Spark Plug Question

[sscates]

Here's the background on this. This car has a known leak down on the #3 Cylinder of 30%. Don't know why. I have heard everything from broken ring, stuck ring, worn valvle guides, etc. I just purchased this car, so the history is unknown. This first pic is of the #3 cylinder. The second is similar to all of the other plugs, where leak down is 15-18%. What is the lighter color on the first plug? I assume the other plug looks pretty good. This engine is running CIS without the lambda unit and relay (on it's way from a fellow Pelican) and crankfire ignition. Your opinions on the high leak down and plug coloration are appreciated.

[Steve@Rennsport]

Hi:

Two comments for you:

1) Leakdown testing is an effective diagnostic tool only when performed properly and the results noted at that time. Raw figures without context are somewhat useless and negate the reason for performing the tests in the first place.
Leakdown testing allows you to not only measure the percentage of compression loss, it affords you the opportunity to locate the SOURCE of the leakage (intake valves, exhaust valves, and rings) so without noting the source of your high rates of leakage, your test results have little value.

My suggestion would be to repeat the leakdown tests and listen at the aircleaner entrance, tailpipe, and oil filler tube to locate the source of your losses.

2) Reading spark plug insulator colors takes a lot of experience and a proper plug cut must be performed for this to be useful. Looking at the plugs after the engine has idled for 10 seconds or more tells you nothing conclusive at all.

Send me an e-mail and I'll return a document on how to do this so the plugs offer an accurate snapshot of the combustion temps and mixture strength.

[sscates]

I agree that the whole motor is tired, based on the other cylinders, but it still makes a lot of power when compared to my Turbo and C2S. I was really surprised at the amount of torque it has. Anyway, Steve, I sent you an email for more advice. I also thought the motor was toast when I bought this, but everyone keeps telling me that there is still lots of life left in it, based on it's performance. Knowing all of that I have budgeted a rebuild in the next 12 months.