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BMW 3-Series (E90 E92) Forum
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N54 Compression Test Procedure
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04-18-2024, 01:56 PM | #1 |
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Hi everyone I went ahead and a did a compression test today, just to check on the motor and get a baseline compression for the future.
Results were cyl 6 175 Cyl 5 170 Cyl 4 178 Cyl 3 170 Cyl 2 170 Cyl 1 177 So I'm pretty happy lol Figured I'd leave a little write up. !!!!! Before starting take your car around the block to get oil circulated. !!!! First step is to pull the fuel pump fuse, whenever I'm unplugging or messing with electronics I like to have the battery disconnected. The fuse box is in the glove box behind a little cover. E9x fuse boxes changed in 09/07 so if yours was produced before that find a diagram that labels the fuel pump fuse. If your like me and have a prod date after 09/07 it's fuse number 70, it's a yellow 20 amp. You'll need a fuse puller as there no way in hell to get your fingers around it. I had to dremmel mine down a bit as it was to wide. Once the fuse is pulled reconnect your battery and start the car, it should die out. Keep starting it until u can crank it without it starting for more than 1/4 second. For me it took 6-7 starts. Once the fuel line is drained re disconnect your battery. Now your ready to pull your plugs out. If you still have the factory cowl you'll need to remove it. Mines been modified so I can help you there. There's plenty of tutorials on that part however. Unplug and pull the coil packs off then remove all 6 spark plugs. After plugs are pulled recconect battery. For future reference when you put them back the torque spec is 17 ftlbs. Your ready to start the actual test now. I used this compression tester from harbor freight. https://www.harborfreight.com/deluxe...ece-64917.html It comes with a 12mm adapter however it was to big to fit down the sparkplug whole so you will need this adapter as well https://www.jbtools.com/lisle-20540-...8aAtDqEALw_wcB Grab some Teflon tape and put the adapter on the compression tester. Tighten the hell out of it, I didn't and when I went to unscrew it from the motor the adapter stayed in the head and I didn't have a socket that fit on it. Ended up putting super glue on the compression tester to get it out. Screw compression tester into spark plug hole and have a friend crank the motor until the needle stops moving I started at cylinder 6 or the back of the motor as it's hardest to reach. Record the results and move on to the next cylinder. The actual number doesn't really matter as every compression tester will read different. I've seen as much as 20 psi differance between testers. Your more so looking for all cylinders to be close to eachother. I've always heard no more than 15% variance between cylinders. Hopefully your results are good. Now re disconnect the battery and install your plugs and put the fuse for the fuel pump back. Start your car and let it idle for a little to clear the fuel lines of air bubbles. Good luck!! |
04-19-2024, 06:54 AM | #2 |
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2062
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Good write-up
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2007 335i, BMS DCI, BMS Chargepipe w/Tial BOV, ARM Catless Downpipes, silicone inlets, Bilstein B12 Prokit Suspension, Whiteline subframe bushings, Front/Rear M3 control arms, G-Plus FMIC, Stage 2 LPFP, Custom E40 tune by Justin (V8Bait), xHP stage 3 transmission flash, RB Two Turbos....10.90 @ 128mph
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04-21-2024, 01:56 AM | #3 |
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08-03-2024, 01:21 AM | #5 |
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thanks for awesome instructions for n54 compression testing, saved myself $500 for doing it myself
Used https://www.amazon.com/dp/B000EVU89I (includes the 12mm adapter) and on my 112K miles warm n54: 1: 180 2: 175 3,4: 170-175, changing at every stroke between 170 and 175 5,6: 175 |
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