Do coils slowly die, or quickly die?

JeffHicks · Post by **JeffHicks** » 18 Jan 2016, 09:55

General question, but it's because I'm still tinkering on my '04 V70 T5.

Do the ignition coils on these Volvos ever just "slowly die" - as in, low spark, random misfire, slowly fading out? Or do they just stop working altogether - specifically, either on or off?

harryhendo · Post by **harryhendo** » 18 Jan 2016, 10:07

In my experience, they start to fail intermittently and fail completely over a period of time. For example, on my 2002 V70, the engine started stumbling a bit on hard acceleration, then after a longish road trip, started to fail even at cruising speeds, then it became evident even on idle about a week later. The best way to diagnose this is to get an OBD-II code reader, and, if you get a misfile code (0301 would be misfire on cylinder 1, 0302 on cylinder 2, etc.), swap the misfiring cylinder's coil to another cylinder and see if the code follows to that cylinder/coil.

JeffHicks · Post by **JeffHicks** » 18 Jan 2016, 11:36

^ I got P0303 & P0304 codes, as well as the generic P0300. I swapped out 3 & 4 with used Volvo coils I got at a salvage yard. We'll see what happens.

JeffHicks · Post by **JeffHicks** » 18 Jan 2016, 11:37

Follow-up question:

Have any of you bought non-Volvo coils and been happy with them? Bosch? Other? Does IPD sell anything but Bosch?

harryhendo · Post by **harryhendo** » 18 Jan 2016, 11:43

rockauto sells non bosch coils and I've never had a problem with them. Very inexpensive too (< $40).

harryhendo · Post by **harryhendo** » 18 Jan 2016, 11:47

Be aware that the misfire codes may be caused by other problems than just a failing coil, so just replacing coils may not solve the issue. Isolating the misfile by swapping around coils and sparkplugs is a good procedure to follow.

JudgeRat · Post by **JudgeRat** » 18 Jan 2016, 14:20

The simplest answer is: Yes - meaning that they do both; sometimes they fail intermittently and sometimes they just fail outright. The advice to swap the coils/plugs is dead on too. I'll add that it could also be something in your wiring so you might want to test it too.

mouseskowitz · Post by **mouseskowitz** » 18 Jan 2016, 15:44

I had one coil pack die on me suddenly and replaced it with a Delphi with no problems to date, maybe 20k miles. $36 on Amazon. When I started having misfires on two cylinders during startup a week or two ago I realized the plugs hadn't been replaced since I bought the car 60k ago. New plugs have fixed that issue so far.

Post by **abscate** » 20 Jan 2016, 09:45

I had one fail a week after a school bus jump pack start. I think the two events were correlated but not certain.

Originals about 120k miles or so, 10 years old

Post by **cn90** » 20 Jan 2016, 13:23

Ignition coil is basically a transformer that converts 12V into 48,000 volts (or something like that).
So it can fail intermittently (shorting across the copper windings) or suddenly.

This is why when we drive cars of this vintage, it is a good idea to buy a 5-pack of used coils on ebay (check what you have in the car before buying used coils to be sure they are the same) or junk yard for cheap. Usually it is around $10-$15/coil. Keep some in the trunk, it could save a bad day.