Low compression or bad testing setup!!???!! Yikes!
#1
Low compression or bad testing setup!!???!! Yikes!
I have an '05 R53 with 160,000 miles on it. I'm pretty sure I need to put a new timing chain on it, But before I go through all that work I thought I'd do a compression test on it to make sure I wasn't wasting money on a shot engine. I borrowed a compression tester from Napa and my readings were alarmingly low.
#1 - 85psi
#2 - 80psi
#3 - 75psi
#4 - 72psi
Notes: I did it with a battery charger on to keep it charged. I left the other three spark plugs in. And I cranked it until the readings wouldn't go any higher which was about 20 seconds of cranking.
QUESTION: If that's as bad as seems, I'm a little surprised that they are as even across the board as they are. I read elsewhere on this forum that the length of the compression hose might effect the readings. One guy had a reading of 90psi and then shortened the hose and got a reading of 160 on the same cylinder. I can't really shorten the hose because the tester is a loaner from NAPA.
Is my engine really junk or is my testing bad. Before the timing chain problem it ran great, started fine, and had lots of power. It did consume a fair amount of oil, but a lot of that is leaking from the valve cover or somewhere else because the bottom is an oily mess. I don't want to throw the car away, but I also don't want to waste my time on replacing the timing chain if the motor is really junk. Any solid advice is appreciated.
Thanks!!
#1 - 85psi
#2 - 80psi
#3 - 75psi
#4 - 72psi
Notes: I did it with a battery charger on to keep it charged. I left the other three spark plugs in. And I cranked it until the readings wouldn't go any higher which was about 20 seconds of cranking.
QUESTION: If that's as bad as seems, I'm a little surprised that they are as even across the board as they are. I read elsewhere on this forum that the length of the compression hose might effect the readings. One guy had a reading of 90psi and then shortened the hose and got a reading of 160 on the same cylinder. I can't really shorten the hose because the tester is a loaner from NAPA.
Is my engine really junk or is my testing bad. Before the timing chain problem it ran great, started fine, and had lots of power. It did consume a fair amount of oil, but a lot of that is leaking from the valve cover or somewhere else because the bottom is an oily mess. I don't want to throw the car away, but I also don't want to waste my time on replacing the timing chain if the motor is really junk. Any solid advice is appreciated.
Thanks!!
#4
I tried with all of the spark plugs out and it cranked noticeably SLOWER (which I had read somewhere) but my readings were about 15psi higher with the other plugs out. I'm guessing the loaner compression tester from NAPA is an inexpensive one. The rubber hose feels soft and flexible to the touch. I wonder how much that is affecting my readings.
#6
#7
I hope you disconnected the fuel pump fuse, as you'd be fuel washing the cylinders! Also, you need to have the throttle WOT so that you can get the highest numbers. Usually the actual numbers aren't as important as the difference in PSI between cylinders. You can throw a oil cap of oil down each cylinder to see if the numbers go up greatly as well. Definitely check the voltage of the battery, as that could influence the numbers you get as well.
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#8
If you get inconsistent values on all tests, it may indicate a worn valve timing chain, affecting all cylinders, but I'm not certain how modern variable-valve-timing mechanisms influence this. Others may know.
#9
#10
Neither gas nor WOT will make a massive difference to the results - but all the readings will be lower so it's harder to tell where the differences are. It's just the 'best' way to do it.
Don't jam the throttle open at the engine end - it's a drive-by-wire system & the synchronisation will get messed up - put a brick on the gas pedal.
For test 2, inject the oil one cylinder at a time - put a rag over the cylinders after you test them - the oil may spray out of those.
I've revised the attachment a little bit.
Don't jam the throttle open at the engine end - it's a drive-by-wire system & the synchronisation will get messed up - put a brick on the gas pedal.
For test 2, inject the oil one cylinder at a time - put a rag over the cylinders after you test them - the oil may spray out of those.
I've revised the attachment a little bit.
#11
Ok. Thanks for the advice. I'm going to replace the timing chain and then re-test the compression and see how it looks. How badly do the timing chain sprockets wear. I see kits that just replace the chain and guides and use the original sprockets. Is that ok to do? That bottom sprocket seems like it can be a nightmare to get off and on again. I'd love to not have to replace it.
#12
#14
quick update in case you are wondering. I replaced the timing chain and tensioner, but not the sprockets. The lower cast aluminum flange right below the bottom sprocket, which seems like it could be intended to hold the chain on the sprocket or at least prevent it from skipping teeth, was broken off. So I changed the oil and cleaned everything back up. It started up nicely and runs nicely. So I checked the compression again with a tester from Napa with the same dismal results of 70-90psi...very disappointing! Then I decided to try a tester from Orielly's to eliminate that I happened to have a broken tester...and my results were between 150-160 across all four cylinders!!! Yay.
Tomorrow I"m going return the tester to Napa and let them know it's a broken piece of junk. :(
Tomorrow I"m going return the tester to Napa and let them know it's a broken piece of junk. :(
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