Hi Scotty, how are you? I need your help in something and the only one I can think of that has amazing advice and is 99.99% correct is you! My mother has a 1999 Jeep Grand Cherokee 4.0L, 3 weeks ago the car starting shaking and vibrating and acceleration was slow. I knew it was the spark plugs because you can smell unburnt gas coming through the exhaust. I was going to fix it but my mother took it to the mechanic, they said everything was fine and nothing to worry and remember it was shaking but a little not a lot.

It's been 3 weeks now and the car got worst. I guessing the engine was struggling a lot and making the other 5 spark plugs handle the load more and cause it to stress. Took it to the mechanic all the spark plugs and spark plug connection that connects to spark plugs were all burnt and damage.

My mother spend $600 dollars on new spark plugs, the connectors that connect to the spark plugs, new gas rail since it was leaking somehow after the mechanic touch the engine and new O-ring for the gas injectors.

I'm a student studying Aircraft Mechanic Engineer, I spend almost 40-50 hours a week in school and I would fixed the issue at the begging and now I feel bad and it's got worse.

After my mother spending $600.00 on parts and labour the car is still throwing out black smoke and shaking! The check engine light is on and service again! The mechanic just said "keep driving it to get all the junk out". But as a person that knows about engines and that you can stress the motor like that and damage it more, if I'm correct.

I have only 2 thoughts in mind why this is still happening. Either there is to much gas in the motor because it's been like that for 3 weeks and maybe there's so much has in the engine that it's clogged and driving it won't work as much since gas is still filling up the cylinder(s) OR one spark plug is not sparking properly and there is properly an electrical problem that causes the spark plug not to work causing it to shake but I don't understand why there is so much black smoke due to one spark plug.

My 3 thought is that there is to much gas shooting out the gas injector and if in the case I'll have to take it somewhere were they can see how much gas in injecting in the motor and fix it from there.

So the car vibrates and shakes, smells like gas, and when you accelerate it stutterers and shoots out more black smoke from the exhaust.



Kevin Manrrique & a big fan

those are notorious for fuel injector failures when that old, but before changing them, often cleaning like this can fix them https://www.youtube.com/watch?v=bKGI9N_yWd0

Also, find a better mechanic. He was probably just guessing.