Potential Air Leak Problems--12 Valve Cummins

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oriont's picture
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Joined: 09/12/2010

Hi,

I was hoping to get a little feedback on some issues I am having after getting a Greasecar kit installed in my 94 Dodge 12 valve.  At this point the engine will idle (a bit rough), but at higher rpm's it will cut out and will eventually die when brought back to an idle.  In watching my turbo boost pressure the engine usually starts cutting out when it gets above 5-7 psi.  My first thought is that I have air trapped in the system somewhere, or worse, there is an air leak or something wrong with my turbo.  I have been able to get switched over to veggie and the engine seemed to have run a little smoother.

First Question--Will the fuel system purge air on its own or is there an ideal location to force air out?  I have tried the low pressure bleed bolt on the filter, but with the re-pluming of the fuel system this does not work as it would pre-veg kit.

Second Question--What is a recommended method for tracking down air leaks?

Third Question--How do I know where the system is under pressure and where it is under vacuum?

My first two Greasecar installs were Mercedes 300sd's, that went off without a hitch, the 12 valve has been challenging to say the least, but I am pushing forth in hopes to have it running smoothly in the next couple of days.

Thanks in advance for any input, it is greatly appreciated.

 

Orion

Billy's picture
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Joined: 08/11/2009

Orion,

I also had air leak issues after I installed my greasecar kit on my 97 cummins. It took awhile to figure out where it was. I finally checked the bolts on top of the diesel filter. One was a little loose and after tightening it my problems were gone.  I also replaced those seals that connect the fuel lines to the filter. That bleed bolt on the diesel filter actually pulls air into the system now that the direction of fuel flow has been reversed. It took me awhile to figure that out. To get most of the air out after install I pulled a vacuum on the line going to the injection pump.   After it is started by bleeding the injectors the remaining air should work it self out just by driving if you don't have any more leaks. If it is idling rough you can open each injector one at a time carefully and bleed the air out of the injection system. I also removed the diesel heater/pre-filter from the fuel system because I heard it was prone to leaking. It's not necessary anyway.

Good luck

oriont's picture
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Joined: 09/12/2010

Billy,

Thanks for the reply, I was at it again all day today, to no avail.  There is still a lack of fuel getting to the injectors, could be air but I am not so sure anymore.  Tomorrow I plan on bypassing the lift pump with an electric pump to see if that helps.  From everything I hear the mechanical lift pump is bomber, but it won't hurt to check.

You mentioned that you replaced the washers for the steel connections on the fuel filter, I am curious if you were able to get those at a parts store or if you had to track them down from the dealer.  I am also curious what your technique was for splicing into the steel fuel lines.  I used 1/4" fuel line for a tight connection to the steel lines and then transitioned to 3/8".  I feel pretty confident with those connections and the rest are barb fittings, so it seems like all my hose connections are tight.  I also bypassed the diesel pre-heater as you mentioned, it seemed like a good idea to take that out of the equation.

Thanks again for you input.

Orion

Billy's picture
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Joined: 08/11/2009

Orion,

The washers are a specialty item.  I got them from a cummins store, you could probably get them from a dealership as well. I don't know if I would say the lift pump was bomber, definately the bosch injection pump but not the lift pump.  If you have an old lift pump you might consider replacing it.  I've heard running grease can reduce the life of a lift pump that is already on it's way out. They are only about $80 to $90 from Cummins because the one with their name on it is manufactured in China for some reason. The Carter pump, made in the USA, is $200 or so dollars, you can get that at Napa. I also replaced the overflow valve behind the injection pump. It's a cheap easy fix and when it goes bad it has symptoms similar to a bad injection pump.

Your fuel connections seem pretty solid.  I used 5/16 fuel line to attach to the stock metal fuel lines.  My fuel switches have the 5/16 fitting but they may have switched to the 3/8 recently. There is also a rubber return fuel line behind the diesel filter housing and above the lift pump that is notorious for leaking so I replaced it as well.  It is pretty hard to get to, but possible, if you don't already have the filter housing off.

Again, good luck. It also took me awhile to get all the kinks worked out on my system but it works fine now.

oriont's picture
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Joined: 09/12/2010

Billy,

Thanks for the continued flow of information.  I was not able to test the lift pump today, but I did drive the truck around for about an hour.  Without giving to much gas the truck runs fine, and I got up to about 50 mph.  As soon as I stomp on it the engine cuts out, same story.  At first it seemed like the air was purging out, but it still won't take very much fuel.  I may drive it around for a while longer tonight, hoping that it just needs a little more time to get the air out.

As far as the mechanical lift pump, do you think it is worth the extra money for the carter pump, or just stick with the pump from china.

Thanks again.

Orion

Billy's picture
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Joined: 08/11/2009

The Carter pump probably isn't any better than the Cummins pump from China.  I often am willing to spend more money to get a product made in the US but the price difference in those pumps seemed ridiculous. I bought another pump made by a company called Airtex. It's also made in the US but not as expensive as the Carter pump. I just found the lowest price on the internet.  Mine doesn't have a bleed hole in the side of it like the old one did.  I think the pump is supposed to push fuel out the bleed hole if the pump is damaged.  Anyway, hope you fix your problems soon.

slatemd's picture
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Joined: 11/26/2007

I have a 92 12-valve.  Every year to year and a half (or so), I change my lift pump.  I found them on eBay for $35.00 each, so I bought 3 of them.  Somehow, I find that veg will deteriorate my lift pump over time.  Since it only cost me $35 for one, I change it as a maintenance item.  It only takes me 15 minutes to change one out.  Also, hook up a wet PSI gauge after the filter and before the IP.  Bring the gauge into the cockpit as so you can monitor your pressure. 

Yes, a 12-valve will purge air out of the system.  Check all of your connections again.  It sounds like you are introducing air into your system.  If it does it on either fuels, then look from your filter to your IP.  If it does it only on veg, check your entire feed line.

Pressures range from 8 to 12-psi on these mechanical lift pumped 12-valves. 

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SunWizard's picture
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Joined: 09/25/2010

On the 94-98.5 cummins the lift pump pressure is 20 psi at idle, up to 35 going downhill.  They have a much stronger piston lift pump than the earlier 1st gen. cummins with a diaphragm lift pump.  A pressure guage before the IP is very helpful to tell how your lift pump is doing, and also lets you know in advance if your filter is getting plugged, which could also be your problem. 

Putting a small clear inline strainer you can get from any auto parts store in the line and moving it around will let you see if and where you have an air leak.

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