Computer Problems

[almostclueless]

A few years ago a friend of mine had a Porsche 924 that was giving him trouble. Intermittently, it would shut off on him. Luckily, one Saturday, it stayed "dead" long enough for me to diagnose the problem (using a DVM, and my scope). The problem was the DME (Porsche equivalent to PCM). I then
proceeded to take the DME apart, and do further diagnostics. The problem I found was in a 5V regulator circuit, which was used for the digital components. The 5V regulator circuit was made up of discrete components (transistors, resistors, capacitors, and a zener diode). I upgraded this circuit with a linear 5V regulator, which had much better characteristics.

What's the continuous current rating of that regulator?

 

[Bob Ayers]

What's the continuous current rating of that regulator?

1AMPERE

 

[Stranger ranger]

So disconnecting the battery will certainly kill the pcm? While running of course, as stated on page 2?

 

[MAKG]

Not certainly, but fairly likely. Inductances try real hard to keep the current flowing (called "Lenz's Law") and will make enormous voltage transients to do so, as the connection is broken. This is how the ignition coil really works (people often assume it's a transformer; it isn't, and it fires when the points/Hall switch OPENS, not when it closes) and how you can get 30-40 kV out of a 12V system.

 

[almostclueless]

(people often assume it's a transformer; it isn't

I agree with everything but this comment. It is a transformer; it has two windings with flux linkage between the two....and if I find a transformer with vastly different winding counts between primary and secondary, put current thru the low-count winding, then disconnect the current, it will induct a big voltage on the high winding.

 

[MAKG]

What I meant was that it doesn't function like the transformer in your PC.

It doesn't just multiply voltage like an AC transformer does. It multiplies CHANGE in voltage (for AC, those are the same thing, but not for DC). If you put a constant current in the primary (even if it's very large), you'll get ZERO out of the secondary.

Sorry that wasn't clear.

 

[Bob Ayers]

I agree with everything but this comment. It is a transformer; it has two windings with flux linkage between the two....and if I find a transformer with vastly different winding counts between primary and secondary, put current thru the low-count winding, then disconnect the current, it will induct a big voltage on the high winding.

An ignition coil (conventional coil, NOT a coil pack) just has one winding, not a primary and secondary. It is the Di/Dt that creates the high voltage.

 

[MAKG]

Bob, every ignition coil I've seen has three terminals. One for primary ground (generally, switched), one for primary power, and one big one for secondary power (grounding through the heads).

Coil-on-plug forms have that secondary power terminal hidden, but it's there.

Coil packs often have a single shared primary power and a separate primary ground and secondary for each coil.

 

[jpwf2020]

1998 ford ranger with 1997 ford explorer motor. Can't find computer that works

Ok, I have just put a 1997 explorer motor in a 1998 truck with the 4l6d transmission. The computer from the truck won't work with the motor and the computer from the explorer, which was a 5sp, won't work the the transmission. will a 1997 automatic explorer computer work with a 1998 ranger transmission? Idk what to do anymore, I've spent two months working on this thing and now I can't even shift out of park. Would it be best just to get a transmission from a 1997 explorer?