I have a 1998 Forester with 275000 miles which had developed a rough idle. Since there were over 80k miles on the plugs and wires, we changed them.
After we changed the plugs and wires and we are still getting a CEL code, P0304. The code definition is, Cylinder Number 4 misfire detected. We checked the #4 plug, not apparent issue.
I tested the Coil Pack with an ohmmeter and it is good.
Looking for other ideas, no other issues or codes.
Hi, Used OEM wires? One thing you can do is, in the dark open the hood and while engine is running look if sparks fly around the #4 coil pack or wires. Some times heat affects the coil pack. It'll look good when cold but when hot, goes bad(intermittent).
As its with the #4 you have to break it down. Coil- fuel injector (swap with another cylender- be awaire the o rings will be bad and you should have a two new sets with you) if you swap the injectors then the problem is the injector. After that you need to do a compression check on the car and a cylender leak down. At 275, I wouldent be surprised to see the engine getting weak. I'm putting in a junkyard engine in my 98 forester real soon- only 80K.
In the 'old days' that would tell you if a specific cylinder were 'dead'. Basically, pulling the wire from the bad cylinder would make NO difference. Then you could pursue spark plug or compression or other issues specific to that cylinder. I guess that could still work if you are having a bad miss at idle.
Hi, Pulling wire when engine is running is not a good idea. If you still see sparks fly around in the dark, prob;lem is still there. high voltage os leaking instead of going to plug. Try washing the engine with dtergent at self serve car wash.
Possibly, but I think that due to the way the coil packs work, both plugs (i.e. 1 & 3 or 2 & 4) have to be connected for either to fire.
In this case, pulling one plug wire will kill two cylinders, and the engine might well die as a result. Additionally, you might damage the coil pack. As the high voltage pulse from the coil pack does not have it's "normal" path to ground (thru the spark plug), it may arc internally, which can leave a carbonized track. If this happens, that is where the spark will go preferentially.
A better solution would be to disconnect one plug wire (with the engine off), and either ground the end of the wire to the engine with a screwdriver or the like, or insert another spark plug and lay that on top of the engine such that it is grounded. Gives the spark somewhere to go, right?
Beyond that, check the compression on all four cylinders. Should be in the range of 140 to 160+ PSI, and fairly even across all four. Try swapping injectors. Is the number four plug coming out black? All should be a light tan color (on the electrode). If it's black, you might have oil control issues; valve guide seals or oil control rings. As a last resort, try another ECU.
Using an OBDII interface with real-time readout and data logging capabilities can be very helpful in troubleshooting these kinds of problems. I like the ElmScan products.
formatting link
Hope this helps.
ByeBye! S. Steve Jernigan KG0MB Laboratory Manager Microelectronics Research University of Colorado (719) 262-3101
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.