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  #1  
Old 06-24-2007, 03:13 AM
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severe 300d fuel problem

I tried bio-diesel once in my 1984 300TD and have been having problems ever since. The problem may not be related to bio-diesel but I am mentioning this just in case.

I have been having severe fuel starving (I think) problems under load. Chaning the fuel filters seems to fix the problem but it re-occurs after as few as 50 miles of driving. I thought it might be crud in the tank so I removed it and completely cleaned and dried it. Still have the problem, maybe worse. the last two fuel filters did not seem to have anything in them on autopsy. I have not checked (just thought of it) to see if it might be a problem with vacuum lock of the fuel tank and maybe the ritual of changing filters releases this.

I measured the fuel pump intake vacuum acording to the manual and also measured the output pressure with conventional vacuum and pressure gauges (not the official test set). Suction and output pressures are both within range but with extreme pulsation. Is the MB gauge heavily damped to read an average value or does this pulsation indicate a bad pump? I haved a spare that I can try but no replacement gasket and am in the middle of nowhere and don't have time to get a gasket. I can make a gasket but do not know if the thickness is critical for correct operation of the pump as it is camshaft driven. Difficult to know what the thickeness should be since the gasket comes off in pieces on such an old car.

I live on a dirt road,far from town so it is very difficult to test preformance. It seems that I can drive most of the day on the highway with only intermittant power problems and that after riding on the dirt road for a while it gets worse and cause the car to eventually stop requiring a filter change again.

Does bio-diesel destroy the valves in the fuel pump? Does the pump or anything related to its preformance change under load? It seems that plenty of fuel is going through the primary filter when I race the engine and watch the filter. Can't see this while driving up a hill, of course.

Is it possible that the expansion tank system is at fault? I can not find any diagnostic information on this system in the shop manual.

Could this be an ALDA problem? Seems to severe for that. I can not climb even a slight hill when the problem occurs. Most recently it does not seem to have fully recovered from the last filter change.


Last edited by spencoid; 06-24-2007 at 03:22 AM. Reason: more information
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  #2  
Old 06-24-2007, 03:17 AM
ForcedInduction
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What kind of biodiesel? Retail Biodiesel, WVO or SVO?
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  #3  
Old 06-24-2007, 03:27 AM
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severe 300d fuel problem

biodiesel used was retail stuff, high bio percentage, not the 20% stuff.
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  #4  
Old 06-24-2007, 07:05 AM
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Thumbs up B-99

Bio-Diesel does no damage, any blend from B-05 to B-99....to anything excepting the rubber hoses....over time, one tank should not cause a problem to the hoses.....

Living down a dirt road, far from town.....same here......so I fully understand....

You mention the fuel filter, I assume that you have changed both fuel filters....

the little clear one, by the Fuel Injection Pump is the one that you mention, but I did not see any reference to the one just behind your power steering pump....looks like a spin on oil filter.....also there is a filter screen inside of the fuel tank.....if you have not changed the filter by the power steering pump, that's most likely your problem......

if you have a relatively full tank of fuel, you should get a decent flow from the fuel supply line at the first filter (the one by the FIP)....if not check the tank screen......

SB
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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG
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  #5  
Old 06-24-2007, 10:49 AM
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severe 300d fuel problem

Please read this post completely. I have checked everything suggested and mentioned most of that it the original post although not as obviously as in this one. I am about to buy a new car. I do not want a new car.

I have changed the secondary (spin on) fuel filter 6 times (at least). Performance seems to improve each time I change it. The last time it did not fully recover. I have changed the primary (clear plastic) filter several times and cleaned them and tested with air pressure. I have completely drained, removed, cleaned, and dried the fuel tank. I cleaned the tank strainer and paid special attention to cleaning the "false bottom". I blew out the lines all the way from the tank to the fuel pump inlet.

I have not done anything to the expansion tank if there is one. I did not know about its existance until I saw it in the manual.

My questions were. Should the pressure from the fuel pump fluctuate wildly when measured with a standard pressure gauge or does this indicate a problem. Even at 3000 RPM, the pressure goes down to almost 0 between pulses. I am using a 0 to 30 PSI gauge inserted into a line between the pump and secondary filter.

Could it be a problem with the vent valve for the expansion tank? How do I test this. There is no procedure in the manual.

Anything else? The last two secondary filters I removed and cut open did not have any crud in them. One was a Bosch with lots of filter material and it looked very clean.
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  #6  
Old 06-24-2007, 10:55 AM
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Quote:
Originally Posted by spencoid View Post

Could it be a problem with the vent valve for the expansion tank? How do I test this. There is no procedure in the manual.
Your problem is unrelated to dirty fuel filters. It's related to a lack of fuel flowing from the tank. And, it's not related to the fuel pump, because the fuel pump doesn't know that you travelled 50 miles so it can begin to fail at that point. Furthermore, the fuel pump can't recover when you change the secondary filter.

Please try this:

Remove the fuel filler cap and keep it with you in the vehicle.

Drive it normally and see if the problem disappears.
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  #7  
Old 06-24-2007, 01:37 PM
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severe 300d fuel problem

Thanks for the suggestion. I do not understand how the tank system works for a diesel of this vintage.

I wish I had thought of removing the cap instead of changing the secondary filter. I have very little time to test for reliability now. Instead of leaving it off, I will drive until the problem occures and then remove it. If recovery is immediate I will know instead of assuming that all is well if it runs for xxxx miles. It could be fine for 200 and then fail in 50. It must relate to tank fill and a bunch of other variables.

I will re-read the shop manual re the expansion tank and vent valve and try to figure out what is supposed to happen and how to test it. It was pretty confusing the first few reads. If anyone has a clear simple explanation as to how this system works and how to test it and what components fail, that would help. I like to follow logical diagnostic procedures as compared with just replacing parts until the car works.

It does make sense that the fuel pump is not the primary cause of this problem, but does anyone know whether extreme variation in output pressure is normal when measured with a standard pressure gauge? It seems to me that the relief valve should hold a somwhat steady pressure. I have not actually found the relief valve yet but will continue looking.
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  #8  
Old 06-24-2007, 03:10 PM
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Arrow Releif valve.....

If you are referring to the pressure regulator that is built inside of the "Banjo Bolt" that goes thru the Banjo of the fuel return line on the back side of the FIP......it will keep a set pressure within the fuel gallery inside the FIP.....I assume that you have connected your test gage between this banjo and the one at the top of the fuel filter......so if you are seeing a large pressure there then you have a problem in your fuel line someplace.....

I must ask....did you fill your secondary fuel filter with diesel, or purge before installation??

You said that you live on a dirt road, as I do.....think back, is it possible that you have hit something, or possibly had something bounce up and hit the underside of the car.....perhaps denting a fuel line???

If you have a full, or nearly so, fuel tank....with the car on level ground.....you should have a decent fuel flow from the fuel supply line where it connects to the primary filter (I tend to want to call that one a strainer, and the big one the primary...a carryover from years of shipboard terminology).......if you are getting a good flow at that point, then your tank strainer should be good.....

SB

Note: you don't state where you live....I am in Central WV...lotsa dirt roads around here....not so many out in Califunya and other places where most of these guys live.....anyhow, if you are within 50 or so miles of either Clarksburg or Parkersburg West Virginia.....I will drive over and have a look see.....

Also.....I have never been underneath and up close to the fuel tank of a Wagon.....but could you have gotten your fuel supply and fuel return lines reversed....when you removed and cleaned the tank??????
__________________

Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

Last edited by Shorebilly; 06-24-2007 at 03:15 PM. Reason: additional commentary
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  #9  
Old 06-24-2007, 05:35 PM
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could be the biodiesel freed up a bit of crud in the tank and the strainer is plugged.
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  #10  
Old 06-24-2007, 05:56 PM
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Quote:
Originally Posted by mespe View Post
could be the biodiesel freed up a bit of crud ... and the strainer is plugged.
He already checked the strainer.

50 miles, or roughly 2 gallons. Seems enough to set up a reasonable
vacuum in the tank if the vent valve is pooft. I think BC is on to it.
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  #11  
Old 06-24-2007, 06:39 PM
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Quote:
Originally Posted by Shorebilly View Post

I must ask....did you fill your secondary fuel filter with diesel, or purge before in
Also.....I have never been underneath and up close to the fuel tank of a Wagon.....but could you have gotten your fuel supply and fuel return lines reversed....when you removed and cleaned the tank??????
Mine have been reversed ever since my tank strainer got stopped up and I couldn't get it out to clean it. Have had no ill effects from that.

FYI.....the expansion tank is inside the spare tire well. Remove the cover and take the tire out. You'll see it. Don't think that has anything to do with your problem. Just thought you'd like to know.

When you remove the fuel cap, ever notice any air rushing in? I too think Brian is right. Probably just a stopped up fuel cap vent.

Cheers,

Bill
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  #12  
Old 06-24-2007, 07:50 PM
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Fuel cap is not vented, the tank vents from the expansion tank to a fitting underneath the car. Perfect size for a mud dauber to build a nest.

Also, check the fuel lines in the engine compartment -- if they are the original fabric covered ones and have fuel on them, they are leaking and you are sucking air instead of fuel into the lift pump. Very common at your age and milage, I'd personally replace them on spec.

Peter.
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1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
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  #13  
Old 06-24-2007, 10:47 PM
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low/no power on WVO

I have experienced similar power loss problems with my 84 300SD on a 2-tank Plantdrive WVO setup (uses a looped return). It's been going on for some time now (weeks) , first it was power loss only on diesel tank, and it worked great on WVO. Then power loss came on WVO too. I suspected a faulty pollak valve and removed it to run my fuel lines direct from the WVO tank. Worked fine for about 300 km (that's about 180 miles)and then the power loss came back. So I went direct fuel lines from diesel tank. Worked for another 300 km and then problems. Now it gets to the point where the engine will barely run or not at all, although it may be because my diesel tank is getting close to empty.

Just like spencoid, I have replaced the primary (clear plastic) and secondary (spin-on)filter, blown through the fuel lines to diesel tank, removed the fuel supply line from the diesel tank and watched fuel flow fast and easily all over my arms and on the floor. I also noticed that when I race the throttle the fuel flows nicely through the primary filter. Although lately there are many very small bubbles in the fuel. And there's always been a large air pocket in the filter where it seems fuel does not fill.

Because of my problems on both types of fuel, I am beginning to suspect a weak lift pump and injection pump, but I really don't want to remove and pay to have it rebuilt if I don't have to. I fear the need for a full diesel tank to achieve better power might indicate this though.

spencoid -- What are the specs for liftpump vaccuum and injection pump pressure? I'd like to test mine. What's the procedure?


A side note - Maybe the pulsation in pressure you measured is reduced/evened out by the cigar hose return line. Isn't that what it's for?


I'm getting a bit sick of this problem too, but I don't want to give up all the work I put into a WVO conversion. One things for sure, at best this car still seem underpowered, like it just doesn't have the "get-up and go" you would expect. But then I'm new to these MBZ diesels and maybe that's just the way they are!

Don
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  #14  
Old 06-25-2007, 12:18 AM
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to measure the suction of the pump you need to insert a tee into the inlet line from the tank to the pump and put a gauge on it. at idle the negative pressure should be .1 bar. this translate to 2 inches of mercury or 27.7 inches of water. to see the max vacuum that is developed you need to restrict the input line by compressing it so there is just enough flow to run the engine smoothly. i used a vise grip to do this.

to measure the pressure, the manual recommends a double banjo connection and special long hollow bolt and captive nut which are part of the MBZ pump test setup. i have a parts car so i just took the spare pump to filter (secondary) hose and cut it to insert a tee for the gauge. the pressure is only 20 psi max so self locking barb fittings work fine on the plastic line.
the manual says the pressure should be .6 to .8 bar at idle which translates to 8.7 to 11.6 psi. at 3000 rpm it should be min .8 bar or 11.6 psi. they also suggest crimping the output hose down as done with the input line in testing suction. they call this nipping the line. the pressures resusting are called "final" and should be 1.1 bar or 15.95 psi at idle and 1.3 bar or 18.85 psi at 3000 rpm.

if the required pressures are not obtained, you are supposed to replace the intake and exhaust valves or the pump.

i think that the gauge in the MB pressure tester must have a restriction to dampen the rapid fluctuation in pressure. somewhere i have gauge snubbers but can not find them.
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  #15  
Old 06-26-2007, 12:31 AM
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testing vacuum and pressure of IP

Thanks for the info spencoid, I'm going to test pressure and vacuum and go from there. I'd be interested to know if you find your problem, and hopefully I'll find mine.

I've heard of fuel lines becoming soft/spongy on the inside and restricting fuel. Even when the fuel lines look good on the outside. I noticed my rubber/braided hoses that connect to the supply and return ports of the tank seem soft. Fuel seemed to flow through, but maybe not under extreme load? Just a thought.

Question: To remove the tank strainer, do I simply use a large pliers and grip the hex fitting on the bottom of the tank and turn it out? Is there more to it? Does the tank have to come out of the car?

Don

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