It is now 8 months since I bough my -91 F-250 7,3. I have to say it is way better now. But I still got one thing I haven`t figured out. It is making a hard knocking sound. I changed all my injectors last night and the return line set. I kind of hoped the knocking would go away together with the old injectors, but it did not. The thing is that if the truck has been parked for some time (several days), I am pretty sure I don`t hear the sound until the engine has been running a few seconds. But at daily use it is there immediately. The sound is follwing the rpm. The sound seems to be the same loudness at both sides of the car. Also hear it good in the cabin. Hear it less from the front of the car. A previous owner changed all the hydraulic lifters. Should I take off the the valve cover and rip apart the valvetrain and look for bend pushrods ..?
Any suggestions what might cause this!?
The car has been driven by at least 2 owners over a couple of years with this sound. I think the sound has become louder, but maybe it is just more annoying since I have fixed all the other problems and sounds :-)

 

It could be the vacuume pump..take the belt off and start it see if its gone or just listen to the pump with a stethescope

 

It could be any number of things.......does the knock go away at all. Is it heard all the time while running........be aware there is a quiet knock/skip within the engine on most every IDI I have heard.

 

A bent push rod will give you a miss to some degree and once they start to bend they will keep going. Have you loosen the injection lines on each cylinder and see if you can eliminate a fuel knock? I have seen gear trains cause this from a chipped tooth but it isn't very common.

 

The knocking sound is loud. You do not have to listen for it.
It is not the vacuum-pump. The knocking is there constantly.
It is not fuel knock. All eight injectors are new.
It could be a bent push-rod, or something else wrong at the valves.
The sound is really hard, so I am worried about bearings further down in the engine, but the oil looks fine and the oil pressure is stabil and fine.
I was told that this sound was first heard after a transmission-rebuild. Then the car had been parked for 2-3 months. Maybe something happend at the first start-up after this long period without any driving?
How much can I find out by taking of the valve covers? Or do you have any other suggestions where to start?

 

If it's an automatic maybe one of the torqe converter nuts is not tight or backed away and hitting the back of the block

 

Thanks, but that is not the problem. Have checked it.

 

This is a WAG but it could be a GP tip that was dropped into a cylinder by a PO. It is mashed into the top of a cylinder but is causing little effect other than noise.....

Check out Ziggster's page for info..... http://www.members.shaw.ca/k2pilot/

 

Just because the nozzles are new doesn't mean they are ok. Also by cut the cylinders out you take the compression power off the cylinder and if it is a bearing or bushing the noise may go away.
If the tube was bent, as long as this has been going on it should have bent enough by now to have slung it and it should be missing or you would have noise in the intake or the exhaust.

Engine noises can be funny things. A few years ago I was looking at a 3406 Cat that was towed in to the shop for a cylinder knocking. It was number 6. I could cut that nozzle line loose and it would ease some and number 1 would make it ease some.{ A knock on a cylinder can be caused by it's companion cylinder.} Make a long story short after checking cyl. from underneath and on top with a borescope and swapping nozzles an old timer ask me to check the crank drive gear. It had a small chip on a tooth and I mean small. That chip was causing the noise and it was loud but not a scored cylinder noise. It was a skirt slapping noise. I tell you this because engine noises can be very hard to pin point.

Can you slide the torque converter back away from the flexplate enough to run the engine?
Crack the lines loose and see if you can change the noise.
Were the lifters changed to try to track down this noise?

 

Thought of something else. I looked at a Dodge pick-up for one of our opwner operators and he coplained of a knock which was a fuel knock. At some point the nozzles were replaced for what ever reason but one of the nozzles had an extra copper seal under it and made it knock. That actually advances the fuel timing on that cylinder because at the point of injection the piston is farther away from the nozzle tip. It could be in there from somebody else awhile back and you didn't catch it because you got the 8 seals that it should only have in there. Idea.

 

Thanks! Now I have some issues to check out. Just need to find the time for it.

 

Ola,

Could you please let me know what you found out? I am having the same problem.

 

I will post it here when, and if, i find the reason.

 

Haven't had any luck yet? What have you tried so far?

 

Hey!

Have just checked the valvetrain, and it is ok. The injectors are new.
Have taken out the injector lines one by one and it missed like it should.
The knocking is really hard. My father in law said today that the last sound he heard when I drove off, was this knocking sound. I am getting pretty sure I have a serious problem here. I think this is a rod bearing or cross-pin. It may also be a stuck piston-ring that make the piston "slam" into the cylinder-wall. (Have some problems with the technical english here). Maybe the next is to loosen the injector lines again. If it is like I think, there should be less knocking when there is a lower pressure in the cylinder, or ???
Is it possible to take down the oilpan without removing the engine?
I was told this sound was first heard after a transmission rebuild. The car had been parked for months. Maybe a dry rod-bearing broke down when it was started?
What should I do next?