I have a 1998 hyundai excel running rough as if only on 2 or 3 cylinders starts 1st time but running realy bad and blows heaps of white smoke I can drive it and you can feel it not running on all cylinders and the harder you accellerate the moore smoke it blows I have replaced plugs, leads and coil pack and made no difference have you any ideas thanks.

sounds like a head gasket.. running rough from loss of compression in one cylinder and it's burning antifreeze causing the white smoke

White smoke is an indication of water in the engine. Like when you see a car with white smoke from the exhaust on a cold morning, it's heat moisture condensate in the exhaust (normal), and is being heated and converted to steam as the engine blows hot exhaust out. To test if it's water in the engine, there are two likely indications, (1) the motor oil will be milky and white, or (2) you can remove the spark plug and see if any cylinder sprays water mist when the engine is turned over. In either case the problem is a bad gasket, maybe head gasket (repairable), or a cracked block (big $$$ fix). If engine will not turn over, there could be two causes (assuming the battery and starting system is good); (1) a cylinder is full of water and hydraulically locked keeping the engine from turning over (removing spark plugs should relieve the pressure and allow you to turn the engine over (* you'll see mist or water coming out spark plug holes), or (2) the engine is seized, therefore the previous troubleshooting is unnecessary, engine replacement is necessary. Best of luck resolving this problem.

You have a failed head gasket

Major repair

Hope you didn't think the stop leak was
a genie in a bottle,never need any product
in any vehicle,just the proper repair

White smoke was coolant ,should have known that

water getting into cylinders cause of your white smoke

Sounds to me like the head gasket is blown, but there may be sealant in the system which is making it intermittently leak antifreeze into the cylinders.

A bad cylinder head gasket will also cause a compromise in compression, which will cause a lack of power.

Time to overhaul or replace the engine's head gasket, or replace the engine with one that doesn't have a blown head gasket.

Good luck on this repair.

the head gaskets are blown you can believe that anytime on any engine gas or deisel that you get oil in the radiator and there water/ antifreeze in the oil pan the gaskets and or cylinder heads are bad

most deffinately an internal issue. 2 possible problems oil seeping through valves when engine not running. sitting in combustion chamber and burns off during start up. 2 piston rings in one or more cylinders bad and letting oil blow by and start up is only time it is really noticeable.

black smoke is usually fuel...white is usually coolant...you may have a warped cylinder head or some other mechanical problem. do a compression test. If you disable the #2 injector does smoke continue? if it does, it's not fuel. When you remove #2 spark plug, is it wet? if so what's on it?

White smoke usually occurs when there is not enough heat to burn the fuel. The unburned fuel particles go out the tailpipe and typically produce a rich fuel smell. It's not unusual to see white smoke in the exhaust during cold weather until the engine warms up.

Faulty glow plugs or control module can cause white smoke on engine start up.

Low engine cranking speed may also produce white smoke.

If white smoke is still visible after the engine has warmed up, the engine may have one or more bad injectors, retarded injection timing or a worn injection pump.

Low compression or air in the fuel system can also be a source of white smoke.

One thing to check is the fuel pressure regulator.
If the diaphram is leaking it will cause gas to be pulled into the vacuum system causing lots of white smoke and extreme rough running.