98 4.0 SOHC running rich on bank 2, PCM adding MORE fuel | Ford Explorer Forums - Serious Explorations

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98 4.0 SOHC running rich on bank 2, PCM adding MORE fuel


Well-Known Member
March 30, 2020
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City, State
Year, Model & Trim Level
98 2-DR Sport 4x4 4.10
Ive been poking at my rich codes for a while now, and this is not the first time ive posted about them, but I think I finally distilled all of my issues down to one photo.


This is Fuel PWM and O2's for bank 2 on top and bank 1 on the bottom. The first part is warm engine at idle with AC on, second half with AC off.

Bank 1 on the bottom is looking ok enough, but bank 2 on the top has something crazy going on there. The sensor shows it as rich, and the computer knows that, but its still feeding it twice the fuel as bank 1!

Is there any explanation as why this would happen?

Other issues include occasional hesitation at acceleration from stop and BERO reading being much too low. Its not bad today, reading at 27.4 when it should be closer to 29.8 (read off an actual barometer, not from weather service). However, at times it reads as much as 10 inHg off from what the accurate reading is.

Only other interesting thing to know is the drivers side cat is cut off and there is a flex line there instead.

I was reading over the documentation for the EEC V code today and did find this graph

It almost looks like im in the midbed overtemp protection mode, but I dont have access to any PID to confirm or deny that. Ill have to read over the documentation later and see if I can disable that check.
Could also just mean nothing tho.

Anyway, anybody know how I might be able to correct for this?

Injectors are new all around. Turning the car from off to run 5 times, then trying to start it with the gas held down results in no ignition so I shouldnt have a leaky injector AND the computer is obviously TRYING to add more fuel for whatever reason.

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Other interesting graphs:


This shows the first ~100 seconds after a warm start. It over fuels bank 2 right from the start. (AC off)


This is the next ~100 seconds after turning on the AC. Its almost like it wants bank 2 to be at 0.9+ volts on the O2 for some reason.


And one more graph because why not. First ~75 seconds is driving with breaks and gas, then last 50 seconds is idling bringing it back under control (bank 1 anyway) with AC on.

The thing is, when im driving they look a LOT closer

So, some interesting data today. The engine was running really rich and I managed to get my hands on an oscilloscope and

The computer thought that the passenger fuel bank was being pulsed for 1.1ms, but...

The scope says its really being pulsed for like 2.1ms (each square is 10V tall and 0.5ms wide)

So, the injectors are being powered for twice as long as the computer thinks. I saw another point where it was trying for 2.4ms and actually getting like 5ms

So am I looking at a bad computer here? It seems like its just throwing way too much fuel in and not even understanding that.

I also stuck the scope on the 12MHz crystal on the inside and found the EEC V clock rate was varying from 11.8MHz to 12.1MHz at the same time the engine was ramping up and down. Almost like time was being skewed for the EEC V

You’re a smart cookie. You’re likely to figure this out before we do

Well at this point, unless anybody else has something to add I think its just time to look at replacing the PCM

Which means PATS and locks and the like unless I get a tuner and start playing with that. Which I might.

Think it might be fun to reverse some code and play with the routines. Add some fun features, stuff like that. Think about having a switch that would change the limiter to 3MPH to mess around with friends using.

"What do you mean it lost power and started shaking like mad! It was just fine!"
*gets in car*
*flips switch*
*Slams the gas and zooms off round the block*
*flips switch back*
"Cool, we good?"