Having wrenched on internal combustion engines for several decades now, I'm only in partial agreement with you. Yeah, that engine has definitely seen better days, and the bad rings are eventually going to be the demise of that motor. However, the compression numbers, while not great, really aren't bad enough to be the source of the rough running, and besides, if the misfire was detected in cylinder 1, that doesn't match up with your compression numbers that are showing cylinders 3 and 4 being the worst.
Since you've already done a good job of eliminating the spark plugs and coils as possible sources, that pretty much just leaves fuel as the last thing to check. So yeah, swap out the injectors just like you did for the coils and see if the misfire moves as a result.
But all in all, based on my experience with import car engines, I'd say the motor is tired but not quite at the end of its life. My guess is it's got another 50K miles to go before it gets to the point where it'll either be smoking or losing power, so it's probably worthwhile to pin down the source of the misfire before resigning it to the scrap heap.
I'd suggest going ahead with the wet compression check just to verify that it's the rings and not the valves that are causing the lower compression numbers you're seeing. You never know; if they all come up you might be able to extend the life of that engine significantly with just a valve job, depending on whether you feel it's worth the investment. My 1996 Volvo is still plugging along nicely after I had to replace a broken exhaust valve. Of course, I had to spend a good $150 for tools and a head gasket set in order to replace a $10 valve, but it was worth it to me.
+
+
=== Update (03/06/24) ===
+
Just as a side note, I was reading an article about misfires and how the engine computer detects them. What it's doing is reading the rotational speed of the engine; every time a piston fires, there is a distinct jump in speed that can be measured, so when one cylinder isn't putting out as much power as it should, that difference is reflected in a smaller rotational jump and can then be flagged as a misfire if it exceeds a certain threshold.
+
+
I know, doesn't really help with anything, but I thought it was interesting to know how the misfire detection works.
Hi Nick,
Having wrenched on internal combustion engines for several decades now, I'm only in partial agreement with you. Yeah, that engine has definitely seen better days, and the bad rings are eventually going to be the demise of that motor. However, the compression numbers, while not great, really aren't bad enough to be the source of the rough running, and besides, if the misfire was detected in cylinder 1, that doesn't match up with your compression numbers that are showing cylinders 3 and 4 being the worst.
Since you've already done a good job of eliminating the spark plugs and coils as possible sources, that pretty much just leaves fuel as the last thing to check. So yeah, swap out the injectors just like you did for the coils and see if the misfire moves as a result.
But all in all, based on my experience with import car engines, I'd say the motor is tired but not quite at the end of its life. My guess is it's got another 50K miles to go before it gets to the point where it'll either be smoking or losing power, so it's probably worthwhile to pin down the source of the misfire before resigning it to the scrap heap.
I'd suggest going ahead with the wet compression check just to verify that it's the rings and not the valves that are causing the lower compression numbers you're seeing. You never know; if they all come up you might be able to extend the life of that engine significantly with just a valve job, depending on whether you feel it's worth the investment. My 1996 Volvo is still plugging along nicely after I had to replace a broken exhaust valve. Of course, I had to spend a good $150 for tools and a head gasket set in order to replace a $10 valve, but it was worth it to me.