Sootblower

You would not necessarily see a fuel leak at the return line since it can introduce air (or combustion gases when running) from the return line from the injectors. The return line gathers all the blowby from the injectors (that small daisy chained tubing at bottom of every injector) and T's it with the blowby/excess from the injection pump before leading back to the tank. If injectors are sealing properly there should be very little gas but my own truck once had a stuck injector introducing combustion gas that caused a lopey idle and hard start. I replaced the two rubber supply and return lines leading to the fuel tank with clear PVC tubing for troubleshooting in order to find it. The PVC is not designed for diesel so I only had it on for two days. I saw solid fuel in the supply line and lots of bubbles from return line. After several minutes the bubbles started appearing in the supply side since fuel pick-up in tank has close coupling between the two lines. Long story but dealer got some black cummins engine paint flakes in the fuel line when installing IP and made one injector stick open. Injection cleaner dissolved the paint luckily after about a week. I still think this air/gas could go backwards into IP if return pressure regulator is faulty but the low pressure path must be easiest to tank? Make sure that tank has lots of fuel so it does not suck air. You want to eliminate all the obvious stuff first.

I can not think of any other way of air getting into fuel without you noticing an external fuel leak. I guess anything is possible when you think of all those small parts in the IP? I suppose faulty low pressure pump could suck bubbles but I can not see two problems occuring at same time?

suzy999

I'm having the same problem (sort of). Fuel is leaking out of the back of the pump, out of a thing that looks like an overflow. Any suggestions/ideas on how to fix this?

darels

Sootblower, I've checked at the fuel input line to the pump, and I'm not getting bubbles there or at the banjo fitting over the filter, so I'm thinking the air is not coming from the lift pump. Your idea about the clear lines to check is good. I'm delayed by work, but should get back on it tomorrow and check whether tightening the fitting on the return line to the IP helped. Will also take a close look at the line itself.

Suzy, if you look back to the first page of this thread, boiler-rat posted a pic of where ours' are leaking, it's between the pump body and distributor head. Not sure if your problem is the same.

darel

darels

OK, I replaced the fuel line and the return line with clear lines, and I am getting air in the return line (expected, I'm getting air at the injectors). But I'm NOT getting air in the line from the tank.

I've checked at the banjo fitting over the filter, and at the fuel input on the IP and still no bubbles. After tightening the return line at the IP, I tried to bleed again today, still lots of foam at the injectors.

There are no fuel leaks anywhere that I can see.

Is it possible that the air is being introduced in the injection pump itself, through something I did or didn't do when I replaced that seal? The pump is not leaking, but then again the engine hasn't actually run since it was replaced.

Any advice would be greatly appreciated.

Darel

Sootblower

When injectors are working good there is no air in return or IP as I have witnessed. When one injector leaks there can be air/combustion gasses introduced and it will still run but with some runability problems - especially lopey idle. When IP produces air in return line it is unlikely to run at all. I still worry that a leaky injector may be feeding air back through IP return flow pressure regulator (that has spring and valve that should prevent backwards flow). I would unscrew it ( it is banjo fitting on return connectionof IP) and look for debris or incorrect assembly keeping it open. I just can not see air getting into injector pump another way unless it shows an external leak?

As last resort you could try squeezing off return flow clear tubing with vise grips and give it a try bleeding and then starting. If it does fire, do not drive with visegrips as IP relies on return flow for cooling/lube. IP will get warm to the touch after awhile when there is no return flow and should never be allowed to get hot. A Cummins service manager suggested this tip for eliminating a bad return flow pressure regulator when I was tracking down an initial rough idle when cold starting below 0 DegF.

darels

No external leaks are showing. I think I'm confused about how these return lines work. I understand that the returns from the injectors go to where they join the return from the IP, and then back to the tank. I thought that excess fuel from the IP went FROM the IP INTO that line (through the banjo fitting) then back to the tank. If I'm understanding you correctly, you are saying that air from the injectors could be feeding back into the IP through the return line, possibly through a faulty return flow pressure regulator? And from there back to the injectors, and around again? OTOH, if IP relies on return flow for cooling, it has to feed back from the injectors, doesn't it? Does it only do that when actually running?

Also, since the clear tubing is in the line to the tank AFTER the union of the injector line and the IP line, will sqeezing it shut actually do anything? It looks like the line will still be open between the injectors and the IP return line, so the air could still get back to the pump. Am I missing something here?

Maybe I need a little return line tutorial. I really appreciate you taking the time to advise me on this.

Darel

Sootblower

If you follow the return line from the pump it does T with the injector drain line and goes back to the tank. Kind of hidden behind throttle assembly and above fuel filter at back of engine I believe? Take a look at Figure 2 on link below, 1st diagram, on extreme right side about 1/3 down for the T. Most of the return flow is from the pump once the engine is running and the rest is just small fuel injector leak-by due to very small clearance between needle valve and bore of injectors at 5000 psi. The pump return flow is on the order of 0.5 qt to 1 qt per minute (guessing from watching flow into a tin can). All this is when engine is at 800 rpm idle or above.



When cranking the return flow will be much less due to the low RPM with our mechanical pumps. I was only conjecturing that if one injector was leaking gas into return line (say 150 psi) it could flow backwards into a mis-asssembled return pressure regulator at the IP.

You may be able to get something out of the diagrams here:
http://dodgeram.info/tsb/recalls/605.htm

I may be way off base but I just can not picture the IP picking up air internally (even if misassembled) unless it also is showing external fuel leak. I would think there would be a sucking and compression cycle acting upon any IP body leak as pump rotated?

It might be worth pulling then KSB wire off the IP while cranking to see if there is a change. The KSB doubles the body fuel pressure (not he 5000 psi output pressure) to give timing advance.

And you are absolutely right - squeezing the clear return line would cause any air to go into IP so perhaps it is not such a good idea. Too bad there is not some easy way to disconnect the return line at the IP and connect clear PVC to a tin can to look for bubbles. At least this would eliminate leaking injectors and narrow it to the IP if you saw bubbles from IP only?

Any person that is keen enough to take one of these pumps apart deserves some help. I had my pump replaced on that Recall 605 above and the "so called diesel mechanic" at the dealer was totally intimidated by the inner workings of that pump. He referred to it as "having 10,000 parts" and he could not even do an R&R with a brand new warranty pump on my truck. I had to get 10 hours of Chrysler approved troubleshooting time at another dealer and a 3rd pump 4 weeks later. They could not find it after that 10 hours and that "clear PVC tubing" trick from a Haynes diesel manual allowed me to find it myself along with a weak LP pump. I must admit Cummins was impressive in that they offered to send pump to Bosch at their cost even though Cummins did not have warranty responsibity. I would have been without transportation for 7 days so that was why I started digging into this myself.

darels

The IP was leaking, so I replaced the o-ring between the body and head. I put it back on, bled through to the IP and confirmed no leaks, and got air at the injectors. I pulled it back off yesterday, pulled the head and confirmed no apparent problems, replaced the control valve o-rings while I had it out, reassembled (only took two tries this time), reinstalled, bled up to the IP and confirmed no air was going into the IP. I'm STILL getting air at the injectors. I bled them a LOT today, 3 then 3, all six, one at a time, over and over. I'm still getting lots of bubbles at all the injectors, and it's not catching, although it seems like it's trying after I bleed all six.

The only thing that has changed is the IP. I haven't pulled any injectors, haven't messed with the lift pump. I suppose there could have been a reassembly problem, but I cranked a bunch trying to bleed it before pulling it again, and didn't see any signs of any problem when I took it apart. It is getting strong squirts of fuel at the injectors, it's just got air in it. There are no fuel leaks anywhere in the system.

I'm pretty much at a loss at this point. I haven't actually taken the whole thing apart yet (skeered), but I guess that's the next step. I don't understand how so much air could be getting in with no fuel leaking out, but then there's a lot here I don't understand. Does anyone have any ideas about where this air could be getting in?

I know several of you advised me to take it to a pro and have it rebuilt, and that's still an option (I may be stubborn, but I'm not stupid). I would just really like to figure out where this air is coming from, and how I screwed up the reassembly.

Any advice would be greatly appreciated.

Darel

wannadiesel

It really sounds like the pump is messed up.

You can to use the primer lever on the lift pump to prime the IP, loosen the banjo on the return line and pump until you see fuel. The pump ought to be able to purge itself of air, so you shouldn't need to do this.

Sootblower

You are right on in questioning only the items that have been removed or touched since it worked perfectly except for the leak. I assume you never loosened or disassembled the return flow pressure regulator under the return line banjo fitting? I keep thinking gas could be getting in there since the IP pumping action is four times per engine revolution and it could possibly suck injector return gas (from injector drain manifold) if the IP return regulator leaks.

How did you verify no bubbles at the pump inlet? If it was the clear plastic tubing then I would consider one more test to eliminate the lift pump sucking bubbles. That rubber diaphram takes a lot of abuse hand priming and could suck air if it cracks? I would disconnect the inlet line at IP and try and place tubing in a small cup with diesel at bottom - enough that tubing is submerged so you will see any bubbles while cranking or hand priming.

Jim Lane

When I replaced the side cover gasket I found the return line from the pump was loose at the Weatherhead "T" at the back of the head. It has a small rubber ferrule that looks like a short piece of hose under the nut.
When they are worn out, you can tighten them as tight as you can but it will still be loose.
I bought replacements at Hose Man and changed all of them
You could be sucking in air from any of these connections.

Since this line should be full of fuel why couldn’t you charge the line with about 20 PSI of compressed air from the return line where it enters the tank up on the frame rail.

With the engine off.

If there is a leak anywhere along the line, fuel should be leaking out.

Also is there a chance you damaged the banjo fitting on the pump or misplaced one of the aluminum washers?

The Weatherhead “T” fitting is at just to the left of the rear lifting eye at the back of the head.
Jim

darels

I was really hoping it was coming through the fuel line from the LP (understandable, at least), so I did as Sootblower suggested and hooked a clear plastic line on the line going directly into the IP and dropped it into a glass jar - no bubbles, just clear fuel.

I also was concerned about air coming in from the air fuel control tube, so I disconnected that banjo fitting and plugged the line with a short bolt (w/washer). Didn't make any difference. I also replaced the washers on both of those banjo fittings (air control and return) with new ones from the rebuild kit, so I'm guessing they're OK.

I guess I'm still confused about the return line from the IP. I thought it just carried fuel out of the IP and back to the tank, but I think you're saying that it could also be sucking air back into the pump. Is this right?

The thing I find most puzzling is that the pump was actually working fine, starting and running fine (well, turning over a little more than usual on start), it was just leaking between the body and head. The only thing replaced in the pump was that one o-ring between the body and head. If that seal is bad (and I can't see how it could be, the new ring looks MUCH better than the one I took out), fuel should be leaking OUT of the pump at the same place, rather than air leaking in, right?

I guess my next move is to tear the whole thing down and replace all the seals. If that doesn't work, I'm giving up and taking it to a pro.

Darel

XLR8R

Considering the age of your truck, and the recent advent of ULSD, it'd be good preventive maintenance if nothing else to replace all of the IP's seals - then you wouldn't have to wonder...

gsjr24

How did you time pump to engine. Also when you removed head did cam disc become displaced. Also there is a timing button underneath the rotor. Rotor has indentation where button needs to go. I'm like you if it was running before maybe its something you missed when resealing pump.

darels

I've been distracted by work, family and weather, but I've got the IP mostly disassembled and am looking hard at every component and seal. No obvious seal breaks, but I'm not done yet. Quick question for anyone that knows anything about these things. There is a vent plug (item #336 on the Bosch parts list, handily posted https://www.dieseltruckresource.com/...ighlight=bosch by Jim Lane).

I notice that I can easily blow air through this fitting either way, i.e. both in and out. There is obviously a diaphragm of some kind inside the plug, but it seems to work easily both ways. Is this a likely source of the air that has been getting into the pump?

Thanks,
Darel