Im not a mechanic but Im fairly certain this sound is no good...

[Finn]

Started doing this after I went fill it up at a gas station. Put 91 in it and drove it home (about 2mi). It's very loud at idle but seems to die down a bit as I cycle through the gears. Also seems to become quieter with RPMs. I took the dust cover off and made sure the flex plate was secured. It was. Checked oil pressure with a mechanical gauge and it was holding steady at 80psi.

It's hard to pin point the noise between the engine or transmission but whatever it is, it's bad. Thoughts on what it could possibly be?

http://www.youtube.com/watch?v=K95WEADonH8

[ACUDANUT]

 Bad gas 

[Finn]

I had that issue once before and it sound more more like a ping than the rattle I currently hear but I won't rule anything out at this point. I'll try draining the tank and putting new fuel in tonight. Man, I hope it could be as simple as that...

[GPULLER]

Balancer didn't take a dump did it?

[ACUDANUT]

I would hold off draining the tank until you get some more ideas.  I would pm fighterfighter also. 

[b5blue]

It does kinda sound like flex plate/torque convertor slapping. I got a 4x4 Ford pickup for cheap and found "that" was all that was wrong.  

[Dino]

I seriously doubt it has anything to do with you putting one tank of 91 in there.  Something went wrong when you shut the engine off or restarted it.

How did you get 80 psi?  I'm happy mine hits 50 or 60 but then again my gauges are not the most accurate in the world.  Maybe I should get some mechanical gauges as well...

[Finn]

70 psi* sorry for the typo. It would reach 80 at higher rpms.

[Just 6T9 CHGR]

Sounds like its TQ converter related.....Sure none of the bolts walked out?

[rattlehead_74]

You might check your exhaust too..I had that happen on a truck I put dual exhaust on...It was fine before the exhaust job ..after it sounded like it was about to lose a rod...it was rubbing on the transfer case...bent it up a little bit and the "rod knock"went bye bye..just throwing that out there...hope its something easy...

[Back N Black]

What condition is your motor mounts? sounds like the headers is hitting the torsion bars.

[Brass]

Sounds like its TQ converter related.....Sure none of the bolts walked out?

If it quiets down a little when it's put in gear then it could be loose flexplate bolts... 

[71green go]

I remember 30 years ago when I was young and stupid...driving home from the bar in my 74 charger I was drunk...and just wanted to get home....on the way the same noise started in my car and got louder......i was so scared the noise would draw attention to me and I would get pulled over.......made it home parked car and next day went to find the noise
It was the bolts on the flex plate and Torque convertor backed out....lock tight and tightened them up and good to go...

that was the 2nd to last time I drove drunk...the next time was the last and most scary

[Mick70RR]

Check the damper hasn't slipped, it happened to me and the damper was hitting the timing cover. Only made a noise at idle and went away when I increased the revs.

[lisiecki1]

Wow.  Almost reminds me of a spun main.  Hope you get it worked out.

[Finn]

Ok guys, here's a list of potential problems as per suggestion and checks I have done/will need to do:

Bolts to TQ ---- Removed the dust cover and got about a 1/4 turn on all four bolts. I was surprised they weren't tighter but the noise was still there when I tried running the engine again.

Bad gas ---- I didn't drain the tank yet but I did the "sniff" test, and its smells fine.

Exhaust contacting something ----- Visual inspection revealed nothing, so I took a breaker bar and pried it gently against the headers at various points while the engine was running to see if I got a change in sound or felt a vibration. Nothing. Also checked all the exhaust bolts and clamps. All were tight.

Motor mounts ----- They are original and I did not do the recommended "bolt through" modification to them. They appear fine, however.

-------------------Questions----------------------

Damper/harmonic balancer slipped/went out ---- How do I check this besides making sure its tight? Timing light?

Flexplate bolts backed out ---- This seems highly likely. Just to confirm my method, I plan on unhooking the front of the drive shaft, unbolting the transmission and sliding it back enough to check the flex plate bolts on the engine. Does this sound like the correct plan of action?

Spun main bearing ---- Oh please no. Would I be able to see this is if I drain the oil and remove the pan?

[b5blue]

Dampener check the ring by hand for tightness, I'm certain it would look out of alignment most likely. Check all the pulley mounting bolts on the front of the engine also.
You can rig a fuel line from a container to feed the pump to bypass the fuel in the tank to check that also. (To be sure.)
Could some part of a muffler come loose inside? (I've seen that happen.)
Check the rivets and mounting of the cooling fan, I've seen fan blades fail. (Unless you have electric.)
You may want to drop the trans. pan to check for junk inside and check the mountings on the TC that the flex plate bolts to. (The weld may be failing/failed.)   

[ACUDANUT]

Getting to the flex plate that bolts to the engine is going to a PITA. The other part (flexplate bolting to the converter is easy).  Keep us posted.
BTW, are you sure you did not break a rocker or something ?

[Finn]

Just got home from work so I'm going to start ripping into it. I guess I could have broke a rocker but I've got probably less than 6 hours of run time since the rebuild, so I would like to think it would have lasted longer than that.

[b5blue]

Good luck! 

[Finn]

Thanks! Balancer is good, just checked it.

[firefighter3931]

Finn...what flexplate bolts are you using ? The correct fastner has a very shallow head so you cannot use a std bolt. 


Ron

[b5blue]

Good point Ron....

[c00nhunterjoe]

That sounds like mine did when I cracked the flexplate.

[Finn]

Just checked, they are shallow headed bolts. I compared one to an original and they're the same. Also had previously taken a sharpie and coated the head of the bolts then ran the engine to see if it's contacting anywhere. Nothing. I've got the trans about 1/2 disconnected at the moment hopefully it will be out enough to check the engine side of the flex plate by tonight.