Originally Posted by jdwestsr

Sorry for the long post, but I want to give as much detail and history as I can.

Here are the particulars:
2000 Mustang with 3.8l engine and automatic transmission.
Around 148,000 miles
Most recently driven by inattentive college age daughter.

First noticed excessive vibration that you could feel in the steering wheel and hear in the dash and interior trim. Also noticed significant drop in gas mileage. No check engine light.

First mechanic said engine diagnostics were good, vibration caused by bad torque converter. Replaced torque converter -> Did not fix the problem.

Next mechanic found misfire on one cylinder. Replaced plugs, replaced one injector, cleaned other injectors -> Did not fix the problem. Parked the car for several months.

Next mechanic found a couple of plug wires that showed heat damage and were arcing, causing intermittent misfires. Also discovered it had a blown head gasket. (I'm pretty sure this happened when I drove it once during the time it was stored. It wasn't a problem when the earlier mechanics looked at it.) I had the heads checked & milled, replaced the head gaskets, plugs, plug wires, oil & filter. -> DID NOT FIX THE PROBLEM.

Very frustrated now. It is not mis-firing, exhaust tune sounds right, and there is no loss of power. However, the vibration is still there. My mechanic believes the engine is 'out of balance' and suggests that it could be either the internal balance shaft & chain, or possibly we could have thrown a balance weight on the crankshaft (I didn't know these engines had weights on the crankshaft - is this true?). In hindsight we should have gone ahead and torn down the entire engine when we had the heads off so we could eliminate all possibilities. The car is put back together now and it seems to run fine except for the vibration that will not go away. I suppose we could just drive it till it fails, then either rebuild the motor or replace it with one from the junk yard.

Any suggestions from the experts here? Is there something unique to this engine that we are overlooking ? Or something obvious we haven't considered? I've spent too much on it already considering the value of the vehicle. However, I really don't like the idea of problem that can't be diagnosed and solved.

Originally Posted by a1 technician

I know exactly what your experiencing. Im a shop owner here in Los Angeles and have been trying to resolve the same problem for 3 days. I repaired the same problem by going to the dealer and purchasing a New harmonic Balance. Also there are 2 different ones that the vehicle cars for. I put on one and the same problem still was there, so I went back to the dealer and found that the vehicle had another option for thAT make and model. Part number is XR3Z-6B321-AA. Also the vehicle had a misfire on cylinder no.1 which wasnt coming up on diagnostic trouble codes. Be sure to have vehicle checked for a misfire, as replacing the balancer will only eleviate one problem or concern of vibration. Hope this helps.