clunk clunk clunk ... sreeeeeeeeeach!

[Heus33]

351W, C4

Once in awhile when I turn off the bronco it will act like its still running for about 3 seconds - I dont think its a carb issue but sounds like the flexplate is still spinning. It would do this about 50% of the time. I didnt think much of it until last night when out for a drive and I heard what sounded like the fan catching the fan shroud - kind of a metalic squink. I pulled into a gas station and shut it off and heard the LOUDEST screeching noise I've ever heard - it lasted about 1.5 seconds. I couldnt tell where it was coming from. Drove it home and turned it off and it did it again. The truck seems to drive and accelerate fine and shift fine. The idle did seem a little rough - almost like it was missing.

Oh - one more thing - it wont make the metailc clink sound when in neutral, only in drive and reverse (under load). I dont know where to start... any ideas????:? ?:? ?:? ?:? ?:?

 

[Scoop]

Sounds like 2 related problems - dieseling and pinging. You probably have some carbon build up in the cylinders and on the plugs. The buildup can remain very hot and become a source of ignition - hence when you shut off the ignition it seems to continue to run for a few seconds. This can make a metallic noise.

I would try cleaning the plugs and moving up a grade in gasoline.

 

[Heus33]

I put new plugs in less than 100 miles ago. Compression is 10 to 1 I believe. Im running 87 but the PO said he retarded the timing to allow for regular grade gas.

Why the extreme screeching? Sounds almost like when you hit the starter after already having the car on - but 10 times worse. And its so loud that I cant locate where the sound is coming from.

Checked all the fluids - oil is fine, transmission fluid is full - almost too full - could that be an issue?

I also did a physical inspection and dont see anything out of the ordinary.

 

[Broncrick]

I would check the bellhousing and starter bolts for the screeching sound. Timing for the 'dieseling'

 

[Kenny]

I agree with Scoop....dieseling and pinging. Dieseling makes some pretty nasty noises (as well as smells), and I believe (but not sure) that it causes your motor to run backwards......maybe screech is your belts running in different direction? Metallic sounds under load are definitely the common description for pinging.....especially in a higher compression motor running with 87 octane. At a given compression ratio, iron heads tend to ping more than aluminum so if you have iron heads even more likely that pinging is one of your problems.

I once had a vehicle that pinged so I retarded the timing, but then it started dieseling so I advanced the timing back to where it should be which fixed the dieseling (can't explain why it fixed it, but that was my observation). Then I used a higher octane gas to fix the pinging. I also recommend some type of product to help clean your combustion chamber. A dirty combustion chamber can increase compression (more pinging) and can create hot spots which can cause ignition after shutting off your motor (dieseling - like Scoop said). There are different products out there.....some that you add to your gas and some that you slowly add to your intake/carb while motor is running. I imagine the intake/carb products are most effective to clean, but can be messy and more work. Your call.

 

[Heus33]

Kenny & Scoop -
Can you recommend any products? Ive got a bottle of SeaFoam that I can use. The tank is 3/4 full - do I need to drain it and start with 91 octane or should I add some octane booster? I've never had an engine that pinged before - what damage can be done?

 

[wpaeb]

I would check the bellhousing and starter bolts for the screeching sound. Timing for the 'dieseling'

X2 on this

 

[wildbill]

%) %) %) If your dieseling I would get a qt. of water run the RPM to about 3500 and use the water to bring it back down to 1500 to 1800. Dont use the water to kill the motor. Do this with the motor hot the water will bust the carbon. And when you get it right fix the timming its off. good luck and have fun.;D ;D ;D Bill%) ;D %) PS this is old school and works very good.

 

[Kenny]

Kenny & Scoop -
Can you recommend any products? Ive got a bottle of SeaFoam that I can use. The tank is 3/4 full - do I need to drain it and start with 91 octane or should I add some octane booster? I've never had an engine that pinged before - what damage can be done?

I've never used SeaFoam, but I've heard that it works well. I believe you can use it in your gas tank and/or your carb/intake. If it was me, I'd probably use it directly in the carb/intake....probably more effective. I hear that you have to poor it in slowly or your motor will stall, and don't worry if you see a lot of smoke.....that's supposed to mean it's doing its job. Make sure to read the instructions and/or check their website for pointers.

With the price of gas, I'd probably try an octane boost rather than draining. When you add it to your tank, it's probably a good idea to top off the tank with gas to help mix better. Don't use the whole bottle.....just enough to get the correct ratio for 91 octane rating.

As far as ping damage (pistons and/or valves), I guess that depends on how long it has been driven like that, how hard it's been driven, and how bad the ping was. Sorry I can't give you a better answer, but it depends on too many things. You could very well be okay, but make sure to fix it soon if in fact it is pinging. Basically, lower octane detonates/explodes at lower temperature than higher octane, and I believe it burns hotter too. The higher the compression the more heat. When your car is under load, it creates more heat. The more advanced your timing, the more heat created during ignition.....that's why previous owner retarded the timing, but retarding too much usually is not the best way to deal with the situation as you're learning. All these things create a lot of heat which can cause your fuel/air mixture to detonate/explode before ignition which causes the ping. Higher octane fuels are less prone to detonation/explode before ignition so that's why they're used in high compression motors . Hope I got most of that right. Once you've got it running okay, probably a good idea to get timing right. I think factory is 6 degrees BTC at idle, but a lot of people like 12 BTC so probably somewhere in that range would be ideal.

Let us know how things work out.

 

[spixican07]

I agree with Scoop....dieseling and pinging. Dieseling makes some pretty nasty noises (as well as smells), and I believe (but not sure) that it causes your motor to run backwards......maybe screech is your belts running in different direction?

I agree with the diagnosis of dieseling and pinging, but is 10:1 really enough to cause pinging with regular fuel?

Could you go into detail of how dieseling could make the motor run backwards? Because I think that would reverse the whole air flow, from intake to exhaust...and blow all the gas mixture out of the top of the carburettor! No fuel no dieseling, right? ?:?

 

[DirtDonk]

351W, C4

Once in awhile when I turn off the bronco it will act like its still running for about 3 seconds.

That's standard dieseling and can be from an idle that's too high, a mixture that's too lean (causing the extra heat in the combustion chamber), caused perhaps by a vacuum leak. Or other things, like the carbon build-up mentioned by the others.
When it does this you can usually stop it temporarily by turning off the engine while still in gear. It's not a fix, but it helps in the piece-of-mind department.

...last night when out for a drive and I heard what sounded like the fan catching the fan shroud - kind of a metalic squink. I pulled into a gas station and shut it off and heard the LOUDEST screeching noise I've ever heard - it lasted about 1.5 seconds. Drove it home and turned it off and it did it again.

A backfire out of a leaky carb gasket, head gasket, or other vacuum leak source perhaps? Cracked manifold? Loose spark plugs?
Just some wild guessing here.

The truck seems to drive and accelerate fine and shift fine. The idle did seem a little rough - almost like it was missing.

Again, classic vacuum leak symptom. Unfortunately too, lots of things can cause a rough idle. But a leak or a carb adjustment are certainly a couple of common ones to look for.

Oh - one more thing - it wont make the metailc clink sound when in neutral, only in drive and reverse (under load). I dont know where to start... any ideas????:? ?:? ?:? ?:? ?:?

Here's where I might need a little clarification. Since we're talking about two separate events I think, is the clinking only when you're driving? More so when you're accellerating?
Unusual to have pinging just driving in reverse since you're not normally under much load or trying to go too fast. Does it happen in reverse all the time or just when you happened to have been pushing hard on the pedal?

The clink is different from the dieseling, correct? Or are you saying you've already tried turning off the engine while still in drive or reverse and it still diesels, where it won't in neutral?
Just trying to make sure I'm on the same page as everybody else.

Thanks

Paul

 

[DirtDonk]

I agree with the diagnosis of dieseling and pinging, but is 10:1 really enough to cause pinging with regular fuel?

Sure. Depends entirely on the engine setup though. In the old days, before EFI computers and knock sensors, you could get serious pinging with an 8.5 to 1 ratio if things weren't right. Happened all the time in fact.
Combustion chamber shape, spark timing and fuel metering, as well as unusually high temperatures, EGR malfunctions or some other out-of-whack detail can have a huge effect on it.
Modern computer controlled engines with efficient combustion chamber shapes can run 11.75 to one and not ping. When all is right with the world that is.

Could you go into detail of how dieseling could make the motor run backwards? Because I think that would reverse the whole air flow, from intake to exhaust...and blow all the gas mixture out of the top of the carburettor! No fuel no dieseling, right? ?:?

You're basically right. But I think they're only talking about running backwards for a second or two. In the right circumstances, like pre-ignition in the extreme for instance, the engine can be turned backwards by an ill-timed combustion occurance but can't normally keep itself regenerating.
I've had two-stroke engines run in full reverse (ran like crap, but ran) but never seen a four-stroke run for more than a couple of seconds. Probably some circumstance that would keep it going, like uncontrolled fuel delivery perhaps, but normally, no.

Paul

 

[Heus33]

Off to check the following:

1) Bellhousing and starter bolts for screeching sound.
2) Seafoam down carb for dieseling fix - also will turn down the idle a bit.
3) Octane booster in tank for pinging

Be back with results...

 

[Broncrick]

Go slow with the Sea Foam injection, and do it outside, the resulting smoke is impressive ;D
Rick-

 

[DRBRONCO69]

Check your motor mounts if your fan is hitting the shroud. Start the truck and have someone watch the motor when you put it in gear ( both drive and reverse )and give it a little skinny pedal. If the motor moves too much, it will cause the fan to hit the shroud. You may have a bad motor mount. Just my .02.

 

[Kenny]

Could you go into detail of how dieseling could make the motor run backwards? Because I think that would reverse the whole air flow, from intake to exhaust...and blow all the gas mixture out of the top of the carburettor! No fuel no dieseling, right? ?:?

I wish I could explain how/why my motor ran backwards while dieseling, but I can't. When my car dieseled, I would put it in 1st gear to stop it.....that made my car want to go backwards. That's how I knew my motor was running backwards while dieseling. Remember, I'm not saying it was normally running backwards, only while it was dieseling for that 1-3 second period.

 

[Broncobowsher]

I agree with the diagnosis of dieseling and pinging, but is 10:1 really enough to cause pinging with regular fuel?
QUOTE]

Yes. It takes a lot of modern engineering to get a modern engine to run 87 at 10:1. With cast iron heads, that is a premium fuel engine.

As for can it hurt things, yes it can. If the engine is running right, the fuel burns. This is why you hear thing like "flame fronts" when you et into the technical documents of an engine running. It only takes a fraction of a second to burn. It's kinda like the nice fireballs you see in movies as someone is running from a movie explosion. Just a fireball growing larger. Just on a smaller, cleaner burning scale.
Detonation is the fuel exploding becasue it isn't stable enough for the heat and pressure in the cylinder. Detonate is the same as detonating an explosive. Best image I have of this is the rocket fuel plant in Henderson, NV that blew up several years ago. Not much of a fireball (not entertaining like the movies) but a huge pressure wave. Basicly take a sledge hammer and beat on the top of the piston. It wil take it for a while, but it will blow out reng lands and other nasty stuff to the engine.

As for the engine running backwards, there are probably 2 things going on. First is diesling. With heat and pressure, the fuel lights off without a spark, like a diesel engine. Eventually it get to the point where the engine stops with air and fuel ready to light off. the crank finally comes to a stop but hasn't reached the top of the compression stroke. The fuel lights off (diesels) and pushes the piston down. Since it hasn't crossed over the top of the stroke, it goes the only way it can, backwards. Stipid parlor trick, give it a little gas as you shut it off, I have had engine I could almost put in gear and drive they would diesel so much with a little extra air, fuel and cylinder pressure.

To fix all this, use premium gas. Turn the timing up to where it should be. This will raise the idle speed. Lower the idle speed. With these changes the manifold vacuum will be increased, the cylinder pressure at idle will be reduced. With the lower cylinder pressure and higher octane gas, it should not diesel. With the advanced timing and 10:1 compression you will need the premium gas. Getting the timing back to where it should be will add power and economy as well.

 

[76bogger]

I wish I could explain how/why my motor ran backwards while dieseling, but I can't. When my car dieseled, I would put it in 1st gear to stop it.....that made my car want to go backwards. That's how I knew my motor was running backwards while dieseling. Remember, I'm not saying it was normally running backwards, only while it was dieseling for that 1-3 second period.

This happens to my bronco alot, some times its so bad that when i shut it off and it in granny gear (NP435) , it will fire back up and squeal the tires and move a few feet, one time i was in town and it took off backwards in to the steet and one time it when over the curb. so now i hold in the cluch untill its done. but i have a 351 cleveland that its build up and its high compression. Its supose to run on at lest 91 but im 16 and have a hard time even afording 87 oct. 91 helps alot cus i've ran it befor but the best is whe i put some of my 112 oct for my racing bronco in it lol but the cost 8$ a gallon

 

[SteveL]

To clean it out we spray a bunch of carb cleaner down the carb with it running. Manually control throttle to keep it from stalling. There was a comparison on here a long wile back on the octane boost products. Some were using a paint thinner called tulene(I think), not sure of the spelling. It did as well as some of the better brand name products. You can buy a gallon of it for a little more than one of those 6 oz. bottles fron the auto store.

 

[Kenny]

Some were using a paint thinner called tulene(I think), not sure of the spelling. It did as well as some of the better brand name products. You can buy a gallon of it for a little more than one of those 6 oz. bottles fron the auto store.

Regarding Octane boosters, I did a search under "toluene" in the archives. Found a few interesting links under this thread: http://classicbroncos.com/forums/showthread.php?t=62781&highlight=toluene