Can someone PLEASE help...

[wonkee]

I have a 1994 Mazda Autozam, automatic. The car is missing badly and has little power. I have just return from the mechanic who replaced the distributor and the spark plugs and says he has no idea what is wrong with it

[MagicRat]

Originally Posted by wonkee

and says he has no idea what is wrong with it

I think you need a new mechanic. Addressing an engine miss is not rocket science. It is simply methodical examination and testing to find the fault.

The first thing is to scan for trouble codes in the ECM. This might (or might not) give the mechanic a clue as to the fault.

If the miss is random, it could be bad spark plug wires.

If the miss is very regular, there probably is one or more 'dead' cylinders. This can be caused by a bad plug wire, defective fuel injector, something broken in the valvetrain, etc.

As I said before, a decent mechanic should be able to pinpoint the trouble relatively quickly.

[jdmccright]

Hmmm, missing badly and no power...never heard that before. Kidding. What I say is going to be general auto advice since I'm not familiar with your car...this thread should be moved to the Mazda section for more knowledgeable poeple to see.

Since we can cross off the plugs (wish we knew what the ends looked like when the "mech" removed the old ones) and the distributor (hoping this guy put it back in correctly), I'd turn attention to the engine's timing, the ignition coil, emissions control and vacuum, and the fuel system. I'll assume he replaced the distributor's cap and rotor as well, which can cause rough running it they're old and need attention.

The plugs weren't a bad move. Old ones can wear away between the electrodes, increasing that spark gap and making it harder to create a good spark that is released at the right time. In a fast-spinning engine, timing is critical to good performance. The new ones ought to be gapped correctly to give consistent performance between each plug.

If your car has a timing belt to keep the crankshaft and camshaft in sync, then it may have become worn or contaminated with oil and slipped a tooth or two. Doesn't take much to make the engine run bad. Check the crankshaft and camshaft for correct position at top-dead-center (TDC)...both shafts should have markings to make it easy to check at that point in the cycle.

Next the ignition coil. A bad coil won't put out the energy needed to light the air/fuel mix in the cylinders. Most of the time, coils go turtle and the engine simply stops running, but a weak one that's ready to give up might cause your problems.

Next, check the car's positive crankcase ventilation (PCV) valve. Usually stuck into the valve cover and a tube running from it to the throttle body. It should be free of oil and sludge and should work only one way.

After this, check the exhaust gas recirculation (EGR) valve. A faulty or plugged valve will cause poor performance also. Usually these can be cleaned, but may need replacing.

Finally, fuel system. Low system fuel pressure will cause hard starting, and poor idle/acceleration. Check/replace the fuel filter, fuel pressure regulator, and finally the fuel pump.

Sorry this is general stuff, but hopefully you're armed with the info needed to speak with someone who can REALLY help you...not this last guy. Good luck!