Cardad02

I have a base, automatic 1993 with 14,000. In the spring of 12 I installed new plugs, wires, battery, K&N air filter, a new thermostat and a new belt. The rear end had the diff fluid changed when the car went in for a state inspection. The work was done with 13,000 on the clock. Other than the fluid change I did the work myself.

Approximately two weeks ago, the car started to backfire and shake from the rear under heavy acceleration.

If I smoothly accelerate, the car will hit 85 MPH without incident. Once I "step on" the accelerator, the car will backfire and shake. The "shake" seems to be coming from the rear end. It doesn't matter if the car has been driven for 10 minutes or two hours. I put fresh fuel in over the weekend, after taking the tank down to a 1/4. Same results.

The rest of the car, less tires and shocks are original.

Any advice on what I should be looking for? Any advice is appreciated.

leesvet

Fuel injectors, stored trouble codes.

That milege is wonderful....but low miles/old age are double edged...

these do not "sit" well. Unless properly prepped and tucked away and undisturbed, they do not do well pulled out of the barn once a yr for short hops.

1st guess is a horrid misfire. There is nothing wrong with the rear end. A bad rear end has nothing to do with backfiring. I'm not sure why you did things that were unnecessary, but thats your call. None of that was necessary unless the car was damaged from improper storage, water or the likes.

Clogged fuel injectors, stuck injectors.
Might be a tank full of water. Whatever the case, the engine malfunctions need to be ID'd to put an end to the misfiring.

Start with the basics...

fuel, pressure and flow, quality.

spark.

adjustments and settings.

Read the codes. Read the FSM. Follow those flow charts to conclusion.
Good luck, too nice a car to let this take place,.

Cardad02

The car sat for six years before I purchased it. The owner believed that he may have changed the oil, at 7,000 mile, back in 2000... No joke. It was kept in a garage, but it was not maintained. The owner acknowledged that he was too large and heavy to fit in the car, so he just parked it and left it.

I changed every fluid except the rear diff, as soon as I purchased the car. I also put tires and new shocks on at the car, so that it would pass the PA inspection.

I decided that it was time to clean up the car and make it 100%. The wires are NOS and the plugs are Bosch.

The car ran awesome for almost 1000 miles. I do not abuse the car or drive it in the rain. I intend to keep it for some time.

What could be causing the rear shake? It honestly feels like the mufflers are going to fall off the car.

The car ran

AirForceOne!

Check your u-joints first.

Did you have your wheels balanced when the new tires were installed?

Did your rearend do this before you replaced the tires and shocks?

I agree with leesvet, check the fuel pressure, filter and injectors outfirst!