I changed my plugs, distributor cap and rotor arm yesterday. I fitted bosch plugs, denso cap and arm. At first the car performed much better but then started to develop a misfire which just got worse and worse. I suspected the plugs so I put the OE plugs back in but the misfire remains. I then putthe original distributor cap and rotor back on but it's still misfiring badly. I've checked and checked the firing order but it IS correct (also, this would not explain why it ran well initially). Any suggestions? PLease help!

 

Are you getting a check engine light?

 

How about the wires?
They tend to go bad in these vehicles and specially if they are old, they are very much suseptible to go bad as soon as you play with them.

 

No, I'm not getting a check engine light. I did read somewhere on here that fitting anything other than volvo plugs could send the engine management computer haywire, but again, it wouldn't explain why it still runs badly with the old plugs back in. The cable problem is a possibility. They look OK but they ARE 15 years old after all. I've never known cables to fail quite like this tho. My main dealer will be deligted. He charged me £11 ($20) for 2 tiny plastic clips yesterday. LOL

 

The more I think about it, the more I think that this could be the cause, especially as the misfire started gradually. I'll speak to the main stealers parts dept on monday. Hope I don't have to sell my house....

 

15 Year old plug wires? Your kidding right? Put all your new stuff back on, install some new plug wires and tear up the town.

 

Thanks everyone. I popped down to my local Volvo main dealer this morning to get a new set, but at £150 ($280) a set here in Denmark, I think I'll take a trip over the bridge to Sweden and save 50% on them there. According to man at Danish main dealer, parts have always been cheaper over there. Unfair, I say!

 

Interestingly though, I've owned cars of various makes up to double the age of my 850 and I've never had a plug lead fail on me. Wierd.

 

I am surprised you have never had to get new plug wires. I have had to replace mine before and it looks like I am going to have to do it again.

 

Maybe the service places were replacing them without your knowledge. Could also be that the Volvo engineers have designed the cars to use so much from the plugs that it causes the wires to wear out. I'm just guessing.