Compression Testing Advice - Alfa Romeo Bulletin Board & Forums
 
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post #1 of 7 (permalink) Old 04-04-2005, 12:47 PM Thread Starter
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Compression Testing Advice

Are there any tricks to preforming a compression test and/or anything I should avoid?

RBK - '87 Spider
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post #2 of 7 (permalink) Old 04-04-2005, 09:19 PM
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Remove all sparkplugs, install tester and hold throttle open to get air supply to cylinders as you crank engine over as few times to get highest reading.

Good engine will have all readings within 10% of each other.

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Last edited by Alfisto Steve; 04-04-2005 at 10:24 PM.
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post #3 of 7 (permalink) Old 04-04-2005, 10:10 PM
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Also a good idea to warm up the engine first. Look for at least 150 psig for a some what healthy engine, around 175 is good.

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post #4 of 7 (permalink) Old 04-11-2005, 04:45 PM Thread Starter
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So being new to the world of auto mechanics – I’ve ventured into trying to run what should be a pretty simply diagnostic compression test.

I warmed the car up, started with a dry test. I removed the distributor wires from the spark plugs and from the distributor to the starter.

I started with cylinder #4 (maybe I should have started with #1? – but I didn’t), screwed the compression tester in and turned the key (in writting this post, and re-reading Steve's advice I see I didn't hold the throttle open). I got a very low reading of ± 63. Scratched my head and tried the next one.

Then removed the spark plug from cylinder #3, screwed in the compression tester and got a reading of ± 76.

Then removed the spark plug from cylinder #2, screwed in the compression tester and got a reading of zero. I tried it again, zero. I checked to be sure the device was properly screwed in, and the quick connect was seated. All ok, tried it a third time – again zero.

Decided to try cylinder #1, got a reading of zero. This time called my wife to turn the key, so I could watch the gauge and the gauge was going up put then moving back down to zero.

Do I have a problem with the gauge (which I borrowed from a co-worker) or is it just me?

Thanks for any advice and/or input.

RBK

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post #5 of 7 (permalink) Old 04-11-2005, 06:21 PM
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Gauge hose end should have a floating needle like valve core in it to trap pressure or else it will go to 0 as you saw. It also should have a bled button on it to release trapped pressure. One of those two must be sticking open or bad.

Also to run a good test remove all plugs first and hold throttle open. Also disable ignition spark if you can.

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[U] BB1 1991 164L w/S engine and A/T now excess to inventory [U]

Daily driver and parts hauler but not car hauler 2004 Jeep Grand Cherokee Overland 4.7L H.O. V-8

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post #6 of 7 (permalink) Old 04-20-2005, 07:09 AM Thread Starter
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Test Results

I've purchased my own compression tester and re-ran the test last night, using the advice from multiple threads. I beleive the results are pretty good (if it matters I do have webers), but would welcome any feedback:

Cylinder dry/wet
1 - 155/172
2 - 162/180
3 - 168/180
4 - 170/180


Thanks,
RBK

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post #7 of 7 (permalink) Old 04-20-2005, 07:32 AM
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RBK: I guess the numbers look pretty good for the 4 cylinders (What is the compression ratio for these engine?). The V6 (which I'm more familiar with) should get higher numbers because of higher compression ratio.

One more thing (for others who are new to this), I suggest disabling the fuel supply before doing the compression test especially for fuel injected cars. I usually just pull the fuel pump relay.

To disable ignition, one can also pull the center distributor wire or pull the Motronic relay.

Bob
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