New and odd sound

What might make a sound something like someone throwing several pebbles in succession at the exhaust system at about 1/2 throttle. Engine runs fine, no CEL, no codes at all, no misfire, stumbling, etc. Just that damned sound: tick-ping-pang-donk-tink (knick-knack paddywhack?). Let off the throttle, and it stops. Step on it again, and it's back.

Just guessing: 1. try a different gas brand 2. Something has come loose inside the catalytic converter?

Tom

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1. try a different gas brand

I considered that, and it was easy enough to rule it out.  On the 1000 mile loop, I had the opportunity to try three full tanks of 93-95 octane Shell, Mobile, and Sunoco.  Same result.

I can't quite tell the exact location of the noise, but it might be near the cats.  I had thought is was more forward, but leaning this way and that around in the car and turning your head sideways to try to pointpoint the location is risky when  driving at 80 mph.

Cats are original to the 1996 Fleetwood, now with 106,000 miles.

Does it make the noise when the car is stationary? Have you looked under the car for loose parts?

I have looked and found nothing below the car or under the hood.  It does not make the noise unless the car is moving.  It is not proportional to vehicle speed or engine RPM.  It definitely comes and goes in response to the amount of throttle applied.  It does not occur every time throttle is applied, but it does occur only when throttle is applied.  Imagine shooting the exhaust system, cat or heat shields with a BB gun.  That's the sound (as heard in the cabin of a Fleetwood... so it's a bit suppressed).

That is the usual symptom for detonation. Pull the plugs, and check them.

Ran home at lunchtime and pulled the two easiest-to-reach plugs (front 2, driver side, see below).  They look fine to me.  Gap is correct.  No cracks or deposits.  There's only about 3000 miles on the plugs: AC/Delco copper cores.  

After replacing the plugs I started the car and managed to get it to make the sound a few times in Park by reving the engine up to about 3000 RPM, holding it for a 3-count, and then releasing the throttle.  It make the sound (bing-ping-pong) as the RPMs decreased.  Repeated this about 12 more times, and produced the sound twice.

I saw a tool recently that had 4 "microphones" to place, under the car, to determine the location of a noise by triangulation. I almost bought it. Can you get someone to help you determine where the noise is while you make the car produce it?

Ah hah!  It sounds a LOT like this, right at about 1 minute and 12 seconds into the video:  

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https://www.youtube.com/watch?v=0Ez5UEiwGZU

A cat converter with loose crap inside?  Now, how does one determine definitively if this is the culprit?

"Now, how does one determine definitively if this is the culprit?"

You might try rapping on the cat with a rubber mallet.

The exhaust mounting on the Fleetwood is so solid that rapping the cat does nothing. I'm going to try to use an infrared thermometer to measure the inlet and outlet temperature of both converters. I have an high-end IR thermometer at work. Temp should be higher at the outlet. If it is more than 100F higher at the inlet than at the outlet, it's probably not working as designed. There are also some pressure tests that could be run to measure backpressure at the front O2 sensor to see if the core is bunged, but that's a job for a real mechanic with tools, experience and asbestos skin.

if you have a good inspection camera you might be able to pull an O2 sensor and go through that opening with the camera to get a look at the cats.

Damn... if I'd only been a proctologist instead of a plant pathologist!

OK.... we have identified the problem, and it's one of the books.  I took the car to a local shop to get it up on a lift to pinpoint the noise, and it was immediately apparent that something was terribly wrong in the cover over the ring gear and torque convertor.  The cover looked like it had been beaten with a ball peen hammer from the inside, and there were actually some extra holes punched through.

When we removed the cover, the cause was obvious.  The aluminum housing of the starter (only 5 months old) had self-destructed and the cover was full of lumps of well-beaten pot metal.  Removed the lumps, ordered a new starter (under warranty), and made my appointment for the free installation.  All is now well. The noise is gone. Amazing that there was no damage to the gear or torque convertor housing, and the starter still seemed to work fine.

The starter nose will continue to break off if the ring gear is not perfectly true.(off center) Might be something to check before replacing the starter. It is amazing it still worked with no front bearing.

dang!

I agree check over the flexplate well and also check that the starter mounting pad is clean. Were the proper starter bolts used?

What is the proper fix if the ring gear is not true?

I had the exact same thing happen to my Fleetwood in the past 6 months.  Asked Nick about it, he said it happens, don't worry about it.  I had another starter kicking around ready to go and installed it.  Fortunately, there is a rebuilder not far from me.  They had an old case and swapped everything over.  Now it's on the shelf on stand by.

Tom

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Now it's on the shelf on stand by.

Tom.... you're doing it again. You just cleaned out your parts stash and the tide is coming back in. But thank heaven for hoarders. Otherwise, I wouln't have the little plastic bit that completed my 1996 Caprice wagon!

Hmmm... I just learned from the previous owner of the Fleetwood that the starter that was replaced in May was also relatively new when it crapped out.  When it was removed in May, the mechanic mentioned that the bearing was so shot that he was amazed that it still worked.  So, this car seems to have a recent history of eating starters, and spitting out the bones.

So, what are the likely causes, and how are they diagnosed and fixed properly?  Why does this car eat starters?  How does one test for a ring gear out of "true", or a cockeyed mounting of the starter?

dmg4 wrote:

Hmmm... I just learned from the previous owner of the Fleetwood that the starter that was replaced in May was also relatively new when it crapped out.  When it was removed in May, the mechanic mentioned that the bearing was so shot that he was amazed that it still worked.  So, this car seems to have a recent history of eating starters, and spitting out the bones.

So, what are the likely causes, and how are they diagnosed and fixed properly?  Why does this car eat starters?  How does one test for a ring gear out of "true", or a cockeyed mounting of the starter?

Mine had 70K when the starter broke like yours did. If I remember correctly, Nick said torque does that. I know guys use the Corvette starter, maybe that would help. Maybe it has to be shimmed?

You probably bought a lemon, just so happens I'm looking for a parts car, what do you want for it?

Tom

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You probably bought a lemon, just so happens I'm looking for a parts car, what do you want for it?

Nice try.

It just so happens that the starter that was eaten alive back in May was a new Corvette starter, and the second one lasted less than 3000 miles. So, this car is eating starters like potato chips, even the heavy duty ones.

From all I can find online, the starter is either mounted out of alignment, with incorrect clearances, the flexplate is somehow flawed, or some combination of the forgoing. Same questions as before: what is the process to definitively determine the root cause, and how is it fixed? I don't want to just throw parts at the issue an do this by trial and error.

You can hand turn the flex plate, and measure clearances at points around the flex plate. Flex plates do not usually go out of true/round, unless the center is broken. I would look at the starter for alignment or mesh issues first.

that's odd, my 90 suburban with plow had a misaligned starter for several months, and when the shop got it supposedly aligned properly the only issue was that it made excessive noise while cranking, in fact that starter is still on that burban

There are likely differing degrees of misalignment, and consequences thereof. This Fleetwood makes yummy sounds and chews them to pieces.

"How does one test for a ring gear out of "true""

Clamp a wooden dowel so that it just barely "clicks" on the teeth. Rotate the engine and see if there is any one place that jams the dowel or leaves a visible gap. Do this on the outer surface of the gear and on the gear face. If you see a problem with your eyeball, it will continue to break the starter nose.

The car goes back on the lift on Tuesday for diagnosis of why it has acquired an appetite for starters. Anyone want to get in on the poll? Cracked flex plate? Wrong bolts? Deliverance syndrome (missing teeth)? Failure to shim to alignment during installation? Bad mojo? Multiples of the foregoing?

I'm guessing they'll find nothing they can pinpoint it to.

Tom

Following...Oddly, my very first wagon, a Fred special, had a similar habit of eating starters. I believe we went thru 4. Hmmm...

I'm guessing that the installer is not confirming proper alignment time after time, the starter needs a few shims to be properly aligned, and that's the root cause.

Stay tuned tomorrow!  That's when she goes on the lift for starter #3.

And the winner is (drum roll).... TOM, with the correct guess of nada.

Yes, it's true. The installed put in a new starter, with the bolts that were supplied with the new starter, no shims, checked alignment and engagement and all was well.

Now well see if all the pot smoke from Cornell is giving my car the munchies, and it eats another starter, or if this problem just fades from memory.

dmg4 wrote:

And the winner is (drum roll).... TOM, with the correct guess of nada.

Yes, it's true.  The installed put in a new starter, with the bolts that were supplied with the new starter, no shims, checked alignment and engagement and all was well.

Now well see if all the pot smoke from Cornell is giving my car the munchies, and it eats another starter, or if this problem just fades from memory.

Keep my prize money and get a used starter, at your friendly junkyard. Then keep it in the trunk. Actually, I should follow my own advice.

Tom

You might want to look at the flexplate teeth and see where the bendix is engaging it. If it is deeper than the FSM pic, that can be shimmed out.

With the history you have, you might try just shimming it out anyway.

The starter that was installed in May was at a local shop and under warranty. The installer had not checked alignment or engagement that time. This time, he removed the flexplate/torque convertor cover and check the condition of the flex plate before installation, and alignment and engagement after the new starter was installed. Everything checks out perfectly. It's a good shop, and the manager does not like having customers return with repair issues. It's odd that this car has eaten two starters in less than 1 year, but so far all we have is an oddity.

As I wrote: nada. Tom remains the winner in this guessing game (for now).