Help please with 94 ranger

[Vonda]

1994 ford ranger 2.3 manual trans 2wd. When you crank it engine light comes on runs bad till it warms up, "you may have to wait 15 minutes to an hour for the engine to warm up to I guess a specific temperature then it will run fine. Does not throw a code. Did change the air idle control module, still not helping. Any help would be greatly appreciated..
Thanks,
Vonda

 

[RonD]

The thermostat has failed and they are suppose to fail open so engine doesn't over heat, engine will not "warm up" in the normal 5-8 minutes if thermostat is open.


This rough running is unrelated to above.
There are a few things that can cause poor cold engine performance.
When an engine is cold the Computer runs a richer fuel/air mix, like a "Choke" did for a carburetor engine.
This richer mix requires a strong spark.
I would pull out a couple of spark plugs and see what they tell you, should be clean and very light brownish color.

There is a 2 wire Engine Coolant Temperature(ECT) sensor, this is only used by the computer, dash board gauge has it's own 1 wire SENDER.

The ECT sensor is a very important sensor, computer uses info from this one sensor to setup all the other engine parameters, cold engine, warm engine operation.

On the 2.3l this 2 wire ECT sensor is on the drivers side of the block towards the front, below the intake.
If the ECT sensor has failed "warm" then the computer thinks you just came back out from the store and engine is all warmed up already, so the actually cold engine can barely run on the lean "warm engine" fuel mix.
Once engine actually warms up then it should run fine.

ECT sensor can be tested with volt or OHM meter, they rarely fail, not never, but rarely

 

[Vonda]

Thank you RonD

Thanks Mr. Ron I will check these things you listed. I appreciate all your help.
Will let you know the out come. I hope I'm replying in the right place to you, Mr.RonD.... Thanks again
Vonda

 

[Vonda]

"Maybe better explanation"

Mr. Ron, Vonda again. Ok this is how it was explained to me "finally".. He said it is at the point of cold/warm when it goes from being cold to warm is when the truck acts crazy and wants to run bad or die. I guess it's right at that changing point, but if get past that point it's ok. I don't know if this changes anything but I wanted to let you know. If he gets off work in time this evening he is suppose to check the "ECT" sensor. If you think of anything else just let me know, I will check back in. Thanks bunches for all your help.
Vonda

 

[RonD]

Yes, that change from cold to warm engine also causes changes in the computer from Open Loop to Closed Loop.

Open Loop is when the computer does not use O2 sensors, it uses "tables" in it's memory to set fuel/air mixture.
This is also "Choke mode", computer will set idle high(about 1,000rpm) and use a rich mix with advanced spark timing(like the choke did on a carb).

As engine(ECT sensor) warms up the idle should slowly drop down to 750rpm at that time computer switches to Closed Loop and uses the O2 sensors.

If your idle isn't 1,000rpm or higher when engine is cold then most likely issue is the ECT sensor, if idle is higher cold and slowly drops as engine warms up then ECT sensor is probably OK.