2001 S60 5MT Base Pulse/Jerk During Acceleration

[oragex]

The fuel pressure sensor is fixed at the right extremity of the fuel rail on which the injectors are placed. But there doesn't seem to be any variation in speed, so don't think it's that.

Is the whole car shaking? How are the upper and the lower (towards the radiator) engine mounts bushings? The hanbrake works smooth and keeps well? There are a few bulbs burnt behind the DIM (actually, not necessarily burnt but usually they don't make good contact, easy to replace from a scrap yard)

[chrism]

"...But there doesn't seem to be any variation in speed, so don't think it's that...."

With a manual trans, the engine can misfire and you won't see much, if any, fluctuation in the tach. That's because the crankshaft is tied in lock-step with the wheels. (No torque converter, etc that would allow the engine speed to fluctuate in relation to wheel speed.) So the rolling mass of the car and the rotating mass of the drivetrain and wheels will "force" the engine to maintain a relatively constant speed regardless of the hits and misses within the engine.

The smooth indicating tach along with the no CEL/codes also makes me think the ignition is operating OK (outside of maybe one or two bad coils or spark plugs) and makes me lean toward a fuel pressure issue. If the fuel pressure testing (no cost) doesn't reveal a problem, I'd throw a new set of plugs in there (almost no cost).

[WarbirdPilot91]

So the CEL just popped on today, P0304. I'm guessing coil or plug (even though I replaced all plugs 3 months ago.) Might be a silly question, but which one is Cylinder #4? Is the count left-to-right, vice-versa, or completely Swedish? Thanks!

[chrism]

Excellent!

Cylinder #1 is on the RH side of the car - by the Timing and accessary belts.

What kind of plugs did you install 3 months ago?

[WarbirdPilot91]

Excellent!

Cylinder #1 is on the RH side of the car - by the Timing and accessary belts.

What kind of plugs did you install 3 months ago?

Great! Thanks for the nugget. BTW, I am aware of the dash bulbs being burnt-out. I have the ones needed to repair it, but I've been too lazy to do it. Lmao. Anyhow, I put Autolite XPs in when I did the job 3 months ago. Now, upon researching them, I have learned that iridium plugs should not be gapped. Well, when I opened them, I noticed to gap was WAYYY to big, so I narrowed them to Volvo specs. Maybe this has finally caught up to them? I plan to pull them tomorrow to see.

I've also read that the XPs have a bad track record with imports, so maybe that is a concern. Regardless, I will get the stock Volvo plugs.

[WarbirdPilot91]

Good news, all! It was indeed the #4 coil pack. Funny how it just crept up, the last coil pack failure I had was very abrupt with no warning. Thanks for the help!