Smoking exhaust - have theories, need input

[Sgt]

I just put a used engine into my car. I replaced a bunch of seals on it in the process. Rebuilt OEM turbos from concept z.

My old engine broke a piston and it looks like one of the old turbos may have had a bad oil seal. I found a large amount of oil in my intake pipes when doing the engine swap. The turbine housing on one turbo had lots of burnt oil/carbon deposits on it.

I got the replacement engine in and got it running. I have to adjust the TPS, IACV and set the timing still. When I first fired it, it ran smooth even for not having these set.

Once the engine is warm, one tailpipe started blowing an excessive amount of smoke. The smoke is grey in colour. I wouldn't say it was blue or white, which my father agreed with. The tail pipe which is smoking is also blowing the exhaust gasses out with noticably less pressure. When the engine is cold, there was no smoke and the pressure between each tailpipe seems fairly equal.

My exhaust is a full turbo back 3" exhaust, with no pre-cats, no cats, no H or X pipe, no resonator, just mufflers.

The exhaust that smokes is the same side that had the bad turbo.

I have been thinking about the possible causes and I have made a list:
1) Possibly bad compression on that bank of cylinders because of the low exhaust velocity, but since they are more or less equal on a cold start, I don't beleive this to be likely the cause. Doing a compression test tonight.

2) Valve stems or seals. Not likely as exhaust smoke isn't blue.

3) PCV valve issues

4) Oil residue left in exhaust and intake piping from old engine and old turbos burning off. Only smokes when engine is hot, as cold starts aren't hot enough to burn residue in exhaust pipe.

5) Timing belt off a tooth or two. Unlikely, as engine runs well and I took care to set it properly and checked the tensioner was set properly.

And finally, my favored theory

6) O2 sensor on that side of the engine is fouled from the oil it was exposed to, causing that bank of cylinders to be lean or rich, causing smoke. I reused the O2 sensors, as they are only a few years old. I beleive the O2 sensors are only functional at running temperature, which would explain why it doesn't smoke on cold starts. The exhaust smoke wasn't black, which would mean that it isn't rich.

So from all of this I am suspecting the O2 sensor on the problem side of the engine is fouled from oil, causing a lean condition at running temperature. Is this a valid theory? Does anyone else have any suggestions?

Thanks a million guys! I can't wait to drive my Z again!

[evildky]

First step is a compression test, I worry you might have a hg issue causing a cylinder to foul once warm, lets hope thats not it. The face that you have no cats means you will have some unburnt carbon and condensation coming out the exhaust and you will get little black spatter all over your bumper, If you still have the cats, i'd put them back on.

[Sgt]

hg issue causing a cylinder to foul once warm, lets hope thats not it.

"hg" meaning huge?

I ran the engine to running temp last night. Haven't done the compression test yet, but I set the TPS, IACV and timing.

I took the oil cap off when it was running and I didn't see any gasses or feel any pressure from the hole, so is it safe to assume my compression rings are okay? If compression tests poorly, it would likely be the heads? I should be able to confirm by pouring a tiny bit of oil in the cylinder when testing compression to confirm if needed?

The TPS was way out and I had to open the sensor itself, as I couldn't get the hard idle switch to be on within 0.4v and 0.5v. I bent the top contact so it just made continuity at fully closed throttle.

After all that tweaking, it seems to idle quite well. Haven't rev'ed it up much yet, as I want to assess the condition of the engine more before doing so.

When the engine was warm, it barely smoked from the mentioned tailpipe, although there was no smoke from the other pipe. This would lend credibility to my unburnt oil in the exhaust idea. It did still have a lower exhaust velocity from that tailpipe though.

I ordered a new O2 sensor, should have it tomorrow. I'm hoping this will solve the issue..

As for my cats, they are long gone. There is already carbon around my tailpipes on my rear valance, perhaps in the future I may get some, but at this point it's kinda pointless.

[Sgt]

Update (sorry for double post, it doesn't want to let me edit) :

I found the conditions for when the ecu goes into open/closed loop for the fuel ratio feedback loop.

With my hard idle switch not set properly when it was smoking, the car was in closed loop one it was hot. This seemed to make the car read the bad O2 sensor and run lean. Having properly set the throttle position sensor and hard idle switch, the car now properly recognises it's in idle and is in open loop.

This seems to reinforce my bad O2 sensor theory.

Having said this, I still observe the difference in exhaust velocity. Will be performing a compression test tonight.

[Sgt]

Did a compression test with hot engine and the wet compression test (in brackets)

.................................#6 : 150 (159)
#5 : 149 (162)
.................................#4 : 135 (150)
#3 : 151 (163)
.................................#2 : 143 (168)
#1 : 160 (169)

I also noted a somewhat intermittent whistling/whining noise while the engine was warming up. I am thinking it could be a sticky exhaust valve or bad exhaust valve seat. Would that be a valid conclusion?

While the plugs were out, I measured the gaps, and some were a bit much, so I regapped them to 0.035". They are NGK BKR7EIX Irridium plugs.

What would you suggest from these results?

Thanks!

[evildky]

hg= head gasket

with 135 on #4 I fear it is in fact the hg, when you say wet, I assume you mean you added motor oil to each cylinder and retested, which would indicate cylinder/ring wear but IIRC spec is still 180 so it's definitely sick, and the valves could be the issue but either way the heads gotta come off.

[Sgt]

Ah, yeah, as I think about it through the day I think the head gasket is bad.

I remembered seeing condensation on the coil pack of cylinder #4.



It seems as if the coolant is dropping and I'm certain I've burped it completely.

I can't drive it like this. I guess I gota replace the HG. Now the debate is if I should rebuild the valve train, and cylinders/pistons/rings.

Given the other compression numbers, would you expect cylinder #2 is low due to the HG as well?

If I just do the HG, I assume machining them would be highly advisable?

[evildky]

If you have the heads off having them check , new seals and a valves lapped in is cheap insurance.
With the numbers you have I'd go ahead and have the block checked, hopefully a rearing is all it needs.

[DCaff300ZX]

^^^^Agreed, do what you should have checked/insured previously with the replacement engine. Before doing the seal work and rest you did, best path would have been to ensure good compression and engine integrity since a worn engine needing seals and such also hints at having similar wear issues with the rotating parts, and which would make that engine a bad choice as a replacement. Before doing any of the work I did to mine, my Z guy checked everything over and found all problems before moving forward with repair and upgrades, since failure to do so would be a waste of my money and his time...

[Sgt]

Live and learn I suppose. Is there a way to test an engine that is out of a car? Is an impact gun on the crank pulley bolt enough to turn the engine for a cold compression test?

[DCaff300ZX]

Yep, I have learned FAR more from mistakes and errors than otherwise so don't feel too badly...we all do the best we can with what we know, we'll try to keep you moving forward!
You should be able to turn the motor with a large socket and bar especially with the spark plugs out, and be sure to read up on the correct procedures for compression testing our motors regarding throttlebodies and warm temp versus cold temp testing. There's another thread here regarding leakdown testing that nissanfreak goes into, the best and most accurate cylinder testing you can do.
Good Luck and post up any further questions!