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Old 06-07-2015, 06:00 AM   #1
Mini-Skoolie
 
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Intl 3800 fuel trouble

I own a '90 3800 dual tank WVO/diesel conversion that I bought from the guy who did the conversion. I'm not a mechanic by any means. I just got back from a 3 week trip that required me to learn some basics about my vehicle. It's ok. I knew I'd never get around to learning if I didn't get myself stuck somewhere.

The good news is that I know a lot more than I used to about collecting/refining WVO, vehicle electrical systems, vapor lock, and where to find my throttle cable when it snaps in the middle of a busy street in baltimore during rush hour.

On the last leg of my trip (cleveland to columbus, oh) I ran on diesel because I was out of veg and needed to get home, but my mileage plummeted. I need to find and fix the problem before I can go on another trip. I think I was getting something like 1-2 mpg.

Here's what I know:

1. I got ~13 mpg diesel when I didn't have veg earlier in my trip.

2. the engine ran fine even when my mileage was terrible. no loss of power, weird noises, etc.

3. I almost certainly have veg in my diesel tank (and vice versa) because I mixed up the return switches at various points on the trip. they were never labled Luckily the weather was between 80 and 90 degrees F during the day while I was on the road.

4. I need to drain my diesel tank to get any remaining veg out and pump fresh diesel back in.

When I saw the fuel gauge dropping quickly I decided to return the fuel to my veg tank because I suspected a clog in the return line. I was able to switch back to the veg tank (all while driving) which I had previously run dry. It took ~15-20 miles of switching back and forth but eventually it took and held without losing power. I made it home on the diesel that had been returning to the veg tank, so there must have been a substantial amount of uncombusted fuel flowing out of the engine. The diesel fuel gauge held steady after switching, so I don't think there's a leak in the bottom of the diesel tank.

Do you all think that a clogged return line is a fair diagnosis for getting terrible mileage? I looked around some diesel forums but, needless to say, most diesel drivers don't have to worry about getting WVO in their return lines, so the causes of their problems are quite a bit more complex, or are related to computer systems that are irrelevant to my vehicle. I hear a lot of ppl saying that if a return line is completely clogged it will cause the engine to shut off or lose power, which clearly wasn't a problem for me. I'm imagining that there might be a filter in the return line that's clogged with WVO and so the extra pressure is causing diesel fuel to spit out of a connection or valve under load. That seems like it would explain why the engine ran well but drained the tank so fast, as well as why I don't see any leaks when I stop the bus and look at it while it's idling.

Does anyone know how to check return lines for leaks and clogs?

Alternatively, do you think my problem might be unrelated to WVO?

Thanks in advance for any insight you bring.
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Old 06-07-2015, 06:03 AM   #2
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TL;DR: bus suddenly getting just 1mpg on diesel. Maybe my return line has a clog? how to fix please help
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Old 06-07-2015, 01:38 PM   #3
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Blow the return line out with compressed air.

Nat
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Old 06-09-2015, 01:02 AM   #4
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thanks, I'll try that.
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Old 06-10-2015, 08:34 PM   #5
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ok plan B a quick lesson in diesel fuel 101, first a clogged return line would increase fuel pressure, increase injection pump temp (because the excess fuel cools the pump and injectors) but won't have a big effect on power or performance. from what your saying the only noticeable problem was MPG. first how where you measuring this? by the dash gauge? if so every bus nut knows to never trust the gauge. on a mech. injection system there isn't much that will change your MPG. most will get the same MPG regardless of what your towing or how much air your rig has to move to get down the road. so some questions for you are how where you measuring the MPG? was there any smoke out the pipe and if so what color? did the engine crank case gain oil level? some supply or lift pumps can leak into the crankcase. if there where no noticeable leaks then the extra fuel has to be going some where. if you have a fuel leak around the exhaust or manifold, it could evaporate before you see a leak on the ground, but even in these cases you should still smell diesel fuel. if you can answer these question i can help you narrow down the problem. i can also tell you this my bus conversion was a 66 passenger international/international body it has a mech. injection pump and rated at 190 horsepower with a after cooler, my first trip with it was to move my furniture up to montana from texas, i averaged 12 MPG caring 22,000 pounds GVW. when i got the bus home and unloaded i raised the roof 4 feet and added a rear platform on it to look like a caboose. {go to my web site to see pictures of it rvingoffgrid.com} with the raise roof my MPG dropped to 7 from 14 and the bus loaded as a motorhome only weights 18.000 pound GVW so the lesson learn here is the more air you bus has to move to get down the road the more fuel it takes. it seams wind resistance has a greater effect on MPG than weight does. oh and my bus will run 63 mph top wide open running against the governor.
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Old 06-22-2015, 12:20 PM   #6
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Thanks for the replies, off grid and natster.

I got under the bus today and noticed a spray pattern around the supply line (where it bolts through the chassis) but not around the return line. I blew into the return fitting and heard fuel bubbling and a hiss from the pressure release. All the fittings looked good-as-new. The fact that i heard bubbling suggests, to me, that there's a heck of a lot more fuel in the tank than my dash gauge suggests, but I dont know how to tell for sure without draining the tank! I'll bang on it to see if I can make up my mind

I'll check the oil level, now. I did notice oil suspended on the bottom of the oil pan. hoping it's from me being messy with the veg lines and not leaking or displaced motor oil.

off grid: thanks for your questions and insight! I did not notice an increase in oil temp or pressure at any point on my trip (except when I was pulling long hills). I did not notice any smoke coming out of the pipe while driving or idling. I did not smell diesel fuel, but I was also dressed in it, at that point in the trip.

back shortly. Thanks again.
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Old 06-22-2015, 01:10 PM   #7
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Made a dip stick to check fuel level and the gauge reads as reasonably accurate. So I am losing fuel somewhere, I think.

It occurs to me that the problem might be one of the return valves. Maybe I'm returning fuel to the veg tank only.


There's also the question of the spray pattern around the supply line fitting where it bolts through the chassis.
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Old 06-22-2015, 01:37 PM   #8
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Veg tank is holding ~25 gallons of diesel fuel, all of which was supplied over the course of a two hour drive through the return line. I'm going to check the return lines by disconnecting them and seeing if anything comes out.

Soon as I can find my fire extinguisher...
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Old 06-22-2015, 03:03 PM   #9
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the good news is that I didn't catch on fire. the bad news is that not a drop of fuel came out of the diesel return line, no matter what configuration I ran my switches in (I ran a clear hose to a gas can in the cab so I could watch it while I sat in the driver's seat and toggled the switches).

Then the engine started sputtering on WVO supply so I cut it back to diesel and shut it off.

here are the switch configurations and what I could see from the cab. the return switch is just marked up/down because the switch is not labeled:

supply :: return
Diesel :: up = strong return to veg tank
Diesel :: down = no return
WVO :: up = no return
WVO :: down = no return

I peeked at my WVO supply lines after shutting the engine off and I'm seeing lots of air pockets in the lines before the engine that were not there before. The engine did die very briefly when it was on WVO supply but came back when I switched back to Diesel.

I suppose the diesel system needs to be in a closed, pressurized loop and that I screwed it up by disconnecting the return line. Everything gets worse before it gets better when you don't know what you're doing, huh? I'm going to give up for now. Any insight you all have is much appreciated.

Thanks
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Old 06-25-2015, 01:21 AM   #10
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Thx for keeping the updates coming.

Nat
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Old 06-25-2015, 06:27 AM   #11
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My bet is you are returning diesel to the veg tank.
Here is a common plumbing map-manual valves or soleinoids work the same way-3 way switches. I'm guessing you have them working in the wrong order.
GreaseCarsystem.jpg Photo by FossilFool | Photobucket
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Old 08-03-2015, 05:59 PM   #12
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Thanks, sdwarf. I don't think the plumbing is wrong because everything is still in the configuration it was in when I purchased the vehicle, back when everything worked correctly. Do you think I might have confused the switches when I put the batteries back in? Perhaps I connected the switches for the valves and heaters to the positive battery terminal instead of the negative one or vice versa? What would that do?

I'll go research wiring diagrams, now, because I have no idea how the wiring for a vehicle like this is supposed to work, and I know I'll need to fix something on it one of these days. Please point me in the right direction if you know of helpful guides for that.

I got back to work this eve. Remember last thing I did was open up the diesel side of the fuel system to try to see if any return was making it, so I knew I'd have air in the lines. I primed the engine, primed the fuel filter, turned the key (to charge the pump), repeated those things and started the bus. It ran for a little while before dying out. I unscrewed the return line between the diesel filter and the tank and there didn't appear to be any fuel in it, even though the filter itself was at high pressure after working the pump for a while. The bus didn't run for very long, but it definitely ran long enough that it should have filled the return line with diesel fuel.

I ordered a new filter from napa, because now I think that the old filter has gotten so gummed up that it has prevented fuel from returning to the diesel tank. I can't tell by looking inside it, but there was some sediment and discoloration (probably iron oxide) in the water catch beneath it.

What do you all think? Could my original symptoms have been caused by something as simple as a dusty fuel filter? Do you think that all of that excess fuel that's missing from my diesel tank could have pushed its way into my veg tank regardless of which way the return switch was pointing? Do you think I'll need to replace the contraption that the filter screws into as well? What is that even called?

I'm in a bit of a hurry because the neighbors need it to move so their cable guy can get to the house and I've had quite enough to do with code enforcement already. I'll be back to work tomorrow.

Thanks again for all of your help!
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Old 08-03-2015, 06:13 PM   #13
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Oh, and if you're confused about what filter I'm talking about, it's a wix filter 533755, going to be a napa filter number 3755. It's located between the diesel tank and, erm, I think the return valve (I can't quite see but what else could it be?). It only has two hoses, not like the Mercedes diagram that blends the supply and return fuel. I think the guy that built the rig wanted to keep the oil and diesel as separate as possible. Guess he didn't consider operator error would be a factor

Thanks again
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Old 08-04-2015, 06:07 AM   #14
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You probably have 2 solenoids-a feed and return. When on veg, both should be activated. When purging, just the return should be. Check to make sure both power up when you throw the switches.
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Old 08-04-2015, 01:04 PM   #15
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Thanks sdwarf. The valves are getting power, and they seem to be working. I switched the return valve to the up position so that I could watch all the bubbles marching out of my fuel system into my veg tank for a while today. When I switched it off the bubbles stopped.

It was hairy for ~10 minutes once I got it started, even after half an hour of priming the injectors and the new diesel filter over and over again but I got it to run smooth after that. No telling if my fuel consumption problem is behind me or not. I'm not about to crack open my fuel lines again until I know what I'm doing.
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Old 08-04-2015, 01:33 PM   #16
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Doesn't look too extraordinary to me, this is the inside of the fuel filter I replaced. what do you think?
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Old 08-04-2015, 04:23 PM   #17
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Quote:
Originally Posted by Plan_B View Post
Doesn't look too extraordinary to me, this is the inside of the fuel filter I replaced. what do you think?

I presume you cut that open? That thing is FILTHY!!!
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Old 08-05-2015, 10:06 AM   #18
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Yes I cut it open. I'm not sorry I replaced it, but it doesn't look bad enough that it would be blocking fuel flow completely.

I think--and this is v embarrassing--that I got the supply and return hoses mixed up when I was trying to test fuel flow last month.

If this bus has any problems at all, I'm its biggest one!

I'm going to try to map out what I think is happening in my fuel system and post for y'all's input. Would this thread be an appropriate place for that or should I start a new thread?
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Old 08-05-2015, 11:30 AM   #19
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Diagram attached

Edit: by valve I mean solenoid valve
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