Do I have a bum ECU? *PICS*

ok, Vehicle in question is 1992 Ford Explorer 5 speed 4x4. 31x10.5x15 tire with 3.73 gears


Symptoms are backfire at low load/idle, seems almost like a skip and/or miss when cruising, Sluggish power, poor fuel economy (10-11 mpg) noxious excess fueley smell from exhaust. Cannot connect to OBD1 scanner.

I cleaned the MAF and changed plugs, wires and tested the coil pack. The failure to connect to OBD1 scanner pushed me to pull the ECU for a visual inspection of the board. I would like your opinion. The first 4 pictures show the overal case and board including the white corrosion on the ECU. The pins appear to be clean without corrosion to me.
The remaining three pictures show the ?test port I assume? As well as the spot that concerns me which is the square chip. Left to right I see a brown/tan build up and a black/green build up. The final pic is the reverse side of the previous chip

What do you all think? Do I need to order a new ECU?

Ford EEC-IVs were not failure prone, some did fail it just would be the last place to look.

It looks OK to me.

Generic OBD1 reader often can't connect to Ford EEC-IV, needed a Ford model in most cases
Does the CEL(check engine light) come on with the key?

Also check other methods to see if codes are there: http://www.therangerstation.com/tech_library/OBD_I.shtml


1992 Rich fuel mix could be failing FPR(fuel pressure regulator), it's vacuum hose sucks raw fuel into intake, check that vacuum hose for fuel.

Leaking fuel injector.
I would test fuel pressure, 30-40psi when running, then it will hold above 20psi for a few months after key is shut off.
You don't have to wait a few months, 10 minutes would be fine

Rich mix will cause back fires as all the fuel isn't burn and some is dumped into exhaust where next cylinders exhaust ignites it.

Burnt exhaust valve causing back fires and misfire which causes Rich mix from O2 sensor.
Compression test, cold engine, ALL spark plugs removed, test each cylinder.
4.0l OHV should be 150+ psi in each cylinder

It certainly could be the computer, it is just way down on the list of parts that fail with age.


Computer uses factory air/fuel mix table on cold start and for the next 3 to 5 minutes.
O2 sensors can't work under 600degF so computer has to wait until it/they warm up.

MAF sensor reads the air coming in and computer compares that to RPM as a sanity check, it then looks up the air weight based on MAF data from the factory table in memory then adds that amount of fuel weight based on 35psi fuel pressure by opening the fuel injectors.
This is called Open Loop operation
MAF--computer tables---burn...............no feed back

After O2s warm up the computer can look at the Oxygen levels in the exhaust, O2s see oxygen not fuel, and uses that to calculate/fine turn fuel injector open time for best fuel economy.
This is called Closed Loop
MAF--computer calculator---burn----O2..feedback to fine tune the mix

O2 sensors last 100-150k miles, if you have been running rich for awhile then you do need to change it or them once you find the problem, Rich running ruins them.
Old O2s do cause rich running, but not as rich as you describe, drop of 1 to 2 MPG at the end of life would be common.

Thank you for the reply. The two colored spots concerned me on that chip. the CEL comes on when i turn the key into run position.
I did check to make sure i was getting 100% throttle via the foot to the floor try to start method. 2 zip ties later it passed that.
I will try the other methods of code reading. and see if I have a fuel pressure tester. Also I need to figure out where the FPR is for that vaccum line.


One question on comp test. if i pull all the plugs is it safe for me to unplug the coil and try to crank for the test?

I have been quite busy trying to start a business and work on buildings on the property as well as other employment. Makes it hard to find the time to work on this rig while I drive it lol

Checked IAC or clogged up cat?

Did you try to find a junkyard that had a similar ECU? I would also contact Ford to see if they have a diagnostic tool or program for testing them...

I don't see how Ford could have produced so many millions without some quality control that would tell them of defective units...

But swapping in a working one would be my first choice if you can find one cheap enough...

To get a good compression reading you need the crank to spin at a good speed.
The compression stroke for each cylinder slows down the crank.
With all spark plugs removed and compression gauge installed there will only be 1 compression stroke resistance for crank speed, not 6.

Engine compression is achieved by metal rings(on piston) pressing against metal cylinder walls and metal valves sitting on metal seats, it is NOT air tight, lol, and it isn't suppose to be.
It is a temporary seal at best, the faster the piston moves up the cylinder wall the less time the air has to be pushed around the rings and out valve/seat seals, air IS pushed out, that's what a leak down test is for, and a little is normal even on a brand new engine.
But for a compression test the faster the starter motor can spin the crank the better the results.


You don't need to unhook the coil, but you can if you want.
But do push down all the way on the gas pedal while cranking engine, this does two things, it allows the most air to flow into the cylinder being tested and it shuts off the fuel injectors.

You want to hear 4 or 5 "hits" before you stop cranking, you will know what that is the first time you do this, when cylinder being test is on its compression stroke you will hear crank slow and then speed up until the next "hit" of the compression stroke.

Write down results

Compression test is not strictly about high numbers.
Battery, starter motor and the gauge itself all skew the results.
The numbers you get are for comparison to each other since the numbers were gotten on the same day with the same conditions.

10% rule is that all cylinders should be within 10% of each other.
If 5 cylinders show 150psi and 1 shows 120psi then there is a problem
10% of 150 is 15
150 - 15 = 135
120 is more than 10% away from 150

Fuel Pressure regulator will be top front of engine, passenger side, on lower intake.
You will see a Fuel line attached, that's the Return fuel line
And you will see a Vacuum hose attached that's the hose to check, on my 4.0l it is a hard plastic line with rubber hose at each end.

Ty RonD. gotta see if i can find a fuel pressure gauge. Will work on it tomorrow with the compression check.

Mark_88 I don't think I would be able to find a similar ECU unless a 92 ranger 4.0 5 speed is the correct one for my explorer.

Bronco2fan the IAC test is on my list for tomorrow as well. I should disconnect the y-pipe in front of the cats. seems to flow alright tho out the tail pipe given I have a hole in the top of my muffler.

Probably not many around but I know of at least two where I am that stock parts like that because they know it will be needed some day...

Most junkyards in Ontario are linked to a huge parts network that pretty much covers all of north America...worth a shot...but sometimes cheaper to just buy a whole truck...if you can find one.

I think I can get the proper ECU replacement for 120 plus core charge at local parts house. Gotta take the 93 ranger in for a scan today, (same place that tried to scan explorer and wouldnt connect) If it connects and reads the 93 ranger codes but not my explorer, I think that may clue me in.

Get the cat converter checked