Rattle or ping? (1 Viewer)

[CurtB]

So I've got the old beast running pretty well with newly rebuilt carb & dizzy from @FJ40Jim. I have a noise that I can't figure out...is it a rattle or a ping? I was convinced it was a rattle at first because it sounds like a loose heat shield or hollow metal with pebbles rattling around inside. BUT, if I retard the timing it diminishes. If I keep retarding, it keeps diminishing but the engine gets all the bad habits of needing more advance: sluggish, backfire, etc.

The noise starts in the mid 2000 RPM range under moderate load...goes away (or I just can't hear it) above 3000. I can't recreate in the driveway. Also goes away under a heavy load. From that standpoint, it kind of acts like a detonation ping but it doesn't really sound exactly like that....more metallic, I guess. If I'm just cruising around town in any gear at about 2300 RPM, I can sustain the noise with gentle throttle. Happens in 2wd or 4wd. Seems worse on a hot engine.

The only other misbehavior at this point is the engine is hard to start when hot. Needs a lot of starter run to get it to fire up. Yes, the carb fan is working correctly. Valves are adjusted. The last time I checked compression was what you'd expect from a 2F with 250,000 miles on the clock.

This is driving me batty...also worried that continued driving might be causing damage if something is really wrong.

 

[g-man]

Can you take a video of this and post it?

 

[FJACS]

Check for an exhaust leak around the manifold.

 

[CurtB]

Check for an exhaust leak around the manifold.

So, there is a little leak around the flange where the head pipe meets the manifold. Hmm...worth addressing but not the sound I'd usually associate with an exhaust leak. I'll give it a go.

 

[OSS]

Is the EGR valve disconnected? (with a factory curved distributor?)

 

[CurtB]

Is the EGR valve disconnected? (with a factory curved distributor?)

EGR and Air Pump have been deleted. Dizzy recurved by @FJ40Jim.

I fixed the exhaust leak with no change in symptoms.

 

[CurtB]

Can you take a video of this and post it?

I tried but you can't really hear the noise in the video.

 

[Seth S]

Gondrive around and get the truck warm. Go find the steepest hill.....if you live in Kansas take a weekend trip to Colorado. Get to the hill and put the truck in 4th gear even as the rpms drop and your speed. If the noise gets louder under load then it’s most likely knock/ping/preignition.

 

[CurtB]

Gondrive around and get the truck warm. Go find the steepest hill.....if you live in Kansas take a weekend trip to Colorado. Get to the hill and put the truck in 4th gear even as the rpms drop and your speed. If the noise gets louder under load then it’s most likely knock/ping/preignition.

I'm in Florida.. No hills nearby but we do have bridges. The noise does NOT get louder under load. I'm leaning toward a vibration thing except it changed so obviously when I adjusted timing.

 

[OSS]

When the gas tank is empty, fill it with premium fuel. See if that changes anything. If the rattly sound diminishes or goes away, the timing is too far advanced for the gas you were using before using premium.
Either use higher octane fuel or retard the timing.

The 2F will run great with more power at certain RPMs and loads with the timing too far advanced. It's a deception though. The timing must be set so the engine doesn't ping at any load or RPM.

Jim's distributor recurve changes the advance curve (obviously). 7° BTDC is a starting point to set timing.

 

[CurtB]

When the gas tank is empty, fill it with premium fuel. See if that changes anything. If the rattly sound diminishes or goes away, the timing is too far advanced for the gas you were using before using premium.
Either use higher octane fuel or retard the timing.

The 2F will run great with more power at certain RPMs and loads with the timing too far advanced. It's a deception though. The timing must be set so the engine doesn't ping at any load or RPM.

Jim's distributor recurve changes the advance curve (obviously). 7° BTDC is a starting point to set timing.

This sound is different than the regular ping...I can still force a slight regular ping if I try really hard (full throttle from low rpm). This sound is louder and comes at moderate throttle only, in the mid 2000 RPM's.

 

[2mountainfish]

I had the exact same thing happen on my 85. It is desmogged,recurved and has been totally re-built. It happened to me recently when I was at sea level. Sounded like pre-detonation. I do believe it was caused by a bad tank of fuel I got near the beach. Once I re-fueled, it appeared to go away.

 

[CurtB]

I don't believe it is a ping...it doesn't behave like one although it kind of sounds like it at times. If I watch my vacuum gauge, it only happens when under moderate/light loads with high vacuum. It doesn't happen when coasting down, but if I just get off the gas in the mid 2000 rpms and maintain load I can recreate it.

There is no EGR and no air pump....is there something that is vacuum operated that could rattle under high vacuum? I can't think of anything..
Valves are adjusted, new plugs, newly rebuilt carb & dizzy, nothing loose that I can find. Compression is between 130-150 across all six.

Is there something internal that would make a "pebbles in a hubcap" sound? Oil pump? It isn't rhythmic like a noisy valve/pushrod.

 

[HemiAlex]

@houstonfj40

 

[houstonfj40]

@houstonfj40

Hemi and I added a little fuel at idle and the noise I had went away. I could feel mine in the clutch pedal, and also up front. We figured it was a lean miss and 1/4 turn or so of the idle fuel screw to add fuel fixed it. Would only happen when engine was warm, like 20 miles or so and at idle. Might not be the same thing since your at higher rpm.

Marc

 

[FJ40Jim]

Connect the ported vac hose to the outer fitting on dissy vac can. If problem goes away, you're good.

 

[CurtB]

Damn, @FJ40Jim. That did the trick. Thanks! What the heck was going on there?

 

[FJ40Jim]

Too much part throttle timing. Moving the hose changes max vac advance from 20* down to 7*.

 

[CurtB]

Too much part throttle timing. Moving the hose changes max vac advance from 20* down to 7*.

Interesting. It sure didn't sound or act like your regular "too much advance" ping, but it is gone now!

 

[ModisetteJ]

When the gas tank is empty, fill it with premium fuel. See if that changes anything. If the rattly sound diminishes or goes away, the timing is too far advanced for the gas you were using before using premium.
Either use higher octane fuel or retard the timing.

The 2F will run great with more power at certain RPMs and loads with the timing too far advanced. It's a deception though. The timing must be set so the engine doesn't ping at any load or RPM.

Jim's distributor recurve changes the advance curve (obviously). 7° BTDC is a starting point to set timing.

I’m currently hearing this.
I had my 60 desmogged by Torfab, and after I got it back heard a pretty gnarley pinging at any load above 2k rpm. Took it back and they retimed it and it still pinged but not as bad. I ran across this comment and put premium gas in it from empty, and it definitely doesn’t ping anymore at low speeds (still pings at 50+ mph under moderate load), and I noticed a pretty decent power increase. Does this have anything to do with the distributor? Tor mentioned it might be a carb issue.