I am driving a 1995 850 GLT. Based on the codes (553, 451) generated under the hood (OBD 1), it is misfiring on cylinders 1 and 3. In the last several years I have replaced the distributor cap, and wires. In the last 6 months I’ve replaced the Mass Airflow Sensor and spark plugs. The car still runs and drives (with reduced power) and I am wondering if the coil could be responsible for two misfiring cylinders or it could be that I need to replace fuel injectors in those two cylinders. Any help would be greatly appropriated.

 

I'd think that a weak coil would cause random misfires not just on 1 and 3 but its certainly possible based on the codes. Have you looked at the spark plugs to make sure they are clean, correctly gapped and correct model for your engine? You may want to consider installing Genuine Volvo plugs to be sure of both. (850s don't really benefit from the newer tech plugs - good ole copper plugs changed regularly will do fine). Have you checked fuel pressure? 850s do tend to wear out their fuel pumps (and the relays along the way) so its worth measuring that. Are you sure the cap/rotor/wires are ok? Did you try misting the wires in a dark garage to see if you see any arcing?

 

The plugs and wires are OEM volvo. I will try to locate a fuel pressure gauge and I had planned on misting the wires some night. I’ll get back with the results. Thank you.

 

you should probably be able to rent a gauge from Autozone etc. Check Youtube for RobertDIY's vid on measuring fuel pressure and comments on possible causes. Also there are date codes on the wires. Anything more than 5 years, time to replace. I've also had the experience to have fairly young wires develop corrosion inside the boot on top of the distributor so it may also be worth a look see. Also have you recently popped out the plugs to check for color to see which one(s) are clean vs oily? Also consider doing a compression test. A slightly burnt valve can cause misfires :-(

 

Iv had same problem and after going through everything ended up was a burnt exhaust valve..start with compression test

 

I will look at the things mentioned and get back to you on my findings.