2000 V70 SE, NA, 255K miles

Have consulted with a couple of local Indy shop experts who work on Volvos for a living.
The car still has intermittent misfires in #3 cylinder, which the codes confirm.

Shops’ compression and leakdown checks are good; all five cylinders show 160+ psi.

Have swapped around plugs and coils several times to confirm all are good. Had a fuel injection system service performed. Cleared the codes. Runs like a top until... cylinder #3 misfires and CEL lights up again. So far the shops are stumped about the intermittent nature of this issue.

Last night the car ran fine when parked. It sat outside during a rainy damp night and when started this morning, very rough running and CEL lights again.

Today I reverted to old school trouble shooting myself, pulling off coils with engine idling and listening for the arcing spark in each plug well. #3 had no spark at first, until I removed and replugged the #3 coil connector several times. Finally, the arc and spark returned to #3. Engine smoothed out and after driving a while the CEL went off.

I’m thinking that the four-prong coil connector is the culprit; or a second possibility is one or more of the thin wires leading into the coil connector are internally broken or frayed.

I’ll start with the connector: Is there a way to tighten up and/or keep dry the plug connection into the coil? Cable ties cinched down in some way? Cleaning and dielectric grease on the contacts?

I think I’ve narrowed this down. Now to achieve continuity to #3 coil without internittent misfires.

Looks like the connectors are available too...

https://www.fcpeuro.com/products/volvo-plug-housing-9456341

Good find in FCP! Thanks,

V70 NA Fitment table:

2001 => 2007 NA
https://www.fcpeuro.com/products/volvo-ignition-coil-connector-housing-genuine-volvo-9494800#fitment

The fitment table doesn't include 2000 model year. Can they be that different?

Have you carefully inspected the wires going to the connector? On mine the black plastic loom covers were completely crumbled-- I have heard of intermittent problems when one of the wires gets pinched while installing the cover, causing a short. I replaced my covers with new loom material from ipd.

If you can't find wire damage, another option would be to get the wires/connector for #3 from a junkyard and splice them in. I would solder and heat shrink the wires.

Good luck!

My loom covers were crumbled too; replaced with ipd looms a couple of years ago.

Good suggestion to source one #3 connector from the junk yard; I'll be on the look out for a donor car.

This reminds me of a nasty problem I had with a distributor cap
that acted up sometimes with moisture. You could not see anything
wrong with it, but it crapped out with moisture.

I'd do a new OEM cap.

Bill

'”I’d do a new OEM cap.”

The 2000 S/V 70 has a multiple coil-on-plug ignition system. From swapping the coils (and plugs) around I’m confident that the five coils are OK.

Still seeking a good solution for a dry and tight wire plug connector to #3 coil. I’ll probably try a cable tie wrapped in a way to support a tight connection.

Btw the car ran fine all day today in and around town and highway driving for total of 100 miles.

Hey maybe just disconnecting and reconnecting the plug a few times has cured it,,,,, :)
--
Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (STILL not road worthy!)

"...maybe just disconnecting and reconnecting the plug a few times has cured it,,,,,"

We can go with that! On the other hand, once a part shows a tendency to malfunction in some way, symptoms are likely to reoccur...

Will monitor for a while. Any shared experiences with returning 100 percent continuity to the coil wire and plug are welcomed. Less than 100 percent guarantees the misfire will occur again sometime, usually when it's most inconvenient, or worse.

If the wire is broken internally, you should be able to make the misfire happen by touching the wire. Di-electric grease might work to keep moisture out, then I would also smear a little on the wire also. Using cable ties sounds good, but that is a non moving part and only should work if the wire is compromised internally.
--
Keeping it running is better than buying new

"...a second possibility is one or more of the thin wires leading into the coil connector are internally broken or frayed. ..."

However, from your problem description, #3 has a problem regardless of which coil is being used in that position.

If the harness connector doesn't turn out to be the issue then maybe you could probe or tie into the wiring where it approaches the coil connection and see if you can detect a break in electrical impulses while the engine is running.
--
Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

“However, from your problem description, #3 has a problem regardless of which coil is being used in that position.”

Correct, #3 is the problem.

Tying into or probing the wires for broken continuity is probably beyond my skill set and resources at home. But I’m sure a competent auto electrician can, if one can be found.

Will start with the coil connector plug.