Solved! 1988 Ranger misfire

[Dirt]

Hello! I have a 1988 Ford Ranger with a 2.9 V6, 4x4, and a 5 speed manual transmission. I just recently purchased this fine machine and I am the 3rd owner. This rig has 192,000 miles on the clock and had sat in the woods for four years before the previous owner bought it in 2017. My problem started last month when my mother was driving it to her workplace about 5 miles away. She said it started to lose power and shake midway through the trip so she pulled off into a parking lot. She called me and I wrenched on it all day with a buddy. We have replaced the IAC valve, TPS sensor, and also have done a number of troubleshooting tests. Since then we limped it home and I've been working on it ever since. Here is what I know: We ruled out fuel delivery because there is good fuel pressure and a clean filter. (30PSI at the fuel rail and a brand new filter) All six cylinders have spark and all of the cables are within specification for resistance. From there, I checked the injector pulse with a Noid light and it turns out cylinders #5, #3, and #6 have very weak pulse (almost invisible in daylight) #5 is ok but not as bright as the other three. All 6 injectors have 12 volts fed to them so I know the problem lies in the (ground) pulse from the ECM. There were two connectors for the fuel injection wiring harness that had heavy corrosion. We cleaned those. On the same day we cleaned the connectors the misfire went away and I thought I had fixed it. This morning when I tried to go get gas the problem was back and just as bad as before. (Today was about 45 degrees outside.) I am sorry to give you so much information but I wanted to cover all my bases. if anyone has insight that could help or tricks to try please help me. Thanks.

 

[rusty ol ranger]

You may have to start tracing wires. Beginning with the ones you cleaned

 

[Dirt]

Looking for broken / sketchy wires all the way between the connector to the computer?

 

[rusty ol ranger]

Looking for broken / sketchy wires all the way between the connector to the computer?

Yes.

 

[Dirt]

You may have to start tracing wires. Beginning with the ones you cleaned

I didn't find any abnormalities in the wiring. The ground signal wire from the computer has good continuity all the way from the computer to the injectors. What to do next? Since the problem is intermittent and changes without warning I suspect the computer itself. Is there a ground for the computer I could check? Or just stab a new one in?

 

[rusty ol ranger]

I didn't find any abnormalities in the wiring. The ground signal wire from the computer has good continuity all the way from the computer to the injectors. What to do next? Since the problem is intermittent and changes without warning I suspect the computer itself. Is there a ground for the computer I could check? Or just stab a new one in?

@RonD

 

[RonD]

Pull out computer, its behind passenger side kick panel

Open it up and have a look at the circuit board, looks similar to this: http://www.auto-diagnostics.info/ford_eec_iv

There are 3 blue capacitors in the above picture, yours will also have 2 or 3 of those, they can leak after 20+ years and cause any number of issue
Free to have a look, under $5 to replace these and clean up the circuit board

Yes, the injectors get 12volts with key on, computer grounds each injector to open it

In 1988 you will have Batch Fire fuel injection, so on a V6 there are only 2 ground wires from computer for the 6 injectors, 3 injectors open at one time, then the other 3 on the next RPM
Generally its 1, 3, 5 and 2, 4, 6 so odd even

If you think its strictly a fuel issue then you should be able to spray gasoline into the engine and start it up and keep it running by spraying in more fuel
This would take spark off the table

 

[Dirt]

Pull out computer, its behind passenger side kick panel

Open it up and have a look at the circuit board, looks similar to this: http://www.auto-diagnostics.info/ford_eec_iv

There are 3 blue capacitors in the above picture, yours will also have 2 or 3 of those, they can leak after 20+ years and cause any number of issue
Free to have a look, under $5 to replace these and clean up the circuit board

Yes, the injectors get 12volts with key on, computer grounds each injector to open it

In 1988 you will have Batch Fire fuel injection, so on a V6 there are only 2 ground wires from computer for the 6 injectors, 3 injectors open at one time, then the other 3 on the next RPM
Generally its 1, 3, 5 and 2, 4, 6 so odd even

If you think its strictly a fuel issue then you should be able to spray gasoline into the engine and start it up and keep it running by spraying in more fuel
This would take spark off the table

I know that it's a fuel issue. I isolated it down to 5, 3, and 6 not getting the pulse from the computer. I pulled the computer earlier today. There is a sticker on the computer that says it's a remanufactured unit. I assume this to mean it has been replaced before? Tomorrow i will crack it open and have a look. If those capacitors are faulty, all I have to do is buy more and solder them on? Where would I find capacitors? (Can you tell I'm not really a computer guy?)

 

[RonD]

Just looked up the 2.9l wiring and pin 59 from computer is the ground wire for injectors 3, 5, and 6, so there's the issue
Showing a tan/red wire at pin 59 which changes to tan/yellow and tan/white at injectors

Yes, you desolder old caps and solder new ones in

But if its a "rebuilt" unit it should have new caps already, thats pretty much what "rebuilt" means in these computers, they are the only parts that go bad except the timing crystal, and then circuit board is cleaned

Google: electronic parts supply

For your location, they will have the capacitors you need, you need to get a correct numbers from the sides of the capacitors
You need to match the uF, like 100uF, exactly, but you can use a higher voltage rating , so if its 16v then 16-250v is fine, just not a lower voltage

 

[Dirt]

It doesn't look horrible in here. I only see one capacitor and it doesn't look like it was leaking or anything. There is a slight bulge on the side of it however. Is this normal? I mentioned the truck was parked for about 4 years and I live in the wet and rainy southeast. I know the truck has some problems keeping dry because even if it hasn't rained the carpet below the floor mat is still wet to the touch. How sensitive are these things to water?

 

[RonD]

I can't say I ever saw anyone using "film" capacitors in these before, the 3 blue rectangle units, but no they shouldn't have a bulge

Yes, moisture/humidity effects these computers alot, which was why they were moved to the engine bay, as odd as it sounds the engine bay has less moisture/humidity than inside the cab, lol
But as long as the board is clean that shouldn't be an issue

 

[MikeG]

Bulges are not good. Any computer that seems to be giving problems, I take the cover off and look for bulges / goo on capacitors. And note if there is any 'ozone' smell. If any of that is true, there's a hardware issue.

 

[Dirt]

I took the best picture of it I could. The round capacitor has some slight residue on the top. Those rectangle capacitors, do they fail internally? What is my best course of action from here?

 

[MikeG]

Usually, the 'goo' I see leaking out of computer capacitors is brown. And the tops are invariably bulged out. That one, I can't say for sure is bad.

 

[Dirt]

So what do y'all think is the best thing for me to do? Do you think it could be a programming issue? Should I try the cheaper thing first and attempt to replace the capacitors and see if that works? Or just order a new computer and be done with it? I have a few friends who are far more electronically inclined than I am. Also, that residue on the circular capacitor appears to be green/clear. It really isn't much at all and it could be just from the glue they used on the casing.