Washed engine, now it is misfiring. Any ideas?

Post by **Blacklab467** » 15 Dec 2022, 19:07

Just washed the engine like I do every 10th car wash or so, this time it seems to be misfiring. I took it home although it was running pretty rough and plugged my scanner into it, P 0305. Okay so misfire on cylinder 5. Took the coil out and swapped it for 4, cleaned the spark plug and checked the coilground, also took a bunch of connectors apart and blew them out with brakclean and compressed air. Still runs the same but no CEL this time. I don’t really have time to check everything tomorrow so I want to narrow down my troubleshooting to save time, any ideas on what to check next? MAF? Is there a resistance test for the coils? They are original Volvo units.

Post by **cn90** » 15 Dec 2022, 20:30

Remove all coils and look down spark plug holes.

This is why I never use garden hose for this. I use a garden sprayer (1- or 2-gallon type) and
gently spray at different places, avoiding the top of the engine. I also removed the cosmetic cover
(that covers the coils) and store it on the garage shelf for good. This gives me quick access to
the coils/spark plugs etc.

Post by **BlackBart** » 16 Dec 2022, 10:12

Moisture in the distributor cap? That’s a classic miss until it dries out.

Post by **Blacklab467** » 16 Dec 2022, 10:51

No distributor cap on this one, but thanks. I think I have it figured out, I changed the #5 coil and put it in #4 position and my P0305 turned into a P0304. Sounds fairly definitive, Right? I've since ordered a Bosch coil set that will be here after Christmas. Going to find a temporary replacement at the boneyard meantime and see if I can find a spec for testing these coils. Strangly this all happened when I was in the carwash and against my better judgement I washed the engine so I assumed this was moisture related. I have never had any troubles with moisture from washing this engine before for over 8 years. Coincidence? Maybe.

Post by **BlackBart** » 16 Dec 2022, 12:46

Blacklab467 wrote: ↑16 Dec 2022, 10:51 No distributor cap on this one, but thanks.

oop!

Post by **RickHaleParker** » 16 Dec 2022, 23:30

Blacklab467 wrote: ↑16 Dec 2022, 10:51 Strangly this all happened when I was in the carwash and against my better judgement I washed the engine so I assumed this was moisture related.

Hairline cracks in the defective coil?

Post by **Blacklab467** » 17 Dec 2022, 04:10

I'm not sure, I didn't really do a visual inspection beyond spraying it with brakleen and air to rule out water ingress although there was no water. Where would I look for cracks, in the body of the coil?

Post by **vtl** » 17 Dec 2022, 06:35

Never washed my engines. Hot tanking their parts - yes

Post by **abscate** » 17 Dec 2022, 09:22

Blacklab467 wrote: ↑17 Dec 2022, 04:10 I'm not sure, I didn't really do a visual inspection beyond spraying it with brakleen and air to rule out water ingress although there was no water. Where would I look for cracks, in the body of the coil?

I’m running tons of these coils with cracks, it’s not a good visual diagnostic.

Okay, not tons, but 25 of them

Post by **kallekula** » 17 Dec 2022, 14:33

My coils usually go bad after I have removed them and put them back, never while driving.