Engine Knocks E450

[spexdr]

My 2001 Ford E450 knocks when under load, accelerating while towing vehicle, or going up steep hill. Had Ford mechanic check vacuum, said it's OK. Using top tier gas. It starts and runs better than any vehicle I've owned and doesn't knock when accelerating w/o the towed car on flat road. Also does 'revert to defrost' when under load; that is, AC from vent is redirected to defrost until reach crest of hill and reduce load. Help! Thanks.

[obedb]

There are many helpful responders on this forum. Someone will be with you soon. What engine do you have?

[Capndave32043]

When it reverts to defrost that is telling me your running out of vacuum. It could be a leak in the vacuum storage container. Mine had that. Ford wanted over 1000.00 to put in a new one. It seems you have to dissemble the whole vehicle to get to it. I had my mechanic put in a different one on the firewall, works like a charm.

One other thing It could be an exhaust noise, that year was famous for that. Knocking when under load.

[dickandlois]

spexdr,

Welcome to the FMCA Forum!!

With the the vent system reverting to the defrost mode, that means there is a loose of vacuum.

Capndave mentioned an issue with the vacuum reserve tank being an issue on his unit, so that is a possibility. It is rare for one of there tanks to fail outright-but there is a possibility of a crack developing where the vacuum line connects to the tank. Plastic items dry out over time and become very brittle !!!

The other item you might want to address or have a mechanic do for you is to just replace ALL the vacuum lines on the engine as they also become dried out and start to crack and this cause the loose of vacuum under heavy loads, like climbing and acceleration. Vacuum issues can also reduce the MPG.

This is where I would start to track down the vacuum issue. There are some other items that can cause a loose of vacuum, but vacuum lines are low cost - with the exception of replacing the vacuum reserve tank that Capndave mentioned and installing a tank in a different location can be far less labor intensive, After you have ruled out all the vacuum lines !!!

The knocking can also be related to the loose of vacuum, that can result in a change in engine timing creating the knocking you mentioned.

Rich.

Note! 6-5-2015- Large engines develop a good amount of Vacuum when idling or under a low load condition. The decreased vacuum condition - caused by small leaks show up under heavy loads. So checking the vacuum while setting in a garage bay does not always find the leaks !

[hermanmullins]

Your distributor may have a stuck centrifugal advance.

Herman

[desertdeals69]

I think there is 2 issues. Check the knock sensor and related wiring and engine computer.

[jleamont]

Check the exhaust manifold bolts, I bought a F250 a few years ago with a V10 that a mechanic told the customer the engine was bad, it only had an exhaust leak caused by broken manifold bolts at the cylinder heads. Very common on this and the 4.6L and 5.4L engines. Ford makes Stainless steel upgrades you can purchase from a Ford Dealer.

On an E-Series remove the interior engine cover (dog box) and look down both Manifolds.

As far as the vacuum, sounds like a minor leak somewhere. I had a class C with a V10 and I never lost vacuum climbing hills.

On these its usually the PCV hose becomes brittle, it is located on the passenger side valve cover, (connects the throttle body to the PCV valve) if you squeeze it it will feel like mush in your hands, replace it with the PCV valve, it just might fix your concern.

[spexdr]

Thank you all for your responses. I will look into the issues mentioned and will let you know the outcome! Happy travels!