91 ranger random misfires

[geowik]

Sorry if this has been posted already but I couldnt find any thru the searches.
So I recenly was given a 1991 ranger that was sitting for a couple of years. The owner had cut the cat converter out which I gutted out and welded back on, put gas in a battery and it started up albeit running very rough. While driving to shop to work on it, it all of a sudden took off and started running great. Since then it randomly switches back and forth to misfiring etc. Changed fuel filter, inj cleaner, air filter etc and still same issue. getting ready to change all 8 plugs and wires on this little 4 cyl but I dont think that is it. Any one have any ideas? Cant find anyone around to read codes on pre 1996

 

[adsm08]

Alright, I can see you are from the old school.

You have no points, you have no distributor, you gain nothing by gutting the cat (unless it is already melted) except the commission of a Federal offense every time you drive the vehicle on a public road.

You have an Electronic Distributorless Dual Plug Ignition system. Each coil pack has two coils hooked to 4 plugs, each coil fires two plugs.


Anyway, your symptom sounds like a bad or damaged oxygen sensor.

 

[geowik]

hmmm, sure looked like 2 distributor caps but?? and yea from old school so I will have to do some searching to find out about the oxygen sensor, what & where it is, & what it does. Would a bad or damaged oxygen sensor cause such a seroious misfire tho?? I mean it goes from running smooth to what seems like running on 2 cylinders barely running at all

 

[adsm08]

The oxygen sensor screws into the exhaust pipe and samples the exhaust gas.

It has a piezo-electric crystal that is capable of producing up to 1 volt when oxygen is completely absent. As the level of oxygen the crystal is exposed to increases the amount of voltage produced drops.

The computer uses this signal to fine help fine tune the fuel mix. The problem is that the computer isn't very smart (on your year anyway). It doesn't always recognize a bad or erratic signal and when the fuel mix is calculated off information from a bad sensor it can do all sorts of dumb things, without setting a code.

I experienced similar symptoms in my truck several years ago with no codes and no light. I replaced everything I could think of and no luck. I finally got down to the O2 sensor. When I hopped under to replace it I found the pigtail just hanging from the engine harness and the rest of the sensor still screwed into Y-pipe.


And your "distributors", do they kinda look like this:

Standard issue I-4/V8 coil pack on most Ford engines after 1989, except the 5.0.

 

[geowik]

oh and there is a check engine light on since I got it but I cant find anyone to read it around here as of yet.
When I say it runs bad I mean real bad, barely able to get up to 55 mph. And it seems to switch back and forth to running good again maybe every other day or so and it usually clears itself up in a short amount of time - half a dozen miles or sometimes more

 

[adsm08]

http://www.therangerstation.com/tech_library/OBD_I.html
http://www.therangerstation.com/tech_library/O2Sensors.htm

Read those two articles.

 

[geowik]

Im gonna start with the oxygen sensor based on your opion and also other stuff I have read. The intermitent running from good to bad is what is weird but after reading that cooler temperatures may factor in to an o2 sensor which may make some sense as this morning it starting running like crap again. Thanks again for your help.

 

[adsm08]

Yeah, O2 sensors don't work very well below about 400*F. They are equipped with heaters, but those go bad too.

 

[1994_4x4]

Yeah, O2 sensors don't work very well below about 400*F. They are equipped with heaters, but those go bad too.

Your patients with this guy are beyond my understanding. Do you recommend changing O2 sensors (on OBDI trucks) as vehicle maintenance or just when they go bad?

 

[adsm08]

Your patients with this guy are beyond my understanding.

Careful. If you go read through my meaner posts, the two groups I like to go after are people who ask genuinely dumb questions and people who appear to have no command of their native language. You seem to fall firmly in the second group.

It was clear to me by some of the things in his first post that this is one of his first forays into EFI.

Do you recommend changing O2 sensors (on OBDI trucks) as vehicle maintenance or just when they go bad?

I just wait until they give me problems most of the time. Most manufacturers do recommend changing them every 100K miles as maintence.

 

[shane96ranger]

Adsm..... I didn't realize you were a doctor.

 

[adsm08]

Adsm..... I didn't realize you were a doctor.

Neither did I.

 

[geowik]

Yea you are correct, I have worked on vehicles for a long time but new to EFI. I did go purchase an O2 sensor $50 but have not yet installed. I spoke with someone else at the Oreilly who apparently knew more of the other Jose or Juan on the phone and was able to read the codes. I wanted to post and see what anyone thought before I changed and not able to return it.

DTC:96 - fuel pump secondary circuit fault/high speed fuel pump relay open

DTC:18 - #1 loss of tachometer input/IDM circuit failure/spout circuit grounded #2 spout circuit open or spark angle word (SAW) circuit failure

DTC:88 - (trucks only) choke relay out of range. Dual plug input control failure. shift solenoid 3/4 - 4/3

Although he could obtain codes, he nor I had any idea what they meant however I will be searching the forums here.

Whats weird is that it ran like crap this am all the way to work & all the way (12 miles each way)to the parts store but as soon as I fired it up at parts store it ran good all the way home? OK, back to the forums. Thanks again Doc!!

 

[1994_4x4]

Careful. If you go read through my meaner posts, the two groups I like to go after are people who ask genuinely dumb questions and people who appear to have no command of their native language. You seem to fall firmly in the second group.

You can go after my grumpy posts for my own good really (or spelling). My understanding of others frame of mind in the automotive sciences is askew. I can admit that.

I just wait until they give me problems most of the time. Most manufacturers do recommend changing them every 100K miles as maintence.

Recommend any brands doc?

 

[geowik]

Well I am going to go ahead and change out the O2 sensor because I dont believe it has never been changed after either 115k or 215k miles.
One thing new is that on my way to work this AM it started running bad again. So when I got to work I opened the hood and unplugged the coil on the intake side and then started it. It ran exactly the same. Turned it off & plugged it back in and then unplugged the coil on the other side and it would not start at all. I did not yet have a chance to check for power to the coil compared to the other side however I think I am getting closer. I am thinking it is the DIS module but have not pulled it off to have Qreilly check it yet. I am thinking I should be able to check it with a test light and compare it the coil on the other side or am I wrong??