ECM/PCM Capacitors

[Mechrick]

Automotive-rated caps are a bit different than run of the mill stuff. If I ever did this, I would use tantalums, as you can now get them in higher voltage values.

 

[pentode]

i do not like doing business with pay pal. but. often tis is the best way. boogers.

Agreed, PayPal is a necessary evil at best. If you want to put a buffer between yourself and a company you don’t know, I guess it can be helpful. For anyone thinking about ordering from Digikey though, they’re one of the very few companies I trust implicitly. They are an absolutely top notch American company, can’t say enough good things about them.

 

[pentode]

Automotive-rated caps are a bit different than run of the mill stuff. If I ever did this, I would use tantalums, as you can now get them in higher voltage values.

Those that I linked to were high temp automotive-grade caps. I was actually thinking about the possibility of retrofitting with film caps. In my experience, the failure modes of tantalum caps would make me think it through pretty carefully. They tend to get a bit explode-y when subjected to voltage/current spikes or high ripple- I don’t know these particular circuits so I can’t say how they’d fare but you probably do know.

The other thing is that there was an absolute flood of counterfeit caps in the 90s and early 00s as a result of industrial espionage gone badly wrong. (They stole an incomplete electrolyte formula missing the ingredient that kept the electrolyte stable) These caps made it into many supply chains including highly reputable companies. I don’t know about Ford but I wouldn’t be even slightly surprised. I have electrolytics from the 70s that are perfectly fine to this day whereas I recapped hundreds, maybe thousands of different electronics in the 00s, all with the same failure mode.

All I can say is I’ve used Panasonic caps in some very demanding environments over the years and I have total faith in them. I figure for a beginner it’s easiest to swap like for like.

EDIT: that history lesson wasn’t aimed at you @Mechrick , more for anyone who was curious as to why capacitors became such a recurring problem.

EDIT2: Longwinded as usual, I know, but there used to be a site called badcaps.net that was devoted to exposing and investigating that problem- turns out they seem to be a general electronics repair site now (probably the internet archive has the old site?) however I did find a wiki entry for anyone who wants more nerdy detail. They call it the “capacitor plague”. To this day I still repair modern electronics that continue to use crappy no-name Chinese caps, and which have failed due to one or 2 caps leaking out all their electrolyte - the good ones only cost a dime in bulk! This is why I still insist on name brand caps from a reputable source.

 

[MaicoDoug]

Pentode is on target. The thing with cap values are: 1) choose the higher temp (105C), 2) lately during the last 15 years, the physical size of electrolytic caps has greatly shrunk, & become much smaller, 3) always go at least 2x times higher rated voltage than the in circuit operating voltage.

Inrush charging current flow can damage other parts of the supply side from over sizing and going up on the microfarad (uF) value. Capacitors are employed to reduce spikes on a supposed DC line. Removing AC waveform components in the DC supply, such as spikes caused from relay load switching, during microprocessor operations. Me personally I use always a combination of a 1Kv .01uF ceramic across a 25uF electrolytic on any of my added in electronics only because long thin wires act as antennas feeding back to the supply source. The term "parallel decoupling" is the key here. Way too technical for most. On a side note-my truck sat for 10 years from a fuse box fire under the hood before I purchased it, one of these days I'll paint the underside removing the black soot stain. With yellow paint, yea I know

 

[rumblecloud]

Pentode is on target. ... Way too technical for most.

Ummmm...yeah.

 

[rumblecloud]

Just a quick update. ...
Did the deed yestersay. A little nervous, but all is well -- at lest so far.
I'll post more later when I have more time.

 

[MaicoDoug]

I would be, just the inrush current from initial charging can cause crazy stuff like unsynchronized digital inputs to the ECM God forbid. As long as it was on the main DC bus & not isolated on the other individual I/O.

Was waiting forever and was finally denied my appointment last week because of some family & their new - used VW. Lots of ECM issues. Something to do with the distrubriter at cold start not retarding and throwing tons of codes, I asked the tech after picking up my truck (for AC work) because they never got to it- "I need to come back tomorrow"? All because of my tech with the VW debacle, in meetings for 3 hours, I asked why can't you use some aftermarket hardware? His answer was it wasn't covered under their "car shield" account. Ah yes, the car shield account, never ever will fall off that cliff, but that's just me. Crazy all the computer poop, just give me my variable valve timing I say!

 

[lil_Blue_Ford]

It’s been so long since I spent much time messing with the guts of electronics…

So, is there a way to check capacitors to verify they are good or bad if they haven’t exploded or poured a puddle of stuff onto a circuit board? I popped open a couple of my ECUs last year but didn’t see any obvious problems so I’m not sure if that means everything is ok or if there’s a problem that I didn’t notice…

 

[pentode]

Generally you can only test them reliably out of the circuit with a capacitance tester. Some multimeters have that function built in, otherwise dedicated testers aren't expensive.
In my experience, if you're dealing with a cap from one of the dozen or so recognizable reputable manufacturers and the cap physically looks good (no leakage, no bulging), it's usually going to be fine.

Edit: I would add that one place I'd be tempted to replace caps that looked good would be in an environment where they've been subjected to a lot of heat. Even then, quality caps rated at 105C are remarkably durable.

Edit 2: oh and since we're talking about caps, it's worth mentioning that electrolytic capacitors don't like to sit- they like to be used. So, say, a barn find car from the 80s that's been sitting for 30 years, those caps would be more suspect.

 

[MaicoDoug]

Look for bulging (on the cap, not the person testing) bloating, torn rubber plugs, & smelly corrosion. Sniff test tells quite a bit. Also they don't like to be spark makers, fyi. They do hold a charge, and it's best to keep them discharged before installation.

>They can also be charged up using the Ohm function on your DMM (Digital Volt Meter), simply test for resistance, then with the cap still hooked up, switch to DC volts & witness the declining volt reading.

The most common ways to test a polarized electrolytic cap or what is intended to be used as such, is to use what is referred to as a "leakage test", and / or a charge up test...easy to do...
Get your favorite DC voltmeter,

Now lets do the "charge up" test first; connect up a small battery, 1.5v, 9v, 12v car battery what ever dc source you have and connect the positive to positive, negative to negative. Turn on the voltage, for 5 seconds. The cap should not get warm, now with the DC voltage source disconnected, test the cap to see how much voltage is retained after the 5 second charging cycle with your voltmeter set to DC volts, pay attention to the decimal point as the auto ranging meters change scales often. This test is in parallel. The test voltage should not exceed the voltage rating printed on the cap.

Second test is the leakage test, it's preformed in a series connection. Connect the positive lead of any cap to the positive terminal of your DC voltage source. Connect up the negative lead also. (just like the above test). Connect up your test leads to the DC voltage source and read the supplied voltage before the capacitor connected, now leave the negative test lead connected, and move the meter's positive lead to the unconnected negative cap lead and look for the very small amount of DC voltage that may or may not make it through the cap. Note, often in this test the cap is referred to a "DC Blocking Cap". Used to only pass AC signal components, not so much for large filter caps like we use to filter out unwanted AC signals in out DC buss supplies.

Good link to read up

https://product.tdk.com/en/contact/faq/capacitors-0015.html

 

[lil_Blue_Ford]

Thanks guys. I do a fair bit of electrical work, so I have a bunch of gear, I just haven’t done much work with circuit boards since I got out of high school so I’ve unfortunately forgot a lot, lol. Just getting to where I’m starting to think I should keep a close eye on the aging electronics and starting to wonder if converting to an aftermarket ECU might not be a terrible idea

 

[4x4junkie]

I'm not sure there's much else in a PCM that can fail simply due to age (transistors/diodes/ICs/(film type) resistors/non-electrolytic capacitors generally are not affected by age). A working factory PCM that has been re-capped should be reliable as anything else.

As for ID'ing a failed cap, bulging/leaking certainly are giveaways, except I've come across plenty of caps on other things that visibly looked fine, but were shorted out, or developed a high IR and not working as they should.
Fortunately these old late-'80s, early-'90s PCMs don't have very many caps in them, making it pretty easy to simply change out all of them proactively.

 

[MaicoDoug]

Sprinkle them all over the circuit board like cracked pepper on yer salad. Often I restore cool old electronics, and it's always the disposable aluminum electrolytics that dry out, incredibly some of them keep going. In the multisection caps, 40s through 70s that pretty looking tall aluminum thing that stands tall next to the tubes has it's guts pulled out & re-packed with the new & much smaller filter caps leaving it looking like it always did, or at least leaving those in their place. Mouser or Digikey are both reputable retailers to buy from.

First question any tech asks about newly restored chassis is, "has it been re-caped"? Inductors in series do the same exact thing as for DC filtering, as capacitors do in parallel, but the cost of doing so is much more. So manufacturers tend to promote buying new products by these manufacturing practices. In the repair & restoration business / hobby you know when they use iron instead by picking it up. Take Henry Radio Inc. for example. They make big broadcast transmitters. Their filter "choke" is the same size & weight as the main power transformer. Their capacitors are the old oil filled type that last forever. Not for anything that travels down the highway.