I'm baffled and at wit's end!?!?!?!?!
 

In follow up to the long saga regarding my fuel starved 84 300TD wagon....and after a stint in a local garage, which didn't fix the problem. I just cant figure it out. No need to go into the long details....at this point, the crux of the problem is that the car behaves as if fuel starved. Both filters are new. As the car is running, when viewing the fuel flow through the small initial filter (the little one just before the fuel pump) fuel flows through slowly, even when revving the engine. Then the filter will fill up as it should, with only a normal little bubble at the top, then again it will draw down, and bubbles come in from the fuel supply line.....this happens every several seconds.....the net result is a lot of air going into the secondary filter. If I drive it like this, it will start to stall, as if not able to get fuel.

This morning I drained the fuel tank and removed the strainer....no fungus buildup at all. With the tank empty, I used a compressor and blew out the fuel supply and return lines from the engine compartment. No apparrent blockage. Everything seemed fine.

Then, since I had every thing disconnected, I ran the engine with fuel from a jar in the engine compartment, with supply and return hoses in the jar....when running like this, the engine ran great, with fuel gushing through the little filter as it is supposed to do. I then ran a can of diesel purge full strength, since I had everything set up for it. The diesel purge ran very clean, just gushing through the lines, as it should.

So then I re-connected all fuel lines, put 5 gallons of fuel back into the tank, started her up, and the same old thing happens....air bubbles from the fuel supply line, and fuel barely coming in from the supply line. I haven't checked the tank vent, but the same thing happens when the fuel filler cap is off.

I will now go out and check the entire length of the fuel supply line for sources of air coming in....but there are no fuel leaks, and this is actually a New Mexico car with no rust, very clean, so I dont expect to find rusty fuel lines.

Any other suggestions????? I just cant figure it out.

Thanks

Mark

There has to be air entering the fuel line someplace between the tank and the filter. The air has to be coming from someplace. IMHO, you need to double/tripple check and tighten every connection in that fuel line. I just can't imagine what else it could be.

There are two short hoses that run from the tank strainer to the hard lines. They are directly above the differential. Normally, they are neglected for the life of the vehicle.

This is the likely source of air entering the system.

Obtain two from the dealer and replace them.

And you are absolutatly sure the supply and return lines arnt switched? Have you tried it with the tank above 1/2, full?

I would put low pressure/vacuum into the line connected to the small fuel filter and plug the other end near the tank and see if it holds.

I'll try it
 

Brian,

I will replace both of those hoses, but wouldnt they be porous and wet if that is where air is coming in.

Added info. I just had the car for a drive...had it up to 90 mph...seemed ok, but then when at idle, same old thing...fuel starved, air bubbled into filter, etc. !?!?!?!?

This really stinks!!! Figuratively and literally with all the fuel everywhere11

Thanks,,
Mark

Pull the clips that hold the hard line to the body....I bet you got a leak under one of them....a pinhole leak.

I found the problem
 

I was tempted to not follow up on this thread, because I am so embarrased...I am a bonehead idiot!!!!! Before I tell you what the problem was, let me just say that last week Sunday night, there was so much air in the system that it wouldnt start, and I just couldnt figure it out, so I brought the car to a mechanic (which cost me $190 to check compression, clean injection valves, check fuel pump, adjust valves, timing) , and rented a car fr the week to get back and forth to work (to the tune of $250). Not to mention, draining the tank, checking the tank strainer, blowing out lines, making a mess in the driveway, making a stinking mess of my clothes (twice), taking all day last sunday and all day today, etc. etc.


Well, I checked the fuel lines under the car and found no leaks. I borrowed a peristaltic pump from work to pump out tank, and at one point, attached both ends of the tubing to the supply and return lines from and to the tank. When I pumped fuel, the tubing was perfectly clear, no bubbles. But when I put everything back together, I still noticed air coming in.

WELL....just prior to going to the parts store to get some new fuel line, I looked at the filter again, and I noticed a little drip of fuel where the hose from the hard supply line connects to the little filter. I got the fuel line, and replaced that section in the parking lot of the parts store....and....as I said before, I am an idiot imbecile bonehead..... the car ran perfectly, with no air coming in.

That little section of hose, had cracks inside where it connects to the filter, and when the clamp was tighted, it deformed the cracks allowing air to come in!!!! Never any leaks though, as pressure is either negative or neutral...never positive on this line, and very little gravity head at that point!!!!!!

While I am in the middle of a real mess in my driveway, I am going out to change the supply and return hoses at the tank!!!

I would like to ask everyone to respond to this by thinking of a better name for me than bonehead idiot!!!!!


In retrospect, the reason why I love these cars is, as I have told many 123 owners, when something goes wrong with the car and you dont know what it is, and you start to think the worst, most often it is something very very simple. Sure enough!!!

Thanks,

Happy Idiot

Don't beat yourself up. Sometimes fuel system issues, with reduced power are quite complex and difficult to find. With a clamp on the hose, you would not think that it would leak air. But, an old hose can do this.

Be thankful that you didn't chase such a problem for a month and change the IP in the process. Ask BHD about that. That was a breather problem that had nothing to do with the fuel supply.

Just congratulate yourself in finding the problem without spending a ton of money.;)

Don't beat yourself up, air in fuel problems are some of the most difficult and time consuming to track down.

Proof positive why you should never discount anything because "you checked that already"

New Mexico (all the desert SW) may not get much rust. But it is hell on rubber, paint and plastic. Especially 20+ year old rubber. If it were me, I'd change every piece of rubber in the entire fuel system.
I don't even want to mention the rubber hoses between the fire wall/ engine compartment:eek: Did I mention brake lines:(

Good Suggestion
 

I still have my original daily driver, now a parts car, with a lot of new/recent rubber (replaced within the last few years) such as all new cooling system hoses, rubber brake lines..etc. Now that you mention it, this stuff is probably in much better shape than the old rubber on my current driver. Good suggestion.
Thanks,
Mark

WAY TO GO MARK!!!:D

Glad to hear you've got that behind you. Being an optomist I can add that now you are assured of the condition of several parts of your car (compression, clean injectors, no woes a the strainer, etc.) that you might not have been if you had replaced the offensive bit of rubber first off.

Marks wagon is sweet, not the ordinary rust mobile I see around these parts....

Hip Hip Hooray!

Thanks Rob!
 

Rob,
It looks like given the recent snow and tonights forecast, we may be pulling the differential and axles with snow shoes on!!! Oh how I wish I made time for this a few months ago!!!
Mark

Indeed. I have a propane tube heater we may have to put into service....

question?
 

Is there a lift pump in that tank had a car one time where the rubber tube that holds the fuel pump on had a split in it that drove me nuts

Added to DIY Links by Parts Category
 

Added this thread to ShopForum > Do It Yourself Links & Resources > DIY Links by Parts Category
Fuel Delivery:
http://www.peachparts.com/shopforum/diy-links-parts-category/142399-diesel-fuel-delivery.html




This may save another owner from massive frustration.

This car doesn't have a pump at the tank, but he found the problem, it was a small crack in a hose.

I'm baffled and at wit's end!?!?!?!?!
 

I have posted this elsewhere on a thread I started months ago. I have an 84 TD and have the same air in the fuel problem but I have replaced everything between the tank and the fuel pump. I have replace the rubber lines at least twice and checked for interior condition etc. I even used the expensive nitril stuff. I replaced the metallic line even though I could not find a leak in the original one. My fuel tank is dented right at the fuel outlet and I am wondering if any internal damage could cause a leak? What about the vent lines to the expansion tank? My car can run all day as long as I stop for periods of at least 5 minutes but continuous driving results is sever power starving and usually stalling. When the car stops the fuel filter is dry and some times, even vigorous pumping with the new primer pump draws nothing. Waiting for 5 to 10 minutes allows fuel to be drawn again. I have put a hole in the fuel cap to make sure it is not vacuum lock. The problem can happen with a full tank or an almost empty one. I have checked the vent valve and it opens at just the factory spec values. The strainer has been checked several times. The tank was steam cleaned. All lines blown out. Cracks in overflow tank fixed and lines to it replaced but I did not replace the rubber between the tank and the hard lines to the expansion tank thinking that air could not get in there and it will require removing the tank a third time.

Could internal damage in the tank allow air to get into the " false bottom" that feeds the supply to the fuel pump? The car runs fine with a tank on the roof. I have replaced the rubber lines from the tank to the fuel pump 3 times. Is it possible that 1/4" line will just not seal and that I need to get the right metric size? I am using worm clamps and they seem to make a good physical connection that can not be twisted.

I have spent something like 40 hours trying to fix this and had to buy a new car because I could not depend on the good old TD. I love that car and want to fix her. What else can I try?

Answer:
 

Test fuel volume from the return hose, use a gallon jug.
Ten seconds engine cranking.
Post the results for further diagnosis.

I'm baffled and at wit's end!?!?!?!?!
 

I measured the output from the return line both with the FIP control pulled to stop to prevent enging from starting so I could measure the output at cranking speed. Also measured it with the engine sort of running with the FIP not in stop mode. Output in ten seconds was a paltry 70 ml at cranking speed and twice that with the engine sort of running 140 ml.

I also replaced the two lines at the primary filter with 1/4" instead of 5/16". Although these lines have been replaced a few times, they did show some cracks at the ends after the hose clamps. Is it possible that 5/16" rubber doesn't compress properly and provide a tight seal? I have to drive 2 hours to get to a place that might have metric sized hose.

I also removed the new primer pump and tested it for leaks. It does not leak at all. I them made a stubby wrench to make sure it was tightened very well.

I want to repeat that when the car failed the last couple of times, there was no fuel in the primary filter at all and the priming pump did not seem to pull any in until I waited for at least 5 minutes. I had removed the tank cap so it was not vacuum lock. The tank has a rather large dent in the bottom near the output line. Is there any possibility that internal damage might allow air from the expansion tank to get into the the supply instead of fuel through the strainer? The strainer was removed quite recently and was not fouled. I am goint to drain it again and look for a clogged strainer but I really want to avoid removing the tank. It is a ***** on the TD. The rubber lines at the fuel tank tha connect to the hard lines going to the expansion tank have not been replaced. The ones at the expansion tank have been. Can air be getting into the system there? I have no idea what the lines do once they enter the tank. The tank needs to be removed to replace these so I hope that is not needed.

I had a primary filter that had a crack in it along the injection mold line. I did not leak, and the car idled fine. It was running down the road that the issue of fuel starvation made itself known. It was a Purolator filter bought at Pep Boys, and it lasted about a week.

I'm baffled and at wit's end!?!?!?!?!
 

I thought of that too and tested it with about 30 psi and it did not leak. Maybe it only leaks once it warms up and leaks vacuum but that is a little hard to believe. I think I have a spare to try. I definitely have some generic clear plastic filters. Any reason one of those won't work?

Need to restate that I could not draw any fuel with the primer pump making me think that the problem is more likely at the tank end. If it were in the filter I would expect to hear a hissing as I tried priming.

I had also replaced the primary pump with one from a parts car. No idea if it was any better than the one I replaced but that would be quite a coincidence if both were bad. The parts car was a sedan, however and I think that the lower tank of the TD might require a perfect pump and totally leak free system whereas the sedan provides a little gravity pressure to make it less critical?

Does my output level sound really low? Should I replace the primary pump?

Maybe the filter was leaking at the mold line. Maybe the tighter fuel line would fix it. It is a part bought from an auto parts store as that was all that was available when I was having biodiesel loosend crud filling up the filters. I think I have an old Merz original that is not clogged and I can try. Will look at the mold line more carefully.

Is there any point in putting a pusher pump at the tank? That might make the whole system a lot less critical?

What happens when you remove the filler cap?

Maybe one of the rubber fuel lines is collapsing internally?

I've also heard of a case (in a non MB gasser) where debris in the metal line under the car would shift and cause a blockage. Stop the flow by shutting off the engine and the debris would settle and allow fuel flow once again. Perhaps you have somethinhg similar.. or some big chunks of fungus that float around and get sucked up against the filter screen.

Perhaps temporarily eliminate the hard line under the car by running a parallel rubber line all the way to the back? If that doesn't fix it, maybe run temp rubber lines further into a separate tank in the back? If that doesn't fix it, then the problem is somewhere under the hood.

Answer
 

Where is or are the DIY Links by Parts Category .....
I tried the "DIY Links" Tab for the site but did not find this thread relocated.
:EDIT whunter: Corrected post# 18 and added a link to it. :)
Fast navigation Do It Yourself Links
http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html

still baffled
 

I did not get notification of new posts so I had no idea there were additional suggestions.

Removing the cap does nothing. I have run without it and had the same problem. I have drilled a small hole in the cap to prevent vacuum lock although the vent valve works fine. Might be some problems with mush ylines between the tank and the expansion tank so I drilled the hole in the cap.

I checked the strainer at the same time that I installed a completely new hard fuel line. The old one looked fine when Icut it in half and ran a fish tape through it. No crud came out. Strainer was quite clean. No fungus.

Running with a tank on the roof it runs great. Ihad posted the results of a crank speed fuel output test at the request of one reader but never heard back whether it suggests that the fuel pump is bad. I had replaced it with one from my parts car early on. At cranking speed with the FIP shut off, it puts out 70 ml in 10 seconds, 140 if the car is allowed to sort of run for 10 seconds while cranking.

I doubt that rubber lines are collapsing because they are all new. I thought of the idea of crud building up at a high spot and falling down in the 5 minute rest period that restores operation but there was no crud in the thank, the lines or the filter.

I also put a suction pump on the line right after the primary filter with a 1 quart trap bottle to watch the flow while I pulled real hard on the pump. I could produce a fast flow without bubbles or any problems so nothing is preventing flow or letting in air until whatever happens when the problem occurs. I had replaced the two lines at the primary filter before doing this so maybe the fact that they were 5/16" instead of 1/4" was the problem all along and it may be solved. Will not know until I drive it 100 miles or so but I still have no confidence that this was the problem.

Again, does anyone think that the expansion tank and the rubber lines to it could be the problem? I don't understand how the expansion tank works. The pcitures in the shop manual do not show where the lines go in the fuel tank or the expansion tank. Can air get into the fuel from the fuel tank to the pump via the expansion tank?