1998 XJ8 3.2, going down a long hill into Wellington (Ngauranga Gorge for the locals)
No brakes and trans in 4th gear to keep the speed down. Get to the bottom and huge amount of smoke from the right hand exhaust.
Just a bit of background. Picked up the car on Thursday last week, trundled around Auckland and tried to replace the dirty air filter, nothing available at a reasonable price, decided to run with what we had.
Under quite hard acceleration the exhaust was quite black. Put this down to the AF being ok on cruise but causing restriction under full load.
Now thinking that this may be the cause of the smoke as well?
The r/h cam cover has the breather feeding into the inlet manifold.
The rescan I am thinking this is because once we were in the South Island we removed the AF and now no smoke after deceleration and clean exhaust under full kick down.
Any thoughts people??

 

Have you checked your plugs to see how they are burning? Rich, lean, spot on...plugs are the true eyes in the motor. Have you checked your catalytic converter? With the smoke you speak of, I'm surprised your O2's aren't crying foul.

 

The white smoke probably was a result of the filter, and you are definitely risking damage to the cats.

 

Give the MAF a clean, part load and full load breather tubes checked.

 

You didn't state mileage, but figuring it's 20 years old, it might be a worn valve stem seal.

Check the plugs. Take them out one at a time and label which cylinder they came from. Then inspect the plugs. You will probably have one or two of them fouled out.
Start on the side that is smoking.

While the plugs are out, do a compression check on the engine.

This sounds like a possible valve stem seal. If you see any residue from burnt oil on the plugs, you prob have either a bad piston ring(Doubt it), or a bad valve stem seal (More than likely). If it is a valve stem seal, that cylinder(s) will have a higher than normal compression ratio.

The MAF should not cause this issue. The problem is in the engine, not outside the engine.

If the valve stem seal is leaking, it would cause the exact problem your describing.

I doubt its a piston ring.

The PROPER repair for a valve stem seal is to remove the head and have it repaired. If you doing that, you might as well have both of them rebuilt..

 

Thanks everyone, just replaced the plugs prior to traveling down to Christchurch and the ones that came out were looking ok as far colour was concerned. As stated once the air filter was removed the smoke disappeared, a scan showed no abnormal readings for the o2 sensors.
I am thinking that because the breather is on the RH bank with a very dirty filter it was creating greater than normal depression in the cam cover, coupled with possible valve seals worn out, drawing oil past the rings?

 

If the air filter was plugged, a significant vacuum could be pulled on the engine, drawing oil past the rings and valve guides. The black smoke under acceleration is another indication of restricted air flow.

 

Good point, it can create an excess draw on the Breather Hose also and pick up oil from valve train and into the intake, into the combustion chamber and out comes ol' smokey.

 

Agree to a certain extent, however the smoke was only from the right hand bank so I am going for worn valve guides causing oil to be drawn up passed th piston rings.
Excess vacuum in the cam cover, worn guides = depression in the cylinders on the R/H bank.

 

Normally, smoke on deacceleration is valve guides, on acceleration piston rings; white smoke is heads; black smoke is an overly rich condition or badly gunked up valves from too much slow motion in traffic or sitting for a very long time. So, clean the MAF, change the air filter, clean the part load breather, clean the throttle plate and bore and drive it. Maybe drive it hard.