Okay, Let me start from what i have ALREADY DONE :

Replaced with brand new OEM or Better :

Ignition Coils (OEM)
Spark Plug wires (OEM)
New NGK Iridium Spark plugs
New Antenna W/Motor replacement
New FPR
New Top Oxygen Sensor
New Thermostat and Therm. Housing (done right, sealed by me)
Has Cold Air Intake from EuroSport tuning (i installed this when i first got the car 2 years ago)

New Dura-Last Driver Side Axel Assy. (Serious vibration issue fixed)

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What the car's problems are :

CEM Unit. (known)
It leaks oil (known)
It misfires on cylinder 1. (New)
It needs all new motor mounts.(known)

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My post is regarding a 2000 volvo S40 1.9T. The car has 216,000 Miles.

I've kept this car running forever and now i'm having a MISFIRE on cylinder 1 CEL coming on.

Given i have changed the Spark Plugs, Plug Wires, and the 2 Ignition coils. The CEL did go off for a little while.

When it came back on the first time... i pulled everything back off and cylinder 1 had porcelain from the spark plug that had broken (none got into the cylinder head) i used an air compressor to get the pieces out. Got a brand new plug. Installed the plug and it ran great with no CEL's at all.

The CEL, After probably 3 weeks of driving without any issues, has turned on me again with the CEL for Misfiring on Cyl. 1.

I know the next thing i need to check is the :

Fuel Injectors
Intake hosing
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I'm looking for your guys' opinion on this situation. Should i focus on the Electrical side of things, Because the misfire stopped when everything was fresh replaced or should i spent the better part of my day pulling the Fuel rail off?

 

I'd concentrate on electrical. Bad coils and wires are very common. Bad fuel injectors are rare.

Be careful with the misfire on #1 as one coil fires 2 cylinders. Your misfire maybe on the cylinder with the spark plug wire. When those coils or wires get hairline cracks in the plastic the spark can jump to the head. And because it's hidden below the cover you never see it or hear it.

Now I've never tried it but I have read you can JB Weld those hairline cracks and stop the arcing.

 

I would swap a fuel injector. Maybe it's running rich or lean causing issues with the plug.

Do you have any other codes?

 

Okay, so pulled the fuel injectors off.... Pulled the FPR off. Cleaned them all. They weren't that dirty.

Put them back on. Cranked the car and the FPR was leaking gas.

Replaced the o-ring on the FPR that goes into the fuel rail and fixed it.

Ran fine for a day or 2.... Did a full oil change and a full radiator flush.

Now the cylinder 1 code is back again.


What's next? Like I said in the original post I Changed all coils, wires and plugs when it first came up.

 

Trying moving parts from one cylinder to another to see if the misfire moves with it --plugs, wires, coil, injectors, etc. also check for oil contamination on the plug in that cylinder...

 

I've already done that. Switched them all around . Gapped them properly. No o-rings leaking oil into the spark plug sockets.

 

Also, it is not seeming like it is misfiring at all.

 

UPDATE------------------------------------------------



Still misfiring.


It seems as though it will misfire only when it is starting. Then it will stop when it levels out the temperature.

Once it misfires on ignition it keeps the light on all day. I'm in desperate need of passing emissions. (yea it sucks)

I can clear the code during the day and drive around without it coming back on. Once it cools off depending on the temperature (if its cold) it will misfire again on ignition.


SINCE THIS POST I HAVE DONE THE FOLLOWING :

RE-REPLACED THE SPARK PLUG WIRES
RE-REPLACED THE IGNITION COILS
REMOVED THE FUEL INJECTORS AND CLEANED THEM (WEREN'T DIRTY)
RE-REPLACED THE SPARK PLUGS GAPPED PERFECTLY.
CHECKED ALL WIRES AND ELECTRICAL CONNECTIONS ON THE SPARK PLUGS.


One interesting thing is that the Electrical Connector that snaps into the Ignition Coil, will not snap into it and the electrical connectors were pulled out slightly (possibly not making a good connection with the ignition coil).

So, i fixed that and checked the fuses to be sure.


COULD IT BE THE CEM UNIT THAT IS CAUSING THIS MISFIRE???!?

I'm at a loss with this thing. i've followed all of the wires and replaced everything conceivable that i can think of.


Thanks!

 

Get a compression check when it's cold. Your description sounds like valves out of adjustment or not seating properly. Once it's warmed up everything expands until it's within tolerance.

Also, if you have an IR thermometer get a reading on the exhaust pipes for each cylinder when you first warm the car up. See if cylinder 1 is colder or hotter than the rest as she comes up to temp.

I have never heard of a bad engine computer that only affects one cylinder.