I finally got a compression test kit and proceeded to check my 4.0. I then did a wet test on the weak cylinders. The readings are as follows:
DRY (Wet) 2nd Test after about 1hr (dry)
1 113 115
2 77 (124) 135
3 100 (125) 185 ***** Blew the gauge out of the spark plug hole twice
4 127 135
5 76 (128) 120
6 126 130

What am I seeing? The old girl starts and runs, almost too cool. But cool is good as far as I'm concerned. It was a barn find and has been overheated a bunch. Head gasket? Rings? Valves? All of the above?

 

Obviously the 70"s suck...the 100 is poor...but all wet are excellent...do nothing yet. Run 2 or 3 full tanks with 12-16oz marvels mystery oil in the gas, OR 12-16oz of lucas top cylinder conditioner in the gas Thats double the normal concentration but you want some extra lube in there for a while. Put 1 qt of marvels NOT lucas top stuff in the oil and run for 2000 miles.... that stuff is magic. It has a very good chance of lubing up those rings and bringing everything back nice and smooth At the end of the 3 weeks ..give or take...redo your dry compression test.. if all over 115 then walk away. If still a bit low keep on lubing up the fuel and oil. If it doesn't change at all then you might want to do some engine work in summer...or just leave until she dies. If the body is really clean...rebuild...My 92 at 30 years had a pretty rough body...wasnt worth throwing in a new cam at 345K

 

Did you disable your fuel pump and bleed down the fuel pressure? I wonder if fuel is washing your compression away?

I like to pull the fuel pump relay while it's running. Residual fuel line pressure will bleed off as it runs. You can also electronically disable the injectors by unplugging them or the CPS.

Then redo the compression test. Still low? Do like the above says. I've also heard of good results from Engine Restore. It'll limp you along maybe another couple years to save up for and learn how to swap an engine.

 

Thanks Bluejeep, Marvels and Lucas on the way.

 

Did you read the new numbers I posted?

 

1) did you run the engine until it was warm before you did the second (dry) numbers to get the oil you put in the first time out of there ? If indeed they were "dry" the compression numbers you got the second time are ok. If you didn't run the engine then the oil you put in the first time was still in there.
2) when you said you blew the gauge out of the spark plug hole that suggests you are using one of the useless gauges that have a tapered rubber plug on the end rather than a hose with a metal fitting with an o-ring that screws in. If that's the case it may well explain the low numbers you got the first time -maybe it was just jammed in harder for the wet tests.

 

I missed the back story…Why all the fuss?

 

Yeah, I tried for an hour to get the adapter to thread into the spark plug hole. I checked and double checked. The 14mm adapter is the same thread as the plug, I just couldn't get the threads to catch. I finally said ****it and used the rubber. I'll keep checking periodically. I may send the kit back.

 

Could you not get the adapter threaded in one or all the holes?

The threads are the same on both of these but the top one won't seat properly cause of the length.
A proper compression tester would have both.

 

Marvel and Lucas and drive it like ya stole it.

 

I know this is contrary to the fans of "rebuild in a can" but if this is a new to you vehicle /barn find/ 300 k you might want to pull the valve cover and see how much sludge is in there before you put the snake oil in the oil (into the fuel is less of an issue). if the mouse milk knocks a bunch of sludge loose and it plugs up the oil pump intake stuck rings are going to be the least of your worries.

 

Take a peek into the oil filler hole and assess the sludge.
The beauty of MMO is that it melts the sludge away and you can monitor it through the filler hole. No worries there.
Use a good filter (Wix). Shell Rotella T3 or T4 also helps to dissolve sludge. We don't know if you have any yet!!

 

Valve cover removed, new gasket, no sludge to speak of. It was obviously taken care of, worked hard (pulling heavy loads with a lot of tongue weight killed the rear leaf springs) NO RUST.