I am having a problems with my engine knocking on my truck and looking for some help on what is causing it.

I have a 78 ford bronco with the 400m engine. Whenever the engine is under heavy load going uphill on the highway or off  the engine starts to knock. It happens when the gas pedal is almost all the way down just before the tranny kicks into passing gear or a lower gear. The engine is not overheating and I had the timing checked and it is where it's supposed to be. I don't know why it is doing this. Would advancing or retarding the timing help? I know knocking is bad and I don't want to wreck the engine. PLEASE HELP!!!

have you checked your oil pressure when going pulling these loads?  how many miles are on your truck?

it could be a lifter collapsing under high the loads you describe.

I bought the truck off an old couple that hardly ever drove it except for hunting in the fall. It only has 70,000 original kilometres. I did notice the oil pressure gauge is on the lower half of the gauge lately though, and it is using some oil but not smoking at all. Do you think the long periods of sitting before I bought it could have damaged the lifters? Or is it maybe time for a rebuild even with the low miles?  

Try shifting the thing into a lower gear and see what happens.

If you have a colapsed lifter you will need to change the cam when you change lifters. The cam and lifters harden in the engin under use and if ou just change lifters the hardened cam can cup the softer lifters and ruin everything.

Years ago when I was doing mechanic work for a living I had a similar problem with a car engin. I drained the oil changed the filter, put in 2 quarts of 15wt oil and karosen, run the engin for about 10 min. at an idle. drain the engin, change the filter again and put in a detergent 10-30 wt oil like Dello 400 that is used in diesel engins. drive it for about 100 miles, change the oil and filter again adding the oil that you want to run. It worked for the dealer that I was working for at the time.

Good Luck

When the tranny kicks down into passing gear,or a lower gear if I'm off road, the noise goes away, then returns as soon as the engine is under load when the tranny gears back up.

Does it still sound like a collapsed lifter?

Are you saying that at high RPM the noise goes away? Bad lifters usually make a ticking noise all ot the time but get louder as the RPM increases. To be safe I would be concidering a rebuild. Check the parts stores that you deal with, you can usually get a remanufactured long block with a warente for a few bucks more and some times even less than having the work done at a shop  

Yes, as soon as the rpm goes up the noise goes away. That's what has me so confused, that it isn't a timing problem.

I guess I just might have to look at a rebuild. Thanks for the help!

have you tried switching to higher octain fuel.  Try switching gas stations.  The older engines are not designed to run with ethonol blended fuels.  Ethonol has a higher flash point than just plain old gas.  i don't know what tranny you have but if you have a chevy with the 700r4 your t.v. linckage could be out of adjustment.  if the overdrive is kicking in at to low of an rpm it would cause that same problem.  You can also have the lock up pressure changed in the tranny, this is done by changing the lock up solidnoid.  

I tried higher octane gas and an octane additive,also tried different gas stations and neither helped. I have a c6 tranny that was rebuilt a month ago and seems to be working great. I had the same problem before I had the tranny rebuilt.

Keep the suggestions coming guys I really appreciate it. The engine seems to run great except for my knocking problem.

when i got my 77 chevy it was dooing a similar thing as your bronco, I solved my problem by adding 1/2 quart dextron mercron (tranny fluid) to the engin and driving it for about 25 miles before changing the oil. it helped bring the lifters back up and restore compression to my engin.  

this is a redneck solution you need to keep good track of your oilchanges after dooing it.

before i get yelled at for telling you that, This is not a prescirbed solution to lifter problems and probably all mechanics will tell you that it will hurt your engine.  

but after i did it my oil losses ended, my oil pressure went back up to normal ranges, and my engine chatter and racket ended.

i dunno, maby, and i mean maby, this will help you.

Thanks, I've actually heard of this before,but it came with a warning that it may hurt my engine also. However if my only other option is a rebuild, I just might give it a try anyway.  

that was the only other choice i had with my engine as well, thats why i tried it and like i said it solved alot of my engines difficulties.  

I Would try the tranny fluid trick but use a ford tranny fluid it is higher in detergent and will clean it out bettter.  As long as you dont put more then 1/2 a qurt in and change in a couple days you should be fine.  Also try barimans (sp) fuel system cleaner.  There are instructions on the bottle for use in cleaning out the engin, make sure it is the carburator style not the injector style there are alot more chemicals in the injector cleaner.  I dont know were your at but any chain style parts store should have the barrimans.  Its a 7 inch tall can white with red stripes.  

Thanks, I'll have a look for it.  

Oh and as a precauion that the tank is nasty from old gas put the rest of the cleaner in with your next tank of gas it does a number on the fule system to.