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Old 11-15-2021, 02:08 AM   #1
lanxer57
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Wrench specifics on compression testing, P0301

I did a compression test, the engine was cold, I tested for 10 "cranking noises" the results:
1;90, 2;110-145, 3;121, 4;130
added some oil:
1;100-145-123, 2;110-145, 3;110, 4;145-120
because I was not sure if this was correct (given the inconsistant results, and how far off they were from 180), I cranked it until it stopped on its own 10 times (usually 4-5 "noises"). this was with oil in the cylinders the results:
1;175, 2;189, 3;170-180, 4;180

How EXACTLY would I get the most accurate readings possible on a compression test? A thread posted in 2003 (that is 1 month older than I am) by canada-eh said it was best to "crank the engine over 10 times", what EXACTLY does that feel/sound like? The sounds that cranking an engine makes are divided into pulses, how many of these "pulses" counts as cranking the engine over 1 time?
I would like to do it correctly next time.

This is on a 1999 SC1 with the SOCH engine, nearly 170000 miles.
I can not drive it until it passes emissions, and it will not pass with a "service engine" light. I have gotten a code P0301 for a missfire in cylinder 1, as well as the "service" light with the wrench. The light usually comes on after a few seconds (although sometimes it does not come on until the engine is shut off and restarted), but my OBD2 scanner usually takes a very long time to detect the error code. I have tried changing the spark plugs/wires, ignition coil packs with the plate they attach to (could not figure out how to separate them), fuel injectors, ECTS (with coolant), idle air control, EGR valve, (and cleaned as much out of the holes as I could), and MAP sensor. I also sprayed carburator cleaner around the intake manifold, it did not run any different. Dad said it smells like it is running rich (my nose does not work) Any other ideas? (do not be afraid to tell me it needs an engine, I have a 2001 SOCH with the transmission sitting on a pallet in the garage)
...
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2001 SC1 2020-2021(wrecked, frame was bent)
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Old 11-15-2021, 10:11 AM   #2
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Default Re: specifics on compression testing, P0301

Did you hold the throttle wide-open while doing these crankings?

Run it for a bit, then take compression again; and be sure the battery is good enough that voltage doesn't drop below 11V while cranking. This time, don't do any of that "adding oil" routine. That is only confusing things. Yes, adding oil can help determine if the rings/bores are worn, but that is rarely the case with these engines because of their oil burning issues. And, if you add too much oil, compression will get falsely raised, possibly even to the point of locking the engine rom turning!

PS: Five compression strokes is enough to get full compression on a good cylinder...
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Old 11-15-2021, 10:52 AM   #3
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Default Re: specifics on compression testing, P0301

See post 2 in these threads

http://www.saturnfans.com/forums/sho...d.php?t=200832

http://www.saturnfans.com/forums/sho...d.php?t=236763

edit: I read your post again, missed this question

Quote:
what EXACTLY does that feel/sound like? The sounds that cranking an engine makes are divided into pulses, how many of these "pulses" counts as cranking the engine over 1 time?
Hard to describe a sound with words, lol. Needle will jump on the compression gauge on a complete cycle. Another thing you could try, take a video with sound for what you think are 10 cycles. Post a link to it, and we can listen / count and tell you what we are hearing.
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Old 11-15-2021, 01:58 PM   #4
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Default Re: specifics on compression testing, P0301

Your compression numbers, are WAY low...

Regardless if you do a wet or dry compression test... your numbers across all 4 cylinders should read at least 185 or better.

The standard PSI rating across all 3 cylinders for the majority of the S-Series run; was 185 on each cylinder.

As you may know- these engines were known for oil burning... and the only way to really do *Some* kind of fix for oil burning, is to drill small holes in the pistons to allow for some kind of oil draining.

I think you may be chasing your tail on this one; as much as I hate to say that... nothing that you are going to do outside of the engine, is going to bring those compression numbers to a decent working number.
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Old 11-15-2021, 03:08 PM   #5
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Default Re: specifics on compression testing, P0301

Yes, I had the pedal all the way to the floor.
I do not know if the results for my compression test were accurate, because they are not very consistant, and I may have been doing it wrong.
I will record a video later today, and maybe edit numbers counting the "pulses" of noise that I am discribing.
If the engine is bad, I have another one that was not misfiring after 181,000 miles (at least, before I crashed the car I pulled it out of).
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Old 11-15-2021, 04:32 PM   #6
lanxer57
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Default Re: specifics on compression testing, P0301

If 10 compression cycles is minimum, how would I count the number of compression cycles?
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