'92 SVX burning out ignition modules?

jlaguardia · #1 09-23-2018, 04:23 PM

I've had a '92 SVX for 8 years or so and fixed a bunch of relatively simple issues over the years, but now I have a bug that I can't find an explanation for. I searched this forum but couldn't find this exact issue. What happens is the car begins to misfire at cruising RPMs (and higher) - it will idle OK and I can usually limp it home. If I turn it off and try to restart it, it will crank but not restart. I had a similar problem once with another car, and took a guess and replaced the ignition module that's bolted to the firewall with a used one on eBAY, and that seemed to fix it - for a while. After a few drives, same thing happened again with the second module. I looked around and found some forums (not SVX) saying that ignition modules in cars of this era can be damaged by bad coils somehow "feeding back" into them. So I bought all-new coils ($$$), and found another used ignition module, and again everything seemed fine for a couple of drives. Then it happened again - rough at high RPMs, limped it home, and now crank with no start. Has this "burning out" of ignition modules happened to anyone else?

92 SVX · #2 09-23-2018, 06:24 PM

Quote:

Originally Posted by jlaguardia

I've had a '92 SVX for 8 years or so and fixed a bunch of relatively simple issues over the years, but now I have a bug that I can't find an explanation for. I searched this forum but couldn't find this exact issue. What happens is the car begins to misfire at cruising RPMs (and higher) - it will idle OK and I can usually limp it home. If I turn it off and try to restart it, it will crank but not restart. I had a similar problem once with another car, and took a guess and replaced the ignition module that's bolted to the firewall with a used one on eBAY, and that seemed to fix it - for a while. After a few drives, same thing happened again with the second module. I looked around and found some forums (not SVX) saying that ignition modules in cars of this era can be damaged by bad coils somehow "feeding back" into them. So I bought all-new coils ($$$), and found another used ignition module, and again everything seemed fine for a couple of drives. Then it happened again - rough at high RPMs, limped it home, and now crank with no start. Has this "burning out" of ignition modules happened to anyone else?

I think that is called the igniter that your describing bolted to the center of the firewall under the hood.
I have had my car for 10 years and still have the original igniter and coil on plugs, I would guess its something else causing the problem

ShiuludeSVX · #3 09-23-2018, 07:05 PM

Quote:

Originally Posted by 92 SVX

I think that is called the igniter that your describing bolted to the center of the firewall under the hood.
I have had my car for 10 years and still have the original igniter and coil on plugs, I would guess its something else causing the problem

It actually sounds to me to be more of a short of some kind than anything else.

Might want to detail check all those lines for pinching to ensure that none of them are bare anywhere. Maybe a line hanging too close to an exhaust, or even the intake which does get very hot sometimes.

jlaguardia · #4 09-23-2018, 08:05 PM

Yes, the "igniter" or "ignition module" or "ignition control unit" is the thing that I've been replacing. Although the problem certainly can be due to something else that is damaging the igniter, please note that the igniter is, in fact, being damaged. For example, after I bought the new coils, I tried the new coils with the first two igniters I had on hand, and the car did not start. I then swapped in the "new" (used, from eBay, but new for this car) igniter and the car ran fine for a few drives, then failed again. This tells me that something (if not the coils, then what?) is "burning out" or otherwise damaging the igniter. Any ideas as to what that might be? I will certainly check again for some sort of "short" - although I'm not sure how that would damage the igniter.

Trevor · #5 09-24-2018, 12:38 AM

Quote:

Originally Posted by jlaguardia

Yes, the "igniter" or "ignition module" or "ignition control unit" is the thing that I've been replacing. Although the problem certainly can be due to something else that is damaging the igniter, please note that the igniter is, in fact, being damaged. For example, after I bought the new coils, I tried the new coils with the first two igniters I had on hand, and the car did not start. I then swapped in the "new" (used, from eBay, but new for this car) igniter and the car ran fine for a few drives, then failed again. This tells me that something (if not the coils, then what?) is "burning out" or otherwise damaging the igniter. Any ideas as to what that might be? I will certainly check again for some sort of "short" - although I'm not sure how that would damage the igniter.

The ignition coils draw a relatively heavy current which is beyond the the switching capacity of the ECU. The "igniter" comprises what amounts to a set of solid state relays, each switched by a low current signal from the ECU and in turn, switch the high current required to energies each of the coils.

The igniter is supplied with current via the battery circuit and if this fails the igniter can not supply current to the coils. This circuit although not likely, could be intermittent.

A short circuit to ground in any of the wires connecting the coils, or a short at a coil connection, or within a faulty coil will overload and damage a power transistor within the igniter.

A direct short circuit would normally immediately destroy a transistor, but your fault appears to take time to develop. Something must move or be affected by heat. Check for something foreign around the coils.

Even though unlikely, also check for possible open circuit in a plug wire, or connection which might cause a intermittent on/off situation thus causing a nasty voltage spike back to the igniter.

Do you have a multi meter and know how to use the resistance ranges?

jlaguardia · #6 09-25-2018, 02:55 PM

AHA! Thanks for the info, Trevor - something like what you're describing is probably the gremlin. I'll check all the wires as carefully as I can - I thought I did so when I put all the new coils on with the most recent igniter, but of course I could have missed something. I have a multimeter - what do you suggest I check? If there is a procedure already described in a previous post that you know of, just point me at it.

Given the time and money already spent on this, I was Googling around for alternatives, and found some guys who upgraded their Impreza-WRXs to new-fangled coil packs that have the igniters right on the coils. This takes the old-style igniter away, but requires some re-wiring of the harness to the new-style coil packs. I think I could figure out how to change their 4-cylinder wiring diagram into a 6-cylinder one. Has anyone tried this on an SVX? Here is the link:
https://forums.nasioc.com/forums/sho....php?t=1192028