Compression Test w-w/o throttle

[NCTerp]

I have recently purchased a '91 325ix (211k miles). Trying to establish baseline engine health. Did comp test- I forgot to hold the throttle wide open as is suggested in the Bentley manual and the "101 Performance Projects..." Book.

Other than that I tested as per page 30 of the "101 ..." Book. Specifically, loosen plugs with engine cold, then tighten lightly. Warm up car, wait 5-10 min. Remove DME relay, remove fuel pump fuse. Test compression.

Results- 95 degree air temp, 400ft above sea level if it matters.

1: 135
2: 132
3: 135
4: 138
5: 135
6: 135

What can be gleaned from these readings? And, how would it be different if I held the throttle open. And lastly, should I do it over with WOT, and then add a tablespoon of oil and repeat?

[ak-]

They're all within a tiny percentage of one another so I'd assume you've got a healthy motor and not worry.

[nando]

they might be a little higher with the throttle open since more air would get in, but more importantly as AK said they're all pretty close relative to one another.

[TobyB]

Thirded- we have a big enough plenum AND the IAC stays open when cranking-
you have a decent motor.

t

[barbierij]

they might be a little higher with the throttle open since more air would get in, but more importantly as AK said they're all pretty close relative to one another.

Throttle open is a necessity. You want as much air as possible to enter the cylinders. A closed throttle could give wrong results because a closed throttle 'could' act as a closed valve. A vacuum test at idle and a cylinder leak-down test will help you determine the engine's health. Did you do a compression test cold, warm, and then test with a bit of oil in the cylinders?

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[TobyB]

I've routinely forgotten to open the throttle, even on the 2002 with sidedrafts, and the
biggest difference I notice is that it takes a few more cranks to build to about the same number....

t

[NCTerp]

Throttle open is a necessity. You want as much air as possible to enter the cylinders. A closed throttle could give wrong results because a closed throttle 'could' act as a closed valve. A vacuum test at idle and a cylinder leak-down test will help you determine the engine's health. Did you do a compression test cold, warm, and then test with a bit of oil in the cylinders?

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I only tested warm.

[TobyB]

You are good to go, at least as far as the mechanicals of the engine...

t