I have replaced many things on my 2.3 engine. And it seems like every time I replace something its runs great! For a day at least.. But then it returns to its normal ways of sputtering and bogging and random idleing issues. The thing that's got me confused is how great it runs when the computer has been reset and it is remapping. It almost seems like the computer is at fault. So i guess my question is
1. What are the symptoms of a failing ecu\pcm or whatever it is
And
2. How do I find the right replacement PCM

It is a 1996 ranger xl 2.3 with a five speed manual transmission

 

What codes are you getting?

You can only reset 1995 and up Ranger computer with a scanner/reader, unhooking the battery doesn't do it, it did on 1994 and earlier.

failing computer wouldn't turn on CEL(check engine light) when key is turned on.
It would store odd codes in memory sometimes.

Computers like these rarely fail, not never but really isn't common at all.
They are very slow and way over built for the application, 1990 vending machine has a "smarter" computer than a car/truck uses.


An engine is still just an air pump, self powered, but an air pump none the less.
They can add computers and sensors and electronic controls but it is still a gas engine.

There are a few easy to use tools that can help you with any gasoline engine.
Your eyes, pull out a few spark plugs and look at the tips, very light brown means good air/fuel mix, darker brown/black is a Rich fuel mix.

Vacuum gauge($25), read here: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine
Tells you the condition of the engine, rings, valves, valve timing, leaks, and if exhaust might be clogging up.

Bluetooth OBDII scanner/reader, wireless, $30-$40, concession to the 1995 and up Ford computers, these work with bluetooth smart phones as their display so not too expensive.
And you can watch live data while driving, can help pin point issues, fuel trim numbers can be very helpful in a poor running engine

"Don't shoot the messenger", the reason a trouble code is stored and CEL comes on is because a sensor IS working, if sensor was not working then there would be no code, because computer wouldn't know anything is wrong.

 

Thanks for all the info. I will definitely do the compression test to make sure the engine itself doesn't need work. And the only code so far is a bad o2 sensor. Can that cause such drastic results? Ill just replace it anyways. As for reseting the computer, I will see if maybe orileys can do it with their scanner. Hopefully I can find a good deal on a nice obd2 reader myself. Ill let you know how things work out. Thanks

 

There are quite a few O2 sensor codes, 99% mean O2 sensor is working fine but engine is running too lean or too rich, because of a mechanical reason, i.e. low fuel pressure, vacuum leak, faulty fuel pressure regulator, ect............

If upstream O2 sensor(closest to engine) has over 100k miles on it then it is fine to replace it, just on spec.

What was the code number?
If you don't remember exact code that's OK, but don't guess.

Since you have a 4 cylinder engine and only 1 upstream O2 sensor an exhaust leak at the manifold can be a big issue, it is for V6 and V8 engines as well but easier to ID.

An exhaust leak in the EGR system or exhaust manifold sucks IN air between blowing out exhaust.
O2 sensors only "see" air(oxygen) levels in exhaust, that's what the "O" in O2 is for.

If air is being sucked in to exhaust system then the O2 "sees" that extra oxygen as a Lean burn, so computer adds more fuel, because this is a False Lean the engine is now running richer than it should, MPG goes down, and so does performance.

Most problems with engines are still the same as they were 50 years ago, mechanical problems.
The electronics make engines more reliable and you don't have to spend one day a month adjusting carbs and resetting points, when newer, when they were older a few hours every weekend was required, lol.

So look for/at a mechanical issue first.

My pet peeve, is the "I wish it was the good old days when I could just adjust the carb or points to fix the car"
Well I was younger then so yes to the "good young days", lol, but carbs and points sucked.
The reason many DIYers back then KNEW how to adjust carbs and points was because they had to do it ALL THE TIME, so you learned how to fix common issues.
Cars to today don't have issue as often, more reliable, but when there is a problem DIYers have not "learned" how to fix it, so it seems a confusing task, but only at first.
Nothing has changed on how a gas engine works, the mechanics are still the same.
Which is why spark plug tip color and vacuum gauges are still first steps to use.

 

I will be doing the vacuum test later today\tomorrow. As for the code, the first time the code was for the o2 sensor reading a lean condition and then the next time I went back they said that it needed to be replaced. I'm wondering if there is a leak somewhere in the exhaust. I will try looking for any later today.

 

O2 lean means O2 is/was probably working.

The computer calculates how much fuel to add to the incoming air based on MAF sensor data.
After adding that amount of fuel, via fuel injectors, it is burned in the cylinder, and the exhaust comes out to the O2 sensor.
If O2 sensor shows too much oxygen(lean) then computer adds a bit more fuel, this is a +1 on the Fuel Trim table the computer uses, 0 is the calculated amount of fuel based on MAF.
If O2 showed too little oxygen, Rich, then Fuel Trim would go to -1, computer adds less fuel.

In the case of too much oxygen the computer increases the fuel trim numbers until O2 sensor shows correct balance of oxygen in the exhaust, if this number is at +20 or higher for any length of time the computer will set a Lean code and turn on CEL.
Engine is NOT running Lean, computer is adding enough fuel for correct burn, the code is to let driver know that the computer thinks something is wrong that should be checked.

It could be O2 sensor, simply pulling out a spark plug and seeing a Black tip would tell you the engine is running too rich so you have a False Lean condition.
Which could be failing O2 sensor or exhaust leak.

But more common issue with Lean codes are vacuum leaks.
MAF sensor needs to "read" ALL the air coming into the engine.
If air is coming in from any other place then MAF sensor air flow data is low, so computer would be adding LESS fuel than needed, so burn would be Lean until computer added enough fuel, and fuel trim number goes up.

Another cause for Lean code is fuel pressure, computer is programmed with expected fuel pressure for the vehicle, in '96 that would be 35psi.
So when computer opens a fuel injector it expects XXX amount of fuel to come in based on 35psi pushing it in, if pressure is 20psi then less fuel will flow in, XX, when burned it would be lean, so computer adds more fuel and fuel trim numbers go up.

A dirty MAF sensor will under report air flow, Ford MAF sensor uses a heated wire, air flowing passed this wire cools it down, the more it cools the more air is flowing, if it gets a coating of dirt on it then it acts like insulation so less cooling and MAF reports less air flowing than there really is so Lean burn with calculated numbers, and fuel trim goes up.



For an Exhaust leak to effect O2 sensor it needs to be between the engine and the O2 sensor, exhaust leaks past the O2 sensor won't effect fuel trim.
But just look at a spark plug tip, it will tell you if there is a false Lean

 

Iv check fuel pressure and it is perfect. It has a brand new fuel pump and filter. I think your right there must be a leak somewhere that's causing wrong readings. I'm gonna give it a good look over

 

Check the spark plugs, they are the "windows to the soul of an engine", poetic, just check them

 

I checked all four intake side spark plugs and they were all light brown in color. Also I ran a compression test and all 4 cylinders checked out at 135 psi. BUT I found that one spark plug on the exhaust side had a large crack in the ceramic so I replaced all 4 exhaust side spark plugs and now IT SEEMS like its running better... Although only time will tell though