Technical article on the Cummins lift pump. Free to Cummins 12V owners.

[cumminsfuelsystem]

Hi We have been working on the Cummins 12v fuel system and lift pump for over 14 months. We uncovered a lot of data, from hundreds of tests. This is article number one in a six part series. I hope you like it. Rob Parelli Here is the link http://torkteknology.com/news.php?newsid=5

[ISX]

Ah you made it over here! So I have been curious as to what exactly the low efficiency does. I know it can keep you from hitting high HP since you won't have as much flow but most of us on this forum are just trying to accomplish reliable trucks that get impressive MPG numbers. I rarely get over 10psi and mainly aim for mileage so I am very curious as to what kind of effect making it more efficient would have on the mpg numbers. Maybe I am getting ahead of you and all of this will be explained in an article to come. Nice work!

[Mopar1973Man]

Killer work! Wow! I always thought the older mechanical pumps where better pumps but now we know the truth! Now I heard of several big player that ditched the mechanical pumps and heading for AD150 or simular pumps for there 12V Cummins to keep the P7100 pump feed during high HP apps.

[flagmanruss]

As an "old school" mechanical mind... I've always wondered about the switch away from the cam driven mechanical pumps I was so familiar with... & which seemed bullet proof. But actual testing is something this topic really needs.Russ

[fishtails]

This is probably a dumb question, but does anyone know of a way to have both the stock Carter lift pump and an electric fuel pump? I have replaced my mechanical lift pump twice when it started making noise (too scared of burning up the HP pump), and now it is making noise again. Everyone knows electric motors fail which would be a sure fire way to burn up the HP pump, hence the thought of having both. I am thinking about a tee connection after both pumps with a check valve on each, but I really have no idea if this is possible or feasible.

[ISX]

What is the HP pump? What are the specs on your truck? The mechanical pump should last a long time. If it makes noise you should add some lube to your diesel. Mine liked to tick so I dumped in some biodiesel and it went away. Electric pumps are very expensive compared to the mechanical one. I'm not sure why yours are going out. Generally, running 2 pumps is not recommended. It is possible but is usually costly and unneeded.

If you can give us some more detail on your whole setup and truck specs it would be a little easier to understand what you are trying to do.

--- Update to the previous post...

Here is a thread on what you are thinking of, though they are thinking of 2 electric pumps since 24V's have no mechanical pump.

http://forum.mopar1973man.com/showthread.php/2304-Nother-Question

[fishtails]

Thanks ISX. That figures that some biodiesel might quiet the noise down. It seems like I always waste money and then find out after the fact that there was a simple cheap fix. A "ticking" noise is exactly what I am hearing (and have heard twice in the past $$). I always assumed it was the lift pump going and when I changed it out the ticking went away. Live and learn! I will try the biodiesel trick before doing anything to the lift pump this time. The truck is a 97 12 valve, 4.10, 4x4, MBRP 4 inch Cat Back, extended cab. The HP pump I was referring to is just the Bosch P7100 High Pressure fuel injection pump. Thanks again for the tip!

[ISX]

Ah. Yeah the biodiesel trick works good because it has insane lubrication in it. There are some people that say it gums stuff up which is from dirty biodiesel. It also gels a lot easier than diesel in winter, I wouldn't even use it if it is under 40F. The more viable option is to just run a light dose of 2 stroke oil through every tank. If you go to walmart and get the TCW3 super tech, just dump half a quart in for every 35 gallon fillup. There is some info on it here http://mopar.mopar1973man.com/cummins/general/2-cycle-oil/2-cycle-oil.htm It is mainly for the 24V trucks, I don't think ours need as heavy a dose. In fact my ticking went away after the tank of biodiesel and never came back and I didn't even fill up with any biodiesel since that time. So I believe it just needs a little bit to get some lube in there and then it lasts for a while. So half a quart for 35 gallons should keep it happy. I haven't ran anything in a long time and that ticking never came back. The 24v's use a quart per 35 gallon but half a quart should be perfect for just a little lift pump. The P7100 is actually lubed by engine oil so if it doesn't get fuel, it just stops running. Nothing detrimental is going to happen to it if the lift pump stops working. The lift pumps on these are pretty long lasting so in most cases it will be something like the overflow valve that stops working that causes low fuel pressure. I have a long article on fuel pressure I will have to link you to when Mike puts it up.

[ISX]

Alright here is the link to the fuel pressure writeup I did. http://mopar.mopar1973man.com/cummins/2ndgen12v/p-pump/p7100-fuel-pressure.htm