Knock Knock

[Jan Larsson]

Some of you probabrly read my thread where I installed the Scanmaster .... plenty of knock ...

Anyway, seems like I have some rattling noice when the car sits at ideal (in Park) but when you rev the engine it kind of follows the rev of the engine. Sounds like something is loose somewhere at lower back part of the engine.

Anyway, took off the crossover pipe and that one was secure and no leaks, also remove the cover over the turbine and same thing secure. Looks like all the bolts for the flexplate and turbine are there and secure but like to see if I can make sure, the 3 bolts holding the turbine to the flexplate can I just remove them and bush the turbine out of the way to get to the 6 (or 8) bolts holding the flexplate to the crank?

Also any ideas what else could cause the rattling sound, defenitly sounds like something is loose and rattles. Checked started, downpipe and other bits but can't find anything. If the motor mounts are dead would they start making a sound at idle? Anything in the engine would make that kind of sound, I would expect that to make a more distinct sound ...

Engine runs smooth at idle (below 1000 rpm) and is not all over the place so the engine itself is not moving around a lot at all. And if I rev the engine a bit (1500-2000 rpm) it lifts just slightly on the driver side but not much at all.

Looked for leaking headers as well but does not look like it's been leaking anyware.

Any ideas, suggestions is more than welcome as I will continue tomorrow.

 

[Jan Larsson]

Been reading on the boards and seems like some lifters are noisy not sure what it would sound like would expect more of a tapping sound than my rattling sound.

Also the converter can be noisy apparently, can I disconnect the converter from the flexplate and run the engine to find out? Would this be safe to try?

 

[SlowTTA]

You can disconnect the Torque convertor from the flexplate to try and rule it out. When you have the TC disconnected it removes the load from the flexplate...if you don't hear the knock when it is disconnected it is probably the flexplate. I have read a few posts about people finding that their flexplate was cracked causing KR. As for being able to able to attempt to tighten the flexplate bolts while the transmission is in...I doubt it.

Is your ignition module secured...when I bought my car the previous owner had forgot the rear bolt and was causing knock from the module bouncing off of the bracket.

Hopefully someone else will give you some more advice...hunting down false knock(if that is what this is) is a PITA

 

[83ttypecooled]

Hi Jan,
I am guessing that your flywheel is tight, because there just aren't that many problems in that area with our cars. I have heard, however, of a lot of valve train noise from the vehicles. My car, specifically,has a tappet noise, especially when cold.I will bet that it has something to do with the FWD 3.0 L heads, and the related valvetrain, that were installed on our cars. Don't know, but strongly suspect, that this is the basis for it. What do you think?
Keep up the work on that fine car of yours!

 

[Jan Larsson]

Flexplate and torque convertar are all good and properly bolted up.

One thing I notieced was that my torque converter cover looked like it was rubbing on the inside somewhere compared it to another one I picked up last year and have had powder coated and mine was badly beat up and kind of flat in the area where it's supposed to clear the crank I beleive. Anyway bolted that one back up and put the cross over back on and fired it up and the rattle was gone Not sure how this affects my knock issues.

Also replaced the bearing in the belt tensioner as I have some noice from the belt driven accessories as well just to be on the safe side, still have some noise from either the alternator, AC or steering pump ... not sure on this one.

I did rev it up to just below 2000 rpm and had 1.4 knock retard on the Scanmaster?

Changed oil and filter, oil looks good as you would expect after only 500 miles or so.

Need to take it for a spin but started raining and it's mothers day so have to be another day later in the week to see if something improved or not.

Looked for any loose coil brackets and others but everything seems to be bolted down properly.

Also looked at my downpipe and frame clearence and have about 1/2" or so that should not be a problem. Shaked to whole exhaust as well and it does not hit anywhere.

I'll take it for a spin as I said and will see what the Scanmaster says.

 

[BlackRob91]

Spun Bearing?!?!?

Usually more than 50% of the time it could also be a spun bearing turbo cars are bug foor that I had a Turbo Supra and it made the same noise your describing also the same thing happened in a firebird that I had. So take off the oil pan and see if you find scraps of metal and there u go.

 

[mark b]

I hate to even suggest this but I chased what I thought was false knock in my GN for years. One day I started hearing a rattling from the rear of the motor and checked all the things you did. Not long after my torque converter went. Less than 50K miles, never raced. The inside was nothing but scrap metal. No slippageor any other indication of a problem.

 

[Jan Larsson]

If I spun a bearing wouldn't I see something in the oil? I even poured a pint of fresh oil in from the top while still having the oil plug removed to drain out any old oil in there and all the oil looked fine as expected from 500 miles .... I will cut the oil filter in half and have a look as well as I have had a magnet (whatever they are called) on the filter to trap any small metal parts.

The actual rattling noise went away after I replaced the inspection cover over the torque converter so as I mentioned the old one was defenitly hitting something as I could see the marks on the inside of it and it was dented in that are as well, so the new (thanks Turbo Lunkan) have much more clearence in that area.

 

[jjvites]

Jan,
I hope this helps you as it haunted me for a very long time. I had a rattling in the motor that could not be pin pointed. It would set of my knock sensor with false knock and loss of power due to retarding of timing by the computer, even in Park. After replacing many parts what I stumbled on surprised me. I believe that this plauges many a driver without them knowing what the cause is of their power loss is. When after replacing the belt tensioner because of a worn area where the pulley bearings fits over, I started the car and everything was good but when I revved the motor in Park it made more noise than before. Well the noise was coming from my new GM tensioner. What the heck? Well it turns out that our cars are VERY sensitive to belt lenght. Originally these cars came with their own specific belt lenght. As GM discontinued this belt and guys started buying belts from the parts stores, sometimes the belts were to long and under load conditions the tensioner will bottom out on itself and cause a knock that is false. I compared several belts at the parts store and found that the actual lenght of similar marked belts differed quite a bit as some were longer than others. Try a shorter belt and see if your noise goes away.
Sorry for the long post but this was so aggrivating for so long I feel sorry for anyone else who is going through this.

Marty

 

[Quiky One]

Buy a 1595 mm belt from napa....

 

[Jan Larsson]

Thanks Guys, I'll try a new belt on there today. Still have a couple of GM NOS belts (1603mm) as well as some other shorter ones I beleive.

So when the belt tensioner gets noisy is it the bearing (I replaced mine last week) or is it the spring loaded arm that gets noisy?

 

[Jan Larsson]

New belt on (GM NOS 1605mm), clears everything. Noise down a bit and knock at idle and reving seems to be way down. Still have knock when driving ..... just accelerating slowly (putting load on engine) give me knock up to 6-8 on the scanmaster ....

Will replace a few bits (knock sensor, ESC module) and see if they are faulty in some way.
By the way cut the oil filter open and it's very clean inside no metal fragments what so ever ....

 

[Jan Larsson]

Tried a brand new ESC module and no change then installed a brand new GM knock sensor along with a new coil back and module (as I had to remove them anyway to get to the knock sensor) and again no change.

My engine tie down was a bit loose so I tightened it a bit and I could then feel the vibrations when I reved it up to like 2500 rpm so I loosened it up a bit again. But before and after I still had the same knock as before I messed with it.

Will look at the spark plugs and see what they looks like next.

 

[jjvites]

Thanks Guys, I'll try a new belt on there today. Still have a couple of GM NOS belts (1603mm) as well as some other shorter ones I beleive.

So when the belt tensioner gets noisy is it the bearing (I replaced mine last week) or is it the spring loaded arm that gets noisy?

Jan,
In my case it was the tensioner bottoming on itself. If you want to see where yours is at, take a marker and draw a line next to the idler arm on the pulley. Then remove the belt and see how much the arm can move before bottoming. Mark again with belt of and then reinstall the belt. Start the engine and see how close the arm moves to the mark near where it bottoms out.
Also check to see if your harmonic balancer loosened up . This has happened on these cars and it will cause vibration.

Marty

 

[Jan Larsson]

Thanks Marty, I'll check that tomorrow just to make sure I have no issues with the tensioner.

 

[Razor]

I had a similar issue, ended up being a bad thrust on the crankshaft. At 2200-2500 RPM it would show knock on the scanmaster.. ran great at WOT. Actually ran 10.9 at BG last year with the bad thrust

Easy way to check thrust, pull serp. belt off.. now go underneath and yank the flexplate front and back. There should be no play. Clearance is like .010. If it has more than that, thrust is going out on crank.

Bad TQ converter killed mine.

 

[mikebart101]

I have the same noise w/ under 10k miles on new motor. Noise seems to go away as the car heats up. Ive taken a stethoscope to the motor and can not locate the noise. But I have a sneaking suspicion that it is either the belt tensioner or clutches in the AC compressor rattling.

 

[Razor]

Take the belt off and run the motor see if the noise goes away..

Easy

 

[Jan Larsson]

I did a top engine clean last weekend and the a complete oil change with some oil flush addative .... new oil and filter car runs smoother and feels better.

Less knock for sure but still get it around 2500 rpm or so .....

Will do a new compression test and a leak down test this coming weekend to see what is going on .... after that determine what needs to be done I guess

 

[mikebart101]

Take the belt off and run the motor see if the noise goes away..

Easy

Can I do that with a hotwire kit?