I know this sounds weird, but my '86 F150 300 I6 that I picked up this summer has this noise at about 1500 RPMS under light load. It does it while driving through the neighborhood in second gear at about 1500-1700 RPM and will do it just revving the engine in the driveway. It's a clattering, chattering kind of noise. It has the feedback carb, which is new, and the computer controlled distributor without vac adv.

With the SPOUT connected, the timing was at 26 degrees at idle. I disconnected the SPOUT and set it to 10* at idle. With the SPOUT plugged in it goes to about 16* at idle, but it still makes the noise. The advance goes to about 40* when revving the engine to 3,000+, and holding at about 1500-1700 RPM it's got 30 some degrees of advance and constant noise.

I'm confused as to why it is providing so much advance. I doubt the system is working correctly since the carb was not installed properly with vacuum lines plugged, and disconnected and whatnot. It's a mess. Anyway, I took out timing until the noise at 1500 went away, which put it at 0* at idle with the SPOUT connected. I don't know if it's detonation from too much advance, or some kind of valvetrain noise or what. Or if the added power from more advance is stressing some weak or broken valvetrain or bottom end components? Yikes.

I am working out plans to do a DSII conversion and non-feedback carb setup, possibly a 4 barrel and EFI manifolds. But, I want to make sure there isn't any major problem with the engine first. It runs pretty well otherwise. It seems kind of sluggish but runs pretty smooth.

 

Are the timing marks accurate? Some types of Ford dampers are notorious for this, the elastomeric (rubber) bonding between the damper weight and casting rots and it slips off axis, making the timing marks useless.

Still, an actual 40° at 3000+ RPM in neutral isn't unusual at all. Lightly loaded, cruising down level highway around 50° BTDC would be typical for any engine in good tune. Check for stupid stuff first, like plug wires in the wrong order.

 

Well, I gave it a full tune-up first, so it has new plugs, wires, cap and rotor. When I got it, the brake booster was sucking air something awful. It was hissing loudly and idling at 1,200-1,500. It also had other numerous vacuum leaks that I plugged up. I still don't think all the vacuum lines are hooked up properly, and I know the carb base gasket is sucking in air. I am wondering if all the leanness and over-advanced timing caused some mechanical problems. I wonder how long the kid drove it like that.

It was definitely over-advanced with 26* or whatever at idle. I guess you're right though, without any load, 40+ would be normal revved up. It's like having the vacuum advance still plugged in, except the computer is applying what the vacuum advance would.

I'm thinking more and more that I'll just go to a yard and snag the engine wiring harness, distributor, and ignition module out of an older 300 I6 with DSII. That way, I know what the timing is, because I can curve it myself. I can give it 16* or so base, another 10* mechanical for 36* total, and another 10* or so for 46* with the vacuum advance. If it still makes the noise then with known proper timing, then I'll know there is some other issue.

In fact, the distributor itself could be making the noise... There's only one way to find out. It runs pretty smooth, but I'll go back and check the firing order, too That's a good idea. And I'll check the damper. Maybe I'll do a compression test too! Although, I'm kind of scared to do that.

 

A mechanic's vacuum gauge connected to a source of manifold vacuum isn't a direct substitute for a cylinder compression test, but it's damn close, and a whole lot easier and quicker to perform and doesn't torture the battery and starter either. It is a remarkable device that should be in everyones toolbox. The method that can be used to infer the health of piston rings is when throttle is quickly goosed, the needle will collapse to around 3" or 4" and then quickly rebound all the way to around +25" or so.

 

I thought to check the vacuum, but forgot. Thank you for the reminder! I played around with the timing and the mixture screw. With it at the timing spec of 10* with the SPOUT disc., 18* with it connected, at 600 RPMs, and the mix screw just a little over a turn out, I get it pretty steady and smooth at 19.5"Hg. And the throttle is pretty snappy. But, the only problem is, it sounds like my buddy's 300 Benz diesel! It's like marbles in a coffee can at 1200-1700 RPMs. You hear it right when you rev it and if you hold it there it's constant. The timing at 1500 RPMs, with the horrible constant detonation, is 44*! That seems way too high to me.

If I take out a bunch of timing and have it at about 0* with the SPOUT connected, it no longer sounds like a diesel. It's sluggish and the vac is only 18*, but there is no pre-ignition/detonation/spark knock. I gaped the plugs to spec when I did the tune up, and I used the correct Autolite plugs. Could there be a bunch of carbon build-up or something?

I think the engine is mechanically sound, so that is good news. But, if I set everything to the factory specs, it sounds entirely like a diesel engine, which seems like it can't be good. Maybe now that I know the engine is mechanically sound, since it idles smooth with 19.5"Hg at 600 RPMs, I should just do the DSII and non-feedback carb conversion. What do yall think? Oh and I think I eliminated all the vacuum leaks. I don't think everything is hooked up 100% correctly, but I don't think it's got any vacuum leaks at least.

 

Strange, it could be excessive carbon but probably not at idle? Whatever is the cause you want to fix this sooner versus later. Can burn a hole in a piston or break ring lands. I don't know enough about sixer dampers. Do they have a rubber sandwich between the outer steel weight and casting (like many earlier V8 engines) or, is it solid? If so, double check and verify for certain that mechanical TDC #1 cylinder on the compression stroke jibes with the damper "0" mark and pointer.

If it slips, the numbers will be way off. (It also won't be absorbing crank vibrations, may launch itself down the road, etc..)

 

86stepsideF150,

My son's 1984 with original intact feedback system was doing the same thing [pinging] at that speed range under load. The MAP sensor was not functioning, so the computer could not tell that the engine was under load and did not retard the timing. Thanks to FordF834, I have several used Motorcraft MAP sensors and one is yours for free if you want it. The MAP sensor is located near the battery with a vacuum line attached.

 

Tedster9, it's not doing it at idle, just at 1200-1700 RPMs and seems loudest at about 1500 RPMs. At 1500 RPMs with the timing set correctly it will clatter away in the driveway all day. At 1500 it's got about 45* of advance. If I take some timing out, so that it has about 38* at 1500, the noise is markedly reduced. I am going to check the damper like you said. But, I will say it runs best with the timing set to the factory setting, it just makes a ton of engine noise exactly like a diesel!

1986F150six, thank you for the offer and for your input. Before I take you up on that MAP sensor, mine doesn't do it under load, just the opposite. It will do it with light load like revving it in the driveway, or barely pressing the throttle in that RPM range. On acceleration, I hear it higher up at about 2100-2200 RPM, just briefly. And it doesn't really do it on deceleration.

I was all ready to pull the valve cover off thinking I might have some mechanical things going on. I was expecting to see some loose rocker arms. But, the noise does not happen when the engine is cold. It only seems to do it, or at least it is loudest, after running for about 10 minutes.

I did pull of the ignition module thinking maybe it was causing too much advance. I swapped in a Pertronix one I had from my 302, but it didn't work at all. That's probably why it was on the shelf - no surprise there. But, I will say the TFI module was light as a feather - even lighter than the Pertronix one - and said "Hong Kong" on the back. Is it possible that I have a really crappy TFI module and it's causing some excessive timing in the midrange?

I guess I am leaning towards an ignition problem being the cause since the timing is so high and there is a definite correlation between the timing and the noise, i.e when I remove timing the noise is reduced subsequently. And it makes 19.5"Hg at idle with very little needle shake, no more than .5"Hg, which makes me think all the rockers are tight, lifters working, no broken valve springs, etc... I'm stumped.

 

I confirmed that with #1 at TDC, the little line on the balancer, which has been previously highlighted for me, lines up with "0*" on the timig tab on the timing gear cover. The electrode on that #1 plug was white as a ghost, not the nice tan color it should be.

Here's a video of it running. At 37 seconds you can hear the dieseling/pre-ignition. For specificity, it starts at 1300 RPMs and continues to about 1800 RPMs, as you can see on the digital timing light.
Can someone tell me what the pistons should look like? From what I could tell, it looked like a flat-top in the #1 hole. I could not see any valve-reliefs or any protrusions or anything. Unless I was looking at the center of a dished piston... It just looked like it had a dot and a circle or something to indicate the center of the piston. I couldn't see anything else around it. I'm just wondering if this thing was rebuilt and maybe I need higher octane fuel.

 

Hmmm... this is going to sound far-fetched, but might cause someone else to think of the correct answer. Many years ago, I had a 1970 VW Karmann Ghia with a stock carburetor and factory air cleaner. Of course [as a young man], I wanted it to go faster and look better, so I purchased a purdy chrome air cleaner. The popular one was made by EMPI, was small in diameter and was flat on the top and close to the carburetor throat. Well, as soon as I went on the highway and began to cruise, the engine began to ping and rattle. The explanation given to me by ones with German engineering background was that the little one barrel [Solex] carburetor when jetted properly actually created a fuel fog inside the factory air cleaner, which was domed, rather than being flat. When the aftermarket low topped/flat air cleaner was in place, the "fog" was disrupted and the engine ran lean. As soon as I returned the original factory [oil bath, by the way] air cleaner to its rightful place, the situation was corrected.

 

Now, me, I would have thought that fuel was supposed to do down the carburetor throat instead of up into the air cleaner. A '70 should have been a 1500 with either a 28PICT1 or 30PICT Solex carb, as I recall, and an oil bath air cleaner. The bottom of the upper air cleaner element inside was flat, not domed... I think someone may have been having you on a bit. HOWEVER in your defense - a lot of British sports cars used to have dual SU or ZSU carbs and when you replaced the single larger two-carb air cleaner with smaller single K&Ns, the difference in air flow allowed a little more air flow but at constant highway speeds you might get a rhythmic blip in the engine as if about every 100th spark was gone awry. Stock air cleaner back on, the blip went away. Been messing with them almost 50 years and was going nuts trying to find that blip till a guy on a Triumph forum suggested it.

 

Well, HoustoDave, you have me second guessing my memory and I made a mistake in that it was not the Karmann Ghia, but rather a 1963 Beetle which had the 28PICT1 and an air cleaner like this: Vintage 1960s 1200 VW Bug Beetle Oil Bath Knecht Air Cleaner Volkswagen | eBay.

Thanks for helping!

Back to the OP... have you recently installed the small air cleaner seen in the video?

 

If a '63 I do believe you may be right on the 28PICT... nice to meet another aircooled VW type. I have had 8 to date.

What I am thinking of is the flat element bottom shown in the pictures. The top of the filter housing is domed, but I'm not sure how much turbulence it actually creates in the inch or so before air heads down to the venturi with gas being squirted down and the 'vacuum' the engine creates in the manifold would tend to work against a fuel-air mix getting that high. That being said, I once didn't believe that a set of brand new Champions would break down in a VW, either - till a set lasted less than 30 miles one time. The old Germans at the kaserne auto shop were real amused by that.

 

Now that would be the epitome of irony, if that damn air cleaner was causing the issue. The whole reason I put that little sucker (pun intended) on there was to find vacuum leaks and clean them up and get familiar with the carb and engine. I put it on a few weeks after a got the truck and stared delving into it. I figured it'd be restrictive but not enough to really notice. I'll put the old air cleaner back on asap! I'm curious now!

Oh and I turned the #1 piston back down into the hole to inspect it. It looks like a "D" shaped dish from what I can tell. So compression shouldn't be too high.

 

I have a few things to report to those who are still interested. Firstly, although I was hoping for it to work in favor of an easy fix, installing the stock air cleaner did not work. I did determine that the problem is almost certainly entirely due to a lean condition caused by an absence of fuel. I held the throttle at 1500 while it pinged away and gave it a squirt of brake cleaner and the RPMs would increase every time and the pinging would cease immediately. If I sprayed too much it would bog down the engine, but the pinging would still stay gone. I turned the idle mix screw all the way out, which made the idle rich and stinky, thinking it would help richen it up at 1500 RPMs, but it didn't really make a difference. If I unplug anything on the carb to try to see if the carb will run richer, it just goes into limp mode and limits the timing to base timing.

Also, the EGR doesn't seem to be working. I can hold it at 1500 RPMs, while it is pinging, and open the EGR a little by hand and it reduces the pinging. This makes sense because the EGR circulates inert gas which would make the mixture require less fuel, not to mention, it cools the mixture. I gave the EGR full vacuum with a line from the manifold to see if it would work and it didn't, so I know the diaphragm is busted. It's a separate issue, but it solidified the theory about it just being way too lean.

I don't know why it's so lean in the mid-range. It's supposedly a "new" carb. But, I found a good non-feedback carb for 50 bucks local. So, I'm thinking I'll bolt that on, eliminate a bunch of the smog stuff, and just run the TFI with total timing all the time. I read that this actually works for lighter vehicles, namely mustangs. I figure I can run at least 32* total all the time and not have any issue. I disconnected the SPOUT and put the timing at 32* and it increased idle vacuum to about 21, smooth as butter, and felt very snappy. This should be good enough until I do the DSII conversion.