compression test results

[aston]

Motor is Golen stroker, running great until saturday.

Backfire, no power, backfire, running barely, backfire, running on 3 maybe 2, backfire....dead.

WTF!

I did a compression test today, cold (duh)

#1 175
#2 175
#3 125
#4 175
#5 135
#6 170

#2 and 4 came up to pressure after 2 or 3 compression strokes. 1 and 6 took a lot longer crank, crank, crank.

I added a squirt of oil to #3 and 5. #3 hit 150 and #5 hit 160 but again lots of cranking was required.

I'll prob take the head off at the weekend and have a look see.

Any ideas or insight???

Oh yeah the plugs. All with light black carbon deposits. None were burnt out or totally shagged. Gap had opened somewhat. They obviously needed changing but nothing to get too excited about.

[Russ Chung]

Chris,

I don't think you need to pull the head yet. With those compression readings, the problem is probably not due to the rings or valves; the engine might run rough, but it should run. The "light, black carbon deposits" on the plugs together with the misfiring might be an indication of a plugged catalytic converter. Shake your cat and listen for a rattle that might indicate that the grids are coming apart. IIRC, you had some problems with the fuel mixture after you stroked the engine. I don't recall what you did to fix that problem but you might check the settings or mods that you made at that time to make sure that they haven't changed.

[aw12345]

For a compression test to make sense you would use the same amount of puffs/ compression strokes for each cylinder or the comparison is useless. hit every cykinder 3 or 5 times as long as its the same amount. Then for more in depth analysis go buy a cylinder leak tester from harbor freight is a great tool will help you determine where the compression bleeds of to

[aston]

Chris,

I don't think you need to pull the head yet. With those compression readings, the problem is probably not due to the rings or valves; the engine might run rough, but it should run. The "light, black carbon deposits" on the plugs together with the misfiring might be an indication of a plugged catalytic converter. Shake your cat and listen for a rattle that might indicate that the grids are coming apart. IIRC, you had some problems with the fuel mixture after you stroked the engine. I don't recall what you did to fix that problem but you might check the settings or mods that you made at that time to make sure that they haven't changed.

Good memory Russ

I did have probs with detonation. I installed an APEXi piggy-back computer and programmed it with a wide band O2 sensor. Once the bugs were sorted it worked great. It was the first thing I checked on the side of the road and it appeared to be doing its thing.

The carbon on the plugs indicates that I am erring on the side of rich, which given the detonation issue, is prob a good thing. Also they are all identical which indicates that all cyls are working about the same.

I was hoping for more conclusive compression test results: is it related to the combustion chamber, or not.

I will recheck the ignition components more carefully now I am in the garage.

BTW fuel pressure is solid.

[aston]

For a compression test to make sense you would use the same amount of puffs/ compression strokes for each cylinder or the comparison is useless. hit every cykinder 3 or 5 times as long as its the same amount. Then for more in depth analysis go buy a cylinder leak tester from harbor freight is a great tool will help you determine where the compression bleeds of to

Good point. I will repeat the test with the exact same method for each cylinder.

[aston]

OK so i looked a little harder and found a broken rotor arm. It was just flapping around and firing at random.

So prob solved, almost.....

I now runs, but it runs rough.

I repeated the compression test with a nice warm motor and counted exactly 3 compression strokes per cylinder, here's the numbers

165, 175, 170, 170, 175, 170 - just about perfect, right.

So what's next?

I am suspicious of the cat. When I had it installed the kids at the shop said, nice muffler shame about the cat, pos etc....

Also there is now a leak somewhere in the front pipe/cat area. Also the front pipe is being mashed by the DS (don't ask). So maybe it's time for a zorst rebuild.

[aw12345]

There is a whole host of things that can cause it to run rough. The compression readings look sound so that is good start with a thorough check of the ignition system, plugs wires, from there check engine vacuum at idle also when you snap the throttle does the vacuum drop instantly? Before changing exhaust components check exhaust backpressure should be no more than 3-5 psi under any driving condition. A partially clogged injector can cause grief also. But since it came on all of a sudden start with the ignition