Cyl 1 misfire
 

Hi,

I have a 2000 SL1 that has been giving a P0301 code on and off for the last year or so. I've changed plugs, wires, and coil pack, but the code is coming up more often as time goes on. It runs fine both at idle and driving. Once I had P0340 and P0341 show up (cam position sensor) but those codes haven't come back. As the cam position sensor is part of the ignition module should I just change that out? It's about $150, so I'm reluctant to put in a new one one on a guess.

Thanks for the help

For background:
From one of sw2cam's recent posts:

"Both P0340 and P0341 both relate to the Camshaft Position Sensor(I will just call it Cam sensor from now on), the only problem is that the S-Series engines don't have a Cam sensor, not a typical one at least. instead, the DIS module watches when the #4 spark plug fires on the compression cycle and fakes a Cam sensor signal from it. the tricky part is that on a DIS waste spark system, spark plugs fire with their mated cylinders(1/4 and 2/3 in 4 cylinder engines) every time the cylinder is at TDC, regardless of weather the cylinder is on exhaust or compression. However, it takes far more voltage to fire a spark plug on the compression stroke then on the exhaust stroke, due to the compressed air(more air molacules, more air the spark needs to jump, more resistance to spark). The increased voltage needed on the compression stroke is detected by the "#4 sensing circuit" inside the DIS module for the Cam sensor signal. if the resistance of the secondary system is not in the proper range or something else is affecting the voltage draw, the "#4 sensing circuit" will be unable to work properly.

Ok -- that's out of the way.

How many miles on the car?
What kinda plugs are in there?
How much oil ya burn?

Is there oil in the #1 plug well (around the boot) before you remove the boot?
When you pull the #1 plug is the plug oil fouled or is there any oil sitting on top of the piston?

Sounds like you have ruled out the more obvious stuff

Could also consider doing a compression check before going out and spending $$ on a DIS.

I found a leaky intake manifold using carb cleaner. Is there anything I "might as well" change while I've got things taken apart? I might do the evap purge valve if it's easier to get to from the top with the manifold off...I've had P0442 code sometimes. Changed gas cap twice, traced as much vacuum line as I could.

In response to your questions...

~140,000 miles.
Usually use Bosch Platinums, put some AC Delcos in last time to see if that made a difference.
I add a half quart, maybe a quart between oil changes.
Plugs and plug wells look normal.

If your not using Saturn or the NGK equivalent plugs then you should be.