1998 S70 T5 Miss on WOT-MVSOLVED w/VOLVO OEM Plugs

Someguy3331 · Post by **Someguy3331** » 09 Mar 2014, 12:37

I have a 1998 S70 T5 and lately I will get a occasional misfire on cylinder 2 or 1 when I go wide open throttle and you can definitely smell the unburnt fuel, letting off just alittle while make it run fine again. Also I can smell a little gas in the oil which made me think the fuel pressure regulator was going bad but I dont have the fuel pressure regulator, my S70 has the pulse damper which I'm kind of unfamiliar with. I was wondering if it was faulty it would give me the same symptoms as a fuel pressure regulator. Also the injectors are pretty new so I don't think it it would be the injectors. Any information would be really appreciated before I just start ordering parts that don't need replaced.

Post by **rspi** » 09 Mar 2014, 12:56

Hi and welcome to the forum.

Please do NOT run WOT. Aggressive driving can be dangerous and the speed limit should always be obeyed.

LOL, Just kidding. What is the condition of your ignition parts? When was the last tune up?

I would do a compression test and go from there. Is #1 missing or #2? A code reader should tell you which.

ChiNorm · Post by **ChiNorm** » 09 Mar 2014, 14:23

These motors are real sensitive to spark plugs. My IM once tore out his hair for over a day trying to cure a miss on my car, then put in a set of VOLVO OEM plugs.

The miss departed imediately.

Weird, but true.

Good luck.

Someguy3331 · Post by **Someguy3331** » 09 Mar 2014, 17:27

All the ignition components are fairly new too, it has be ungraded with the ipd kit (I think it's the msd coil and the blue wires). That's why I was leaning towards a fuel issue especially since it never misses unless you put your foot to the floor. I should probably add that I am running the 19t turbo with the ARD blue tune. I did do a compression test and got 120psi in all cylinders. Planning on making a trip in town to pick up a new fuel pressure tester, but I'm not sure if it would read anything abnormal because the car runs perfectly fine unless you go WOT. Also it misses on mainly cylinder #2 but I did scan it once after it missed on me and the reader said #1 and #2 both misfired.

ajm · Post by **ajm** » 10 Mar 2014, 08:21

Someguy3331 wrote:I dont have the fuel pressure regulator, my S70 has the pulse damper which I'm kind of unfamiliar with. I was wondering if it was faulty it would give me the same symptoms as a fuel pressure regulator.

If I'm not mistaken I think you do have a fuel pressure regulator in addition to the pulse damper, it's just not situated on the fuel rail. If I'm right, it's probably situated just above the steering rack on the RHS of the car (i.e. the same side as the fuel filter + filler neck)

I know a lot of people have had this kind of trouble with non-Volvo spark plugs on these cars - personally I've always used the genuine plugs so have never had issues (they're not really any more expensive than other decent plugs so no reason not to use them.)

Post by **rspi** » 10 Mar 2014, 09:05

Someguy3331 wrote:I should probably add that I am running the 19t turbo with the ARD blue tune. I did do a compression test and got 120psi in all cylinders.

Ouch!!! Those are really low numbers for your motor, let alone the upgrades you have. My compression numbers last checked with over 200,000 miles were between 174 - 179. I'd say that you have found your problem, however, short of a rebuild or lower end replacement you are not going to cure the misfires.

Are you running full synthetic oil?

Someguy3331 · Post by **Someguy3331** » 10 Mar 2014, 09:36

Hmmm I may have to do another compression test with a new tester, mine is pretty old. I have been running part synthetic high mileage oil. And I was mistaken there is a fuel pressure regulator I was just a little confused by it not being directly on the fuel rail.

Post by **erikv11** » 10 Mar 2014, 10:06

It's not compression. Low compression will misfire all the time not just at high rpms, and low across the board will not cause codes in just one cylinder. If those numbers are right they are not good, but they are also not likely the trouble here.

Post by **erikv11** » 10 Mar 2014, 10:18

Maybe a boost leak? How is the CBV diaphragm?

Someguy3331 · Post by **Someguy3331** » 10 Mar 2014, 18:34

I have not actually pulled the cbv out to look at it but the whole turbo is pretty new. Its definitely not older than 2 years old. As for a boost leak I seem to be reading the correct amount except for when it misfires of coarse. But I did recently replace the pcv breather system and I'm wondering if the intake bolts loosened or I did not get them tight enough when reinstalling the intake. Would it be possible for boost to leak out there cause cylinders #1 and #2 to not get enough air and cause no abnormal readings on the gauge?