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Sorry if this is long winded, but I've got some complex thinking going on even though the problem seems pretty simple.

1986 Trooper with Carb'd 2.3L, mechanical fuel pump

First some background. Cracked the head about a year ago, cracks into #2 and #3 cylinders at the exhaust valves. It sat for about 6 months, then I picked up another trooper real cheap. Pulled the head off the donor (had low oil PSI and some rod knock, or I would have swapped the whole motor. I didn't drive the donor much, but did put around 100 miles on it with no noticable change in oil level. Now with the donor head on and a thousand miles or so on it, I'm seeing crazy amounts of oil consumption. 100-200 miles a quart in fact. Tail pipe puts out a very faint trace of blue sometimes, sometimes starting about a minute after startup then lasting 5-10 minutes and then some slight blue/black if I really wind it out. I've driven some rigs that out smoke this by a long shot, and they didn't use 1/10th the oil. No drips though, not a drop shows up on the driveway, and the only trace of wet underneath is around the front main seal and it is very minor.

I did not replace the valve stem seals, so obviously they are a suspect, but the donor did not seem to exhibit this behavior.

I did replace the cam shaft seal, but I checked and it is not leaking.

I replaced the fuel pump with a new unit, had a new one on hand and it was way easier with the motor apart.

Compression could be higher but not terrible, don't have numbers in front of me, and adding oil to the cylinders gave me less than 10 PSI more than dry. All cylinders where within 15 PSI of each other.

So, I'm trying to come up with a theory or two as to the cause of the oil usage. Given the amount it is using up, I am very surprised not to see a puddle underneath or a cloud coming out the back. Very little PSI jump from oil on the compression check makes me think the rings are not too bad. Once in a while it does smoke a bit at start up, like it was leaking around the exhaust valves, but nothing extreme. Valve guides are the only obvious idea I have, but the donor motor did not seem to have that bad of a problem.

So, my other theory is that there might be something wrong with the fuel pump. Both the original, and the one on the donor motor leaked oil out of the breather tube on the pump. Not much, but enough to drip in the driveway a little bit. The new pump isn't leaking a bit, but I wondered if it was possible for it to leak internally. If my missing oil was leaving through the carb mixed with gas, it might burn fairly clean and not smoke. I know it sounds a bit of a stretch, but I thought I'd throw it out there and see if anyone had an opinion on it.

Other than tearing the motor apart again, I only really have a couple options and niether of them are simple. I can swap the old fuel pump on and see if it makes a difference, but it is buried under the intake. Not a fun project. Option 2 is to replace the valve stem seals without pulling the head. Also not a fun project. Neither of the two has much guarantee to it either. I could pull some lines off the fuel pump and see if I can get it to send oil out the wrong tubes, but that is almost as much work as pulling/swapping it. So would be bypassing it and running an electric pump.

So, I would really appreciate any ideas on other causes to look at, and any input about my working theories.
 
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