue than EEC.
EEC warranty is long over so you can pop the top and have a look at the circuit board
Look here: Ford EEC-IV
Thats what it should look like inside
Also you can test some of the wiring at EEC from diagram
Since you can't "talk" with EEC it could indeed be faulty, just not as likely as other problems
Last edited by RonD; 01-02-2017 at 02:35 PM.
#3
01-03-2017
Join Date: Jan 2017
Location: Indianapolis Indiana
Posts: 2
Likes: 0
Received 0 Likes
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0 Posts
Welcome to the forum
On cold start the idle RPM should be 1,100 or higher
EEC runs engine in Choke Mode when cold
Which includes Rich fuel mix, advanced spark timing and high idle.
Cold or warm engine is based solely on the ECT(engine coolant temp) sensor.
ECT sensor is a 2 wire sensor ONLY USED by the EEC
Dash temp gauge uses a 1 wire SENDER for temp.
Both are located just above thermostat housing on lower intake
As engine coolant warms up the EEC will start to close the IAC valve to set lower idle
Automatic trans "target idle" would be about 750
Manual is 625
When you shift an automatic into gear EEC should bump up idle about 50rpm, same if AC is turned on.
That bump in idle won't raise idle RPMs much it is mainly used so it doesn't go down with added engine load.
When engine is fully warmed up and idling
Unplug the wires on the IAC Valve, RPMs should drop to 500, or engine may even stall, either is OK it means no vacuum leaks.
If idle stays high then there IS a vacuum leak.
Air is what controls engine RPMs not gasoline, if you add more gas to idling engine you get a flooded engine.
If you add more air you get higher RPMs
That's the point of the IAC(idle air control) valve
Since a fuel injected engine has no Jets it can't use a Choke plate to suck in extra fuel on cold start, and idle screw won't work for same reason, opening throttle plate without adjusting fuel mix causes Lean burn and engine damage.
So EEC needs to control idle so it can also adjust air/fuel mix at the same time.
IAC Valve is a throttle plate by-pass, EEC adjusts the air flow by opening and closing this valve, and it is VERY accurate, my '94 manual 4.0l idles at 624 to 628 warm.
IAC Valve is a 12volt motor with a coiled spring holding it "closed", IAC Valve gets 12volts with key on and EEC controls its Ground wire.
For starting EEC Grounds the IAC valve so motor turns against spring pressure to open valve all the way, after starting the EEC Pulses the Ground, which in essence lower the voltage and spring pulls motor back and valve closes a bit, the slower or faster the EEC pulses the ground controls the position of the valve.
EEC also "remembers" what pulse count = what RPMs on the engine, this data is stored in the KAM(keep alive memory) in the EEC, and this is the data that you clear if you unhook the battery, like clock or radio preset memory.
After KAM is cleared it can take a few days/drive cycles, before idle will be steady, EEC is relearning pulse counts
EEC's don't often have problems, they can of course, but more likely a wiring issue than EEC.
EEC warranty is long over so you can pop the top and have a look at the circuit board
Look here: Ford EEC-IV
Thats what it should look like inside
Also you can test some of the wiring at EEC from diagram
Since you can't "talk" with EEC it could indeed be faulty, just not as likely as other problems
On cold start the idle RPM should be 1,100 or higher
EEC runs engine in Choke Mode when cold
Which includes Rich fuel mix, advanced spark timing and high idle.
Cold or warm engine is based solely on the ECT(engine coolant temp) sensor.
ECT sensor is a 2 wire sensor ONLY USED by the EEC
Dash temp gauge uses a 1 wire SENDER for temp.
Both are located just above thermostat housing on lower intake
As engine coolant warms up the EEC will start to close the IAC valve to set lower idle
Automatic trans "target idle" would be about 750
Manual is 625
When you shift an automatic into gear EEC should bump up idle about 50rpm, same if AC is turned on.
That bump in idle won't raise idle RPMs much it is mainly used so it doesn't go down with added engine load.
When engine is fully warmed up and idling
Unplug the wires on the IAC Valve, RPMs should drop to 500, or engine may even stall, either is OK it means no vacuum leaks.
If idle stays high then there IS a vacuum leak.
Air is what controls engine RPMs not gasoline, if you add more gas to idling engine you get a flooded engine.
If you add more air you get higher RPMs
That's the point of the IAC(idle air control) valve
Since a fuel injected engine has no Jets it can't use a Choke plate to suck in extra fuel on cold start, and idle screw won't work for same reason, opening throttle plate without adjusting fuel mix causes Lean burn and engine damage.
So EEC needs to control idle so it can also adjust air/fuel mix at the same time.
IAC Valve is a throttle plate by-pass, EEC adjusts the air flow by opening and closing this valve, and it is VERY accurate, my '94 manual 4.0l idles at 624 to 628 warm.
IAC Valve is a 12volt motor with a coiled spring holding it "closed", IAC Valve gets 12volts with key on and EEC controls its Ground wire.
For starting EEC Grounds the IAC valve so motor turns against spring pressure to open valve all the way, after starting the EEC Pulses the Ground, which in essence lower the voltage and spring pulls motor back and valve closes a bit, the slower or faster the EEC pulses the ground controls the position of the valve.
EEC also "remembers" what pulse count = what RPMs on the engine, this data is stored in the KAM(keep alive memory) in the EEC, and this is the data that you clear if you unhook the battery, like clock or radio preset memory.
After KAM is cleared it can take a few days/drive cycles, before idle will be steady, EEC is relearning pulse counts
EEC's don't often have problems, they can of course, but more likely a wiring issue than EEC.
EEC warranty is long over so you can pop the top and have a look at the circuit board
Look here: Ford EEC-IV
Thats what it should look like inside
Also you can test some of the wiring at EEC from diagram
Since you can't "talk" with EEC it could indeed be faulty, just not as likely as other problems
Thank you for the information!
Very informative.
My engine did infact die when I unplugged the IAC. So looking like no vacuum leaks.
I will be looking into that eec wiring diagram and removing the ecm to check it out this evening. Thanks!
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