I just want to make sure I'm translating properly and that M = 100, thus what we want for each PCM is the following Radial-mount Electrolytic capacitors:

Qty 2 4700 uF 25V 105C
Qty 1 1000 uF 63V 105C

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Adding this (1/22/13) to clearly indicate what you actually need (especially since this post is at the top of the page)...

Qty 2 47uF 25V 105C
Qty 1 10uF 63V 105C

From what I have witnessed firsthand, all the Bronco/F150 PCMs of this era use the same caps, though I'm not sure exactly what the date-range is - so far, I've only looked at '91 - '93 PCM's, but I suspect the range may be '87 - '95.

 

mfd=microfarad, not 100.

 

2 47 mfd 25v
1 10 mfd 63v

I would be checking actual values as from one pcm to another these values could change a bit , always check the original , the high temp rating will remain the same I am sure , but there could be small variances in capacitance and or Voltage , if you read the posts you will see that I raised the voltage rating ( regarding the 25v caps ) on the replacements a little , the originals were lower and in my opinion to close to being maxed given the wide range of regulated outputs from the alternators , some can be as high as 15.2 , so I felt raising it was a necessity for the life of the component , I did research on the specs and the Panasonic Caps would remain at spec down to around 5v , so there was no problem with raising the voltage rating in this case and will most likely extend the life considerably since it will in effect reduce the working load on the component

Guy

 

Thanks for the response and correction. I do recall reading that you advised increasing the lower voltage parts from 16 to 25v. I guess you saw no such need for the 63v parts? Why would such a high voltage part be spec'd any way on a "12v" circuit?

Looking at the caps again now though, I can see they say 47 uf and 10 uf, so the same numbers you've quoted but different identifier. Are the mfd and uf acronyms used interchangeably?

 

At the risk of over-analyzing (but hey, I do that), it's interesting to note that Panasonic rates their 105°C capacitor (PANASONIC ECE-A1JGE100) at 1000 hours at 105°C and their 85°C version (Panasonic ECA-1JM100) at 2000 hours @ 85°C.

This is for the 10uf 63v capacitor, but seems to hold true for the 47uf version.

 

This is why I commented on that in the threads , that temp and voltage rated versus operating voltage would determine life , its life is twice as it is rated according to it temp rating , another reason why I went with 25V instead of 16V which it was originally and in my opinion to low , they are estimating life in a 105C environment working as it may be full load , seeing we do not know the load it is working under which I assume is maybe in the 50% or less area , then the only other factor which would affect it would be operation temp , I could not find a higher rating temp for that application that would have fit the PCB , so raised the Volt rating and stuck with the temp rating of the original , there is no way to tell why it failed seeing that all other components were fine , but if I had to guess I would say the higher volt rating of the new ones should put the life expectancy much further down the road than with only a 16V rating which in my opinion is very marginal .

Guy

 

The 10 uf @ 63v Electrolytic capacitor is on the battery voltage coming into the computer. This high voltage rating is needed if someone takes the battery cable off the battery while the engine is running. The voltage could could go as high as 100 Volts. If the Electrolytic capacitor is not rated 63 Volts or above it would blow up into very small pieces. At a 63 Volt rating it may blow anyway if the battery cable is removed.
Doing this can also take out the radio and other modules.

The other two Electrolytic capacitors (47 uf @ 25v) are filters on the 5 Volt supply and the 5 Volt keep-alive power supply. So 25 volts is more than enough.

Note also that the voltage ratings on all three caps is 5 times the working voltage in the circuits that they are in. That is about the rule of thumb for Electrolytic capacitors in a circuit.



/

 

Thanks for the thorough details. Not to counter Guy's recommendation on upgrading the 16v capacitors to 25v too much, but from what you're saying, since those are actually 5v circuits rather than 12v, might the 16v parts be the best choice? I think Guy had indicated earlier in this thread that the 25v parts function fine down to a bottom range of 5v. Might we be at the ragged edge of the spec for those 25v parts?

No disrespect intended on challenging your recommendations Guy - you certainly know more than me on this topic, but perhaps you made an error in assuming it was was 12v circuit rather than 5v?

Quick funny (sorta related) story as it relates to why the 63v capacitor is warranted on the 12v circuit. An acquaintance (certainly not a "friend"), had a 2010 Silverado that he wore the battery down to nothing by keeping the radio on all day while he worked. Of course he was unable to start the vehicle at the end of the day to drive home. Couldn't find anyone to provide a jump so he had the awesome idea of clipping off the end of an extension cord and providing 120v to the battery to jump-start the engine. No, I'm not kidding. I think he only took out a master fuse and the battery IIRC. Lucky he didn't set the car on fire.

 

Awesome pic
And yes they are generally overrated but since the specs would not be affected by extra protection then I saw raising it a bit as a good way maybe to afford some extra life out of the cap .
Thanks for identifying the working voltage on the 2 47mfd's , I was very curious about that

Guy

 

After seeing that these died / ruptured , it was the only option I saw maybe to grant them extra life regarding their service , they may have died due to manufacturing issues or possibly situations where the temp reached rating many times , both are possible , but in repairing electronic equipment regarding caps , I always try and bring the ratings within reason as high as I can , this is why I did some serious research on the caps to make sure that even if in a low voltage circuit they would provide the specified capacitance rating , the Panasonic Caps will go down below the 5V working voltage comfortably , so in the end all you have is the same function with better protection/life , I do not want to have to go through this mess again in my lifetime , I could not find a higher temp rating without increasing the size dramatically , so that was not an option , and regarding spikes in voltage , I still felt 16V was too low or possibly marginal , in a perfect world , we would be able to determine the cause of the failure , I do know that it must not be any issue as my ECM is working fine and I have had no further issues with intermittent issues or false codes regarding it or being able to communicate with it

Also , I did not "make an error" , and I take no offense at all to questions or challenges , this is why we are all here , but I merely did that for increased life in the application , I was reasonably sure it was not a 12V circuit , was more concerned with preventing future failure , the Volt rating on the cap has little effect on the function per say , unless underrated and then of course early failure , the only variable you have to be careful of is that many times when you raise the Voltage rating you have to be careful that the Capacitor will function/operate at the proper capacitance at the working voltage , sometimes when Volt Rating is raised too much you can actually move out of the working voltage range , this is why I did some serious spec homework on these before I used the higher rating , it would have been a serious mistake to install these if they were not able to work in the circuits working voltage , the Panasonic Caps are able at 25V to dip well below the 5V working voltage and maintain their values , so all good , the only thing that will mean is more life


Guy

PS - When you service this stuff on a broad range of applications , you find generally that specs are cut fairly close as to curb mass production costs , so if you do your homework on the replacements and make sure that spec changes will not affect intended operation , then all you have to wory about is extended life of the component , which is not really a worry

 

Yes they are interchangeable , it depends sometimes on the manufacturer or the age of the components as to what they use , for example , old school for the most part is MFD , uF is just a shorter version so to speak

Guy

*On mine it was actually MFD , where as on the New Panasonic Caps it was indentified as uF

 

Here is the wiring diagram of those Electrolytic Capacitors.
The Electrolytic Capacitors are C2, C4 & C111.



/

 

Great, thanks very much for the extended response. I bee a liddle smardr now.
If only out of curiosity, the one lingering question for me is why the capacitors are so much more prone to failure in this application than other Ford PCMs of the same era. I've dis-proven my own theory of perhaps an inferior brand being used - I've re-checked several I have here and found they all use Nichicon capacitors. But again, only the F150 PCMs have failed capacitors (100% of the ones I've checked) vs. one capacitor on a single PCM for the others I have on hand here (roughly 10 checked, all from the late 80's / early 90's).

 

Either they are spec'ed a bit too close regarding voltage or it is a Operating Temperature Issue regarding location/placement , and then you have to consider manufacturing , maybe they changed the manufacturing process regarding the dielectric materials used possibly as well , no way to really know now , this is why I did the homework and bumped the voltage rating , if it was that then at least that is taken care of , location could have allot to do with it regarding temps , other than that , it has to be spec related in my opinion.
And this is a '89 P/U , so it has been out there for a long time and like all vehicles , we really have no idea how they have been treated , could have been a over charging Alternator , Short , Battery etc , I am just glad after replacing that the bench test proved all good , so that means it was nothing else wrong as well as it was not another failure that caused this failure , we could guess forever , but Electrolytic Caps have never had a reliably long life anyway , in many many applications they are a very common part to fail , especially amplifiers, Voltage Regulators and transmitters

Guy

 

Having pulled apart at least ten PCMs to examine more closely the capacitors, I've got some additional data that I believe supports my previously proposed theories of why the F150 PCMs of this era are more prone to failure.

For starters though, all of the circuit boards use Nichicon capacitors rated at 105' C. From there, things get different in two ways. First, and perhaps most significantly, the F150 caps are physically smaller than all the others. The ones used in the F150 PCM are 6.5mm in outside diameter while all the others use caps that are 8.3mm in O.D.

Second, the specs for the F150 caps are unique, as follows:
Qty 1 10uF 63V
Qty 2 47uF 16V

Compare that to what is used on the others I examined ('88 - '94 Mustang & Ranger):
Qty 1 3.3uF 63V
Qty 1 47uF 10V

Or, for those that also use three capacitors ('87 - '89 Merkur XR4Ti):
Qty 1 3.3uF 63V
Qty 2 47uF 10V

Lastly, I had one EEC5 PCM that used the following (1997 Explorer):
Qty 1 47uF 63v
Qty 1 47uF 10v

My best guess is that the smaller physical size may be the biggest thing that's causing the earlier death of the caps in the F150 PCM. Smaller size would likely mean greater heat build-up.

I don't understand the ratings well enough to have much of a valid opinion there, although it's interesting that Guy's approach was to increase the voltage value of the replacement caps for the lower voltage part (from 16 to 25). It would seem however that the factory went in the other direction, from 16V down to 10V. Of course, I'm assuming that this is the comparable 5V circuit doing comparable work.

Note, I hate questioning Guy's recommendations, as clearly he know more than me on this topic and his replacement solution has worked. I thought it might be worthwhile to bring this data forward regardless if only because it does finally point to some reasoning for why this problem is so much more prevalent with the F150 PCMs.