Random misfire 2003 s
 

Thanks in advance for any help. I am having a mechanical problem. I come up with a P0300 random misfire code, yep it is misfiring. I did all the simple stuff first, plugs and wires and then hooked up a fuel pressure gauge. It comes right up to the 51 LBS on prime but when the engine is running it drops off to about 41. the next step was changing the fuel filter in the tank it was pretty black when I got into it so I was hopeful. Yesterday I pulled the fuel pump and found about a teaspoon full of dirt. I had just received a new pump but decided to clean the filters on the old on and give it a try because everything I have read indicates they either work or don’t. Still the misfire so I went ahead and put the new pump in and it is about the same.
I would think if it were cylinder specific I would receive a code for that cylinder so I think that is a good sign that I don’t have internal damage.
I’m thinking fuel pressure regulator or coil next. The vac line looks ok to the pressure regulator and I have tested the injectors by unplugging them one at a time to see them cause a misfire.
Any suggestions offered will be greatly appreciated.
(2003 Mini cooper S ~ no mods)

Have you replaced the coil pack ???

Thanks for the reply, haven't done the coil pack yet, but leaning that direction. I was surprised to find that AutoZone has one on the shelf but was debating if I should order the MSD and if there would be any advantages. Also, I'm still wondering about the fuel pressure drop and would sure like to know if that's normal or if i may have a bad fuel regulator.

I've got the MSD with the Magnacore wires ... I can't say I saw a huge improvement
Misfires are normally ignition related , I'd try the coilpack first and see if that cures things...
I've never checked fuel pressure to make a guess on that

Thats the way mine went out ... As the heat increased the CEL would pop on ... I'd reset it then awhile later it would do it again ... I thought about putting a thermal barrier under it but never followed thru

coopy is alive
 

Thanks for your suggestions. I picked up the coil pack from AutoZone but had to modify the mounting bolts (remove the metal sleeves). It ran worse than it did before; good news is that it produced a new fault code, P2304. One of the possible causes is a short in power wire to the coil pack. Better news is that sure enough the insulation was rubbed off all three wires at the point where the wire tie holds the harness in place about a foot away from the coil plug. Fixed the wires and it runs great. Had I not replaced the coil I could have been forever finding the true cause.
The education was not a free one but I have new parts that were close to their life expectancy anyway. Hopefully this will help someone else down the happy road.
:)

I'll go out and check mine to see if it might be a production problem

Nice job
 

Well bit of advice for misfires,I take some soapy water and spray the wires and coils/or pack. Don't drown it though lol(light mist), if you see sparks on wire or coil area. I have found a few wires, rubbed wrong in Mini's. They seem to have found bad wire harness designs, but over all awesome cars.

I need to ask a question. Should you check the oil once a week? I have a mini cooper S 2005.