Help! Smoke and low compression.

[synfrag69]

Hello everyone!

I am new to both the site and the 240sx so flame me if this is stupid.

Here is the rundown:1991 240sx Coupe.Stock KA24DE (I was told it only had 60K mi on it) the car has 145keverything else is stock still as well.

Here is what I am seeing and have done.

When I start my car it sometimes (50/50) puffs a little smoke out the exhaust and when I open the throttle it increases. It's not an insane amount of smoke but its enough to worry me. It does not smell like antifreeze which I just parted my VW VR6 due to. It actually smells like it's running rich (that burn your eyes and nose smell) but it is white/blue smoke not black.

I have done a compression test and it is 125psi across the board with about a 1-2 psi variance between cylinders. I did not do the test at WOT would this make a 55psi difference? 3 of the 4 plugs i pulled had white deposit and one was black. The car does not overheat, there is no oil in the coolant (yet) and my oil is clean (was just changed before I purchased the car). It seems to run quite strong even for a 2.4L but as I said I'm new to the 240. I am not sure if the motor was rebuilt or if it was pulled from another car. The only exterior leaks I can detect is the valve cover leaking a bit from the front. I plan on watching my oil and coolant colors to see if i can spot one seeping into the other and emulsifying. Does this sound like a blown HG or rings? in my experience both a blown HG and bad rings usually only show up in bad compression on one or two cylinders, and unless it was run dry not all 4. I just need the verification before I buy my builder block to replace it. Also how long do you guys think it will last in this state? I plan on having my KA24DET done by September so I need transportation for 4 months.

on a side note and different issue. Would I feel shudder from my diff if it was going bad? I have had a couple of instances where i rounded a corner in 2nd got on the throttle and felt no acceleration but i do get RPMS. I'm not hitting the throttle very hard at first so i'm not "Breaking" anything loose but I'm trying to figure out if it's the clutch or Diff.

Any help is appreciated.Thanks,Charles

[ard]

sounds like piston rings, 125psi is ~8.6bar. i don't know what compression should be on ka24de, but it seems low. firstly you should to put oil catch can. if problem solved then it should be compression rings. if problem continues, it should be oil rings that constantly leaves oil on cylinder walls.blown HG always makes funny smoke, so i don't think that it is the main problem.

[mister2nr]

best thing to do is a leak down test on the cylinders to see if it is caused by that before buying any parts. a leak down test is pressurizing each individual cylinder to see if there is any piston ring, cylinder wall damage. If there is on the gauge you will know. If its 20% or more than its bad. If you have the technical skills to do it its a fairly easy test which will give you positive or negative results.