Misfire Diagnosis

[norcaltim]

Hi all,

 

Wanted to get some thoughts from the brain trust before I throw parts at this issue. 2001 Boxster 2.7, no mods besides some audio stuff.

 

Was driving in 2nd the other day, punched it every so slightly and the engine grumbled, CEL blinked for ~3 seconds, then everything went back to normal. No issues since then. Finally pulled codes today and got P0300 and P0304.

 

No engine work recently, but I did pull the heater core to fix my heater flap (the heat works again, woo!). I drove around for a week with the bleed valve open, kept topping up coolant, put the valve back down once the level settled.

 

I've noticed that my idle is a bit rough at times, though this didn't get worse after the work mentioned above. Sometimes while at a stop the RPMs will drop a tad and then fluctuate (~100 RPM maybe?). Besides that I've been driving the car more recently, multiple ~100 mile trips over the past months out into the Texas hill country. The car feels (very) strong outside of the minor idle thing and this misfire incident.

 

I need to change my oil and was going to swap my plugs later this year.

 

So... bad coil pack? New plugs? Something else entirely? If it's a coil pack, should I change all six or just the offending one?

 

Thanks for the help!!

 

 

 

More info--I had a compression and leakdown test done in Nov. 2013, results below:

1: 210 - 5%

2: 215 - 8%

3: 205 - 5%

4: 210 - 5%

5: 215 - 5%

6: 210 - 5%

 

Even more info:

RMS/IMS/AOS/H20 pump all replaced ~30k miles ago. Spark plug tubes replaced in Dec. 2013.

 

And here's a pic for fun:

[Philip Adler]

I had a CEL, and had the code PO306, which indicated a cylinder 6 misfire. Didn't hear, feel anything wrong with the engine.

Bit my lip for a week, but it never happened.again. (1999 Boxster Base 2.5L).

[JFP in PA]

Hi all,

 

Wanted to get some thoughts from the brain trust before I throw parts at this issue. 2001 Boxster 2.7, no mods besides some audio stuff.

 

Was driving in 2nd the other day, punched it every so slightly and the engine grumbled, CEL blinked for ~3 seconds, then everything went back to normal. No issues since then. Finally pulled codes today and got P0300 and P0304.

 

No engine work recently, but I did pull the heater core to fix my heater flap (the heat works again, woo!). I drove around for a week with the bleed valve open, kept topping up coolant, put the valve back down once the level settled.

 

I've noticed that my idle is a bit rough at times, though this didn't get worse after the work mentioned above. Sometimes while at a stop the RPMs will drop a tad and then fluctuate (~100 RPM maybe?). Besides that I've been driving the car more recently, multiple ~100 mile trips over the past months out into the Texas hill country. The car feels (very) strong outside of the minor idle thing and this misfire incident.

 

I need to change my oil and was going to swap my plugs later this year.

 

So... bad coil pack? New plugs? Something else entirely? If it's a coil pack, should I change all six or just the offending one?

 

Thanks for the help!!

 

 

 

More info--I had a compression and leakdown test done in Nov. 2013, results below:

1: 210 - 5%

2: 215 - 8%

3: 205 - 5%

4: 210 - 5%

5: 215 - 5%

6: 210 - 5%

 

Even more info:

RMS/IMS/AOS/H20 pump all replaced ~30k miles ago. Spark plug tubes replaced in Dec. 2013.

 

And here's a pic for fun:

garage.jpg

 

Plan on pulling and replacing all six plugs, and carefully look at all of your coils, particularly the one on the misfire cylinder #4.  Any signs of crack or other damage, replace them.

[norcaltim]

 

Plan on pulling and replacing all six plugs, and carefully look at all of your coils, particularly the one on the misfire cylinder #4.  Any signs of crack or other damage, replace them.

 

 

Ok, will do. Thanks!

[pkust]

I had a coil pack failure at 18 years and 67k miles and replaced them all, seat of the pants feels like it runs better than ever, so when one goes, bite the bullet and do them all. Save the old ones and carry a spare, you will NEVER have another fail, as long as you have that spare with you. Murphy's law.

[norcaltim]

Update: started pulling things today, didn't get very far as I started late and had to buy a new tool at every step. 1/2 inch drive 19mm deep socket? Check. Larger breaker bar? Check. Metric allen sockets? Yep. Also need a medium-sized torque wrench between the two I already own? Certainly. Anyway...

 

Pictures here (too large for uploading). These are from cylinder 3 (passenger side, rear). I'll remove the rest tomorrow.

 

Do the crack and small hole warrant replacing the coil?

[Ahsai]

Absolutely and the rest of the coils too, just like what John said in post #3,

[norcaltim]

Ok, will do. I wasn't sure whether that level of crack warranted replacement.

 

Thanks!

[JFP in PA]

Ok, will do. I wasn't sure whether that level of crack warranted replacement.

 

Thanks!

 

Basically, and signs of problems (cracking, discoloration, etc.) and the coil should be tossed.  Replacements are not that expensive, and on some models, just getting at them is a chore.  So if it looks at all questionable, it goes.

[norcaltim]

 

Ok, will do. I wasn't sure whether that level of crack warranted replacement.

 

Thanks!

 

Basically, and signs of problems (cracking, discoloration, etc.) and the coil should be tossed.  Replacements are not that expensive, and on some models, just getting at them is a chore.  So if it looks at all questionable, it goes.

 

 

Good to know. For some reason I thought they were much more expensive.

[Ahsai]

Check Paragon products for good deals on Beru coils.

[norcaltim]

Another update:

 

Coils came in Thursday, finally had a chance to do the work today. Replaced all six coils, plugs, and plug tubes. The tubes were in good shape; next time I'll just do the seals. Nothing wrong with having a spare set around, I suppose.

 

All of the plugs looked about the same, and all the coils were cracked. The pictures I posted earlier are approximately what everything looked like. Cylinder 4 didn't look any different than any of the others, so I suppose it was just the first to exhibit symptoms.

 

All in all I think it took me about four hours, and I wasn't trying to set any speed records. Cylinders 4 and 1 are a pain due to location; I think they took about an hour each. Glad I have a plethora of different ratchets and extensions and such.

 

The car feels excellent, starts more smoothly, pulls harder, idles better, etc. I think the battery may need to be changed, it seemed to struggle turning everything over, but that also could be because I haven't driven the car in a month. I'm going to change the oil and do a few other things tomorrow, I'll see if there's any change after my hour drive this evening.

 

Thanks for the help, all!

 

Edit: here are some pictures, because everybody likes pictures.

Edited April 24, 2016 by norcaltim

[cbonilla]

Coincidentally I had a similar experience this past week in my 03 986S (100k). Friday evening I was coming home, accelerating hard and I got a flashing CEL. Had never seen that before. The car was running fine the whole time. When I got home I plugged in my scanner and got a P0301 pending code, indicating that a misfire had been detected on cylinder 1. It never actually threw a code. That weekend I took it out for a hard, fast drive in the country with no repetition of the problem.

 

Car ran fine the entire time. I'm chalking it up to a temporarily clogged injector. Plugs were new 6 months ago, and I should have replaced the coils then, but I cheaped out as I I had done a lot of work on the car. New coils are now on my list, but I feel that I don't have to stop everything to do them right away.

 

CB