91 Navajo idling rough

[Ranger Al]

I am about to give up on this stupid thing, HELP!! The thing start out with bad Purge sensor at the canister. I tried cleaning it and doesn't clear the code, so I replaced with a new sensor. The code when away and about to test drive it. It spitted out a new code, faulty IAT (intake Air Temperture). Again, tried cleaning it and doesn't work. Replaced it and it goes away. I also check the MAF sensor and it is clean as well as the filter. I've also replaced the O2 sensor (I could only locate 1 on this vehicle). The Key On Engine Off (KOEO) Malfunction Indicator lamp is all cleared.

When I start the engine it would run smooth for a few seconds and the Check Engine Lamp would come on. This time it flashed code 998 which indicate "Hard fault present".

I am thinking of replacing new spark plugs and wires and hopes thats would solve it.

Anyone have suggest????? HELP, HELP, its my Inlaw and I am only trying to be the good son. Already, I think they are pissed off at me for working on it little as a time.

 

[MrShorty]

I have no answers, mostly questions:

1) What part of the test is this "998" code coming from: KOEO, CM, KOER? What do you get for the others (recognizing that it may not even perform the KOER test if it's a KOEO 998)? See my "notes on pulling EEC-IV codes" in the EEC-IV forum if you need to.
2) Is this a true '91 model year Navajo, or a '92 model year built in '91? I would expect a '91 model year Navajo to output 2 digit codes rather than 3 digit codes. Were the CANP and IAT codes you pulled 2 or 3 digit codes? Just want to make sure we are reading/interpreting the codes correctly.
3) In relation to the previous codes pertaining 1st to the CANP solenoid and then the IAT sensor, are you certain those components were bad? Codes point to faults within circuits, of which the sensor/solenoid is only one part. From your description, it almost seems like the fault "jumped" from one component to another until the computer can't decide anymore where the fault really is. This kind of behavior suggests to me a wiring fault. Have you verified the computer's grounds? Computer (and the rest of the EEC-IV system) has proper power supply?
4) Have you looked at non-EEC-IV controlled/monitored stuff? Fuel pressure correct? Fuel pressure regulator diaphragm ruptured? If it's missfiring, can you isolate the misfire (via a cylinder balance test) to one or more cylinders or is the fault uniform over all cylinders?

 

[Ranger Al]

I'll try to answer your questions as much as I could get from my experince...

1. The code came on with the engine on (flashing check engine lamp) of 9 blinking then another 9 blinking and lastly 8 blinking. With the "key on engine off" I only get single flashes, according to the book it suppose to mean it is ok.

2. The vehicle is built in 02-91 so it is a 1991 model. The purge soleniod circuit fault put out 2 digit code (12 code). The IAT code put out another 2 digit code of 112.

3. After new part replace, it simply put out another code. Although, I did have to change rotten vacuum hoes to the "purge soleniod". I really have not check the computer for ground. Now come to think of it, her little brother was trying to install stero system on the truck. I'll check that out.

Is the computer locate under the driver side dash or the passenger side????

4. I have not check the fuel pressure, due to the matter that the engine run smooth the first few second before the computer goes into the system check then it run rough. When I said I am going to check out the spark plugs and wires, I am going to be doing that anyway. I notice my 2000 Ranger doesn't like Autolite and had to use only Motorcraft plugs only.

I appreciate your input, Mr. Shorty. I hope this clear the question. By the way, Isn't Spanish Fork is just south of Utah Lake? I drove threw there all the time visiting her sisters family in Orem.


RangerAl