compression test help

tphaeng · 04-19-2019, 06:54 PM

I'm about to purchase a n54 135i. I asked the owner if he could do a compression test since the car is heavily modded. The tester that was used for a harbor freight one.
All cylinders ranged from 95-105.

Is this a low reading?

Maybe it's the tester?

The seller says he's used the tester on 3 cars before and it always reads low. highest he ever got it was 110.
Looking for some insight.

thanks!

Mybimmer · 04-20-2019, 02:19 AM

Yes the readings are low however, could be the cheap gauge. More importantly though each cylinder should be very close in readings. The test should have been done with the engine warm, all plugs out and throttle held wide open during each cylinder test. Note disconnect all fuel injectors while doing the test. A quality tester is recommended. Go back with this info and a quality comp tester.

04-19-2019, 06:54 PM	#1
tphaeng Captain 82 Rep 966 Posts Drives: derrrty Join Date: Sep 2010 Location: Florida iTrader: (5)	compression test help I'm about to purchase a n54 135i. I asked the owner if he could do a compression test since the car is heavily modded. The tester that was used for a harbor freight one. All cylinders ranged from 95-105. Is this a low reading? Maybe it's the tester? The seller says he's used the tester on 3 cars before and it always reads low. highest he ever got it was 110. Looking for some insight. thanks!
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04-20-2019, 02:19 AM	#2
Mybimmer Private 20 Rep 85 Posts Drives: F20 118d & E82 135i Join Date: Oct 2015 Location: Emerald VIC, Australia iTrader: (0)	Yes the readings are low however, could be the cheap gauge. More importantly though each cylinder should be very close in readings. The test should have been done with the engine warm, all plugs out and throttle held wide open during each cylinder test. Note disconnect all fuel injectors while doing the test. A quality tester is recommended. Go back with this info and a quality comp tester.
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