1998 V70XC P0304 (Cylinder 4 Misfire) Under Hard Acceleration

bubbeck · Post by **bubbeck** » 01 Feb 2019, 20:55

Hey fine folks,

I've been having some trouble with my 98 V70 turbo wagon stumbling and misfiring under hard loads and acceleration lately. Normal around town driving is fine, even most highway, but when accelerating hard up long hills the engine stumbles and rpms drop slightly. This problem finally got bad enough today to throw a blinking CEL P0304 (Cylinder 4 misfire.) I pulled the plugs (NGK 6962 coppers, see pic) and while none looked terrible in my opinion, the gaps were all .033 - .037 (put these in ~15k miles ago). I plan to throw some new Bosch coppers in and see how it goes, but any other ideas for what could be going on here? I replaced the fuel filter recently (after this problem started though) and did a compression test about a year ago - ~163 psi on 4, ~170 on the rest. Cap/rotor/wires are bosch, probably about 50k miles in. Thanks!

Post by **precopster** » 01 Feb 2019, 21:03

Wires should be Bougicord genuine. Bosch can get wires (and oil filters in my experience) terribly wrong.

Nothing I've read has confirmed a happy Bosch spark plug wire customer long term. Can you swap one of the other cylinder wires over and see if the misfire moves to another cylinder?

Post by **misha** » 02 Feb 2019, 05:03

As far as i know...spark plug gap on turbo car should be 0.028 and it's critical.
Being a turbo car....you could have some large vacuum leak which reveals itself only at wot.

Post by **abscate** » 02 Feb 2019, 05:55

Gap of 0.028 is important and has to be set on new plugs

WhatAmIDoing · Post by **WhatAmIDoing** » 02 Feb 2019, 12:57

A gap of "0.037" is way out of spec. New copper plugs gapped to 0.028 would be a good diagnostic start. A new compression test would not be a bad idea either.

bubbeck · Post by **bubbeck** » 04 Feb 2019, 09:11

I definitely gapped the plugs to .028" when I put them in a year and a half ago, wonder how they grew so much... Will throw some new ones in and report back! If that doesn't solve it, would y'all move on cap/rotor/wires ($100, easy), vacuum lines ($40, more work), or servicing/replacing injectors ($100-$150, easy) next?

Post by **abscate** » 04 Feb 2019, 10:42

wonder how they grew so much...

Boost

bubbeck · Post by **bubbeck** » 06 Feb 2019, 22:41

Hehe probably

Ran a cold, dry compression test today, and got 170, 165, 170, 155, 170 on cylinders 1-5. So cylinder 4 (the misfiring one) is a bit weak but 155 psi still seems fairly ok no? Still within 10% for what its worth. I ended up pulling the distributor cap when I put in new plugs, and there was a good bit of oxidation on the cap contacts. Unfortunately while brushing them, I knocked the center brush out, then managed to lose it so guess I'm doing cap/rotor/wires now too anyway.

WhatAmIDoing · Post by **WhatAmIDoing** » 07 Feb 2019, 08:33

A warm compression test and especially a leakdown test will identify if cylinder 4 has bad rings. Under heavy load it may not be maintaining compression.

Klausc · Post by **Klausc** » 07 Feb 2019, 09:05

Seems that most of your driving is at low rpm. Try driving in 2nd around town, keeping the rpms above 2000, to clean off the valves. Besides, it makes for a lot of fun driving!

I am surprised that the CEL blinked, that usually only happens when more than one cylinder is misfiring.