I have a 1977 F150 with a 300CI 6cyl. Auto. It is making a high pitched whine that fluctuates when I step on and off the gas pedal. It starts at freeway speeds. When you come to a stop you hear the sound for awhile and then it will disappear until you get the motor rpm's back up with freeway driving. I though it was a belt problem however my belts are new. I sprayed a little belt dressing just to see if the sound stopped. No change. Since it stops soon after you slow down I can't seem to pinpoint it. Any ideas would be appreciated.
Thank You!
Wayne

 

You might have a vacuum leak. Check all the vacuum lines and any vacuum caps. Also check the intake manifold. If you have A/C check the vacuum lines under the dash and also the vacuum switch on the control panel.

 

If you sit idle in the driveway and hold the rev's at highway rpm's (2-3500rpm) do you hear it, or is it just when you are moving?

Does it sound like a small gearset whining? Torque converter?

 

Mike & Duane,
Thanks for the tips on what the high pitched whine problem may be. I will check out both suggestions. I thought some pictures of the engine and carburetor area may help with the diagnosis. Another symptom worth noting is that my gas mileage is terrible! I am getting about (10) to (11) miles to a gallon which just can’t be right for a (6) cylinder engine. The attached link to pictures show the engine and carburetor area. The truck has 136,000 original miles on it and I am the original owner. The engine has never been rebuilt and is still running many of the original parts. The suggestion from Mike regarding a vacuum leak got me thinking about the film on the side of the carburetor that shows up in these pictures. Is it possible that I have a gasket leak in the carburetor? Would that make the sound and impact the mileage. Duane I have not tried your suggestion yet; however, I will before the end of today. Thanks to both of you for the suggestions!
Wayne

 

I still suspect a vacuum leak. I don't believe the film on the front of the carb has anything to do with your problem.
A vacuum leak could account for your poor fuel mileage and the high speed whistle.
One simple check you could do is first check to make sure the carb is tight on the manifold but don't overtighten. This could warp the carb base, then you would have a leak. Do the same on the manifold.
If everything looks okay check the condition of the vacuum lines and whatever they are hooked to.
A whistle like you describe, my money would be on a leak in the carb or manifold.
How does the truck idle?
If it idles a little rough that would be another indicator of a vacuum leak.

 

HHHMMM! Does this motor have an EGR valve? I seem to recall my gasket went south and created quite a noise, also I think the valve itself made a heck of a noise too when it went bad.. I could be wrong though.

 

No, 77 300 I 6 would not have an EGR on it. I think it is a vacuum leak too!

 

or the carb needs a rebuild.
Is the stuff on the front of the carb oil?
Can you smell gas when you are at hwy speed?

 

Hello fellow FTE’s,
Reply to 70sfordguy: The stuff on the front of the carburetor is oil and dirt. I plan to investigate further when I start my tune up rebuild process. No, I do not smell gas when going down any road; however, I always smell a strong gas odor after I park and turn off the ignition. I’ll update you on the carburetor after I begin the rebuild process.

Here’s the latest update on my high pitched squeal which starts at freeway speeds and then slowly disappears after the truck is stopped for about three to five minutes. I exited off the freeway when the sound was nice and loud and popped the hood to try to locate the source of the sound. It was definitely coming from the front of the engine area. It was quite loud and sounded like it was coming from the water pump area. I could not be sure; however, that’s what it sounded like. The squeal slowly faded and completely disappeared after parked for about five minutes.

Now here’s my dilemma with nailing the water pump as the source of the sound. It was replaced with a rebuilt one at (129180.0) miles. My current mileage is (135535.0), so that’s only (6,355) miles which does not seem possible unless I have a defective replacement. The alternator has also been replaced within the last five years with a rebuilt one. The belts are also new within the last five years. The power steering pump on the other hand is the original one that came with the truck when purchased new in 1977, so I’m wondering if that’s what may be making the sound.











My plan it to get the center out of a paper towel roll and use it like an old fashioned ear trumpet to help me pin-point exactly where the sound is coming from. I’ll report on my findings when finished.

Just to follow up on the suggestions made by fellow FTE participants. I am ruling out the torque converter (engine to transmission) because I have heard the sound when the truck is stopped and because I’ve heard the sound coming from the front of the engine area. The transmission has had service within the past four years. The fluid level is good and nice and red with no leaks.

The vacuum line and carburetor check suggestions are waiting on some tools and parts I have ordered. I decided that I might as well go all the way with this problem, so I bought a used SunTune (CP-7708) tune up kit off ebay. It comes with a timing light, vacuum check gauge, compression tester, and meter which test for tachometer, dwell, and some other readings. I never heard of SunTune so I hope I don’t end up with some junk equipment. If anyone knows about this company please let me know as I could not find any listing for the company. I have also ordered a carburetor rebuild kit, PCV valve, fuel filter, and crankcase ventilation filter. The air filter was replaced about a month ago. When all the parts and test gear show up I’m going to have some fun learning how to do a rebuild and tune-up.

Oh just to let you know I have a full set of Ford 1977 Truck shop manuals, so I have a basic source of book information, and the wonderful resources of the FTE web site for real hands on experience if needed. Hope my troubleshooting efforts help others with a similar problem.

Wish me luck and I’ll keep you posted!
Wayne

 

I have heard an alternator with a bad bearing squeel when it gets hot.....or a cracked fan blade(at the bolts) but you would hear that just revving the motor.
Check for play on the alt. & fan shaft front to back and side to side.(with the belts off)
Try removing one of the alt belts and run it with one. If they are not the same length the loose one could squeel.

 

Here’s the latest update on my trouble shooting steps to identify where this sound is coming from. As suggested by 70sfordguy I removed one of the dual fan belts to see if the sound stopped. After going about two miles on the freeway the squeal sound began and started to get louder. What a bummer that was as I was really hoping a bad belt in the pair would be the problem. I exited off the ramp and popped the hood. I used an old Christmas wrapping paper roll as an old fashioned ear trumpet to amplify and hopefully single out the source. What I found out was that the sound seemed to be coming from a spot on the intake manifold. It was suggested by some FTE members that a vacuum leak may be the problem; however, I was not thinking about the leak being on the intake manifold itself. I thought it would be a rubber hose or plug. Anyway take a look at the first picture I’ve posted. My finger points to the spot where it seemed to be the loudest. One of the things I noticed was a small metal pin that looks like it may be coming out.



<O</O
I took another picture of the intake manifold with the pin near the center of the picture.
<O</O


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Is this pin coming out? Does it just need to be knocked back in with a hammer? I’m looking in my service manuals but have not found any information or pictures about this pin. Does anyone know anything about the intake manifold pin? Any thoughts would be appreciated.
Thank You,
Wayne

 

Sounds like it could be the power steering pump.

 

That pin is for alignment and making manifold installation easier. The pin itself shouldn't have anything to do with your problem.
Like I said in post #5, I suspect a manifold vacuum leak, all the symptoms fit and it looks like you've narrowed it down to the front intake manifold port.
The only correct way to check it is to pull the manifold and change the gasket.
A kinda half-a**ed way to check is if you could get silicon sealer all around the area where the manifold and head meet and see if that makes a difference.
Because it only starts at highway speeds, I doubt the usual methods of checking for manifold leaks would work (spraying WD-40, starting fluid, etc.).

 

Sorry about the delay in updating the status of this problem but here’s the final report. Other had mentioned a possible intake manifold leak, so I decided to put a torque wrench on the bolts that keep the intake and exhaust manifold in place. To my surprise the very first bolt near the front of the engine was loose! I must have put two or three full turns on it before it started to snug up and finally reach its proper torque level. I went through the rest of the bolts and found the second one near the front of the engine also loose. The others were just slightly off their proper torque. I took the truck for a spin up the freeway and the sound was gone. Once back home I decided to check out the manifold area thoroughly for damage, fit, and anything else I can find. I’ve attached a few pictures to show you what I found.

The intake manifold looked good; however the exhaust manifold had a crack under the intake manifold. You can’t see this unless you get some light shining under the intake manifold. If you look closely you can also see where black carbon soot has stained the engine where it exits during driving, which tells me that this was cracked before I tightened it. I plan to replace the exhaust manifold, gasket, and maybe the intake manifold as a future project.

In summary the high pitched squeal was caused by loose and below torque top and bottom intake/exhaust manifold bolts. I never thought to check this because visually they looked fine. I also found the carburetor had some loose screws (nothing to do with the whine). The carburetor halves are held in place by screws which go down from the top, and up from the bottom. Some of these screws are near impossible to tighten because of the limited access. I decided to replace all of these screws with Allen heads and new lock washers. These Allen screws will allow me tighten with an angled Allen wrench without any trouble.

Thanks to everyone who shared their thoughts, and to those with a similar problem maybe this information will help you find your problem quicker.
Take care,
Wayne

https://www.ford-trucks.com/user_gal...id=228932&.jpg

https://www.ford-trucks.com/user_gal...id=228933&.jpg

https://www.ford-trucks.com/user_gal...id=228934&.jpg

https://www.ford-trucks.com/user_gal...id=228935&.jpg

 

Glad to see you got it fixed.
It's nice to hear back on whether our advice was worthwhile or not.
Thanks for the update.