• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

1998 S90

grain2077

grain2077

New member
Joined
Sep 30, 2025
Back in September I brought a S90 with a broken off headbolt, a few minutes with a drill bit, some sockets and a extractor and my dad had extracted the 1.5 inches of broken bolt. Since then we've had the head sent off to be skimmed and checked (5 bent valves) and gave her some love she needed, replacing and repairing non vital parts while my dad was busy like the steering column trim, replacing the dead alarm siren with the alarm horn and other bits. With a day or so spare, we managed to get her up and running in time for the UK Owner's club BKV show. (Sadly didn't place first or second in the 700/900 category)

We've had an issue with a misfire, I've replaced the coil pack wiring as the rubber in the connectors had gone crusty, the wires themselves were still good. Replaced one of the two non volvo coil packs as it was a bit dodgy, with one from a S40 (one with two bolt holes as opposed to single bolts like the rest) Thinking the misfire was fixed, we drove to and from tesco (3 miles to and from) and right as we got home it started to misfire again :/

It doesn't do it often enough to try and see what cylinder it is, but it doesn't generate any codes. What are ways to test the ignition modules and coilpacks? as I replaced the coil pack wires already.
u18boC20.png


Edit: Forgot to mention we did do a compression test at one point, forgot the exact number but all the cylinders are roughly all the same at I think 175 bar.
 
Last edited:
If your injectors don't have a good spray pattern. That can foul out a plug with the liquid gas causing a misfire. Make sure to change the fuel filter if you change injectors.
What kind of plugs are you using? I've had issues with white blocks needing the correct plugs. Even though the plugs in there say they are correct they didn't work causing lots of misfires.
 
dl242gt said:
If your injectors don't have a good spray pattern. That can foul out a plug with the liquid gas causing a misfire. Make sure to change the fuel filter if you change injectors.
What kind of plugs are you using? I've had issues with white blocks needing the correct plugs. Even though the plugs in there say they are correct they didn't work causing lots of misfires.
Click to expand...
OEM Volvo for the b6304. Did test the injectors and they all spray the same amount.
 
my 960 same engine as yours has a wierd mis and stalls randomly in hot weather.
its totally ignition related despite going through all the diagnosis procedures to not find any issue.

started after I replaced a blown coil pack. my guess is the ignition wiring gets wierd or degrades once the car is old and I have a short or grounding somewhere not visible.

ive just been driving it a year this way
 
There's a test port near the back of the cylinder head for the coil packs - it's basically a live wire that's synced up to the #1 cylinder's coil pack and is supposed to be some kind of signal for a test unit. On my car it wiggled around a lot and would ground out against the firewall, which shorted and caused the #1 coil pack to catch fire and melt. Probably most of the time I owned that car it was running on 5 cylinders or less.
 
rearwheelpeel said:
Dave Barton sells replacement wiring for the coil packs - definitely worth replacing. They get very hot and brittle over time and can crack causing poor connections.
Dave Barton coil repair harnesses
Click to expand...
Been there, done this. Can recommend Dave's B6304 plug harness repair kits. (But it sounds like the OP has done this already).

Another cause of misfire could be a dodgy igniter. There are two of 'em (IIRC one does 1-3-5; the other 2-4-6) and they're tucked away on either side of the inlet octopus. They are a real mongrel to get to. They're different part numbers to the LH 2.4 cars. They may not throw codes if they're faulty.

As others have said - plugs, another bad coil-over-plug, &/or dirty injectors can also be causes of misfires.
 
You must log in or register to reply here.
Back
Top