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Showing results for tags 'compression test'.
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Hi everyone! It's been awhile. I'm surprised I remembered my password! A few years ago, I was plagued with a cold idle issue, low manifold vacuum, a lean-mixture issue, all kinds of fun stuff. I learned so much about the EFI, tested my AFM as an issue, replaced it with a new one from Motorsport, and adjusted it to its ideal setting. Though I'm still surprised how big a difference a few teeth make going either direction. This sensitivity might be symptomatic of other deeper issues that I've discovered recently. So I had my car in the shop last week for a brake job. Got new pads, shoes, shims, springs all the way around and when I was getting this done I also asked for a compression test. The results were not good I'm afraid. Cyl 1: 100lb Cyl 2: 105lb Cyl3: 95lb Cyl4: 100lb Cyl5: 90lb Cyl6: 105lb A little history behind the car: The motor has 140k original miles. INo head work, never been rebuilt. I bought the car from a schoolteacher in 1990 when it had around 85k on it. I put the 55k on myself. The car has always been maintained, never raced or abused. I've always changed the oil every 2-3k miles. Faulting the air regulator for the cold idle issue, the car gives about 1k RPM on startup but quickly bogs down to 600 and slowly rises as the engine temp rises. When it's fully warmed up I get a healthy idle as well as a healthy performance though I admit I haven't run it at high RPMs to know for sure. This could be a feeling relative to how bad it is when cold. What I'm wondering now is if the issues I'm having with a cold engine are compression related. When the engine warms up, the piston rings would seal up in the cylinders and presumably give an extra 10+psi or so and I presume this make a noticable difference with the way the car runs, however I also read that motors with compression this low would be hard to start, if they even run at all. Is it even possible to have a motor running this good with compression this bad? My car starts up quickly every time. I'm not completely confident that the low numbers aren't the fault of the mechanic doing the test so that lack of trust has made me want to test the compression again myself. Before I do, I will need a few extra tools. I already have a compression tester I bought from Actron. I am going to get an Actron remote starter and I hope that would be appropriate to the task. For posterity, here is an excellent guide to doing a compression test on AtlanticZ: http://atlanticz.ca/zclub/techtips/compressiontest/index.html But as newbie proof as that might be, I still have a few questions I hope you guys can help me out with. 1. With the plugs removed, do I just leave the spark plug wires dangling? I'd like to leave them plugged into the distributor but if the coil steps up the voltage to whatever the spark plugs need and the plugs aren't there, is there any danger in this? Can this hurt the coil or the distributor? Or me? 2. What is the electric fuel pump going to be doing during this operation? Since the remote starter is going to be cranking the engine, won't there be fuel spraying into the cylinders? I'm guessing if I need about 30-40 seconds of cranking to finish the test in all cylinders, won't the cylinders be flooded with gas? 3. The guide says to hold the throttle linkage open. Does this mean to have someone else hold the linkage to full throttle? Is this necessary or does it just aid with the reliability of the test? Does this keep gasoline from injecting into the cylinders the same way a carbureted car would work? I read another post on here where someone was getting really low compression numbers and when they corrected their stretched timing chain they got 40-50 lbs back. I wish I could say the numbers are tight if low but with cylinder 5, I can't even say that. I'm not sure why all the numbers are divisible by 5. I guess that's as closely as the guy wanted to look at the gauge when he was doing it. 90/105 is still 85.7%, so likely not a "problem" that AtlanticZ referred to. Let's say those low numbers are accurate. How is that possible? The cylinders/rings all wore down that much? That just doesn't seem plausible knowing the history of the motor. I've done everything I can to tune the car up at this point (new plugs, wires, cap, rotor, filters, timing, AFM, connectors cleaned). The only part of the tuneup I haven't done yet is the valve adjustment. I need a few more tools before I do that (a torque wrench and maybe a brass hammer to tap off the cam cover if it's too sticky). My questions above would enlighten me to doing the valve adjustment myself as I presume I can use the remote starter to turn the camshaft. I'm unnerved about this too because I don't know what steps to take to make sure the engine doesn't start when I'm playing with the valvetrain I'm sorry again for being so wordy here. I know I sometimes write disjointedly and my racing thoughts wind up splattered all over the place. Maybe thinking out loud has its merits when things need to get technical hehe. Really, I only need enlightenment on the three questions I numbered above. I hope a few of you can handhold me through my questions even if they're not that good. Per AtlanticZ, to get my results as high as possible, I intend to: Test on a warmed up engine Remove all spark plugs Keep my connection fittings tight Keep throttle open Test cylinder 5 twice if the results are relatively poor for me too, the 2nd time with a squirt of oil in the cylinder Thank you all in advance! FastWoman and Zed Head and others gave me more help than I was worth about a year or two ago. -
My high school auto mechanics is pretty rusty... I have been working on this 8/70 Z that has been sitting since 87. I've gone through all the basics, hoses, belts, gas tank, all fluids, rebuilt the carbs, etc. The last thing I did was rebuild the carbs. The front 3 carbs were getting no gas to the engine - I adjusted the float and then I heard what sounded like a loud exhaust leak somewhere towards the front of the motor. I ended up taking off the intake and exhaust manifolds and was ready to start putting it back together when I thought - wait what if it wasn't an exhaust leak but something worse? So I got a compression tester from Autozone and here are my results: 1-50, 2-60, 3-105, 4-130, 5-55, 6-110 I didn't take all the plugs out (mistake maybe). This is the 2nd gauge I used - the first one showed no compression at all on 3 of them so I figured it had to be bad. I'm pretty sure the gauge is OK. I have no antifreeze in the oil, had no blue smoke when it was running. Is this still a valid test with both manifolds off? I can't think it would be that big of a deal. I'm thinking if the bottom end of the motor was bad, I'd hear different things or see blue smoke. Should I pull the head off and get into that whole bucket of worms or am I getting paranoid? Any words of wisdom for this amateur mechanic would be appreciated...