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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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Old 10-11-2016
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98 ranger. Cold start rough idle

My 98 Ford Ranger4.0 is having an issue when it's cold starting it's hard to start and has extremely rough idle it sounds like it's only running on 4 cylinders then after about 30 seconds to a minute you hear another cylinder kick in and then all of a sudden all of them kicking it runs smooth and never have a problem. I have replaced IAC valve,mass air flow sensor, clean the throttle body replace spark plugs and wires and it's still acts up I'm at a loss as to what it can be. I do have a check engine light that reads code 1451 which is the canister solenoid I replaced it and the problem still persists once the engine warms up and all cylinders fire it never misses a beat and she goes down the road just fine.any idea
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Old 10-11-2016
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I am: Ron Dean
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Welcome to the forum

What did the old spark plugs look like?
They are the window to engine operating conditions

Google: spark plug condition pictures


Try this test
Cold engine
turn on key count to 3 then turn off key
Repeat that 3 times
Then try to start engine
If it starts right up and doesn't misfire then your Check Valve in the fuel pump is bad, you are losing all the fuel pressure when engine is off.


All cold engines need more gasoline to run, that is what the Choke Plate did on a carb.
Fuel injection can't use a Choke Plate, no Jets, so computer must "know" engine is cold, and then bump up the fuel mix to Rich so engine will run correctly when cold.

Computer uses the ECT(engine coolant temp) sensor to learn engine temp.
This is not the same device that is used for the temp gauge, that is a SENDER, not a sensor.

Lets see if ECT sensor is working.
When you turn on the key the computer will open the IAC Valve all the way for starting, hot or cold.
When you start engine cold, do not touch gas pedal, the computer will keep the idle above 1,100, so when engine starts RPMs should go up to 1,500+, IAC Valve is open all the way, then RPMs should drop a little as computer starts to close IAC valve, how far it closes is based on ECT sensor temp, colder temp higher idle.
Then as engine warms up computer will start closing IAC valve bit by bit until engine is at operating temp and "Target" idle is set, 650 on manual trans, 750 on automatic

Does your system work like that?
If not replace ECT sensor, they are not expensive, $6-$8, but make sure it IS the Sensor not the Sender you are replacing


EVAP system codes can take two weeks to go away, they can not be reset like other codes, once you think you fixed it you have to wait.
It will clear faster if you drive with gas gauge between 1/4 and 3/4, so don't fill up, it won't run tests unless gauge is between 1/4 and 3/4.
You can not force a test, and computer takes it's sweet time running the tests, EVAP system must pass test 2 or 3 times before code will clear.

Last edited by RonD; 10-11-2016 at 07:55 PM.
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Old 10-12-2016
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Thanks Ron for the response. Tried the cold start test and no change. Will try the ECT. Could you tell where it is located?
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Old 10-12-2016
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I am: Ron Dean
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The ECT sensor AND ECT sender are located next to each other

Lower intake at the front and top
Follow upper radiator hose to the engine, it connects to the Thermostat housing which is bolted to the front of the lower intake.
Just above that on the top of the lower intake you will see the two temp devices.

ECT Sensor will have a Light Green/red stripe wire, and Grey/red wire
I think Sender uses a Red/white stripe wire


Also another test
After engine is warmed up and idling, unplug the wires on the IAC Valve, it will close all the way and RPMs should drop to 500 or so, or engine may even stall, either is good, it means no vacuum leaks.
If RPMs stay at 700 or higher you have vacuum leak, and that can cause a cold start issue since engine needs richer mix when cold.

The EVAP code made me think of a vacuum leak
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Old 10-17-2016
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I am: Jim
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Ron thanks for your continued help. Today I replaced the ECT and the air intake temp sensor I recleaned the throttlebody and had the battery disconnected the whole time so when I hooked it back up it would read the new sensors vehicle started right up and ran smooth now this afternoon it did the same problem again only for a much shorter duration of time say5 to 10 seconds and then kicked right in and ran correctly so I don't think I have a licked yet. Any other ideas?
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