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Old 11-12-2016, 06:37 AM
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Compression check for 79 Jeep 304v8

Will anyone please look at this photo I have attached to this post and give an opinion on the results of a compression check I performed on my amc 304 v8 engine? It starts and runs fine but smokes when idling and consumes oil. I am hoping to get some good advice on how far to go with repairs that I will do myself. I would appreciate any comments.

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Old 11-12-2016, 06:39 AM
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Re: Compression check for 79 Jeep 304v8

The numbers in photo are as follows:
Top = Dry test
Mid = Wet test
Bott = Difference
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Old 11-16-2016, 10:17 AM
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Re: Compression check for 79 Jeep 304v8

Not familiar with your engine, but the compression values don´t seem to far of. They normally state to have a max of 20 psi of difference between the highest and the lowest, which passed it a bit.
Smoke while idling (high inlet vacuum) and many times a puff of smoke while driving away, is normally caused by worn valve stem seals. Due to the high inlet vacuum, oil will pass past the worn valve seals and will be burned of. I would change the valve stem seals and run some de-carbonizer or seafoam through the brake booster vacuum line to remove carbon build up in the cylinders.
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Old 12-25-2016, 08:13 PM
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Re: Compression check for 79 Jeep 304v8

Nice photo & layout. Very professional. At first glance 6 & 7 look like your oil issue (only if that's an oily deposit), but this is not definitive. I don't think your compression numbers are pointing to anything specific. I would want more info. For example: what's the rate of consumption? (quarts of oil per miles driven) when is it blowing smoke (what color)? If you have blue smoke on hard acceleration - that indicates rings, where as if it only smokes when you let off the throttle after smokeless acceleration - that indicates valve guide seals. If it gives you a puff of blue smoke just at start up (first few seconds) that would indicate oil build up in the valve cover seeping past the valve guide after shut down (plugged drain passages). On the other hand if it smokes heavy blue like a mosquito fogger on start up that clears after the engine reaches 200f coolant temp for a few minutes - that indicates worn pistons that snug up after they warm up (collapsed or scuffed skirts maybe). If your smoke is white/white-ish, that's water (could be condensation in the muffler/pipes). If it smells sickly sweet also, that's coolant (look at 2, 4 or 8). 304's were pretty stout engines, but wear & tear or poor storage could cause any of these issues. Take a short video and post it on youtube - give us a link.
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