98 V70 NA 155000 Miles = misfiring?

Post by **98v70dad** » 15 Nov 2016, 20:24

For months I've been trying to address what feels like something loose or worn in the suspension that causes front end vibration at 65 to 75 mph. The wheels have been replaced. I've got new continental tires and the wheels/tires have been balanced three times. Almost everything in the front end suspension and steering has been replaced with top quality stuff including all of the engine mounts. Its been aligned several times. The car feels like its riding on rails (road feel) except it pulses down the road. Tonight I've been brainstorming what else it might be and I think a good way to describe it is that its like someone giving a subtle tug on a rope to jerk my car down the road between 65-70 mph. Its like I'm chug chug chuging along but at high speed. The vibration seems to be coming more from the engine than the road.

This made me think about the possibility of misfiring. The plugs were replaced with volvo plugs at about 120,000 miles along with beaugicord wires and a bosch distributor cap and rotor. The coil is original. I know that I'm nowhere near replacement time for the plugs, rotor or wires ... but who knows? I have noticed that my vibration issue doesnt happen all of the time. It happens a lot more and is worse when its hot and humid and almost never in the morning when its much cooler. I have not gotten any codes. i get 26.9 mpg on the highway and 24.9 mpg combined.

Thoughts on the possibility of misfiring causuing my vibration issue? Which item would be the most likely culprit?

s10lowrider1994 · Post by **s10lowrider1994** » 15 Nov 2016, 21:36

Motor mounts?

Post by **abscate** » 16 Nov 2016, 01:25

If the vibration ends immediately when you coast or back off the throttle it's probably misfiring.

Pull the plugs and look to see if one tells the tale of bad cylinder.

I believe you should be using the three pronged plugs on an NA

Post by **98v70dad** » 16 Nov 2016, 04:52

s10lowrider1994 wrote:Motor mounts?

Replaced last weekend.

Post by **98v70dad** » 16 Nov 2016, 04:56

abscate wrote:If the vibration ends immediately when you coast or back off the throttle it's probably misfiring.

Pull the plugs and look to see if one tells the tale of bad cylinder.

I believe you should be using the three pronged plugs on an NA

I'll pay more attention to that, but when I take my foot off the gas the vibration stops. I'll check the next time I'm out on the highway if its immediate. It seems to happen the most when I'm accelerating. I don't know how to tell if I have a bad cylinder by looking at the plugs. The Volvo plugs I put in (a few years ago) were three prong - Volvo blue box.

Post by **abscate** » 16 Nov 2016, 05:28

You pull them out, keep them in order, snap a pic and post it here

If you get your hands on a known good coil you can try a swap. The coil can fail under load.

Post by **shaker_chi** » 16 Nov 2016, 07:21

Is the car throwing any codes. If you had a misfire your CEL would light up immediately. If you have multiple misfires your CEL will flash. I've only had the misfire issue with turbo cars, never with my n/a. Check your plugs and I would recommend either Bosch Copper or Volvo plugs. These cars are very picky about the plugs you use. Also, check all your spark plug wires. If they are original I would replace using only o/e or the 8mm versions from IPD. Lastly, check your cap and rotor and replace if needed. Good luck.

Eddie G

Post by **abscate** » 16 Nov 2016, 08:23

If its a subtle misfire you cannot rely on misfire codes to be set. Likewise, if its really running crappy, you will get spurious codes that lead people to throw good parts at good parts - and not solve the problem.

When I had a a slight turbo induction leak, my 1999 threw misfire codes about 1/3 the time, knock sensor codes (phantom), ETM codes, cam codes, you name it, OXS codes, and a couple more I don't remember,

Post by **sleddriver** » 16 Nov 2016, 13:08

A NA motor runs at a higher compression than a turbo motor. 12.5:1 vs. 9,5:1 I think. What grade of gas do you run? Driving 75mph for your commute is more stressful/generates more heat/etc. than driving 60 or 65 for example. Try a couple of tanks of premium or 93 and see if you notice a difference in both performance and MPG. You've mentioned using a FIC like Regane in the past, so I take your word.

What are the odds of any unmetered vacuum leaks?
Check the routing of your coil wire. It should be routed away from both the crank & camshaft position sensor wiring.
Dirty MAF?
Front O2 sensor going Tango Uniform?
Intake manifold gasket leak?
Wrong plug gap?
Fuel Pressure Regulator, dirty filter or fuel pump problem?
Research the repair database.

Post by **98v70dad** » 16 Nov 2016, 18:50

shaker_chi wrote:Is the car throwing any codes. If you had a misfire your CEL would light up immediately. If you have multiple misfires your CEL will flash. I've only had the misfire issue with turbo cars, never with my n/a. Check your plugs and I would recommend either Bosch Copper or Volvo plugs. These cars are very picky about the plugs you use. Also, check all your spark plug wires. If they are original I would replace using only o/e or the 8mm versions from IPD. Lastly, check your cap and rotor and replace if needed. Good luck.

Eddie G

Thanks. With the exception of looking at the current condition of my plugs and cap/ rotor, all of which are at about 50% of their recommended life, I've done all of that. I wrote a pretty detailed original post. Its all in there.