weird compression test readings

[D@$uPeRc[-]@RgER]

I have a 92 240sx coupe with a 5 speed and 157,xxx mile and i thought that I should do a compression test. The first day I did it without using oil and forgot to depress the accelerator . so the numbers were in psi:

1. 1602. 1903. 1754. 30

the next day I do the compression test again and i get different results:

without oil:1. 1372. 1713. 1814. 25

with oil:1. 2252. 2303. 2404. 25 on the first attempt then poured in some more oil and got 32

i suspect that the battery might have been slightly tired by the second round of tests. So whats up with cylinder 4? I mean it makes no sense cuz the motor does shake quite a bit but it idles great and NEVER stalls! it even revs quite nicely....but once in a while i do see some smoke comin from the back half of the engine. The car used to be my uncle's and has been off the road for 5+ years cuz it never passed emissions so its been lying in the back yard for all that time. The radiator also has a leak and it only can hold water for an hour.

the interesting thing is that even after 5 years,when i cranked the car, it started immediately!

i hope that someone can make sense of the compression numbers

[SERMasta]

Well this is my guessI may be right I may be wrong but make sure your plugs are sparking and that you valves are opening and closeing if they aren't thats where your smoke is coming from. How I always test compression (the very few times I do) Is by takeing out the spark plug and holding my thumb over the hol. Then turn it over by hand till the exhast stroke pushes my thumb off of the hole thats what I do but I'm not that great off a mechanic. Thats the best help I can give you good luck.

[PapaBurgundy]

Sounds like you have a blown head gasket, or barely any ring on your piston (less likely). I actually almost bought two 240's with blown head gaskets, and they both ran great. BTW a thumb does not even remotely substitute a compression tester.

[D@$uPeRc[-]@RgER]

I was thinking on the same lines. but would a blown head gasket really give you that low a compression reading?

[PapaBurgundy]

Would you get that low of a reading with a good gasket? The only other things would be internals or a seriously screwed up valve, and that would probably be really noticeable.

[PapaBurgundy]

BTW is there any coolant accompanying the smoke from the back, coolant smell etc.? I just reread your post and noticed you saying that it smoked, I'm 98.47% sure its your head gasket.

[ShootToKill]

i have a similar problem but mine is a 98 KA24de with 67k miles on it. i got 180 on 1,2, and 4, and 150 on 3. if you poured oil into the cylinder and you got a higher reading it most likely bad rings. either way its not good. when the car is running does it sound like an un-corked subaru? is it real lazy to rev? either way i would just go the route of a rebuild or just replace the motor with a lower milage one or one that runs well for sure!

[D@$uPeRc[-]@RgER]

the car is sorta lazy to rev from idle but after 3k's she sings also the car does sound like an uncorked subaru boxer motor but only at idle and below 2.5k's. what puzzles me is that the motor idles soooo nice that you wouldn't be able to tell that somethings wrong with it. respect for the ka24de that its still smooth even though its only runnin on 3 cylinders

btw...i only need the motor to run for another two years and am plannin to swap it out after that. So i just want it to be reliable for a while and am not really intersted in racing it much before the swap. I'm on a college budget and really just want it to take me from point A to B. basically...i just want a cheap fix

[assassin7420]

How in the hell did you get above 190 on a ka?

[vancouverbc]

How in the hell did you get above 190 on a ka?

its a 240 so you should get 240 especially with oil

[redsx13]

its a 240 so you should get 240 especially with oil

???

[vancouverbc]

???

just checking if people are awake.

[ELEMENT692121]

ive seen a few cars with broken rings or ring lands run fine and compression test about the same .. if it runs ok i wouldnt think its a valve .. is the smoke blue in color if so your sucking oil back past the rings and out the exhaust .. id be willing to bet a ring or ring land is your issue also considering it sat for 5 years possible a ring was frozen and broke the land or the ring itself when u started it after sittin all that time .. when i say ive seen a few i mean at least 10 all with the same simptoms

[TurboTagTeam]

I'd run a leakdown test just for thouroughness. Its most likely a headgaket or some worn rings like as been allready said.

Good Luck

[Ka24de240sxS13]

Headgasket would not make that low of compression... it has to be either the rings or valves. take the hose off of your valve cover, and run your motor, if you see smoke out of the valve cover, it confirms that your valves are f***ed. If you get no smoke you most likely have a compression ring problem. Also, have you ever rebuilt this motor? because if you ring the piston incorrectly, you could create a huge compression problem.

[D@$uPeRc[-]@RgER]

the most peculiar thing is that there is virtually NO SMOKE coming out of the exhaust that's what's puzzling me.... and how exactly do you to a leakdown test?

The only smoke that came out of the exhaust was when i did the compression test using motor oil. But when i'd rev the engine to get rid of the oil from the cylinders, there was also smoke coming from the back of the motor... . now all the evidence so far points to a blown head gasket but how can the compression be that low(25psi!! ).

looks like i'll just have to get the motor rebuilt. btw..will a rebuild run me cheaper or just a used motor from a junked 240??sorry that i'm such a noob...

[ELEMENT692121]

there is a different tester that you run compressed air into a cyclnder with at the top of its compression stroke .. and it will tell you how much is leaking by .. you can also pull the cap off your radiator see if you see bubbles this way also pull off your oil cap and see if you can hear air rushing into your crankcase .. all a compression test dose is tell you there is no compression a leakdown helps you figure out where its going .. i have seen numbers that low on a car that had broken the ringlands off the pistons and the car ran fine also just felt a lil slugesh ..

[assassin7420]

@RgER]the most peculiar thing is that there is virtually NO SMOKE coming out of the exhaust that's what's puzzling me.... and how exactly do you to a leakdown test?

The only smoke that came out of the exhaust was when i did the compression test using motor oil. But when i'd rev the engine to get rid of the oil from the cylinders, there was also smoke coming from the back of the motor... . now all the evidence so far points to a blown head gasket but how can the compression be that low(25psi!! ).

looks like i'll just have to get the motor rebuilt. btw..will a rebuild run me cheaper or just a used motor from a junked 240??sorry that i'm such a noob...

used ka's go for 150 to 400 dollars. At least out here.

[D@$uPeRc[-]@RgER]

Thanks a million everyone for helping me out

one final question...how much would a rebuild for the ka cost me? would it be cheaper than swapping in another ka? i'm on a college budget and want the cheapest fix

[Vegascorbin]

We are in the middle of rebuilding our KA24E with stock parts (it's for a stock class race car. no upgrades allowed.) We will be into it for about $600 by the time we are done. Thats full rebuild kit (all gaskets etc, new rings, beerings etc, new oil pump, new water pump, new timing chain and guides etc.) without new pistons or rods. Block was cleaned and inpected. Honed only no overboring required. The crank was posished only again no over size required. The head is being done now. cost wil go up if new valves are needed. Milling of the head was included.

We did the tear down and will be doing the build up ourselves. Good local machine shop did the block and crank and is doing the head.

Hope that helps.

[D@$uPeRc[-]@RgER]

Thanks for the info man! and everyone else thanks for the help.this site rulz!!

[ShootToKill]

yea just buy another KA, long block if you can and just swap everything over. i picked up mine for 250, with 67k miles on it and fired up on the first shot, after we got the timing right!