Just bought a 1996 F150 with straight six, 4.9L It has an engine knock when put under load that sounds like a bad exhaust system. I couldn't see any obvious problems there. It also overheats, discharging coolant, going up hills. Otherwise it runs fine. Could these two problems be related to timing? Could the knocking sound be head gasket, manifolds or something more serious? Thanks

 

It depends on where the knock sound is coming from. You suggest timing, which is a kind of an odd suggestion, so I'm inclined to think that you aren't sure it's set right. Timing that is too far advanced can causing spark knock, which you can hear from the cab. It has a high metallic pinging sound. If you're getting that, your timing is probably too far advanced.

Where is it leaking coolant from? It wouldn't be related to timing. I would flush the cooling system and try to isolate the leak.

 

if it is blowing coolent out of the cap then replace the cap it is no good coolent should only go into the overflow tank. are you sure it is over heating or are you just assuming it is because the coolent is coming out of the cap?

 

It is blowing off coolant at or near the cap. I hope you're right and will replace cap first. thanks

The only reason I suspected timing was that there is a new distributor cap and plugs and wires done by the seller himself. I heard timing could cause spark knock but I didn't know what that sounds like. thanks

 

If your gage doesn't show overheating then you probably are not overheating. but a good flush and thermostat change is not a bad idea. be sure to use a 195 deg. thermostat.

the thermostat & radiator cap and colling system are the most neglected of all service items and are responsible for more than 80 % of all rode brake downs.

check your hoses. and replace when you flush the system.

 

Are you using premium gasoline? It could be the gasoline you put in it has too low an octane. Drop in a can of octane boost. If ping/knock goes away, it was the gas.

 

the 4.9 is built for 89 octain. it could be a lot of things making it knock

 

I think it's actually 87 octane. If your truck doesn't run right on 87 octane, then something is wrong.

 

thanks alot. The new cap worked. Tom Nixon

 

As for the knock, it may be that it's just an exhaust system leak. thank you all for your help. This is a great site. Tom Nixon

 

let us know what you find. that is the only reward we get is the feeling that we were able to help someone.

 

laugh as you may, but my best buddy has an 87 with a 300....his gets a pinging....about every other month he'll dump a measuring cup of Marvel Mystery Oil in a full tank of gas.....quiets right up......i've witnessed it....if i hadnt id still laugh too

 

I had a 67 ranchero with a 5.0 GT40 engine that would do exactly that and Marvel Mystery Oil in the gas is the only thing that would make it stop. that car would flat cook with that Marvel Mystery Oil

 

Is the exhaust hitting the frame??? As the exhaust turns down the passenger side of the truck it runs right next to the frame and directly over the cross-member support for the transmission. Most of the time the support hangers become rusted and become loose so you might want to have the exhaust system checked. If you have any leaks you want to get those fixed pronto...otherwise you will be paying for the head-work in the long run. Exhaust leaks allow cold air to become entrapped in the exhaust port causing the valve to warp due to the expansion and contraction of the air and metal. This in turn causes your cylinders to run "lean" and to become very hot allowing the head gasket to fail. Just a few pointers to help out in the long run.

-Cheers

 

My 93 with the 4.9L pings like crazy if I don't use premium. I brought it in to the shop and they adjusted timing and could not see anything else. It really made very little difference. If I run even 89 it will ping.

What could be the problem??