[Unknown User]

My 77 280z smokes in a way I have not seen on other cars. At first I thought it was valve seals, then I thought rings, now I'm not sure. It smokes after startup, but not immediately as in leaky valve seals. It waits until you rev the engine then it smokes. If you back off the throttle, the smoke goes away. Throttle up again and it comes back. Some days it's smokes pretty bad, others it's not so bad. If it smoked all the time I would conclude it's the rings. They are tired, 250k miles, and compression is in the low 140s dry and in the mid 170s wet. But it only smokes for the first 20 to 30 seconds of actual acceleration, and then it almost completely goes away. If it were rings I would expect it to smoke all the time. Is there a failure mode of the crankcase ventilation system that can cause this? A plugged vent or something? Or do Zs just have a unique way of smoking with bad rings or valve seals.

Bruce 77z

 

[Ian]

> My 77 280z smokes in a way I have not seen
> on other cars. At first I thought it was
> valve seals, then I thought rings, now I'm
> not sure. It smokes after startup, but not
> immediately as in leaky valve seals. It
> waits until you rev the engine then it
> smokes. If you back off the throttle, the
> smoke goes away. Throttle up again and it
> comes back. Some days it's smokes pretty
> bad, others it's not so bad. If it smoked
> all the time I would conclude it's the
> rings. They are tired, 250k miles, and
> compression is in the low 140s dry and in
> the mid 170s wet. But it only smokes for the
> first 20 to 30 seconds of actual
> acceleration, and then it almost completely
> goes away. If it were rings I would expect
> it to smoke all the time. Is there a failure
> mode of the crankcase ventilation system
> that can cause this? A plugged vent or
> something? Or do Zs just have a unique way
> of smoking with bad rings or valve seals.

> Bruce 77z

I think you have a case of bad oil rings...sounds to me like they seal when hot and expanded. Your compression is really good for an engine w/ 1/4 million miles. Here is how to fix:
step 1: drive car
step 2: check oil
step 3: add oil as necessary
step 4: continue to drive car
step 5: replace or clean spark plugs when fouled
step 6: continue to drive car
If I have a motor that lasted 250K miles, I'd have it bronzed!!!

 

[Ron]

believe it or not ..
Clean your F.I. thermo temp sensor connections located on the thrmostat
housing.