My wife and I just had a terific 4 week vacation in our 850. On our way back to Southern California, while passing through Oklahoma, the engine started missfiring. Knowing that the distributor cap and rotor were due for a change I replaced them, no help. So I bought a set of plugs and found that #4 was running very rich. The missfire was still there with the new plugs so after running the engine about 1 minute I pulled the #4 plug and found that it too was fuel fouled.

I did all of this while traveling so by now we were in Gallup New Mexico, hence no Volvo parts. Thinking that I either had a bad plug cable or a bad injector I bought a set of Accell yellow jacket wires from Pep Boys and replaced the #4 wire, no help. So we sputtered home to SoCal.

Now that I'm home I've replaced all the plug wires, the fuel filter, and the #4 injector. But I still have the same problem! After doing the work today I test drove it about 3 miles. When I returned home I pulled the #4 plug to find it dripping with fuel. If I push the pressure release valve on the fuel rail there is no residue pressure.

I'm stumped. All that I can think of doing is to inspect the wiring to #4 injector and then take it to the dealer. Can anyone give me a clue?

1997 850 GLT
103500 miles
I'm pretty well caught up with recommended maintenance, the fuel filter being the only thing I've ignored.