Delica Canada | Mitsubishi Van Club

So I recently had my compression checked ive got the standard 4d56t, I'm at 220 220 220 200. which if im right, seems very low, plus i'm getting a bit of blowby, nothing crazy, but according to my shop its more than normal (though they mainly work on modern american diesels, not familiar at all with these)

Its been blowing quite a bit of black smoke, though it is definitely time for a thorough tune up, air filter is a bit old and dirty, so hard to say if the smoke is because it needs a tune or if its a result of the compression.

Strange thing is that the gas mileage seems acceptable, just recently did a road trip, got about 200 miles to a tank but driving on steep mountain roads which hurt MPG on any car, seems to have good power, no noticeable difference since i got the van 16 months ago. and about all i'd expect from this engine. it starts up easy every time, it sounds fine, basically like a noisy diesel, maybe a little clicky which again im assuming is more due to needing a tune up.

Any thoughts what could be causing this? I'd think with numbers that low that Id be getting very bad mileage, it would be hard to start, etc.. I'd really like to get another year out of this engine at least, though a new or solid rebuilt one is in the plans sometime in the future.

Those numbers are very low- the workshop manual says the lower limit is 273psi: That said, a compression test is only meaningful if everything in the intake system is also within spec. If your clogged air filter causes 1psi of pressure drop, it'll show up as a 21psi reduction when compressed (in theory ). Your valve clearances also need to be correct before the test (0.25mm when the engine is hot), if they've closed up a bit your compression readings will be much lower. EGR/blowby gunk clogging the intake manifold and valves can also restrict inlet flow and lower compression readings.

I'd do a tune-up and test the compression again.

4D56s are notorious for having more blowby than other engines. It's usually harmless until it gets to the point where the engine is running on its own oil fumes, then it's *very exciting* as your engine revs and won't stop. If you still have a functional EGR system the oil can combine with the exhaust soot and clog up the inlet manifold and valves. On intercooled engines it can clog up the intercooler. Fitting an oil vapour separator in the breather line should avoid those issues, but if you're planning on rebuilding the engine soon it might be overkill.

Alright thanks, I looked at the air filter today and it's definitely dirty, got a new one on the way, just removed/blanked out the EGR today too. Checked the blowby at the oil cap and I was getting little bits of oil on my hand after holding it there for 10 seconds. It was enough to move the oil cap around some with it just sitting on top. But not enough to really push it up much, some YouTube videos I watched looked quite a bit worse.

I think with how well it seems to be running im leaning towards just going with a solid tune up and see what that does. Hopefully get another year or two out of it.