2007 V70 2.5t SSS (start studder stall)

[abscate]

I wish we had a good one in the MVS tool program. You don't want a bad measurement when you are troubleshooting a tough problem like this.

[zanzabar]

Im not on board buying that it is an octane issue. Fuel is fuel. There is a fuel delivery problem of some kind. How about monitoring fuel pressure at the rail while experiencing the symptom?

I agree that it's worth chasing fuel pressure numbers, but it will be hard to measure when this occurs because it is so intermittent. And when it does happen it is typically just a slow stumbling start then when it catches everything is fine. It might not happen then for another few days.

But it certainly does seem to be octane related, I only get it with 91 octane. I didn't believe it either, but now I do. I think I'm going to have the ECU updated and tuned by ARD.

[zanzabar]

Followup: it was a combination of the crankshaft position sensor and weakening battery.

I believe if you notice your tach needle bouncing around on startup, that is likely a sign of a failing crank position sensor.

The slow starts have been solved by replacing the battery.

I am going to go fill up with 91 octane gas (have been using 89 recently) and see if that makes any difference.

[zanzabar]

Followup to the followup: I still have this issue intermittently. Early on it was likely a multi-issue problem. I have replaced the fuel pressure sensor and that made some cold start stumbling go away. But the tach jumping, and occasional slow start is still present. There's no pattern to it that I can figure out.

It's not an octane thing, as many of you have likely already concluded.

I now am pointing my suspicion at the starter.

[zanzabar]

Wet weather a few weeks ago caused this weird startup condition and CEL, and wet weather yesterday has brought it back after I thought it was fixed. I also assumed it was unrelated to the earlier SSS condition I was experiencing, but now am not sure. When this happens I get a stumbling at idle and when first driving before the engine warms up. It's fine when warmed up. The misfire codes are ECM-3100 (Misfire, at least one cylinder, startup), ECM-3110 (Misfire cylinder 1, startup), ECM-3120 (cylinder 2).

Could the humidity and/or cold and wet conditions be causing this? The first time it happened it didn't seem like the slow start and stumbling along with the tach needle jumping that occurred previously. It also seems different than the SSS condition with the tach needle jumping in that the engine misfires and stumbles for longer period of time, maybe 2-3 blocks. Then, like with SSS, it's fine for the rest of the day.

What I've already tried to do to fix this issue: compression test (all ok), swapped coils from cylinders 3 &5, replaced spark plugs, replaced fuel pressure sensor.

[mrbrian200]

Cylinder 1 and 2's coil packs share a chassis ground wire attached via a ring terminal underneath the plastic cover next to the CPs. Cyls 3-4-5 are on a separate ring terminal.

That said, the wire crimp at the back side of the ring terminal often gets contaminated with oil, so merely cleaning the ring and contact surface on the valve cover and tightening it back down may or may not do the trick. But try that first (cleaning).

Misfires grouped on cyls (1-2) or (3-4-5) on the 5 cyl, or (1-2-3) (4-5-6), on the L6 engine points strongly to these chassis ground points.

If this solves it, please do keep us posted (including whether the tach needle jump during startup persists or goes away). Someone else is having this problem (hard starting + tach jumps).

Edit: The following is hypothetical: I have not observed this on a running engine... After a little thought project it also occurred to me that a failing coil pack could be sending high voltage spikes back through the ECU. If the ECU doesn't recover fast enough the next cylinder in the firing order might be affected. If this were the case, a bad coil pack on cyl 1 might also result in a miss on cyl 2. If the bad CP was on cyl 2, next in the firing order would be cyl 4. Firing order is 1-2-4-5-3. Take that with a grain of salt, as I would probably expect the tach to continue showing erratic behavior after the engine is running/starter disengaged. However, faults may induce different symptoms while cranking as the starter pulls the system voltage down below 12v. After running the alternator brings voltage back up between 13.5-14.7v

[zanzabar]

Good info, thanks!

[zanzabar]

Misfires grouped on cyls (1-2) or (3-4-5) on the 5 cyl, or (1-2-3) (4-5-6), on the L6 engine points strongly to these chassis ground points.

If this solves it, please do keep us posted (including whether the tach needle jump during startup persists or goes away). Someone else is having this problem (hard starting + tach jumps).

I added extra ground wires to each of the coil pack group ground terminals (1&2, 3&4&5) and ran them out to a cam cover bolt then to a body ground point over near the ECM. So far the few times I've started the engine it has done so very smoothly. I'll update if I have the tach spike and studder at any time in the near future. Wet weather coming our way next week and I'm curious to see if it comes back then.

[mrbrian200]

I added extra ground wires ... to a body ground point over near the ECM.

Be aware, should the main engine ground ever go bad -> the large gauge one that attaches between the engine and the subframe near the bottom of the radiator, the ground wires you added could melt or become a fire hazard unless they are equal or larger wire size as the OE ground cable, and attached on both ends to a adequate size bolt, and to heavy gauge steel on the chassis.

The main thing we're looking for here is that the CP grounds are good to the valve cover. If you're not sure about the main engine ground, that's a separate issue to address properly.

Edit:if you go by the rule book: electricity will follow all paths to ground equally (if all paths have zero resistance), assuming the main engine ground is good an additional engine to chassis ground should be no less than two thirds the size of the OE ground wire. Which in this case is would probably around 1/0 AWG. The only place I can think might be suitable for a higher current connection up top under the hood might be the bolts that hold torque brace that spans the strut towers (with a large ring terminal under a bolt at the strut tower). On the engine you would need at least a 13-14mm bolt that isn't torque sensitive to hold a seal.

Note, this isn't really applicable to that small braided ground strap in that same general area. Those fine wire braided straps have current limiting properties.

[zanzabar]

Wet cold weather brought on a couple slow starts and the tach jump has occurred a couple times. I no longer have gotten the startup misfire on CPs 1&2 since the new grounds though.

Where the heck is that tach jumping coming from?