I'm a newbie and have seated everywhere on how to do a compression test step by step. I have minimal tools right now, and need to get this done. I've searched the threads and have an idea, but if someone can point me in the direction of steps in would really appreciate it. Jake 760 717 5127
76 2f compression test help
- Thread starter BOSOXFJ40
- Start date
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I would bet you have a head gasket leak between cylinder 2 and 3. If two cylinders together have a much lower compression number then the rest it is usually a head gasket leak. The 120 #'s are low but acceptable. Was the engine warmed up and the throttle and choke wide open with all spark plugs removed.
- Thread starter
- #4
2nd test warmed engine
Radiator back. 100, 100, 95, 90, 90, 85. All plugs were in except for the one I was testing. Choke was all the way out. I turned the engine over, checked the gauge and then shut it down and moved to the next one. If I gooned it up let me know and I will do it again.
Radiator back. 100, 100, 95, 90, 90, 85. All plugs were in except for the one I was testing. Choke was all the way out. I turned the engine over, checked the gauge and then shut it down and moved to the next one. If I gooned it up let me know and I will do it again.
Choke should be open along with the throttle so there is no restriction going into the engine. So the choke knob should be pushed all the way in. All the spark plugs should be removed. This allows the starter to crank the engine faster. The engine should not be running while you test it.
Drive it!
One question, though: What prompted you to do the compression test? Is it not running right?
Do not drive it if you get numbers like this
150, 90, 85, 120, 120, 120.
If you have a leak between two cylinders like those numbers would indicate. It could go from needing a new head gasket, a simple and cheap job to needing a new head and engine block. As the cylinders fire, if the head gasket is leaking it can literally start melting the head and block where the leak is, and over time it will go from needing the head and or block milled to a much larger problem. Do a good compression test and if two cylinders are both low and next to each other you will want to replace the head gasket. Other might chime in, I think a leak down test can narrow it down more, but driving it with a leak is bad. Driving it with those number due to warn rings would be ok, but the head gasket leak no.
150, 90, 85, 120, 120, 120.
If you have a leak between two cylinders like those numbers would indicate. It could go from needing a new head gasket, a simple and cheap job to needing a new head and engine block. As the cylinders fire, if the head gasket is leaking it can literally start melting the head and block where the leak is, and over time it will go from needing the head and or block milled to a much larger problem. Do a good compression test and if two cylinders are both low and next to each other you will want to replace the head gasket. Other might chime in, I think a leak down test can narrow it down more, but driving it with a leak is bad. Driving it with those number due to warn rings would be ok, but the head gasket leak no.
- Thread starter
- #10
Final test with all plugs out, WOT - 149, 145, 140, 135, 135. I guess all and all not bad.
I decided to do the test because I did a valve adjustment and with the choke pushed all the way in I'm getting a sluggish response and backfiring at the carb. Runs great with the choke pulled out 1/2 inch and have tons of power. I'm learning the ropes as this is my first FJ. So I guess I'm doing process of elimination, next will be researching how and where to check for vacuum leaks.
Then fixing my bouncing tire carrier that I just welded and finished...... It never ends!
I decided to do the test because I did a valve adjustment and with the choke pushed all the way in I'm getting a sluggish response and backfiring at the carb. Runs great with the choke pulled out 1/2 inch and have tons of power. I'm learning the ropes as this is my first FJ. So I guess I'm doing process of elimination, next will be researching how and where to check for vacuum leaks.
Then fixing my bouncing tire carrier that I just welded and finished...... It never ends!
Definitely sounds like a vacuum leak. Grab a can of carb cleaner, and while running, start spraying around the intake manifold where it bolts to the head. if the idle changes, you have a vacuum leak there. The manifolds on these things are prone to warping. Also look for cracked vacuum hoses and damaged vacuum operated emissions gear. Could also be a bad brake booster.
My bad, I missed post #6. Those numbers look good and nothing to worry about. Drive it. Follow the direction and look for a vacuum leak, doing the valve job could have knocked off a vacuum line for cracked one. I would also double check your valve adjustments. You did do it while engine was hot correct.
Check the timing as well while in there
>>WOT - 149, 145, 140, 135, 135.
This is only 5 cylinders, right?
This is only 5 cylinders, right?
