One cold snowy morning last month, I started my 1993 7.3L and heard a loud knock in the engine. This quieted somewhat after a few minutes, but did not go away. I drove the truck to work (3 miles), then drove it home that evening. On the trip home and when I arrived home it was quieter, but had not gone away. It was almost gone when idling, but was louder with increased RPM. It seems to be coming from the second or third cylinder back from the front of the engine on the passenger side. It seems to be in the head or valve cover area. The truck has approximately 176,000 miles.

I called my mechanic and had it towed his shop. The first thought was that a piece of glow plug had fallen on top of a piston. A check of the glow plugs did not show any problems. We next thought it was a lifter. After a new set of lifters the problem was not solved. We next removed the duel weight flywheel and had it checked at the Ford dealer. They did not believe it was bad. It was returned to the truck and the knock was still present. Next the head was removed and does not appear to have any problem. My mechanic and the local automotive machine shop checked the valves and valve guides and everything was determined to be in spec. A vacuum test on the head did not reveal any leakage. There did appear to be wear on some of the rocker arms and both sides were replaced. While the head was off, the piston tops were indicated and we do not believe that a wrist pin is bad. There is no sign of damage to a piston or cylinder wall. After returning the head to the truck, the knock was still present.

The truck was then started without the serpentine belt. The knock was still present.

Next the engine was pulled and the lower end checked. It was found that two of the rod bearings had loose cap nuts. These were not finger loose, but were not at the proper torque and had resulted in more wear to those rod bearings. The crankshaft was not damaged. At this point the lower end was rebuilt. New rod and main bearings, seals and a new throw out bearing. Upon returning the engine to the truck, it was started and driven several miles and returned to the shop without the knock present. The problem was thought to be solved. However the next time the truck was started the knock returned.

The truck was driven to another mechanic, and he believed that the knock had to be coming from the duel weight flywheel. The duel weight flywheel was replaced with an after market solid flywheel and clutch assembly kit. The knock did not go away.

The injectors were switched from one side of the engine to the other the knock did not change sides.

The knock is still present.

Any suggestions, we have run out of things to check?

Thanks for any help you can give.

 

As I was reading your post I was thinking how about the injectors, check them before removing heads, clutch, etc. What's the possibility of more then one injector being bad and maybe there is one bad in each bank. Then when you change them there's still one on each side making noise?

Man, gotta make you want to get an electric vehicle.

 

Welcome to deisel reality. I had mechanic after mechanic including dealerships milk me for thousands every year to keep my 7.3 alive. It was the happiest day of my life when that pos finally blew the rods out the side. That ended a 10 year long ordeal I will never repeat. Color me one happy 460 transplantee. About the same milage. I can now talk in the cab and doubled my pulling power on the hills. I went from 26 mph to 60+ on the same grades.

If your lucky it will blow up soon and then you can swap in a real engine. It sounds like you have covered the bases. I would put in a set of new, not remaned injectors in it and put a bunch of Stanadyne fuel additive through it and I bet the noise goes away. That stuff is miracle fluid. It prolonged my suffering for years.

 

hired gun its sad to hear you had enough probs to swap in a GAS SUCKER,i now of several 7.3s that are at 250,000 and have never even had pump or injectors,or any other major work.you couldnt give me a GAS SUCKER,my old 7.3 might be slower,but i'll get 300,000 out of mine.i dont know of any 460 getting 300,000 on it without major work.what kind of fuel milage do you get with GAS HOG doing 60+ up hills?
bharris,i will agree with hired gun about the nozzles.but i would have a good diesel shop check them.if one is bad,they can find it on a nozzle tester.sounds like you spent alot of money,when you should have started with the simple basic stuff first.should have come here first!

 

i bet its yar transfer pump. arm could be wore or somthen like that. ive had more then one knock before it quit on me. its located on the passenger side of the block pretty far down. least on my 6.9 iam pretty sure the 7.3 used the same setup.

 

diesel engine: 12 mpg highway 8 with the trailer. 9 city
gas engine--AKA Gas Hog: 11.5 highway 10 with the trailer going 60 up the hills four barrels a howlin' 7-8 city.
Both engines with 4.10's and c-6
Best tank ever in 10 years or 180,000 deisel miles was 14 mpg with the wind going downhill on the freeway and 3.54 gears. With my trailer and the 3.54's it wouldn't even run 55 in a strong headwind. With the 460 I can bury my 85 mph speedo in any wind now. The old van even did it's first ever Gas Hog burnout the other day on dry pavement. I bet the patch was near 200'. My stinky old oil squirter couldn't slip a wheel if it tried. I was just so cool I couldn't bring myself to let up. With a cam and a converter and a bunch more traction this old E350 may even pop a wheelie.....Whooopie!

 

Thanks for the idea on the transfer pump. We will look in to that.

 

We have removed the transfer pump, but unfortunantly have determined that it is not causing the knock. Thanks for the idea.

We are thinking of removing the head again and having a different machine shop check it.

Does anyone know of anything else to try?

 

Have you cut open the oil filter to determine if there is any wear going on? Have you put in new injectors? Bad ones pound like a mechanical knock. Have you ran the Stanadyne? One whole bottle to one tank? If you have answered yes to all of these then welcome to a perfectly healthy 7.3. They are just noisy. If it's not making metal in the filter and there is no oil in the water or water in the oil and compression is over 400 pounds in every cylinder or smoking white or black, it is in perfect health Thats how they sound. Join AAA Auto club so if it does blow it won't cost a fortune to get towed in. I cured my bucket of bolts with a gas engine swap.

 

Each of the injectors were individually disconnected. The knock did not change. Also all of the passenger side injectors were switched to the drivers side, the knock remains on the passenger side. If it is a bad injector why did the above not isolate the problem?

Thanks for your continued response.

 

The fuel pump is on the drivers side. The knock could be getting telegraphed back to the pump. You have come this far. Try the Stanadyne fuel conditioner first for a tank and if that doesn't get it then put in a new set of injectors. I went through this many times and thought each time my engine was on it's death bed it sounded so bad and the Stanadyne fuel conditioner fixed it 95% of the time. Nothing else can do what Stanadyne will do.

 

I'll take an obvious stab at this....

How is the diesel fuel you are putting into it?
After running for a while, does it still knock when you switch tanks?


I suppose it is possible it could be injectors....
Is it like a 'clang' metal on metal knock?
The fact that it increases as the RPM increases would point me toward a piston, rod or crank. Either something is bent, broke or touching (rapidly mind you).
Like Hired Gun said, cut open the oil filter and fuel filter.
Could be you find something....

Seems like you have spent a lot of dough and had a lot of people looking at this. I hate to say it, but these things can nickle and dime a person to swap to a gas guzzler....

 

Change the timing just a bit. look over the top of the pump housing you will see a hash mark on the housing and the pump it self. Advance the timing the width the head of a nickel. it should make the knock go away. It sounds like a fuel knock to me. If you have moved injectors around it is a heavy fuel load knock. try that and see what happens.

 

ONe more thing, make sure you have the injector lines on correct. there two lines you can cross and it will cause it to knock as well. If have taken all of the fuel line brackets loose and the individual lines apart you could possibly have 2 lines crossed cant remember which two lines can be crossed, been there and done that.

 

Has the power dropped off?

Is the oil pressure dropping off?

Does it sound like the knock is worse when the engine is warm?