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No matter what --- the flashing light is telling you that you are killing your cat.

I've always said that just a flashing light without a small hammer that comes out of the headrest to really get the attention of the driver, is a waste of a good light bulb.
 

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Does the smoke linger or disappear quic6? (*quick)

Smell it ... is it sweet or sharp enough to water your eyes or smells like hot coolant?
 

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Fix this NOW. MAYBE you can still save the catalyst. Maybe. (Probably not, given the amount of time the misfire has been going on. Might as well budget for catalyst replacement, and then hope for the best.)


That sounds expensive.

Next step is to do a cylinder leakdown test. Find out where the compression is going. If you hear air escaping out the throttle body, the intake valve doesn't seal. If you hear air escaping out the tailpipe, the exhaust valve isn't sealing. Either way, you're likely pulling the cylinder heads for a "valve job".

If you see air bubbles in the coolant, you've got a cracked casting, or perhaps a failed head gasket. Again, the head(s) are coming off.

You're going to hear air escaping at the oil fill (remove the cap), the question is "how much", which is why you need the leakdown tester--so you can use the pressure gauge(s) to determine acceptable leakage from excessive leakage.

When it was my money, I bought a leakdown tester intended for Continental/Teledyne aircraft-engine use. The important parts are the orifice size (.040, for engines with a bore size of 5" or less, tapered inlet) and the Master Orifice which allows you to "test the tester". Without the Master Orifice, you need to use the tester on several "Known-Good" cylinders having the same bore size as the engine you're trying to diagnose. At minimum, you'd need to test the other seven cylinders that aren't giving you trouble, and compare the results to the reading from the Problem Child.

I think it's really "swept volume" of the cylinders that are the testing criteria, since one engine with a 5" bore and a 3/4" stroke is gonna be miles different from an engine with a 5" bore and a 10" stroke.
 

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I have by now seen not just a few 4.2s with followers that have jumped off the camshaft and cease to motivate their intended valve ... hence: loss of compression.

Oops! You've got a 5.3 --- nevermind
 

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Nope.

The leakage is past the rings. Bore diameter has a major impact on ring circumference, and ring end-gap, both of which have an effect on leakage. Big bore = tendency towards more leakage. Smaller bore = tendency for less leakage.

The cylinder length/stroke length is of no importance for leakdown testing, since the piston is held at TDC or very close. Which works out well, as "most" cylinders have the most wear at the top, so not only are you testing ring leakage, but you're testing it in the part of the bore that's most-likely to be worn, and within a few crankshaft degrees of maximum cylinder pressure when the engine runs. Some folks do the leakdown testing at about 7--10 degrees past TDC, but I don't bother.

So--for engines with a bore diameter of less than 5", a .040 orifice in the leakdown tester is correct.
You're doing a static blowdown? That's so 1960-ish.

The Snap-on dynamic version can use cranking or running blowdown tests that are pressure wave readings through the sparkplug hole to plot air bypassing the rings in an either high or low value, plotted by a piezoelectric sensor.

Mucho more accurate because it is dynamic, mimicking actual operation conditions and not in just one place (tdc).

Rings that are worn can show a false disadvantage at tdc where the bore, coupled with ring land wear might show high losses, but at lower than tdc position, the rings become moved closer into the piston land bottoms --- and out of the land bellmouth --- and they will be more than adequate in holding compression pretty much in any place out of tdc anyway.

Low pressure static testing doesn't mimic any actual operating condition in an internal combustion engine and I've had rings with less than 1000 miles on them test as bad ... so I quit using the test you recommend as grossly inaccurate and drawing to absurd convictions when it was used by me.

Power contribution values should all be within 10% of each other per cylinder for a good running engine that is nearing its prime-of-life downcurve.



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Really when it comes down to what component is leaking, it becomes moot in a production shop because if its rings, a hole in a piston, a bent or bad valve or a blown head gasket... it's surgery time anyway.

Over diagnosing an engine against a slam-dunk loss of compression is great in academic theaters, but of little practical value in the field.

I've had scrolling compression testers, aneroid and mercury column styles, but unless I'm trying to sell a job, they're time consuming and damnably expensive up front.

The Snap-on dynamic tester is in my shop ... somewhere .... it was for me when I owned 1/2 interest in a Citabria and considered getting an A&P ... and I used it a few dozen times automotive-ly, but not once more in over 40 years now.

But I just use a blower nozzle in the spark plug hole and I know it's going to come out somewhere ... exhaust, intake or oil filler and possibly the dipstick. If I can catch the cylinder at TDC ... I can usually get some blowby at very low air pressure on most any engines because of the cylinder taper or ring gap ... this I tend to ignore because ... again ... it ain't dynamic.

If the leak is very subtle ... I've always got my Steelman Electric Ears/Stethoscope. If it's MY engine ... I'll play with it for a while ... but low or loss of compression will always start with excision of the valve cover .... and from there it's progressive revelation.

Dig we must!


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I still want to know what it is he's doing.

Is there some sort of a mechanical device or is he forcing oil under very high impact/pressure to free something up or releasing a mechanical lock ... etc?

I see it and don't get it.
 
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