I also posted this on TB.

1988 244 GL NA automatic. I have two ignition Control Units. One is marked 1346107, the other is 3517641. Both are listed as appropriate for my car. The Volvo dealer shows them as interchangeable. I assume that there are functional differences between them; likely in the advance curve. I would appreciate any information that anyone might have.

You don't trust the dealer? You have two ICUs in hand or two options?

Try part search here: volvopartswebstore It may help you figure it out.

I wasn’t clear. I have the two ICUs in hand. My Volvo dealer is great, but their last good 240 mechanic just retired. Lots of other good guys there, just not much experience with 240s. I got to know these guys well when I bought a new 1999 S80 T6. It seemed like it spent more time with them than it did with me.

I appreciate the link, but nothing there other than they both show as interchangeable. I know that either one will work in my 1988 240 GL, but there are likely differences between them; most likely the advance curve. I imagine that they are much like ECUs. I know of at least three that will work with my car, but there are differences between them. Just curious about the differences and want to run the one that has the quicker advance, if that is the difference. I also suspect that one of them came into being as smog requirements became more restrictive.

thanks for clarifying. Have you seen this thread: http://forums.turbobricks.com/showthread.php?t=99726 ?? I found it typing "1346107 volvo" in google. An easy way to search TB is use google instead: "site:turbobricks.com [search words]"

Thanks. I had seen that post and as you noticed it does give the advance curve for one of them, but not the other so nothing to compare. I appreciate your posts, but guess this is such and oddball question that it is better to just forget about it and run whichever one is now on the car and save the other for a spare.