1998 C70 2.0 T5 (B5204T3) – WOT Misfire

Gregory91PL · Post by **Gregory91PL** » 17 Sep 2026, 13:06

Today I installed the pump 0 580 454 168 and I can confirm it's a plug-and-play replacement.

Unfortunately, it didn't solve my problem.

I pulled out the spark plugs to check their condition after 1,000 kilometers, and out of desperation, I reduced the gap from 0.7 mm to 0.6 mm. That didn't help either.

I've booked an appointment at a dyno for next week for a power run and an AFR measurement, because I'm out of ideas.

I'm also attaching a photo of the spark plug

Post by **Sveedy** » 17 Sep 2026, 14:44

If all else fails, you might try switching to a colder spark plug. I had the same problem/symptoms at WOT until I switched to a colder plug, based on the advice of my tuner. Now my 850 is far from stock, so we're sort of comparing apples and oranges, but switching to the colder plug cured the spark "blow-out" as he called it.
In my case, I went from the stock Volvo plug to the NGK BKR7E #4644, which according to my notes is 1* colder than stock.
Just a thought ....

Post by **Sveedy** » 17 Sep 2026, 17:16

And that plug looks fine.

Post by **scot850** » 17 Sep 2026, 17:42

Sorry, but I had to go back to the start to check what had been replaced and checked.

First question, do you still have the plastic cover in the distributor below the rotor arm?

Did you check for PCV back pressure (glove test). The reason for this is it is possible for oil to leak into the distributor when the seal fails causing misfires.

Have you checked the cam and crank sensors? You have to be careful with the routing of the cam sensor. If it runs too close to the distributor it can lose the signal as the distributor kills the signal.

Good luck with the tuning check.

Neil.

Gregory91PL · Post by **Gregory91PL** » 17 Sep 2026, 21:55

The PCV glove test was one of the first things I did. It’s okay. The plastic cover below the rotor arm is there, it’s in good shape, and it was clean inside.

Both the cam and crank sensors have been replaced. Also, running a boost test at 0.3–0.4 bar while bypassing the TCV rules out any issues in that area.

To be honest, the only logical explanation left is that it's running either too lean or too rich under full load. The only way to verify this now is with a wideband AFR gauge.