vincer77

To rule out the ground strap, you may want to run a separate wire temporarily from the battery to the engine as a test

BesideTheBox

Bought a dual gauge leakdown tester from OTC and performed a leakdown today. Pretty easy to DIY if you have a compressor, jack stands, and a few tools.

Here's what I got (90 psi input):
1. 87 psi 3.3%
2. 87 psi 3.3%
3. 87 psi 3.3%
4. 85 psi 5.6% (worst one of the bunch)
5. 86 psi 4.4%
6. 88 psi 2.2% (surprisingly the best - I previously had P0306)

My feeling is that these numbers do not confirm a valve issue. There might be a valve issue, but these numbers do not support that.
I have very low oil consumption. I don't see any drop in oil level since my oil change in February (3K miles).

This eases my mind a bit about the misfires at idle when the engine is warm. Still don't like the bumpy idle.

The one thing that does seem to eliminate (mask?) the misfires and the bumpy idle is to switch on the air conditioning.

Any thoughts about the leakdown percentages? I am going to leave the car apart for an hour or so in case someone has a suggestion for investigating further - perhaps on cylinder 4?

Pre-purchase inspection had the leakdown percentages at
1. 3%
2. 2%
3. 3%
4. 3%
5. 3%
6. 4%

jcochran1

There is a lot of content here but I don't remember you ever saying you tried another muffler. Did you ever rule that out?

I chimed in earlier stating that I had the same noise your car had in the original video. Last month I swapped to FD Stage III's and I cannot hear that same noise anymore. It is very possible it is being drowned out by the much louder mufflers but even at idle, when I'm looking for the noise, I can't find it. I don't want to state the muffler was my problem but I am curious if you've tried the same with a stock replacement muffler.

Vorsicht

Not sure where you are but if you are in the Bay Area you are welcome to borrow my mufflers and cat. They are currently off the car for a rebuild. Don't know if my mufflers would fit (95 C2).

BesideTheBox

Yeah. Lots of content.
Congrats on the new stage III's. I think from what I've read about them, there is a lot more 'burble' at idle, so I'm pretty sure this would go a long way toward masking the noise.
A while back, I talked with Darin at FD. He offered a set of mufflers to try if I was interested in paying the shipping. Generous offer! I did not do this because I'm pretty sure that the source of the noise is not the muffler. I believe the source of the noise is due to misfires.

Peter, thank you for the generous offer. I'm in MN and would love a cross country trip. It would be so cool to see how you are coming on your engine rebuild.

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Here's why I don't think the noise is coming from the muffler:

When I switch on the AC, the noise is nearly eliminated. I wondered if this was due to additional noise due to the increased idle or the increased idle itself.

So I disconnected the idle stabilization valve. This raises the idle (much more than switching on the AC), but does not reduce the misfiring noise whatsoever.

I suspect that the increased electrical load from the compressor does something to improve the idling conditions.

Another item to support the electrical load theory is that when I switch on the headlights, the noise is nearly eliminated, just like turning on the AC.

This needs further investigation to figure out why this might be and what is really going on here.

JasonAndreas

The ECU adjusts the ignition timing slightly when the compressor is activated.

BesideTheBox

Okay, slight timing advance w/ A/C results in a higher idle.
The misfiring also goes away when I switch on the headlights.
Does the DME do anything when the headlights are switched on?
I'm guessing not, but I'm hoping to get some confirmation.