well then

[oolbreeze]

So my 1991 v6 ranger is running perfect getting 18mpg, running smooth no knocking or rattling shifts smooth and accelerates well. The only known issue is the thermostat is bad and the bolts want to break so for now there are holes in thermostat keep it cool; however, the check engine light flashes randomly so I decided to hook the code reader up everything passed not one code. The problem is the code reader is only picking up my motor as a 4 cylinder. any ideas on that?

 

[Mark_88]

I've heard or read on here recently that some code readers are not compatible with the older OBD systems...there is a special reader that you need to get but I can't remember off-hand the specifics...

I searched the site just now to see if I could find the post (recent) by AllanD or RonD as I'm sure it was posted by one of them...checked their recent posts...could not find what I was looking for so maybe someone else has an idea of why your engine is not recognized properly...

 

[oolbreeze]

That is true but I have the obd1 reader for my truck and it has served me well to get the truck to the point it is at now from the nonmobile piece of lawn art I started with. It has always read as v6 except once but it switched back the very next time.it is not correcting itself this time.
Being that it is reading the computer I am curious rather or not the cylinders are just not being read by the sensors or if the distributor I have been having trouble keeping tight is not hitting to plugs to fire them.
the thing is the truck is running perfect nothing to indicate something like that is wrong. It would be like a push button shut off of 2 cylinders was an option and It just seems odd.
Thought the code reader gives code to help the truck how do you get code to help code reader.

 

[Mark_88]

That does seem odd...but I really don't think it works that way. The reader takes information directly from the PCM and all that should be stored in some identification string that is stored somewhere on the computer.

Did you try resetting the computer by simply unplugging the battery and letting it sit for half an hour or so?

The flashing CEL might be an indication that there is an actual connectivity issue (grounding) with the computer. I remember working on my 96 and there were two or three ground wires on the main harness and one on the back end of a metal plate (where it comes through the bulkhead and connects to the firewall).

On the older Gen I and II the PCM sits on the passenger side behind the kick panel and there should be a ground wire or two there...I would pull the screw or bolt on that to see if it is corroded and maybe relocate it if it is...and use some dielectric grease on it...although I don't recall there being any on my connections...but the ground wires need to be clean and free of oil or rust.