S40 Misfire on 1 and 4

mcnabbr1 · Post by **mcnabbr1** » 13 Apr 2016, 19:05

Hello! I’m the new owner of a 2003 Volvo S40 1.9T with 84k miles from Georgia (United States).

While accelerating from 40 up to 65 mph, I simultaneously had both Cylinder 1 and 4 misfire while accelerating but resumed normal operation once at a constant speed. The car drove fine for 2 hours with a stop in between, until I got home and tried restarting the car. The car hardly started and was accompanied with audible misfires. Once again I had both Cylinder 1 and 4 misfire. So I changed the spark plugs and performed the In-line diode spark plug check. The only effect I now have is that both ignition coils now have codes.

P0301 Cylinder 1 Misfire
P0304 Cylinder 4 Misfire
PO351 Ignition coil A Primary/Secondary Circuit
PO352 Ignition coil B Primary/Secondary Circuit

Just below is a list of the troubleshooting I’ve performed since the codes appeared;

-In-line diode spark plug check (looked fine to the naked eye)
-New spark plugs gapped to .028
-Compression test (went great, all cylinders were within 1% of each other)
-Fuel injectors swapped between good and bad Cylinders. All injectors checked great with the Ohm resistance check and audibly with mechanics stethoscope
-Swapped Ignition coils with new Ignition coil (had no effect)

I’ve ran out of ideas at this point. I look forward to hearing your thoughts!

mcnabbr1 · Post by **mcnabbr1** » 13 Apr 2016, 20:00

Additionally while i can get the car started amid all the misfiring, if i turn the air conditioner on or put the car into gear it will often stall out.

Post by **alschnertz** » 14 Apr 2016, 14:51

I'm not familiar with the "In-line diode spark plug check".

I've heard that these engines are sensitive to the brand of spark plug used. Of course "Volvo" plugs are recommended, but obviously Volvo does not manufacture spark plugs. They keep a good secret though on who does manufacture their plugs. So if you find some definitive information, please share it. I'm a fan of NGK plugs, but did switch to "Volvo" plugs when I was having a problem.

I had a misfire issue a few years ago similar to yours.
My '01 would run fine, but if pushed really hard while accelerating, it would miss and set a code. Unfortunately, I don't remember the code.
But, I eventually traced the problem to a failed coil. I could see a crack and a spot where it was arcing. I did need a magnifying glass to the the failure.
Changed the coil and all has been well for a few years now.

mcnabbr1 · Post by **mcnabbr1** » 14 Apr 2016, 17:44

I've tried both a new coil and swapping spark plugs from the bad with the good. It still misfired the same. I am running the NKG plugs as well

mcnabbr1 · Post by **mcnabbr1** » 15 Apr 2016, 06:03

Solved!
Not a bad coil, but a bad connector to the coil.
It's a 2003 so it's not surprising that the inner plastics of the connector were starting to come apart. My temporary fix until I salvage another connector was to pull the positive and negative wires from the connector and directly connect the wires to the coil. I additionally used electrical tape to shroud the open wires ( a temporary fix)

There's one coil which goes to both the #1 and #4 cylinders. While I performed an inline diode check on the spark plugs. Finding the occasional miss which causes your misfire is very difficult (if your cars idling at 1200 rpm/4 cylinders your looking for the spark plug to flash 5 times in a second) it's very easy to miss a misfire.