91' Ranger Running Rough....Sometimes

I posted something about this a while ago. I can't find the post so I'll start over.

1991 Ford Ranger XLT. 2.3 Liter with AC/PS/5 speed manual transmission. Owned since new. 186,000 miles.

My old Ranger is acting weird. Sometimes it runs just fine. Other times it acts up. Seems to bog down and smells like it's getting too much fuel.

Tach doesn't work either.

Codes Are:

29-VSS or Vehicle Speed Sensor signal voltage too low.

48-VAF or Vane Air Flow sensor voltage signal too high
or
DIS or Distributorless Ignition System-coil 3 circuit failure
or
Loss of left side tach signal
or
EGO or Exhaust Gas Oxygen sensor-signal voltage indicates opposite
from fuel.

66-MAF or Mass Airflow Sensor/VAF or Vane Airflow Sensor voltage signal too
low.
or
TOT Transmission Oil Temperature Sensor signal voltage too low.

I replaced both coil packs and cleaned the MAF sensor. Tach still didn't work but it ran fine. I took it out on the interstate. Got about ten miles before it started bogging down again.

Freaked out a lady and her kid. She pulled up beside me and said my truck was on fire. The cat was red hot so I can see why she was trying to get my attention.

Anyway, my old Ranger needs something but i don't want to just throw parts at it. My step dad said I should replace every sensor on the truck because of it's age.

If I get it running right again, I'm going to put a new exhaust system on. I'm not going to run a cat this time. That is if I can.

The red hot cat is the clue to why it is running poorly, or at least partially. The cat is designed to help burn off excess hydrocarbons (fuel) and it usually does that without a problem The problems start when too much fuel is dumped into the cat.

Too much fuel can be dumped if you are getting too much air or the MAF is not measuring properly because the computer thinks there is too much air and tries to bump up the fuel by holding open the injectors a bit longer than normal.

So error codes 48, 66, indicating the air flow and distributor malfunction make more sense from that persepective. It adds up to rich fuel mix...

Instead of trying to sound like I know what I'm talking about I will borrow a page from RonD on what to look for...

This was for a 1992 Rich fuel mix issue...which should be applicable to 1991 also


-failing FPR(fuel pressure regulator)- it's vacuum hose sucks raw fuel into intake, check that vacuum hose for fuel.

NOTE: If you smell fuel in the vacuum hose then the diaphragm in the FPR is ruptured and needs replacment...no fixing those...at least not without more work than tolerable by most.

- Leaking fuel injector.

I would test fuel pressure, 30-40psi when running, then it will hold above 20psi for a few months after key is shut off. You don't have to wait a few months, 10 minutes would be fine...if the fuel pressure bleeds off then there is an injector leak (open)...then you'd need to find out what one...one in four not hard to find and replace...but the plugs would tell you if there is excess fuel by the colour of it so pull them and inspect.

Since you didn't mention backfires this is NTK (nice to know)...

Rich mix will cause back fires as all the fuel isn't burn and some is dumped into exhaust where next cylinders exhaust ignites it.

Burnt exhaust valve causing back fires and misfire which causes Rich mix from O2 sensor.
Compression test, cold engine, ALL spark plugs removed, test each cylinder.
2.3 should be 150+ psi in each cylinder

- certainly could be the computer, it is just way down on the list of parts that fail with age.

Computer uses factory air/fuel mix table on cold start and for the next 3 to 5 minutes.
O2 sensors can't work under 600degF so computer has to wait until it/they warm up.

MAF sensor reads the air coming in and computer compares that to RPM as a sanity check, it then looks up the air weight based on MAF data from the factory table in memory then adds that amount of fuel weight based on 35psi fuel pressure by opening the fuel injectors.

This is called Open Loop operation
MAF--computer tables---burn...............no feed back

After O2s warm up the computer can look at the Oxygen levels in the exhaust, O2s see oxygen not fuel, and uses that to calculate/fine turn fuel injector open time for best fuel economy.
This is called Closed Loop
MAF--computer calculator---burn----O2..feedback to fine tune the mix

O2 sensors last 100-150k miles, if you have been running rich for awhile then you do need to change it or them once you find the problem, Rich running ruins them.
Old O2s do cause rich running, but not as rich as you describe, drop of 1 to 2 MPG at the end of life would be common.

********************

Hope that helps...

Been trying for over an hour to reply.. my internet is NOT cooperating this weekend...

Anyway, this problem screams ignition module, the tach signal is driven by the drivers side coil oddly enough, the passenger side is the primary coil. If there is no spark there is extra fuel AND air in the exhaust which means a very hot catalyst, extra air will help it heat up, extra fuel will actually cool it down unless there's extra air in the mix...

Anyway, most auto parts stores should be able to check the module for you, since the tach isn't working it should fail off the bat but intermittent issues like that make it hard as you will get a false pass at times... They are expensive so get it tested first. The only other thing that comes to mind is a crank sensor but those usually cause a no start no run...

scotts90ranger said:

Been trying for over an hour to reply.. my internet is NOT cooperating this weekend...

Anyway, this problem screams ignition module, the tach signal is driven by the drivers side coil oddly enough, the passenger side is the primary coil. If there is no spark there is extra fuel AND air in the exhaust which means a very hot catalyst, extra air will help it heat up, extra fuel will actually cool it down unless there's extra air in the mix...

Anyway, most auto parts stores should be able to check the module for you, since the tach isn't working it should fail off the bat but intermittent issues like that make it hard as you will get a false pass at times... They are expensive so get it tested first. The only other thing that comes to mind is a crank sensor but those usually cause a no start no run...

Click to expand...

That actually makes more sense...added to my notes...I thought about the Ignition Module but thought that would cause no starts as well...

Thanks for the good replies. I'll make a list and check these things out.

I've been wondering about the ignition module. It would expalain a lot of things.

I knocked off what was left of the muffler today. I hope to get these other things fixed first before i drop money on a new exhaust system. I can't believe the old exhaust and tail pipe are still good after all these years.

I went to this site got some good info.

http://easyautodiagnostics.com/ford/2.3L/icm-and-crank-sensor-tests-1

As far as seeing if the coil towers are firing, it seems to me you could just use a timing light. Most of today's timing lights are inductive so I bet you could clamp the lead to each plug wire to see if it is firing. If not then follow the instruction to see if the ICM is not firing the coil towers. I replaced both of my coil packs but that's not what's wrong.

Same thing happened to my 94 2.3L many years ago.

Cat was red hot, but I didn't notice. I thought it was the clutch burning up (from all the smoke being created). I changed the clutch, which needed to be done anyways.

Eventually, I figured out the ICM was burnt up.

Replaced it.

Problems solved.

I would have started to look for an electrical problem. With all that happening as quickly as I suspect(may be rong)... it would make sense that power or ground was lost somewhere, causing all the feeds and reported data the computer is complaining about to be caused at once, by something else than what is being received. Things really don't all break at once, though it may seem that way.
tom

I agree, although some unrelated codes can point to other issues... unusual airflow happens if there is no fuel or spark which can point to an airflow code when that isn't the problem, but a bad ground to the ignition module can be the cause of the issue. There are a lot of deceiving codes that can happen on engines, we get it a lot at work, in the industrial world a lot of engines run on propane and those engines run on vacuum controlled diaphragm carburetors and fuel pressure regulators, if the tank is ran out of fuel they will get an "O2 sensor fuel trim fault data valid but above normal" so a LOT of oxygen sensors get changed for no good reason... that is the bad part about throwing parts at the problem without doing any troubleshooting, chasing the wrong problem...

scotts90ranger said:

I agree, although some unrelated codes can point to other issues... unusual airflow happens if there is no fuel or spark which can point to an airflow code when that isn't the problem, but a bad ground to the ignition module can be the cause of the issue. There are a lot of deceiving codes that can happen on engines, we get it a lot at work, in the industrial world a lot of engines run on propane and those engines run on vacuum controlled diaphragm carburetors and fuel pressure regulators, if the tank is ran out of fuel they will get an "O2 sensor fuel trim fault data valid but above normal" so a LOT of oxygen sensors get changed for no good reason... that is the bad part about throwing parts at the problem without doing any troubleshooting, chasing the wrong problem...

Click to expand...

Years ago my wife's car had a vacuum leak. It threw all kinds of codes. Turns out that Chrysler used vacuum fittings that had little check valves in them.

I didn't want to just replace parts til I found the problem. I figured you guys would point me in the right direction.

A lost ground connection can cause all kinds of problems. Something to check out.

Been awhile since this post but I need to finish up.

Got out today since we had a break in the heat. I got tired of struggling with the codes. 48, 66, and 29 showed up but since I replaced the coil blocks, I decided to replace the DIS unit or ignition module.

That was it ! My old Ranger runs great now. Going to make a few test runs. Reset the computer. If everything checks out, going to change out the plugs, plug wires, water and heater hoses. I guess an oil and filter change wouldn't hurt either.

Thanks for the help folks.