'93 8.3 Cummins Fuel Starves Uphill

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LeeTN
Posts: 18
Joined: Sun Oct 27, 2019 5:44 pm
Location: Eastern Georgia, USA

'93 8.3 Cummins Fuel Starves Uphill

Post by LeeTN »

My 8.3-300hp Cummins started missing on a trip the other day while climbing hills. It got progressively worse until I had to pull over. I thought it might be the fuel shut-off solenoid as I've had trouble with it in the past cutting off or no start. I removed the plunger and secured the shut-off arm in the up position so it should have been fully closed (run). It ran better for a few miles and then started losing power again going up hills and soon it was barely drivable even on level ground. I ended up stranded on the side of road. It seemed to me to be fuel starvation, so I replaced both fuel filters. I had about 3/4 tank of fuel, but since it seemed to be worse going uphill, I filled up the tank just to be safe. It took a while to get it started, but once running it seemed fine. Drove it about an hour more and made it to RV park.

I sat there for about ten days and started back home. It ran okay, but still seemed not to have normal power going up hills... but no big loss like previously. I had driven about 120 miles and pulled off at the exit ramp which was uphill. At the top of the hill, the engine died and would not restart. The fuel gauge was a little below 3/4 tank. I went and got five gallons of diesel and put it in the tank. Took a few minutes, but got it started and it seemed to run fine. I got the bus off the ramp and parked at a lot nearby. I only had one gas can, so I went and got another 5 gallons of diesel to try and be sure I could make it home (about 15 miles). Added the extra five gallons reattached the toad and drove about five miles and it completely died and would not restart.

This happened yesterday and it was almost dark, so I just left the rig and drove the toad home. I'm going back later today or tomorrow morning to see if I can get it home. I plan on taking 15 gallons of diesel with me and maybe a couple of new filters. The only thing I can think of is either the fuel has a bunch of gunk or rust and is clogging the filters up or maybe the fuel pickup (which appears to come off the top of the tank) has a hole in it near the 3/4 tank level. I would really appreciate any help with this as it is currently stranded in an old, closed store parking lot that has no parking signs posted all around it. Though I can't imagine them getting anybody to tow it anytime soon.

I always add ClearDeisel with new fuel and keep the tank topped off or pretty close when parking. I saw no water in the big fuel filter that has the plastic bowl before changing the filters.
Lee
1993 Continental 40'
Oshkosh Chassis -- Cummins 300 -- Allison 6sp
TDJohn
Posts: 551
Joined: Sun Oct 27, 2019 11:34 pm

Re: '93 8.3 Cummins Fuel Starves Uphill

Post by TDJohn »

Lee,

It's possible that you have a deteriorated fuel line that is gradually letting air in. When the tank is full, the filter head is under pressure, as the level drops it starts sucking air. If you are not seeing air, then the other possibility is that your low pressure lift pump, that is on the side of the block on the passenger side, is failing and again, when the fuel tank get low enough, the gravity pressure goes away and starts starving of fuel.

Clogged fuel filters will exaggerate the problem, especially if it is the lift pump. You might have gotten a bad batch of fuel that has algae in it. Algae will clog filters very quickly. You will need to run boicide additive to kill the algae and will go through a couple of fuel filter changes as the gunk passes through the system. If you have a clear bowl on your primary filter, you will see the stuff as black or dark brown settled at the bottom of the bowl.

I would check the fuel pump and also see if you can prime the fuel system. That pump has a primer button, if the fuel is primed up, it should be pretty hard to push in. If it goes easily, or there is not resistance, and the pressure won't build up, even with a full tank, then the fuel pump diaphragm is likely shot.
Last edited by TDJohn on Wed Feb 08, 2023 4:04 pm, edited 1 time in total.
John
'95 Serengeti, Cummins C8.3-300
Allison 6spd.
wolfe10
Posts: 216
Joined: Sun Oct 27, 2019 4:12 pm

Re: '93 8.3 Cummins Fuel Starves Uphill

Post by wolfe10 »

Have you verified that the fuel lift pump is tight and not either dripping fuel or sucking air?
Brett and Dianne Wolfe
Ex: 2003 Alpine 38'. Ex 1997 Safari Sahara. Ex 1993 Foretravel U240
Moderator, FMCA Forums 2009-2020
Chairman, FMCA Technical Advisory Committee 2011- 2020
Moderator, http://www.dieselrvclub.org/ (FMCA chapter) 2002-
LeeTN
Posts: 18
Joined: Sun Oct 27, 2019 5:44 pm
Location: Eastern Georgia, USA

Re: '93 8.3 Cummins Fuel Starves Uphill

Post by LeeTN »

Thanks for the advice, John/Brett. I ordered a lift pump about a week ago, but it has yet to be delivered. The lift pump was not leaking at first, but over the last ten days, I’ve pumped it so much that it began leaking from the little finger pump button. Though it only seems to leak when pumping it. I added about fourteen gallons of diesel, which was about as much as it would take. Primed it up with about 75 pumps and it started after a couple of twenty-five-second starter burst. It ran rough for a few seconds and then cleared up. After a few minutes of warm-up, it would rev up to 2500 rpms and sustain that with no problem. I then was able to drive it home (about 15 miles up and down hills) with no problem. I left it for a few minutes on a hill in my driveway and it ran fine.

I forgot to mention it, but my fuel primer bulb (like you see on outboard boats) had a bad check valve and I replaced it with an electric fuel pump which is supposed to be good for 30 gal/hr... I got it at O'Reillys. I was stuck on the side of the road in Atlanta and no boat supplies were open. The original primer bulb was inline after the primary filter and before the secondary filter... and that’s where I installed the little electric pump. As I understand it, the lift pump on the side of the block is the only fuel pump installed by the factory. I think I’ll move the electric fuel pump to the line just before the primary filter or maybe closer to the tank (somewhere where I can get to it easily). Unless you folks think that’s a bad idea.

I’m going to either pressure test the entire fuel line system (at maybe 20psi) or replace all the rubber fuel lines before I take it out of the driveway again. Once I do that and replace the lift pump I’ll see if I can drain the tank down enough to where the problem occurs. Currently, it has over a hundred gallons in the tank and even getting it to below ¾ tank will be a challenge unless I use five-gallon buckets or something.

On another note, I going to start a thread on the side-of-the-road repairs and towing. I had very little luck getting either while being stuck on the side of the road in a large US city. I paid $185/hr for two hours to have a "diesel" mechanic help me... and I knew more about it than he did. Seriously.
Lee
1993 Continental 40'
Oshkosh Chassis -- Cummins 300 -- Allison 6sp
TDJohn
Posts: 551
Joined: Sun Oct 27, 2019 11:34 pm

Re: '93 8.3 Cummins Fuel Starves Uphill

Post by TDJohn »

Lee,

Did you verify that the electric lift pump is working?
If it is working, did you test what pressure and flow it puts out?
Even if the pump is working, it might not have enough flow capacity to keep the engine from starving fuel, especially if the fuel hose from the tank to the primary filter block has deteriorated. If you are getting are in the system due to a deteriorated hose or a loose connection, that electric pump might not have enough lift and flow capacity to overcome the small air leaks on the suction side of the fuel system. Considering the age of that hose, it would not be a bad idea to change that hose. Since the tank is full, I would poke around and look for leaks or at least wet spots. If the hose looks wet or oily, than it needs to be replaced. If connection points look wet, tighten them down, seal them up.

Having a primer bulb installed after the primary filter, indicates that likely the mechanical lift pump was starting to fail. Those pumps can fail completely, where the stop pumping fuel, but they can also fail by developing a small leak, kind of what you are describing now. If they develop a small leak, when the coach sits for a bit, the fuel system past the point of the pump loses its prime, and makes it hard to start. Likely the previous owner didn't realize what was happening and installed a primer bulb to help mitigate his starting issues.
John
'95 Serengeti, Cummins C8.3-300
Allison 6spd.
chuckster
Posts: 286
Joined: Thu Aug 27, 2020 4:53 pm

Re: '93 8.3 Cummins Fuel Starves Uphill

Post by chuckster »

Great answer, John. Also, a great contribution by everyone here that is chiming in. That's what makes this a GREAT platform for SMC coaches.
Chuck & Mitzi
'01 Safari Zanzibar 3646 (side entry)
Cat 3126B / Allison MD3060
Magnum M-Series "Blue Max" chassis
2016 Jeep Grand Cherokee Overland toad
LeeTN
Posts: 18
Joined: Sun Oct 27, 2019 5:44 pm
Location: Eastern Georgia, USA

Re: '93 8.3 Cummins Fuel Starves Uphill

Post by LeeTN »

Thanks for the help, John. Sorry that it took so long to post back, but I've been super busy the last few weeks. I presume it was the lift pump. I replaced it and a good bit of the old fuel line and the problem did not occur again. I also changed the primary filter again and found that the so-called "diesel mechanic" that replaced the last one had left off the square O-ring that goes on the threaded part of the mount. But I don't think that had anything to do with it not running uphill.

I drained 35 gallons of fuel from the tank, ran it uphill, downhill, and almost every way, and had no problems. I removed the electric fuel pump completely and moved the fuel primer bulb to just before the primary fuel filter. I have since sold the RV. The new owner was actually on the first drive with me after replacing the fuel pump.

The pump would have been easy to replace had it not been right next to the frame rail... which made a twenty-minute job into well over an hour. I had to bump the starter several times to the crankshaft (or maybe cam) back to a position where there was not much resistance on the plunger rod. To anyone doing this... BE CAREFUL when pulling the pump in and out of the block. The plunger rod will easily pull out of the pump and would probably fall down inside the engine if not very careful. It would most likely end up in the bottom of the oil pan, so getting it back out would not be the end of the world, but still would be a pain. That's mostly why it took so long to install... I was working blind behind the frame rail and being cautious not to let the rod fall out. Another person would have been helpful.

Thanks, everyone!
Lee
1993 Continental 40'
Oshkosh Chassis -- Cummins 300 -- Allison 6sp
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