Have a Volvo 760 turbo 230bf engin, 4 cylnd. I changed the spark plugs
(first time i have ever done this) and changed the air filter and the
spark plug wires. The car runs fine, but now gets worse gas mileage.
Went from about 21 mpg to about 15 mpg instantly. Other than that,
no problems. Could I have done something wrong when replacing plugs/
wires? New wires are Bosch, about same size as the old ones in length. The plugs were the Volvo recommended ones and gap set at .028
according to manual. Any help? should I have used a torqe wrench?

any help appreciated!

Todd Martinson

Other thing could be the type of plugs, I have a 90 740 GL and I put bosch plugs in and the car actually ran worse! I went to the dealship and got the OEM plugs and things went much better after that.

Given the specifics, it is most likely that you have the plug wires crossed somewhere. It is also possible one or more of the plugs aren't seated properly, but I understand they will work their way out shortly if they are really loose.

Check the distributor cap for the wiring numbers. I think the Bosch caps have the cylinder numbers on them. #1 starts from the front... Also check to ensure the plug wires are firmly in place. If NONE of this shows any problems (and I expect it will), check the new wires for resistance with a digital VOM. I think the spec is in the Haynes manual, but you're really looking for one wire with an open condition (infinity ohms), possibly when the wire is bent at the ends. This would give you a dead plug.

HTH,

someguyfromMaryland