93 knock under load
 

Hi i just signed here, i cant seem to find exactly what im looking for so i thought id sign up and ask. I havea 934x4with manual trans, 217k miles. It has a deep dull knock/rattle under load. The harder i work it and higher i rev it, the louder it gets. also my gas pedal and floor boards vibrate like crazy. It gets most significant over 15 pounds of boost (i have no tach.) Its even worse when im pulling. Ive been scratching my head for a while now. Rod knock? Main bearing? Otherwise it runs great and doesnt use oil, not lacking power, starts quick as ever. Any thoughts or ideas would be appreciated, thanks!

signs of too much advance
 

Have you checked the engine timing?

You will start hearing that distinctive rattle like two marbles in a plastic cup. It’s pretty hard to miss. You will start hearing the “knock” when loading the engine or when using low octane fuel. On the Cummins B-series engine you will start to hear what I refer to as a “hard” metallic sound.

Advancing the pump too much (moving the top toward the head) gives white smoke, but not the amount of engine fuel knocking or rattling that you would get from
advanced timing with an in-line P7100 pump. Better mpg may occur with advancing the VE pump timing slightly from stock. Retarding the pump timing will generally result in lower engine power.

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Bosch VE Injection Pump (’89-’93 Vintage)

The VE distributor type injection pump came out in the 1970s
and was used in the Dodge Turbo Diesel application from
‘89 up through the ‘93 model year. This pump has been
widely used for diesel engines up to about 33 horsepower
per cylinder output (about 200 hp for six cylinder engines).

It weighs only about ten pounds and is relatively compact in
dimensions. It is moderate in cost to buy and to repair. It
is lubricated by diesel fuel only, so it is very sensitive to fuel
quality. Its maximum design output fuel pressure is 700 bar
(10,150 psi). It uses a single high-pressure piston, so it has
fewer parts than many other designs of pumps. Idle speed,
maximum speed, and maximum fuel delivery quantity are
all externally adjustable. Tamper-resistant caps or seals
are put over the adjustment screws at the factory.

The VE pump is limited in fuel delivery volume and
pressure, compared to the pumps used in later model
Turbo Diesels. The volume limitation became important
when greater horsepower was sought. The low (10,000
versus 17,000 psi) pressure meant that new emission
regulations for 1994 could not be met. To meet these EPA
regulations, higher pressure was needed to bring in enough
fuel quickly, during the time period when it would burn most
efficiently and produce the least smoke. Higher pressure
also improved atomization, especially if larger injectors
were used to increase fuel delivery for more power. In the
early 1990s, these concerns were coupled with problems
from the advent of low-sulfur fuel, and with the concerns
about poor fuel quality or cleanliness. These issues made
it clear to the manufacturers of diesel engines that they had
to discontinue use of the VE pump for our Turbo Diesels
and for other over-the-road applications.

There are official tools and procedures for setting the timing
of the VE pump. Many years of working with these pumps
on Dodge applications have resulted in some “quick and
dirty” procedures that you can use on a try-and-fit basis.
You can try small incremental positioning (turning) of the
pump to see what effective timing works best for your truck.

How do i go about checking the timing? Is there some way to verify its right without changing it? Ive never changed or adjusted it. Also i get no white smoke.

Bad fuel perhaps.
What do you know about the previous history of the truck? What other did to it. The previous owner of one of my trucks did a lot of things he didn't tell me about causing all kinds of hate and discontent later down the road.
Timing is hard to check without the proper equipment. Outward visual signs are not always apparent. There are supposed to be a mark on the timing case that aligns with a mark on the side of the injection pump. However, a common practice is to jump a tooth on the injection pump gear that you cant see.
Make sure that no part of the engine, including the exhaust down pipe is hitting any part of the frame or body. Next would be have your injectors cleaned and pop tested. When was the last time the valves were adjusted?

This is the best picture I have of the timing mark on the timing cover. My injection pump was not marked when the recall was done. If you note the bolt in the pump adjustment slot, the pump has been turned counter clock wise. It should be approximately in the center of the slot. The reason mine looks like that is the PO jumped a tooth on the gear and timing was too much for the injectors it had.

Yes, i bought it from the original owner bone stock. The only work done was the injection pump was replaced at 114k. I remember when he bought it in 93 as he is one of my dads old friends. It now has 217k. but possibly his mechanic could have changed the timing or got it wrong with the new pump?

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Also i adjusted the valves 3000 miles ago and re checked them 500 miles ago

I'd say at this point, get your injectors serviced. The IP is probably fine. As your injectors wear, they open sooner advancing the timing.

I got to thinking more about it, could it be a harmonic balancer issue? It dont appear bad without pulling it off. Runs true and the rubber isnt sticking way out. Is there a good way to eliminate the possibility of harmonic balancer or am i thinking too hard?

Sorry I didn't get back to you sooner, I'm on the road.
If the harmonic balancer looks like it is running true, then it probably is.