2000 xj 4.0. When the electric fan kicks on I get a vibration that vibrates the whole Jeep. As soon as the e-fan kicks off it stops instantly.
I recently had to replace the battery but it was almost 4 years old. The vibration problem started with the old battery. I am thinking electrical. Ground or alternator?

I also know the 2000 injector that vaporizes after it sits hot and it's not that. Although that pisses me off a lot.

 

First, check to make sure that your electric fan is in good shape. Make sure it has not lost a blade, or portion of a blade.

 

obviously sounds like the electric fan is broken lol. Missing a blade or about to fall off or something.

 

2 screws and a plug to remove it for inspection.

 

The fan looks to be in tact. The vibration is much greater than a missing fan blade on the e-fan. My seat becomes a back massager. The sensation is similar to what happens when I start it when the injector had vaporized.

 

It may seem like an odd question, but how do you know it's happening when the fan comes on? Are you just hearing it from the driver's seat, or have you actually watched the fan come on and then heard the vibration?

 

I know it all sounds weird but I am letting it sit in the drive while observing the fan click on and off around the 213 temp mark. It feels like a fuel issue but to be timed perfect with the e-fan seems unlikely to me.

 

Well then, next to check is probably the system voltage when the e-fan comes on. Does it drag the system voltage down? (that could cause a variety of problems).