M30 noises -- audio pop quiz

[everysandwich]

Hi folks -- I bought a 1991 Infiniti M30 with 56k on it off ebay. Apparently it was owned by a Florida snowbirder who drove it a few months a year but never maintained it. I just put $2600 into it -- much of it neglected maintenance. I'll include the list at the end of what was done. After all the work, it seems to drive okay, but there are two sounds that aren't normal. One is a tapping from the engine compartment and the other is a strange mechanical sound, almost like a stuck cd changing mechanism. This seems associated with the climate control system since it doesn't seem to happen when the air is blowing from the dash rather than from beneath. Here's the engine sound. It happens regardles of whther the car is moving. http://www.handsacrosstheporch...e.mp3 and here's the climate control sound http://www.handsacrosstheporch...n.mp3

Here's what was done window amplifier to make driver window function -- oil change -- new timing belt -- distributor cap -- plugs and wires -- fuel filter -- oil pressure sending switch --camshaft or crankshaft sprocket -- crankshaft oil seal -- transmission oil pan gasket -- valve cover gaskets -- remove two broken bolts from plenum -- replace injector connectors

[Q451990]

Not sure on the engine... doesn't sound good. Can you localize the area it's coming from? I would get a mechanic's sthescope like this to localize it. http://www.harborfreight.com/c...41966

The nosie from the climate controls sounds like one of the door actuators trying to do something and jamming. Does your car have the automatic climate control?

Unfortunatley I don't have a factory service manual. It might be worth downloading one for a 94 Q45 at http://www.phatg20.net and see if the climate control will go into self diagnostic using the same steps.

Good luck!

Heath

[Jesda]

Could the blend door be stuck or sticking?

The tapping could just be injectors if its faint, or HLA noise if its loud. HLA tapping is generally non-serious and can be alleviated with a bottle of Marvel Mystery Oil or a motor oil high in detergents.

Hopefully its a tapping and not a knock. Can you take an audio clip and share it with us?

[everysandwich]

Thanks Jesda and Heath. Two votes for stuck doors makes that sound likely to me for the climate control thing. As for the tapping, what's weird to me is that I didn't hear it before I had all that work done it. (It's astounding to me that the mechanic didn't test drive the car after the huge sum I dropped with him. I'm not a mechanic, but if I were, that would be policy before I made a call to have a customer pick up the car.) Anyway, the audio files should work if you click in the original post, Jesda. I can't really pinpoint the tapping sound without that nifty stethoscope, but at least now I know that tool exists. Also, the John Mayer link cracked me up. I appreciate it, guys.

[Q451990]

The fact that the engine noise is only there as the engine revs down concerns me a little. Typically HLA noise is a constant tapping related to engine speed, but you'll hear it reving up and down.

I once had a peice of melted pre-cat on a Q that was rattling in the exhaust that caused that sort of noise. My dad was convinced that it was piston slap or a rod bearing... I was almost to the point of being physically sick until I found it with that sthethescope. It might also be worth your while to let the guys at T3 look at your car. They probably the premire independent Infiniti shop in the nation!

http://www.t3auto.com

Heath

[everysandwich]

UPDATE -- Well, the mechanic thought my noise was from broken bolts on the exhaust manifolds, so he took those out and replaced them. The sound seemed to disappear, until the thing ran for a bit. He subsequently identified a bad bearing, (which would have been nice to know before I spent the now $3,000 repairing an engine that's now suspect.) I saw the old bearing, which was scored. So he put in a new bearing, and the engine sounded better but still made a noise, though less of it. He looks around for an oversized bearing but can only find on from nissan/infinity that he thinks is too big -- 8/1000ths bigger, I think. He tells me he can't tell if the crank shaft is scored, but it doesn't look bad on the bottom.

So now, from what I've been reading, I suspect this oversized bearing solution will be short term, at best, and I'm trying to find options. I understand the M30 will take a bigger Nissan engine. Does anyone know which ones and where I should look? Any info on that is welcome, including ballpark costs.

Lastly, how do you think a car with 56k on it has broken exhaust manifold bolts and a bad bearing? Having seen the air filter out of this car I suspect no maintenance ever occurred to this car, so all I can guess is that they never changed the oil in 56,000 miles.

As you can tell, I'm not much of a gearhead, so I apologize if some of this is unclear. Also, if you want to know the dealer from whom I bought this on Ebay (for your own shopping protection,) email me. I could not feedback him because I used "buy it now."

By the way, the guess on the stuck doors in the climate control system were correct, but fixing them involves removing the dash. At this point that issue is not high on the priority list. Thanks for the help so far, good people. I think I might be visiting T3.

Update of the update: After paying the mechanic another $320 to tell me it's not the bearing, I took the car to T3. They listened and thought it was very "weird" that a car with this engine and only 56k on it would be that sick, detailing torture tests they had done on this model engine by way of expressing it's durability. It came down to the worst case scanario. It's probably a wrist pin, but whatever it is, its location requires tearing down the engine, which costs as much as getting a new one installed -- three to four thousand dollars. I wish I'd come here and learned of T3 before I paid some clueless mechanic three grand on fixing a doomed engine.

I still don't know how someone can abuse a car this well made badly enough to destroy an engine in 56,000 miles. That's a special talent. Thanks again for the tips and feedback.

Modified by everysandwich at 10:29 AM 8/17/2007
Modified by everysandwich at 6:56 PM 8/22/2007