Odd Vibration During Acceleration
 

So for the past couple of weeks I've been getting an odd Vibration while accelerating. It only ever vibrates three times and it is much louder under heavy acceleration compared to light acceleration. It also only seems to happen between 3,000-4,000 RPM. Sometimes I think I feel it even when staying under 3,000 RPM, but I'm not sure, it's very light if it is happening. It also only seems to happen in second gear, none of the other gears are affected. This thread has me thinking it could be the fuel pump, since I do think I'm experiencing a slight lack in power, however I do not have a supercharger like the poster of that thread does.

The car is an automatic '99 with 130,000 miles on it. The check engine light is on but I haven't read the code yet, I just assumed it was an evaporative system failure, since I got that code repeatedly around this same time last year. Would a fuel pump that is going bad cause a CEL?

Thanks in advance for any help you can give.

driveshaft assembly, motor mounts, front sway bar assembly. probably one of those, check out some threads of mine and my dads (joe1602) and you should have a good start. We had the same thing happen on ours, SAME THING. hope it helps, good luck

Yes, take a look at some of our earlier posts about this. I have to now replace the center carrier bearing. I am almost sure that is the knock. I am actually going to replace the whole driveshaft with a remanufactured one when the funds & lift become available. Ours however is a 5 speed and I am not sure of the mechanics of the automatic driveshaft. Ours knocks at the same RPM in 1st and 2nd gear only under HARD acceleration. Good Luck!

Inspect the guibo for cracks or disintegration.

Thanks for the tips everyone. Turns out I won't get to give it a proper inspection until next weekend. I'll be sure to take it easy on the throttle until then and bump this thread when I have something to report.

So we took a peek under the car yesterday to see what was up. Unfortunately we spent most of the day repairing the driver's side window which was on the verge of falling (again), so we only got a few minutes underneath the car. We didn't see anything obviously broken. One of the universal joints near the cat was a little loose so it might be that. We're going to dedicate an entire Saturday to diagnosing this problem in about two weeks. I wish it could be sooner but at least I'll have plenty of time to read the prior threads on this and look up some diagrams on realoem.com so I can tell what I'm looking at. Thanks again everybody!

If that is, in fact, the case- I'm about 99% certain that is where the problem is. Replace the driveshaft and giubo (and transmission mounts, as long as you're going to be in there) and be done with it for another 100k+ miles... :)

Driveshaft U-joint. It took me 2 months a two guibos and center support bearing to figure this out. I need to remove the driveshaft and actually exercise the U joint to feel the binding.