91 manual 2 plugs no spark

[stephenH]

Hope someone can help with my first post, I have 91 legacy estate manual 2.2 non turbo car will not start because the back 2 spark plugs are not firing. Have checked coils as per this BBS advise, swapped igniter from known good car, checked continuity of all wiring from ECU through igniter to coils all ok. Cecked fault codes from ECU & all clear.

Cut switching lines from ECU to Igniter & reversed them , now have rear plug spark but not front therefore proving ( I think ) that signal from ECU to igniter on one side is incorrect. ( have checked with multimeter & both sides hold 12v when ignition on & around 9v turning engine which as far as I know is correct ? )

Have tried intentionally disconnecting both cam position sensor & crank sensor & checking for fault codes, ECU registers them correctly ??????????

I'm totally stuck now !!!! Im thinking somehow the ECU is defective on only one side ? is this possible ?

I have a ECU from a 92 automatic legacy 2.2 but they are different codes & the wiring loom appears different so I'm scared to try & swap them around in case I damage the automatic ( which is running fine )
91 ECU D7 22611 AA670 A11-000 RA5 0523 with RA5 on connector
92 ECU G1 22611 AA940 A18-000 RF7 2122with RF7 on connector

is it safe to try & swap these.

Please please help I need both cars running desperately.

Thanks in advance,

Stephen.

[vrg3]

It does sound like your ECU's damaged.

I don't know so much about non-US models, but it should be safe for you to swap your 91 manual ECU with your 92 automatic ECU; I wouldn't worry about damage to the ECU... But before you go ahead and try, how does the wiring loom appear different between the two cars?

[stephenH]

thanks for your rapid responce vrg3

the differences ( as far as I can remember cause im not next to cars ) btn the wiring that I noticed straight away was on the RA5 connector of 91 from inboard end there are 2 wires then one missed space then 2 more wires which I think are the ones going to the ignitor on the RF7 connector in the 92 looking from the same end there are 2 wires then TWO MISSED SPACES then more wires so I recon at least one wire is different, is this to do with the transmission ? ive noticed a brief reference to a wire relating to transmission but havent found out which it is ( yet ) like I mentioned only just found this BBS.

Am I being paranoid ? there may be other differences but I didnt look much further after noticing this difference & becomming demoralised.

do U think its safe to try the ECU swap from 91 manual into 92 auto first just in case there is a fault in the 91 car other than its ECU , dont want to fry a known good unit 92 ECU in a dodgy system ?

Again maybe just being paranoid ?

Im new to Subaru's having spent the last few years repairing old Saabs now it looks like the same learning curve for old Subies, still at least they are both more interesting than Euro Fords !!!

Thanks again for your help,

Stephen H.

[vrg3]

Well, there will certainly be a few small differences. The automatic has a park switch and the manual doesn't. The automatic transmission computer also receives a barometric pressure signal from the ECU.

Do your connectors look something like these, though? http://www.graphics.cornell.edu/~v/ecupins/

Are they yellow?

If the looms are mostly similar (the particular thing I'd watch for is yellow-with-red-stripe wires all being in the same place; these carry +12v power), I would expect the ECUs to be somewhat interchangeable. I know among 1st-generation US models pretty much any non-turbo ECU can be used with pretty much any non-turbo car and it will at least run. But if one of the ignition wires on one is missing on the other, that points to bigger differences...

Here's another gotcha: If a short in your car's wiring killed the ECU's "channel 3/4 ignition" transistor, it's conceivable that if the short is still present it could kill the same transistor in the other ECU. The only way I can imagine this happening is if the wire going from the ECU to the ignitor is shorted to +12v, though, and even then it doesn't seem likely since they do try to build these things to be very rugged. But it is a possibility.

[stephenH]

Hi vrg3

the connectors appear to be very similar if not identical , they are all slightly off color white appart from the ignition related connector which is yellow.

is there any way of testing/replacing the transistor you mentioned ?

im no electronics expert but could probably handle removing & resoldering a component if told which one to remove or are these things "sealed" against such interference ?

Thanks again,
Stephen

[vrg3]

In the one ECU I've disassembled far enough to know, the ignition transistor is part of a transistor array chip which you might be able to find if you looked hard enough. You'd have to pop your ECU open and follow PCB traces to know.

They're not really sealed, but the boards do often have a thin layer of some kind of clear sealant that you'll have to chip away.