Cummins 5.9

[MyFirstRV]

I have a 12 valve 5.9 Cummins in my 1994 holiday rambler 33’ endeavor le. I will be removing all the carpet which will require I remove some of the furniture. While I have the bed out I will also do some needed work on the engine. My p7100 injector pump is leaking motor oil so it will be repaired or replaced. I would like to know if there is anything I can do to boost fuel mileage while I’m at it. It currently gets between 11 and 12 miles per gallon which isn’t bad but if I can squeeze some more out of her without losing power all the better

[Skip426]

JMHO; Although the 5.9 is the fuel economy king when it comes to powering motor homes , there are limits and I'd say your at the limit .
I worked at a Dodge dealership on the 5.9 Cummins through 4 different fuel systems ( 93>07) and every time the systems changed and the engines developed more power , owners of new trucks would show up complaining that their new trucks didn't give the same fuel mileage as the old one they traded in. So even mods for more power may reduce the mileage your getting.

I would have to ask ; also ; if you are aware of engine work that can be preformed to make sure your engine doesn't fall victim to the " killer dowel pin " ?
If you are already removing the pump , the fix could be done with only a few hours more work.
BTW: A 5.9 , with the 7100 series pump was the only engine that I worked on that fell victim to the dowel pin issue.

[MyFirstRV]

Originally Posted by Skip426

JMHO; Although the 5.9 is the fuel economy king when it comes to powering motor homes , there are limits and I'd say your at the limit .

I worked at a Dodge dealership on the 5.9 Cummins through 4 different fuel systems ( 93>07) and every time the systems changed and the engines developed more power , owners of new trucks would show up complaining that their new trucks didn't give the same fuel mileage as the old one they traded in. So even mods for more power may reduce the mileage your getting.



I would have to ask ; also ; if you are aware of engine work that can be preformed to make sure your engine doesn't fall victim to the " killer dowel pin " ?

If you are already removing the pump , the fix could be done with only a few hours more work.

BTW: A 5.9 , with the 7100 series pump was the only engine that I worked on that fell victim to the dowel pin issue.

Dowel pin issue? Please explain or can you attach a site where I can find out more.

[Skip426]

The dowel pin , is an alignment point for the engines timing gear cover, in certain years the pin ( hardened steel ) would work it's way out of the block, through the gear cover and drop into the crank and cam shaft drive gears , causing gear, crank , camshaft and cover damage. $$$$$

Google " Cummins 5.9 killer dowel pin " for more horror stories and the fix.

I'll see if I can narrow the search and post a site that has the fix. But at the moment I'm in an RV park with the worlds slowest internet.

[MyFirstRV]

Originally Posted by Skip426

The dowel pin , is an alignment point for the engines timing gear cover, in certain years the pin ( hardened steel ) would work it's way out of the block, through the gear cover and drop into the crank and cam shaft drive gears , causing gear, crank , camshaft and cover damage. $$$$$



Google " Cummins 5.9 killer dowel pin " for more horror stories and the fix.



I'll see if I can narrow the search and post a site that has the fix. But at the moment I'm in an RV park with the worlds slowest internet.

Well that sucks, I will definitely look to see what I have and can I assume there is a replacement for that pin?

[Skip426]

Not a replacement but a plate mounted; inside the timing gear cover ; in a way to lock it in place.

[MyFirstRV]

Originally Posted by Skip426

Not a replacement but a plate mounted; inside the timing gear cover ; in a way to lock it in place.

Well that sounds like a real problem, my 5.9 is mounted inline and doing anything to it is a real stinker. As in stand on you head just to see the injector pump. It is my understanding the pin is located under the pump?

[GraySeal65]

Originally Posted by MyFirstRV

Well that sounds like a real problem, my 5.9 is mounted inline and doing anything to it is a real stinker. As in stand on you head just to see the injector pump. It is my understanding the pin is located under the pump?

KDP mod Cummins 5.9


Pull the radiator and CAC

[GraySeal65]

The P7100 pump responds very well to (tweaking) install a fuel stop plate that's good for 80 HP, my 93 Bounder ran like a raped ape and I averaged 11 MPH. You will HAVE to install a boost and EGT gauge, adding fuel to any diesel will increase the exhaust temps.

[Skip426]

Originally Posted by MyFirstRV

Well that sounds like a real problem, my 5.9 is mounted inline and doing anything to it is a real stinker. As in stand on you head just to see the injector pump. It is my understanding the pin is located under the pump?

The 7100 pump literally weighs a ton !
You'll need the instructions for setting the engine to TDC and locking the injector pump to prevent internal movement , before you remove it .
GraySeal65's two photos of the pin and retainer plate location, posted upside down , the pin can drop into the two gears shown or bounce around till it finds another place to jam up .
The easiest route for access to the pump and removing the cover from the timing gear housing is to remove the rad and CAC, as shown in his last picture .
You will need access and help to remove the pump... it is that heavy.

[Skip426]

The dowel pin is behind the cover in the area of the yellow circle.

[GraySeal65]

Thanks Skip426, I didn't notice they rotated during post.

[tizzyfit]

Just to be clear, this dowel pin issue applies only to the 5.9 12 v, and not the 5.9 24v as well, correct?

[BarryG20]

While there is a dowel pin on the 24v it has not been an issue. The 12 valves are the ones that are susceptible to it and it can cause a lot of damage if it lets go though there are cases of where it ended up falling out and doing no damage but is pure luck of the draw as to where that pin bounces around and ends up. There are a couple different fixes for it. If you go to a website like turbodieselregister.com and do a search you will find a lot of threads on the fixes. As I am sure just doing a search on google or the like will also provide answers. The TDR at one time had regional jigs that you could request and the local keeper of the jig would send it out to you for the cost of shipping and then you returned it or sent it the next person on the list. Though the jig method has been pretty much superseded by the tab method and I would suspect that by now the jigs are long gone. Using the jig you could do the job in about 90 minutes or so and required a lot less tear down to get to it you essentially just screwed the kdp through the case.