Misfire at idle, occasionally low speeds. Lots of details

[drmegadan]

Well. It's not the FPS.

On to spark plugs.

[drmegadan]

Finally found some time yesterday. Pulled the plugs and did compression test. #4 plug came out with the insulator in many pieces. Hmm. The plug was tight so I'm not totally sure it didn't shatter when the plug popped loose; but I don't think that was the case.

Compression was 135-155 across all cylinders; car was warmish but not hot. Numbers are a tad low but not concerning. I had a set of the same plugs but in a 7 heat range (one step colder) sitting around from my 300zx and chose to drop those instead of swapping them from the other Volvo. A test drive yesterday showed no symptoms, as did a drive today to work. I'm going to give it a few days before I consider this issue resolved; as last time I made some changes things seemed good at first.

I'm finally getting a check engine light, but no codes are stored. Ugh. Going to clear it and see if it comes back; it reared its head when the misfire got much worse (due to broken plug?) I cleared it and it stayed away until I did the compression test which likely brought it back.

[oragex]

Try see if there is a bad coil anyway www.youtube.com/watch?v=fnYUQh23p7Q
Also look at the wires to the coils, then at the wires to the injectors. You may even want to remove the injectors and test them with a small 9v battery pushing distilled water - look at the shape of the spray (check Youtube)
As others said 43psi is too low for a turbo, it usually stays 55-60psi idle/driving. You may want to swap the PEM module if your spare car has one, and look at the fuel filter if it's external.

[drmegadan]

Try see if there is a bad coil anyway www.youtube.com/watch?v=fnYUQh23p7Q
Also look at the wires to the coils, then at the wires to the injectors. You may even want to remove the injectors and test them with a small 9v battery pushing distilled water - look at the shape of the spray (check Youtube)
As others said 43psi is too low for a turbo, it usually stays 55-60psi idle/driving. You may want to swap the PEM module if your spare car has one, and look at the fuel filter if it's external.

I don't believe I've specifically tested the coils; but I did swap them between vehicles and that didn't result in any change. Wiring to coils was crusty, but the wiring itself was intact.

Between my wife and myself we've put roughly 15 drive cycles and 400 miles on it without another CEL or hint of a misfire. I'm not going to concern myself TOO much with the fuel pressure as it was measured with torque (granted I trust those numbers in my other vehicles). I'll get a physical fuel pressure tester and check the rail at some point. Fuel filter was replaced by the owner before me (supposedly). I think I remember seeing it all shiny and new; so it's not a concern either.

For now I'm going to consider this issue resolved. Now I need to figure out where the occasional coolant smell is coming from. I'm losing 1/4" of coolant from the reservoir over 1000 miles or so. Darn. Thanks for all the help and suggestions getting me to this point.