Intermittent stumbling issue in stop and go

wwilme · Post by **wwilme** » 23 Jul 2012, 18:41

My ’01 V70 T5 now with 172k miles has an issue with a heavy miss or stumbling when it’s in stop and go traffic. I have a 40 mile commute each way with about one third in stop and go, and the rest at highway speeds. I’ll leave in the morning and everything is normal for the first 25 miles until I hit the Capital Beltway (495) stop and go. After a few minutes I feel the car begin to stumble and then I’m running on four cylinders instead of five. This condition will continue until I get to work, although if the lights are with me on Connecticut Ave it will go away. On the return trip it’s the opposite. I am in stop and go immediately after leaving the garage and once the car really warms up after about 10 minutes the stumbling begins. If traffic is moving at a good clip once I'm on the beltway the stumbling will go away after a while, although its hard to notice exactly when at 60 mph. The same thing will happen if I am using the car for errands around town with repeated starting and stopping, but once I get out on the open road to return home the issue will go away after a while.

I narrowed it down to the no. 4 cylinder by pulling each plug till I found one that made no differnce and then swapped out the coil pack with an extra new one I kept on hand for just in case after having one go bad a few years ago. Swapping it out did not cure the problem so I experimented with a little game of musical coil packs, but I have five apparent good ones and it’s still the no. 4 cylinder which is the problem. To eliminate the possibility, I replaced the spark plug in that cylinder, but that did not fix it. I’ve checked the connector plug and it appears fine. The wiring leading from all the coil packs is mostly exposed now since the plastic loom has crumbled away, but I found no breaks, worn insulation, serious kinks, etc in the pinkish no. 4 wire which goes back to the car’s brain I guess. I followed it out of the cylinder head area and down as far as I can without peeling off a large loom where a bunch of other wires come together. Also checked the green and blacks to the point where they are spliced together with the same colors from the other cylinders. We are taking the car on vacation this weekend and don’t expect to hit traffic, but it would be nice to have this issue resolved first. Has anyone else experienced the same thing?

Post by **jimmy57** » 23 Jul 2012, 19:46

No check engine light?

I had a car with the ECM box cooling stuff all disconnected that had the behavior you describe. make sure all the ducts are in place to the box. It set an overtemp code for ECM but I don't remember the CEL or any messages on display.

Post by **igel513** » 24 Jul 2012, 15:56

Jimmy, does the ECM cooling stuff you mentioned above also apply to 03 S60 T5?

wwilme · Post by **wwilme** » 24 Jul 2012, 20:06

Oh, yeah forgot the CEL. A few days ago it was throwing three codes according to the local AutoZone guy:

1. Ignition coil cylinder D (guess that means no. 4)
2. Random multiple misfires
3. Undetectable

Jimmy - you may well be on to something with the ECM box. Wondering if it is burned out fan - I'm pretty sure I used to hear a fan of some sort under the hood (although not a loud as radiator fan) after I shut the car off, but come to think of it I'm not sure I still do. Not supposed to rain tomorrow so maybe I'll just remove the ECM box cover for the day and see what some good ventilation will do.

Strange there's an air inlet in the box cover which you would think would be hooked to a hose coming from the front of the car like on the older 850s, but the knockout appears to be still in place in the neck.

wwilme · Post by **wwilme** » 25 Jul 2012, 09:58

Well the ride to work this morning was painful with the top side of the Capital Beltway backing all the way up around to 295. And removing the top of the ECU box for ventilation did nothing - the car ran on only four cylinders throughout the stop and go back up. Outside temp was not more than 77 degrees according to the car - not excessive as it has been recently.

The guy who read the codes for me called the car "one of those FDOs" meaning "F*&%ing Dealer Only" to get a full read on codes sufficient to fix the problem.

Post by **DGM** » 26 Jul 2012, 06:01

This document contains a lot of information on how to diagnose misfires.

http://www.autotap.com/techlibrary/diag ... sfires.asp

wwilme · Post by **wwilme** » 10 Sep 2012, 22:16

Following up on this, cleaning the MAF cured one code and replacing the no. 4 fuel injector cured the other three. Strange that the fuel injector problem only happened in stop and go traffic and it sounded same as the other 4 through a stethoscope. Changing it out with a rebuilt one off ebay cured the issue and all has been well for about three weeks.