2G 1 cylinder low compression and smoky exhaust

[XIT]

I've read a bunch of threads over the last few days and I am still unsure of my issue. I feel like it could be HG or valve stem seals but I'm open to other suggestions. The only reasons I'm not leaning towards rings, is the color of the smoke and the wet compression test results. With that out of the way, here's the story.

I just bought the car. It's a 1998 gsx with low miles (~88k). I bought it from a kid that really doesn't know anything about working on cars. He noticed it smoking while driving and decided to park it until he could afford to take it to a shop or could have a friend help him figure it out. His friend suggested to him that it was the hg. One year later, he sells it to me.

When I went to pick it up, the exhaust manifold and turbo were removed along with the intercooler tubes (stock smic and tubes) and the radiator. The cylinder one exhaust port looked wet but all the plugs looked the same (cyl 1 wasn't wet or black or anything). I put the car back together before buying it so I could see how it runs and test drive it. It started up well and idled fine with no smoke. It did not smoke while revving up, but only while rpms come back down after a rev. Higher rev = more smoke. After revving when the engine catches idle, no more smoke. The smoke is white/very very very light gray but no sweet smell. This was still without refilling coolant (maybe burning the coolant that's still in the engine?). It does not seem to be losing any oil. I went on a short test drive and the car felt like it had good power down low but had a little hesitation when getting up in rpm. I didn't drive it hard, I just wanted to verify the condition of the drivetrain and went around the block. Never had it under full throttle but it did build boost.

I live about an hour from where I store the car so I'd like to go work on it with an optimal game plan. I already ordered an entire gasket and seal set for the engine and ARP head studs. I want to do all maintenance and get it in good running order before I do anything else with the car. The car is pretty much completely stock except for an aftermarket muffler and BOV. The timing belt was replaced recently. I plan on doing a pressurized cooling system test and I have to get some supplies to make a bl tester. I was considering filling coolant and seeing if it smoked more/lost coolant but I would rather not just in case the oil and coolant were to mix and cause more damage.

Any other suggestions or is there anything I'm missing?

The compression test was performed cold. Only cylinder 1 was tested dry and wet.
Compression test results: 1 - 120 d, 130 w 2 - 155 3 - 160 4 - 160

Thank you in advance!

 

[laserRSawd]

Do a leak down test.

 

[streetraceboi]

Sounds like rings to me but a leakdown test would let you know for sure.

 

[XIT]

I'll start with a leak down test.

 

[pauleyman]

You should also perform the tests warm if at all possible.

 

[XIT]

You should also perform the tests warm if at all possible.

Perform all tests warm? Should I repeat the compression test warm as well? Or is that redundant with the other tests I'll be doing?

 

[pauleyman]

It's redundant. Leakdown will show what you need. naturally coolant test must be done cold.

 

[XIT]

Update: leak down test performed. Cyl 1 (worst comp) had roughly 13% leak. Cyl 4 (highest comp) had roughly 9% leak. The leak was the loudest in the valve cover. Some from dipstick tube. Nothing from coolant full. Couldn’t hear through air filter. Cylinders 1 and 4 both had a similar amount from dipstick tube, 1 being very slightly more.

 

[XIT]

Okay bigger update here. Previous leak down test was done warm-ish (did not get up to full operating temp). I’ve put a few miles on the car. I took it down the block a while after the leak down test. When cold, the engine felt like it had low power and sounded like it was breaking up under boost. Fast forward to the next day, I started the car (started up fairly quick but more cranking that my other cars) and let it get up to full temp. I then drove it down the block again. Power felt great, better than my old 16g car and much better than my old 1g. Absolutely zero smoke from exhaust. I turn it off and try to start it to compare it to the cold start. It started up great. I redid the compression test now warm and used a different tester. Cyl 1 was 105 and 2, 3, & 4 were all 130. That doesn’t make much sense being that the results were much higher on the cold test with the first tester I used. I assume this tester is just off. Anyway, I repeated the leak down test and had almost absolutely zero air coming from the dipstick. I could only hear it a tiny bit with my ear right next to the dip stick hole after I took the dipstick out. The air was coming from the valve cover. I popped off the oil cap and the leak got much louder. I’m at a loss here. The car runs and drives phenomenally once warm. Any ideas?

 

[AWD-Tony]

Does the oil smell like fuel?

 

[XIT]

Does the oil smell like fuel?

Not at all

 

[AWD-Tony]

Did you listen for air out the exhaust when doing a leak down test? This will tell you if exhaust valves are bad. Stock injectors/ecu? What’s the pcv set up?

 

[DSMPT]

It did not smoke while revving up, but only while rpms come back down after a rev. Higher rev = more smoke. After revving when the engine catches idle, no more smoke.

When revving up = Less vacuum in intake and cylinders = Less oil is sucked through stem seals/piston rings into combustion chamber = Less smoke.
Higher rev + Throttle closed = More vacuum = More oil is sucked through stem seals/piston rings into combustion chamber = More smoke.

Could be #1 has the most worn stem seals/piston rings/cylinder wall, and now #1 valves are not sealing well by chewing carbon deposit. Maybe that's the reason why #1 has a bit lower compression and it smokes when you throttle off.

 

[XIT]

Did you listen for air out the exhaust when doing a leak down test? This will tell you if exhaust valves are bad. Stock injectors/ecu? What’s the pcv set up?

Yeah I didn’t notice anything from exhaust. The car is completely stock

 

[XIT]

When revving up = Less vacuum in intake and cylinders = Less oil is sucked through stem seals/piston rings into combustion chamber = Less smoke.
Higher rev + Throttle closed = More vacuum = More oil is sucked through stem seals/piston rings into combustion chamber = More smoke.

Could be #1 has the most worn stem seals/piston rings/cylinder wall, and now #1 valves are not sealing well by chewing carbon deposit. Maybe that's the reason why #1 has a bit lower compression and it smokes when you throttle off.

Would that make sense with the smoke completely disappearing when warm? I’d assume whatever deal is blown is expanding with heat and re sealing. Revving, driving, coasting down while in gear, all conditions have no smoke once warmed up.

 

[DSMPT]

Would that make sense with the smoke completely disappearing when warm?

Yes. But this does not guarantee that this is your case. I just said one of possibilities.

Revving, driving, coasting down while in gear, all conditions have no smoke once warmed up.

Because once you have oil in combustion chambers more than usual for some reason, you can't burn all the oil in combustion chambers with just idling. You have to drive the car at least like 20-30 min with operation temp. Once the engine burns all excess oil in combustion chamber (at that moment you would see a lot of smoke coming from tail pipe for a while), after that, smoke won't be so visible any more as long as you keep driving the car.

 

[XIT]

Yes. But this does not guarantee that this is your case. I just said one of possibilities.


Because once you have oil in combustion chambers more than usual for some reason, you can't burn all the oil in combustion chambers with just idling. You have to drive the car at least like 20-30 min with operation temp. Once the engine burns all excess oil in combustion chamber (at that moment you would see a lot of smoke coming from tail pipe for a while), after that, smoke won't be so visible any more as long as you keep driving the car.

Okay thank you. So at this point is there any other tests I can do to narrow it down or is it time to start throwing parts at it? If it’s time for parts, where should I start?

Edit: Also, the smoke completely clears up just by idling until it gets warm. Once idling until warm, no smoke while driving or revving. The only time there is any smoke is when the engine is cold.

 

[AWD-Tony]

Sounds like valve stem seals is the cause for smoke.

 

[XIT]

Sounds like valve stem seals is the cause for smoke.

That’s kind of what I thought as well. Too bad that doesn’t explain the compression issue. How likely is it that the rings are a little worn down in that cylinder only? Most of the time I’ve seen bad rings, all cylinders are somewhat low or one is drastically low.

 

[AWD-Tony]

Possible? Sure. If you had a lot of air from the dipstick when performing leak down in that cylinder, rings are a possibility especially if it went up after adding oil.

 

[XIT]

Possible? Sure. If you had a lot of air from the dipstick when performing leak down in that cylinder, rings are a possibility especially if it went up after adding oil.

Almost none from dipstick when I did the leak down at operating temp. Only from under valve cover. The first leak down test was done warm ish and all cylinders had some from dipstick. Comp only went up slightly with wet test. Which is tough cause of the dish on the piston it’ll do that if oil pools.

 

[XIT]

Also, I parked it overnight in the driveway and let it run in that spot for about 20 minutes and when I pulled away there was some milky oil on the ground. I don’t think it would get milky if it was clean oil that dripped onto wet pavement. I’ll drain the oil next weekend to see if it’s got coolant mixed and that’ll point me towards a hg. I’ll be on vacation all this week so it’ll have to wait.

 

[DSMPT]

Okay thank you. So at this point is there any other tests I can do to narrow it down or is it time to start throwing parts at it? If it’s time for parts, where should I start?

The only time there is any smoke is when the engine is cold.

If I were you I would check cylinder wall condition by using a borescope and replace the valve stem seals and see if it would get better.

Edit: Also, the smoke completely clears up just by idling until it gets warm.

This makes the situation more complicated in general. The point is if you start the engine and turn off before the engine gets very hot, then next time when you start the engine you would have more oil in combustion chamber. If you do this more and more, you get oil more and more. More oil = more smoke.
You are actually getting a tiny bit of oil into combustion chambers always even with a healthy engine. The amount of oil would depend on the condition of engine, such as ring gap, ring condition, PTW clearance, piston skirt shape, cylinder wall condition, valve stem seal condition.
For instance, even if the engine is healthy, if the engine is started very often but driven only for very short moment/distance each time (maybe a few min max), that would sometimes cause smoke and it's normal. In that case, once you drive the car for a while, it would stop smoking.

 

[XIT]

If I were you I would check cylinder wall condition by using a borescope and replace the valve stem seals and see if it would get better.


This makes the situation more complicated in general. The point is if you start the engine and turn off before the engine gets very hot, then next time when you start the engine you would have more oil in combustion chamber.
You are actually getting a tiny bit of oil into combustion chambers always even with a healthy engine. The amount of oil would depend on the condition of engine, such as ring gap, ring condition, PTW clearance, piston skirt shape, cylinder wall condition, valve stem seal condition.
For instance, even if the engine is healthy, if the engine is started very often but driven only for very short moment/distance each time (maybe a few min max), that would sometimes cause smoke and it's normal. In that case, once you drive the car for a while, it would stop smoking.

That makes a lot more sense. The car had been sitting before I got it and I haven’t taken it in a long drive yet. Just idle time and up and down the block a few times.

 

[motomattx]

You have a piston ring issue in cylinder one if your doing your compression test properly.