Codes- a real science

[IronIndian]

The usual surging/hesitation- got codes!

Hello all,
I have a 91 Navajo 4.0L that has just started giving me problems this past week. I replaced the Fuel Pump Relay because the pump would not shut off after the truck was turned off. You'd literally have to smack the power distribution box to make it stop . Just recently the "Check Engine" light would come off and on-usually at idle, but also when the engine would hesitate/surge on acceleration. Does this sound like a dirty MAF sensor to you? I have a cheapy Actron code reader in front of me and tried the KOEO test and it gave me codes that befuddled me Should I be receiving 2 or 3 digit codes on the reader? The first code was a 11 and the second code was a 66. The book it came with tells me that "after all codes are sent, the whole group is sent again just one more time (so you can double check your code list)." I assume that the 91 4.0L uses the MCU (Microprocessor Control Unit) and not the EEC-IV correct? Thanks all!!!!

P.S. I'm going out right now to try and get some KOER codes.

 

[RiverRat]

IIRC you are EEC IV. code 11 is a KOER pass. code 66 is a memory code.

 

[IronIndian]

I think I am MCU because the only codes I am getting are 2 digit codes...I cleaned the MAF sensor and replaced the TPS. The spring inside the TPS sounded like it had broken in numerous pieces. Mind you, this looked to be the original TPS from 1991. I think it did a damn fine job for holding up this long! I drove it tonite (this morning) and it seemed much better. The idle was much more smoother, and the acceleration was much better. I'll see if this solves my hesitation/surging on acceleration from idle. The truck is going to be driven approx 30 miles roundtrip tomorrow, so I'll know for sure if something seems ill- as well as if the CEL comes back on...

 

[MrShorty]

EEC-IV can also put out two digits. It depends on the application. EEC-IV was used at least as early as '86 (when the 2.9 was introduced to the Ranger/BroncoII. I'm not certain if the 2.8 L used EEC-IV or not). Through '91, all of Ford's engines put out 2 digit codes. Starting in '92 certain applications (the 4.0 L V6 included), the EEC-IV system switched to 3 digit codes, while others still used 2 digit codes. In '94, all of Ford's systems were outputting 3 digit codes until '96, when everything went OBD-2/EEC-V.
I don't know how good the instructions that came with the code reader are (I prefer the voltmeter method for retrieving codes, so I've never read the instructions that come with code readers), but you may want to double check the instructions with something from a better manual. You can find instructions for running the "quick test" at www.dalidesign.com/hbook/eectest.html and you may also want to try a library and see if you can get your hands on a good manual (Motor, Mitchell or other).
As for the specific codes you got, the code 11 indicates a KOEO pass.
the continuous memory 66 indicates a low reading from the MAF. This doesn't necessarily mean that the MAF is bad. It could just as easily be a bad connection between the MAF and the PCM, or other circuit fault. If you've ever run the engine with the air intake disconnected, that will set a code 66.

 

[IronIndian]

Thanks so much Shorty!
The info you gave me is priceless!!! The book that accompanied the code reader said that MCU only gave 2 digit codes and EEC-IV gave only 3 digit codes- OBVIOUSLY WRONG! Well, you get what you paid for...I'm going to look for a real-time digital reader. That would help alot My father took the truck to work, so I'll get an update as soon as I see him today. Thanks for everyones help!

 

[MrShorty]

While looking for a real-time digital reader, be sure that it will actually do what you want. I've looked before, and learned that about '92 and earlier Ford EEC-IV computers don't have the ability to send real time data to any kind of scanner. Somewhere '93-'95 is where this functionality was added to the PCM. I just don't want you to end up paying $300 for a glorified code reader.

 

[IronIndian]

ACk!!! Well, that just bites a fat one! Well, my pops just got home and he says the truck runs like a champ! He said the truck ran smoothly and crisply. I think cleaning the MAF sensor/housing and replacing the faulty TPS sensor made the difference. Like I said, it doesnt stumble/surge/hesitate anymore. Plus the idle is way more smoother. The truck doesn't vibrate anymore at idle as well...Scratch one for the shadetree mechs eh