techman1

Would a valve not closing all the way cause a popping at idle that would disappear at higher speeds?

BesideTheBox

I thought of this and ran a compression test on Saturday. I hope that this was the right test to tell me if I have a valve issue or not. The results were:

1. 185
2. 190
3. 192
4. 180
5. 190
6. 190

I appreciate the input! Should I also run a leakdown test?

techman1

I would think a leak would be more evident than 5 psi. If it has just recently started it may be a hot spot in the cylinder or something. Your earlier issue with only 1 distributor was another datapoint that does not seem to help.

In all honesty, with the symptoms, I would run a few tanks of fuel system cleaner and italian tune-up driving to make sure combustion chambers and valve seats are clean, then recheck it.

Shade tree talk, no professional diagnosis contained....

BesideTheBox

What I believe I found was that the middle lower side boot did not fit into the other holes. IOW, boot for bottom spark plug 2 did not fit in the hole for bottom spark plug 3. I do not have a picture to prove that however... The next time I have the car jacked up, I'll check.

Yes. All successfully unthreaded and rethreaded and then checked with the ohmmeter.

I really need to know... Can the wires ohm out perfectly, but still not operate properly at high voltage?

I'm pretty sure that I don't have arcing going on. I don't hear any, and I could not see any in pitch dark.

But I must admit I am getting closer to buying wires so that I can rule them out.

I know it doesn't make sense. Probably not one of my better ideas.

Except for the 50K mile plug that I found in 6 under the power steering pump, and this has been replaced with new (well, they all have), I don't see why 6 is special. But the popping does come out the right side of the exhaust.

Heck, the lower side plugs wires for cylinder 1 and 3 were swapped for a year before I figured this out. Never a CEL. I figure that the wires were likely swapped when the top end was done at 44K miles.

BesideTheBox

Mike,

I set the engine to TDC. Now I know that there is a red mark on the flywheel in my car. Oh, and notice the nice new Porsche OEM belts



And this is where the rotors were pointing. Both at the molded in bump on the side of the distributor bodies. The angle of the picture is not the best, but they are definitely pointing to the right spot.



I removed the rotors and the gray plastic caps to see what was underneath. Here is the shaft driven distributor. I think that is the hall sensor in there? Service records show that the hall sensor was replaced at 48K miles in 2003.



And here is a picture of the crud that is in the belt driven distributor. I cleaned most of this stuff out with a Q-tip. In the picture, it looks yellow, on the Q-tip, it looks darker, a bit greasy. I could see the belt, but I wouldn't know how to assess its condition.

Mike J

Yeah, looks good. I usually use the caps/rotors to make sure that the correct lines, so if you slap the rotors/caps back on, they both should point to the #1 firing, unless you are on the other side of the cycle (i.e TDC exhaust, not compression). No matter, I doubt if that is your issue.

And yes, even though an ohm check is correct, the wires can behave weirdly when high voltage pulses are being put through them. If the test failed, then the line is failed, if it passes, there may still be an issue.

Your compression is Ok except for 4 - even that can be a variation. did you it a few times? I doubt if this is the issue.

I listened to your video again - it sounds like the exhaust is dead steady, and above it is a weird mechanical noise that is random and sounds like something crunching. Its hard to tell from a computer, does that describe it in real life? Remember a misfire can be from a number of things, including the computer picking up a vibration in the sensors that bridge across the pistons on each side of the engine. A mechanical issue could be misread as a misfire if it causes enough of a vibration in the engine to trigger the sensor. If the engine is idling and doing that noise, does the engine shudder or any vibration correspond to that random noise?

Really stupid ask - does it stop when the clutch is in?

Ok, if we also take in the data that the car runs smooth on one distributor, but not on two (and that is repeatable), that implies the two distributors are fighting each other. I assume you double checked all the spark plug wires, none were crossed and they are all running to the correct sparkplug? Visual is not enough, continuity testing works. I like Alex's suggestion of swapping 4 and 6 - but of course #6 is the worse one of all to move. Do you have spare wires around to swap? Is the tin off the engine so #6 upper is easy to get to?

Does that noise happen when the engine is still cold?

Cheers,

Mike

IXLR8

The wires themselves from M3 terminal to M3 terminal have near zero resistance (far less than an ohm). Its the cap that will have 3K ohm resistance. The original Beru wires are tin plated copper. I do not see them being intermittent unless you have a break in the wire.

Brad, you now stated that you have this issue while running on either distributor. The chances of both ignition cables, both caps being faulty to cause a P0306 fault seems strange.

If George or Loren can confirm, I am under the understanding that codes P0301 through P0312 are for misfires...I take it this is strictly electrically related and not affected by any other mechanical issue (sticking valve, etc).

BesideTheBox

Not sure how I missed this, other than to say that I was initially assuming the coil was fine since the engine runs fine at high rpm. So it may have been shortsighted to dismiss it.

George had previously posted a misfire diagnosis chart(https://rennlist.com/forums/993-foru...-p0306.html#14). It gives the static measurement specs for the coil at 20C. My coil measures out of spec. Doesn't necessarily mean this is the issue, but it does mean it should be investigated further.

At 20C, the resistance between terminals 1 and 4 at 20C: 5.0 to 7.2kOhm
My measurement at 8C: 7.9k Ohm
My measurement at (warmer than 8C - engine was warm): 8.5k Ohm

Resistance at 8C is too high and resistance is higher when the coil is warmer.

Mike J

I had a muffler once that rattled - I could of sworn it sounded like a failed rocker or valvetrain - very weird. The internal baffle weld had cracked and it became loose. It had a random feel like this one, swapped in a different muffler, no noise... but I did not get misfire codes.. !

BesideTheBox

Mike - Lots of good questions.

I think things are lined up right.

This is good to know. I don't believe that I'm having an issue with wires, but I think I am going to start looking seriously into having a spare set.

I did several of the cylinders two or three times. I don't recall if I did 4 multiple times or not. My assessment is that doing a compression test is not an exact science. Since I was doing this myself, I'd crank twelve revolutions, then switch the key off, run around the back of the car and throw myself onto the pavement so I could read the gauge. Kind of amusing.

I would say that the popping does have a metal like sound to it. I thought for a long time that there might be something loose in the right muffler. I can't remember now why I ruled that out. Maybe the muffler has to reach a certain temp and airflow for the noise to occur. I will look into pulling off the muffler. I'm guessing that bolts are going to be snapping and I'm not looking forward to that. I do have some PB Blaster.

Regarding engine shudder, I do have shudder when the engine is warming up as it is idling from a cold engine. If the popping is actually something with the muffler, then this is likely a different issue.

Not a stupid question at all. No, it does not stop when the clutch is in.

I certainly though the other day that the distributors were fighting each other. Then I was getting the popping even from a single distributor. So those tests should be deemed non-repeatable.

I have double checked all the wires, none crossed, all are running to the correct cylinders.

Yes, but not as obvious until the engine is warm.

Mike J

Oh, I just remove/cut/break off the old muffler clamp bolts, and replace them with stainless steel fasteners - much better corrosion control, and a high strength connector is not required there.

It still can be a weak coil, but the nature of the noise disturbs me. Usually a misfire is directly in the tone of the exhaust, this sound is almost like its on-top of the sound.

If you can do a quick muffler swap, try that, or at least take the existing ones off and shake them - if there is a rattle, that can generate noise.

Cheers,

Mike

BesideTheBox

Snapped both bolts and pulled the right muffler. No rattling when I shake it. A little bit of fine balled up steel wool came out. Normal? Could not get any loose / rattling noise out of it. Should I tap or smack it with a rubber mallet or similar?

Started up the engine and although it was loud, I -think- there was irregular firing. Really, really hard to say definitively.

jcochran1

My car has been making this exact same noise for about 1500 miles now but with no misfire codes, and also only coming from the right side. I chalked it up to something wrong with the muffler because thats what it sounds like, and I'm currently waiting on a set of Fisters. I will report back with my findings once I install them. It looks like you're working quickly to fix this though so you may have an answer before I do. Good luck!

ToSi

1) pictures of lower plug wires please.
2) triple check you have the wire <-> cap routing correct.

Alex posted this before:

BesideTheBox

Awesome! You are the first person to say you are also having this noise. With the Fisters, will the noise be gone? or will the noise become unnoticeable? That does not need an answer... just something to think about.

Please do follow up.