Squeak Sound
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Freshman User
Joined: Sep 2010
Posts: 42
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From: Rockville, MD
Squeak Sound
Recently there has been a squeking sound coming from the front left side of my motor that sounds like an air leak but I can't tell what it is. I've tightened at the bolts on the intake and exhaust manifold and just recently installed a new gasket and bolts for my carb. Sound goes away when I hit the gas. Does anyone have any idea what it could be?
I have a 1985 Ford F150 with Inline 6 and an Offenhauser Intake and 4bbl Holley Carb.
I have a 1985 Ford F150 with Inline 6 and an Offenhauser Intake and 4bbl Holley Carb.
Fleet Mechanic
Joined: Apr 2007
Posts: 1,429
Likes: 4
From: patricia ab canada
vacuum leak would be my guess,check all of your vacuum hoses,and try the propane test.use a propane torch,open the valve and move it along all your hoses and mating surfaces .if the engine revs up when you pass an area there's the leak.
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
Mine has been doing that for awhile as well. Still haven't found any leaks anywhere. It only does it when I pull a hard hill, then top out and start going down hill, with my foot off the excelerator. It slowly quits after about 30 seconds. It doesn't do it any other time. Sounds exactly like my problem.
I believe it might be the thermactor Air Diverter on mine, where it dumps air from the air pump to the atmosphere while decelerating, or a bad check valve that is leaking exaust back into the thermactor system. Do you have any of the thermactor system left on your truck?
Only other thing I can think of is vacuum leak like mentioned earlier.
I believe it might be the thermactor Air Diverter on mine, where it dumps air from the air pump to the atmosphere while decelerating, or a bad check valve that is leaking exaust back into the thermactor system. Do you have any of the thermactor system left on your truck?
Only other thing I can think of is vacuum leak like mentioned earlier.
Thread Starter
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Freshman User
Joined: Sep 2010
Posts: 42
Likes: 0
From: Rockville, MD
Mine has been doing that for awhile as well. Still haven't found any leaks anywhere. It only does it when I pull a hard hill, then top out and start going down hill, with my foot off the excelerator. It slowly quits after about 30 seconds. It doesn't do it any other time. Sounds exactly like my problem.
I believe it might be the thermactor Air Diverter on mine, where it dumps air from the air pump to the atmosphere while decelerating, or a bad check valve that is leaking exaust back into the thermactor system. Do you have any of the thermactor system left on your truck?
Only other thing I can think of is vacuum leak like mentioned earlier.
I believe it might be the thermactor Air Diverter on mine, where it dumps air from the air pump to the atmosphere while decelerating, or a bad check valve that is leaking exaust back into the thermactor system. Do you have any of the thermactor system left on your truck?
Only other thing I can think of is vacuum leak like mentioned earlier.
Moderator
Joined: Nov 2007
Posts: 22,415
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From: Denver Metro Area, CO
In the following picture, the smog pump (aka Thermactor) is on the left and has
the pulley attached to the front of it.
On the side opposite that which has the pulley attached is a small length of
rubber hose; attached to that hose is the air diverter valve you speak of. It is
vacuum operated and has a small nipple for a vacuum hose to be attached.
Source: Ford Fuel Injection Actuators
I believe it depends on the truck's model year and Calibration Code for knowing to
where the air is diverted; in this case, it appears to be diverted to the atmosphere
instead of the catalytic converter. Somebody will correct me if I'm wrong.
the pulley attached to the front of it.
On the side opposite that which has the pulley attached is a small length of
rubber hose; attached to that hose is the air diverter valve you speak of. It is
vacuum operated and has a small nipple for a vacuum hose to be attached.
Source: Ford Fuel Injection Actuators
I believe it depends on the truck's model year and Calibration Code for knowing to
where the air is diverted; in this case, it appears to be diverted to the atmosphere
instead of the catalytic converter. Somebody will correct me if I'm wrong.
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Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
In normal cruise mode, the air pump (thermactor) sends air to the catalytic converter.
When decelerating, or going down hill, the thermactor air diverter valve, diverts the air from the catalitic converter to atmosphere to keep the converter from overheating. There are check valves to prevent exaust from leaking back into the thermactor lines.
If the air is whistleing out the thermactor diverter valve's air release ports, (which is what I think it's doing with my truck), then it would cause these symptoms. Or if the air check valve is bad, exaust could be sent back through the valve backwards also causing a whistle effect.
There are different calibration codes, and my diverter valve is in a different place on the back of my engine, connected to it with metal pipes and hoses, so it may look different than pictured.
Your truck also has a thermactor bypass valve that bypasses the air from the catalitic converter and sends it to the exaust manifold instead.
This is assuming that the truck still has these components and they havent been removed. Even partial components may have simular effects.
When decelerating, or going down hill, the thermactor air diverter valve, diverts the air from the catalitic converter to atmosphere to keep the converter from overheating. There are check valves to prevent exaust from leaking back into the thermactor lines.
If the air is whistleing out the thermactor diverter valve's air release ports, (which is what I think it's doing with my truck), then it would cause these symptoms. Or if the air check valve is bad, exaust could be sent back through the valve backwards also causing a whistle effect.
There are different calibration codes, and my diverter valve is in a different place on the back of my engine, connected to it with metal pipes and hoses, so it may look different than pictured.
Your truck also has a thermactor bypass valve that bypasses the air from the catalitic converter and sends it to the exaust manifold instead.
This is assuming that the truck still has these components and they havent been removed. Even partial components may have simular effects.
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