Looking for a nudge in the right direction

[Metal Man]

OK guys lost here. I have a 93 ranger 4x4 4.0 Auto. I have a weird issue with my little truck.

This started in the spring. My truck runs really rough at a certain temp (outside temp) I been driving the truck since last spring and its not always done this.


When the outside temp is in the 50ish to 70ish range is when i have the problem. On days in this temp range the truck starts fine.After its ran for about 30 seconds the idle will start dropping and the engine will pick up a random miss (sometimes the engine will die). This fit will last about 1 minute then level off and run fine. If you try to drive the truck during this fit its acts as if its super lean. You can ease along at a slow pace but if you try to give it any gas it just falls on its face till you let up on the gas pedal. Once the truck is warm,if you shut the engine off and start over its not as not as noticeable but still there( starts fine..30 seconds later runs rough....1 minute later all is fine.

On cold mornings i have no problems. Just get in it and go.

I work at a salvage yard so i have access to used parts to try if i need them.

So far i have changed the MAF,TPS,IAC both coolant sensors and air intake temp sensor. I've also replace the fuel pump and fuel regulator. Added new plugs,wires and air filter. Replaced the coil pack. Replace upper intake gaskets and checked all vacuum lines for leaks. I even went as far as swapping the intake and throttle body for another.

I have not tried another ECM. And i have not replace the O2 sensors yet. Cats were gone when i got the truck. And i do have an exhaust leak were the exhaust pipe hooks to the manifold. .When i changed the plugs they looked great. Nice tan color.
.
The truck does not give a check engine light during this fit. I do get a check engine light after about 5 minutes of drive time( truck is running good by this time). But its done this since I've had it, long before this new problem started.

I really don't know what to do. Looking for some help here.

 

[RonD]

You didn't mention the fuel filter but I am sure you did that, although I can't see that causing this problem.

30 seconds after start does sound like something in the cold idle system, and from your description it does sound like the ECM is cutting the injectors down to warm idle(lean) no matter what the engine temp is or the throttle plate is doing.

The MAF does set mixture, and your '93 should also have a IAT(intake air temp) sensor on/in the air plenum or on the upper side of the intake, two wire sensor.
4.0L 1993 through 1999 had these.
Not the same as the IAC(idle air control)

This is a really good how to on the MAF
http://www.therangerstation.com/tech_library/CleanMAF.html

 

[Metal Man]

Defiantly not the MAF. I've replaced mine with another from a known good running truck and that did not fix it. I even had a buddy at Advanced let me try a new one straight out of the box...same thing.

I've also changed the IAT. No change.

I have not changed the fuel filter on the frame but i have changed it in the tank when i added the new sending unit and pump.

It feels more like an electrical issue then it does a mechanical based on the fact its temp related. Soon as we get a 93 ranger in like mine I'm gonna swap the ECM.(My interchange says it will not work out of an explorer.....and i got two of those)



Thanks for the suggestions Ron D. Keep the ideas coming guys

 

[RonD]

I put the MAF link in so you could check the voltages on the cables, swapping out the MAF is fine if the MAF is bad, but if its not getting the correct voltage then even a new MAF wouldn't help.

Not saying that is the problem, it is just a free test you can do.

Testing:

With the engine running at idle, use a Digital volt meter to verify there is at least 10.5 volts between terminals A and B of the MAF sensor connector. This indicates the power input to the sensor is correct.
Then, measure the voltage between MAF sensor connector terminals C and D. If the reading is approximately 0.34-1.96 volts, the sensor is functioning properly.

Because sensors all use power and often resistance is used as the sensor "level" an intermittent ground can produce odd behavior, like temperature sensitivity or high and low humidity sensitivity.
Never use teflon tape on sensors, it can isolate the sensor from a good ground, dab of sealer on threads is better.

You can often test sensor grounds with a volt and/or ohm meter, unplug sensor wire, connect meter to that wire and the other meter wire to sensor's metal housing, depending on the sensor you can either measure voltage or OHMs, remember or write down that number, now move the meters wire that was on the sensor's housing to the "-"(ground) on the battery, this should produce the same number, if not check the ground wires/straps that are being used for that sensor's location.
The key may need to be on to test most sensors.

 

[Metal Man]

Thanks Ron, I'll check it out tomorrow.

 

[Metal Man]

Found the problem. The ECM was burnt up. Replaced with another one and truck is running good again.

Once i pulled it out i could smell it was fried.

 

[matticus420]

Hmmm sounds like my truck....
Where can u check the ecm?

 

[Metal Man]

On a 93 Ranger 4.0 its located on the driver side inside the firewall. Right behind the inner wheel well. You will have to access it from under the hood.Just follow the main wiring harness till it meets the fire wall on the driver side. The ECM "computer" is a metal box. The wiring harness hooks to the ECM with one 10mm bolt. Its a rectangle shaped plug. Not the round one you will see in the same location.

 

[matticus420]

Cool thanks man ill check it ou when i get a chance