Help!! Snow is coming!!

[ponddweller]

Hey all,
I have viewed posts on here many times and I have got an incredible amount of help from you all. I think of all the "FORD" forums out there TRS is the best and most informative. Now on to my question...

I have a 1993 Ranger STX 4.OL V6 that I use for plowing snow(awesome plow truck by the way)We haven't had a lot of snow the last coupe of weeks so she hadn't been started much. The local forecast called for some precip so I went to make sure all was well with the old girl in case I needed her and as always when I turned the key she fired right up.
I drover her around my lot a bit to make sure she was plenty charged and ready for action when mother nature's furry arrived. After parking in her usual spot I left her running and got out to look over the plow gear and a funny thing happened. The engine kind of fluttered up and down a little and then died..funny I thought.. but got in to start her back up. There was a god awful smell of burnt something and she would crank all day but not start. (not the familiar hot wire smell). After two below zero days of testing and chasing this and that, I determined it was the ECM/PCM. I removed the PCM and when I opened it up, sure enough there were two resistors or capacitors(not sure) burnt.
Knowing I needed a PCM, I ordered a reman from the local parts store and it will be here Tuesday 1/28/14. My worry is, in all my testing I can't find what made it burn up. It is 21 years old so I guess it could have just been it's time but I am worried about blowing the new PCM when I put it in.
Any help is appreciated....snow will not hold off long and without old faithful, I can not get out...pavement ends three miles from my house.

 

[ponddweller]

Here are some pics of what was inside the PCM. Maybe someone knows what parts these are and what could have cause them to burn up.

 

[RonD]

Brown with a few stripes are resistors
Black with one silver stripe is diode

The burnt part sticking up looks like whats left of a capacitor, like the other capacitor to the right(green tube)

Circuit looks like it was being fed power from the voltage regulator on the lower side of pic.

If you have an OHM meter you may be able to find what pin(s) on the connector are connected to that circuit, then look up what sensor or control it was for, then test that circuit for a short.

This page has an image and IDs for parts inside EEC-IV
http://oldfuelinjection.com/?p=3

 

[ponddweller]

Thanks Ron. That could be the culprit.... The Fisher plow I have is an elect/hyrd and when you raise or change direction of the plow it puts quite a load on the alternator, in fact it pins the volt meter...maybe it finally shorted the internal voltage regulator. I think I will pull the alternator and have it bench tested.
I have searched and searched the web but can not find a pinout for the 60 pin connector to the PCM. I would like to know what pins should have voltage and which ones should have ground... tracing these circuits will hopefully help me find where all that power came from to burn up the PCM.
Any idea where the pinout for the EEC-IV PCM in a '93 w/4.0 V6 could be found?

 

[adsm08]

Since you are in Maine I assume your truck is not California Emissions. Here are the 49-state Pinouts.

 

[ponddweller]

After reading my reply and looking at the pic from the link you added, I realize you meant the voltage regulator inside the PCM...Duh. But what would cause that. And is there any merit to what I said about the alternator?

 

[ponddweller]

Oh wow, thanks adsm08 !!! I have searched high and low for this!!
Do you have any thoughts on a cause for this catastrophic failure?

 

[adsm08]

Insight, not really. Something overloaded the circuit, but without knowing what that circuit is for I couldn't guess what fried it.

 

[ponddweller]

Well, I'm gonna get out my test light and meter tomorrow and poke around on the pin-outs. Thanks so much for the help. Will post my findings tomorrow.

 

[Andy D]

Just curious would this pinout be the same as a 94 4.0 ? TIA

 

[ab_slack]

The black (or brown) cylindrical part sticking up with a cross pattern on the shiny aluminum end is an electrolytic capacitor.

Those are a polarized type of capacitor which generally have limited voltage ratings. They are typically used in circuits for filtering voltage regulators and filtering noise.

Those capacitors also have a tendency to lose electrolyte over time which usually results in greater noise in the circuits they are filtering. It is very common in vintage electronics for the large capacitors to have lost so much electrolyte that it significantly degrades or prevents operation. It is not uncommon for people refurbing old electronics equipment to replace such right away.

They usually don't just explode but it isn't unheard of. Partly because most older equipment didn't use switching converters which tend to put more stresses on such parts.

The biggest way to make them blow up like that is too much voltage, reverse polarity, or too much ripple current. Since you weren't connecting/disconnecting battery I doubt polarity reversal and I also doubt ripple current.

The Fisher plow I have is an elect/hyrd and when you raise or change direction of the plow it puts quite a load on the alternator, in fact it pins the volt meter...maybe it finally shorted the internal voltage regulator. I think I will pull the alternator and have it bench tested.

If it makes the voltage spike high, or overloads the regulator and it makes high voltage that certainly can put enough voltage to overload that part, especially if it has been weakened by age which I am sure is a factor.

In other words, I think yes check your alternator and resolve whatever is causing voltage to spike. Keep in mind even a short voltage spike, far to short to catch with a meter can kill parts. So if you can actually see something that is really bad.

 

[adsm08]

There are a few parts that can cause ripple issues.

The alternator has a series of diodes to convert the generated AC voltage into DC. If those diodes wear out it can allow AC bleed through or ripple.

Also, a number of solenoid-type devices like the IAC, Motorcraft ones were equipped with diodes because the were frying PCMs with flyback voltage as they shut down. Many aftermarket units don't have the diode.

Finally, the RFI capacitor on the coil may have gone bad allowing flyback into the system.

 

[ponddweller]

So today I took the alternator off and had it bench tested at a local alternator repair shop. It passed with flying colors....crap..that would have been any easy fix.

I also did what testing I could on the PCM connector pins(given that the PCM is not in) this is what I found.
On a hand full of pins with key off I got a very very weak ground signal that would barely show on the meter, but then got power on those pins with key on. I'm not familiar with this at all so I don't know if this is some sort of "leakage" or "ghost" reading or if there is a problem.
P=Power G=Ground WGS=Weak Ground Signal

PIN # KEY OFF - KEY ON
1 P- P
6 G- G
8 G- G
10 G- G
15 G- G
16 G- G
17 G- P
20 G- G
21 WGS- P
30 G- G
37 WGS- P
40 G- G
52 WGS- P
57 WGS- P
58 WGS- P
59 WGS- P
60 G- G
All other pins had no response.

Does this make sense to anyone? Do you see anything that would point to a bad circuit? Especially one bad enough to fry the PCM.

 

[RonD]

The WGS would be normal on many circuits, like 37 and 57, 58, 59 are on the same wire as the fuel pump relay, a relay is just a wound wire to ground.

If you go to this page:
http://www.therangerstation.com/tech_library/EDiagrams/index.htm

Then look at the three 3.0/4.0 engine wiring diagrams you will see what the pins are for

 

[ponddweller]

Still can't seem to find the problem that burnt up my PCM. Everything seems to be as it should be. May be and hopefully it was just old and tired.
Parts store had a delay in shipping so my new PCM wont be here until tomorrow Thursday 1/31. I sure hope it doesn't fry when I put it in, that might push me over the edge...