why would my miata be smoking alot when i run it for a long while then let off the gas and get back on it again?
Sounds like vavle seals. If compression is good (good rings and valves), then valve seals would be the next possibility.
I may be off the mark…
My 90 smoked (only a bit of black smoke) and had an off throttle backfire. Replaced the oxygen sensor and it cleared up. A compression check as texases indicates is on order.
I found the problem by following the troubleshooting guide in the factory service manual.
What color is the smoke?
How much oil does the engine consume between changes?
How’s the fuel mileage?
Smoke could be from oil burning or too much unburnt fuel. The smoke color will be different depending on what’s going on.
If the smoke is blue, then it could be a sign of oil blowing by the rings. This is pretty much the classic test for the condition of the rings, run the engine up a few rpm and it hold it there for a bit then off the gas. Let the rev’s drop a few thousand while you are off the gas petal, then a quick punch on the gas and look for smoke out the tailpipe.
Do the test, and if you get a puff of blue smoke a compression check is next. If you drive the car a bunch you may need a motor overhaul. If this is a weekend driver you may just live with a little smoke and add oil now and again.
If it blows blue smoke when you take your foot off the gas at highway speed (look in the rear view mirror), it’s the valve seals; your engine vacuum created is sucking oil past the worn seals. Those are not difficult to replace.
If it’s blowing blue smoke on acceleration, you have bad rings; that’s very expensive to fix, and you would be better off with a used engine from a low mileage wreck.
In any case you need to have a compression check done to see what problems you actually have.