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Final Results (vehicle at operating temp):
Compression (in psi), Dry Test
Cyl 1: 204
Cyl 2: 202
Cyl 3: 212
Cyl 4: 215Compression (in psi), Wet Test
Cyl 1: 211
Cyl 2: 217
Cyl 3: 224
Cyl 4: 234 (full 3 squirts)Did verify, visually, that all cylinders contained oil but control of volume difficult.
Your low and high readings are pretty far apart on the wet test. 23psi to be exact. That seems significant to me. Looks like you have some compression loss that may be causing issues for you.
So then a leak-down test at cylinder 1 may be needed? I will have to have that done at my local shop as I don’t have shop air available.
I also want to run an exhaust restriction test (for learning purposes, mostly) but my exhaust system is in bad shape (a couple leaks-at cat flange and muffler has a large hole in it). Will this skew my results in any way? Should I wait on this restriction test?
Unless there’s some issue with oil consumption I wouldn’t worry one second about those readings, dry or wet. You’re in new car territory with those readings. 🙂
[quote=”EricTheCarGuy” post=93814]Your low and high readings are pretty far apart on the wet test. 23psi to be exact. That seems significant to me. Looks like you have some compression loss that may be causing issues for you.[/quote]
May I bend your ear just a little bit more on this topic (as I am trying to understand)? Thanks 🙂
Wet Test
10.4% difference: High (cylinder 4 @ 234 psi) vs low (cylinder 1 @ 211 psi), according to my calculations.Spec: Standard 190 psi (minimum), Service Limit 180 psi (minimum)
Is 10% enough to indicate an engine-mechanical issue?
The following information is one of the reasons I am embarking on this journey: I have a rhythmic machine gun sound in the exhaust at idle (most pronounced at 2200 rpm, and a little at 900 rpm) which might indicate a misfire (but no codes). I also do have a little evidence of white residue on the plugs (NGK-non-iridium, that I just installed last month) which was not present on the old plugs (NGK Iridium, brown-tan residue, no white). White residue would indicate oil burn, which could indicate worn piston rings…which is why a leak down test was recommended (I would happily be running a leak down test myself if I had shop air 🙂 )
Couldn’t I test whether this vehicle is burning oil by running an exhaust restriction test (assuming it has been burning oil for a while. I wanted to run it anyway as a learning project)? If it has been burning oil a while (don’t know if 30 days is enough to cause that much build-up), the exhaust system will clog with carbon causing the car not to “breathe” properly. I have seen this condition before (in my 2001 Saturn SC2-departed).
I have another issue: when I shut the car down, the tachometer moves from idle (900 rpm) to 0 very slowly. I noticed this happening after I replaced the O2 sensor (at the same time that I changed out the plugs and wires last month). What could this be? Could it be related to the compression issue I seem to be having or could it be related to an exhaust system that can’t breathe properly? Or could it be something totally unrelated?
I guess what I am trying to say is this car has several issues and I am trying to decide which to address at this point. With all these issues (which may or may not be related), I am not sure where to go from here…
Whew! Thanks for reading and responding. I appreciate all your guidance with this 🙂
[quote=”Bluesnut” post=93839]Unless there’s some issue with oil consumption I wouldn’t worry one second about those readings, dry or wet. You’re in new car territory with those readings. :-)[/quote]
I wish! This car has 188,000 mi on it 🙂
It is having a slight oil burn issue (white residue on plugs) that seems to have come about within the last month. 🙁
The residue on the plugs sounds like you’re burring oil. Your compression numbers also indicate this possibility. An exhaust restriction test really won’t tell you much in my opinion. Not as far as oil consumption is concerned anyway. If the plugs have evidence of oil consumption and you have low compression, that’s enough for me. As for the percentage of difference, you’re right on the border. If you have uneven compression in the engine, it won’t be able to run smooth. It can also sometimes cause misfires. It also sounds like you have some electrical issues. Hard to say what exactly though. That said, with a vehicle that has multiple problems, you really have to decide on what’s important and work toward repairing those issues, or get rid of the vehicle and find a new one with all new problems.
[quote=”EricTheCarGuy” post=93888]The residue on the plugs sounds like you’re burring oil. Your compression numbers also indicate this possibility. An exhaust restriction test really won’t tell you much in my opinion. Not as far as oil consumption is concerned anyway. If the plugs have evidence of oil consumption and you have low compression, that’s enough for me. As for the percentage of difference, you’re right on the border. If you have uneven compression in the engine, it won’t be able to run smooth. It can also sometimes cause misfires. It also sounds like you have some electrical issues. Hard to say what exactly though. That said, with a vehicle that has multiple problems, you really have to decide on what’s important and work toward repairing those issues, or get rid of the vehicle and find a new one with all new problems.[/quote]
Ok, I understand now. I think my confusion was due to the number of 30% difference being thrown out there as the cut-off but I got it now.
I think I will focus on the compression issue. I’ll try to find someone with an air compressor and then modify my compression tester to just run shop air through and listen at the various areas paying close attention to the crank case.
Thanks, Eric for all your guidance.
PS you ever consider starting a Tech School?
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