A new problem

I am having problems with my 89 Jeep 2WD 4.0 again. Now, I am getting a strong shudder at about 45 mph and a gas smell when I stop. Idle is fine however. But as the rpm's go up, the shudder gets worse (at about 45, it rattles your teeth), take my foot off the gas, it stops. I checked, and I am getting spark to all the plugs, and I poured in a fuel injector cleaner to see if that would help, it didn't. I wish I could give you rpm's but all my jeep has is the dummy lights. and a very large gas gauge.

The "shudder" sounds like one of the injectors is not working correctly, causing extra gas to be dumped into the cylinder( sort-of choking it out). Not sure on trouble shooting it, outside of removing the injectors and testing them individually.

Does it do that in park and you rev the engine or only when it's under load?

Yes, it does do that in park and when I rev the engine.

Fixed the problem, turns out I had a fouled plug.

I was going to suggest you run the engine and pull a plug wire and see if it's worse, then reconnect it and pull the next one. When you pull one that doesn't make it worse, you found the faulty cylinder.

Good thing it was as simple as a plug. Any idea how it got so fouled?

Not sure how it got so fouled. When I pulled it, (the plug at the front of the block) it had a pretty good carbon deposit on it and some white calcification. Did I get water in the oil? Could the piston ring be bad?

Does it smoke at all? How's your coolant level? Check the compression in the cylinder.

Yes, if I sit at idle, it will leave a small amount of gray smoke, coolant level is fine, does not lose.