300zx 2+2 automatic with engine vibration and knock

[TorresGluck]

I would like advice on a problem with engine vibration and knocking on my 1996 300zx. The car has 115K miles and has been very very carefully mainained. The only major repair the car has had was replacement of the mass air flow sensor, and driveshaft, which were done about 10K miles ago. This was done at the dealership.About 1 month ago I started noticing a knocking sound coming from the engine. It hapens at a frequency of 2-3 per second and only occurs when the car is in gear, not in neutral or parking. It seems to have gotten slightly worse since I first noticed it. More receently, about 1 week ago I also noticed a vibration. It occurs at all RPM's, but seems to be significantly worse when, in acceleration, the car is between 1500 and 2500 RPM. It occurs equally in idle or when the car is moving. I took it to a mechanic who, after driving it for a while and putting it on a lift told me that my engine is shot and the only remedy is to have it replaced. I believe that although not a Nissan specialist, he is a good mechanic. I am, however a little incredulous that an engine that has been painstakingly maintained and hardly been abused would be about to suffer such an early death. Any ideas about what else could be going wrong or what else I should look into. I am not knowledgeable in mechanics to figure it out on my own, hence my inquiry within this forum. Thanks

[evildky]

Welcomew to Nico!it can be difficult to give a diagnosis without experiencing the problem first hand, it is very unlikely for a Nissan engine to develop a rod knock at only 115k miles, if you do have a rod knock then yes rebuild or replacement are the only options, I highly recomend taking the car to a Z specialist, the Z32 is a very unique car with some very complicated systems and I wouldn't suggest having it serviced by anyone not experienced with them

[TorresGluck]

Thanks for your input. Today I made an appointment to bring the car to be checked out by the local Nissan dealership. I have always believed in the concept of a second opinion. The guy who diagnosed it first, howevere, I think is sharp. When my car developed problems several months ago he told me off the bat that it was a defective mass airflow sensor. He was terribly busy and for that reason could not do the work himself so I went to the Nissan dealership. There I was told initially that I needed a new transmission. A couple of days later they told me that the transmission was OK, that the mass airflow sensor was broken and went ahead replacing it, restoring the car back to its original performance. Unfortunately, auto mechanics is not my thing, and I am afraid of being taken for a ride: having an expensive repair now and then having to replace the engine anyway in six months. But again I am weary of the fact that this is a car that has been meticulously maintained in every regard and that has hardly ever been "abused."

[evildky]

when dealign with a 12 year old car, going to the dealer might not always be hepful, the tech looking at your car might have never seen a z32 in person, you might have a dealership with very low turnover in their shop and lots of tenured teches well versed in Z32's but it might be the new guy taht gets assigned to it, just be sure the tech sho looks at it has experience with z32's wether he is a nissan tech or not

[TorresGluck]

Without knowing anyone in the area who is a Z32 expert I just decided to take it to the dealership for a second opinion. They say that the vibratin might be the harmonic balancer that could have worn out eccentrically, thus wobbling when it spins. About the knocking sound they say they think that it may be that the timing belt, which is now 55K miles. The belt may be loose and thus may have jumped a tooth. I am a little suspicious of their diagnosis for several reasons. First they asked me to authorize 3 hours of labor on it in order to do some diagnostics. They asked me to leave the car overnight. When I picked it up they say that they were going to waive the charge for 3 hours of labor they had requested. They told me they recommended that they bring the car for more diagnostic tests and to replace the timing belt. Somehow I have the feeling that they didn't even look at it! Second, I ran it by Tommy, the first mechanic to whom I took the car initially. He thinks they are totally off. He thinks the harmonic balancer is fine and does not think that a problem with the timing belt would have presented with an engine knock. At this point I am a little torn about what to do. I surely don't want to replace the engine if all it needs is to have these two items replaced. But at the same time if the engine is shot I don't want to spend unnecessary money in repairs that will ultimately be fruitless. I don't want to buy a new saddle for a dead horse expecting it to ride better. What would you suggest?Joey

[Ill give u a head start]

i have a sure rod knock on my 93 TT only gots 89k miles. Although it makes the knocking sound in every gear from 2800rpm and up and in Neutral.So thats kinda weird if yours doesnt do it in neutral for it to be a rod knock.Btw mine is a 5 spd if that makes a difference

[TorresGluck]

In my case it's weird. The knowcking sound only occurs when the car is in gear and only at low RPM. In neutral or parking it is completely absent and when in gear the knock disappears above about 1500 RPM.Could the problem be the tranmission?

[Ill give u a head start]

duno but if i were u i would find a Z specialist close enough that u could drive to

[scottbrownloans]

I wonder if the noise you hear might be a hydrolic lifter in the engine, I have the same noise comming from my engine also.... "its just a thought"

--Scott--

[ironwill]

one of my friends had the same problem and he replaced the chip and it fixed the problem