Reconstructing Fuel Feed System: 1983 300TD

[Vikingdad]

First thing I would like to get out of the way. I have almost 20 years experience in the distant past as a master automotive mechanic, primarily working on Japanese cars (specifically Honda/Acura) and a working knowledge of diesel theory and I have owned diesel trucks (Fords) and cars (1985 Volkswagen Jetta turbodiesel and a Peugeot) over the years, all of which I have worked on and kept maintained and running over the years. I am also working with limited cognitive functions due to years of chronic illness, this is important to understand as while I have "forgotten" much of what I once knew, I do have the ability to re-learn it and remember things. So please be understanding when I don't initially grasp something or when I take time to get a grip on something that is said.

I just got this car a couple of weeks ago and when I got it somebody had previously tried to reconfigure the fuel feed system to get it running. The primary fuel filter was missing entirely, they had taken the fuel inlet hose and routed it to the outlet on the filter housing (effectively looping the fuel) and on and on.

So I have replaced the fuel lines and configured them back to the correct routing (thanks to the Internet for finding the correct routing) but I am left with a car that still won't start and I have a few questions.

The "cigar hose". What is its function and is it critical to the proper running of the fuel system? I suspect that it is required as it is mentioned everywhere. Does it prevent air from bleeding back into the low pressure fuel system when the engine is shut off as I suspect?

The injection pump low pressure check valve: I have read a lot about this banjo bolt check valve but it has left me confused. Is the spring pressure critical? Is there any way to measure the internal pump fuel pressure (on the low pressure side) to determine if this check valve is working correctly? Is this banjo bolt check valve available again (I have read it was discontinued by MB)?

I did put in a clear fuel hose on the outlet side fuel return (back to the tank) to see if there is any air bubbles circulating back to the tank. That does not appear to be happening, but when I leave the car sitting overnight, all of the fuel drains out of this line. That indicates to me that there IS an air leak somewhere.

This one may not be related but I will mention it anyhow. It appears as though on the last time (or nearly so) the car was driven, the driver ran over a rock that smashed in the oil pan directly where the sump pickup is located, smashing the sump pickup and restricting oil flow into the pump. Hopefully there was enough oil available to lubricate the engine well enough. I have ordered a new pan & gasket and sump strainer assembly which I should get on Wednesday and install this week. My question is, might this oil restriction/starvation cause the engine to not run (outside of catastrophic engine failure- which is possible but it does have compression and it does crank over well and it almost wants to start)?

I think the fuel lines from the tank and the tank itself are OK, as I do not see air in the pre-filter at any time.

Any help is much appreciated!

Edit: Here is a picture of the old girl in her hospital bed.

[Zacharias]

Welcome to the group. I can provide some limited answers. Some of this may already have been obvious to you, with your background.

The cigar hose is not critical to the function of the fuel system (or for starting), but it's helpful on the turbodiesels. It's designed to dampen pulses from the fuel return.

Many people say their car runs fine without the cigar-style hose installed in that particular position, but in the past I have read posts from others who say that minor idle issues were cured by its installation, where they acquired the car without it. They are not expensive if you shop around, I vote to keep it original.

After any work on the fuel system, it is not unusual for the turbodiesels to have stubborn air locks. My '85 300d is the worst of the six or so I have owned. Generally I have to enlist a helper to pump like their life depends on it while I crank the car over. It's even difficult after just changing the spin-on filter. My earlier Mercedes diesels were far less prone to this.

Another problem is the manual primer pump. You did not mention having used it. There are two styles. If yours is white/creamish in colour and has to be unscrewed to operate, it's very old and more than likely leaking air into the fuel system.

If yours is the "new" black style that is pump-and-go, when you pump it, do you feel like you are pumping anything? If it feels like you are pushing air, then the seal is gone inside. It is also possible for these to not leak fuel out, but to suck air in.

I don't believe that the banjo bolt valve you mention is critical to starting, but some people have said their on-the-road performance improved from installing a fresh or upgraded one (available from Greazzer on this forum).

Since you say someone had messed around with the hoses, was the car run on any form of alternative fuel? If this was the case there could be other issues with the lift pump, injectors....

I am assuming that you have checked that you have voltage at the glowplugs, etc.

Bottom line is, if you are not getting a serious smell of diesel out the tailpipe as you crank, then you probably have an airlock.

[Vikingdad]

Originally Posted by Zacharias

Welcome to the group. I can provide some limited answers. Some of this may already have been obvious to you, with your background.

The cigar hose is not critical to the function of the fuel system (or for starting), but it's helpful on the turbodiesels. It's designed to dampen pulses from the fuel return.

Many people say their car runs fine without the cigar-style hose installed in that particular position, but in the past I have read posts from others who say that minor idle issues were cured by its installation, where they acquired the car without it. They are not expensive if you shop around, I vote to keep it original.

Cool. I have ordered the cigar hose and will install it when I get it, but won't worry about not having it. Thanks.

After any work on the fuel system, it is not unusual for the turbodiesels to have stubborn air locks. My '85 300d is the worst of the six or so I have owned. Generally I have to enlist a helper to pump like their life depends on it while I crank the car over. It's even difficult after just changing the spin-on filter. My earlier Mercedes diesels were far less prone to this.

Another problem is the manual primer pump. You did not mention having used it. There are two styles. If yours is white/creamish in colour and has to be unscrewed to operate, it's very old and more than likely leaking air into the fuel system. If yours is the "new" black style that is pump-and-go, when you pump it, do you feel like you are pumping anything? If it feels like you are pushing air, then the seal is gone inside. It is also possible for these to not leak fuel out, but to suck air in.

I do have the "new" black plunger primer pump and I have used it. I do get resistance when pumping it, but it does not get "hard" as though a pressure head has built up- with my tractors (Massey Ferguson) when I pump it will eventually stop pumping because it has gotten up to pressure, a very different feeling than if it is pumping air or has bubbles in the system. The MB system has recirculation built into it so I imagine that this will work differently than my Massey. Am I right? In other words, the plunger will go full stroke as long as you pump it, and as long as you have resistance (pumping fuel, not air) you are OK?

I don't believe that the banjo bolt valve you mention is critical to starting, but some people have said their on-the-road performance improved from installing a fresh or upgraded one (available from Greazzer on this forum).

I have ordered one through Pelican.

Since you say someone had messed around with the hoses, was the car run on any form of alternative fuel? If this was the case there could be other issues with the lift pump, injectors....

I am absolutely certain that no alternative fuels were attempted in this car. The guy who screwed the feed system up was in idiot who had no clue what he was doing, but he couldn't get it running and the family who owned the car never tried any alternatives in it.

I am assuming that you have checked that you have voltage at the glowplugs, etc.

Oh yeah! Forgot to mention. This is the first thing I checked. I found that the idiot had replaced the glow plugs with new ones and at the same time he replaced the blown glow plug relay fuse with a piece of wire!

I found a replacement at the wrecking yard that works and the glow plugs are now getting voltage (where they weren't with the old re-"fused" relay.). Glow lug system is now working as it should.

Bottom line is, if you are not getting a serious smell of diesel out the tailpipe as you crank, then you probably have an airlock.

I have not gotten back to the tailpipe to take a whiff... though I do not think there is a smell of diesel at the tailpipe and I suspect that there is still an airlock somewhere.

Thanks so much for the reply. Very helpful to have another brain helping my decrepit one along...

[Clemson88]

I'd start with a valve adjustment. If you read much here you'll come across this a lot.

Pressure will build in the lift pump as you pump the button on top but it will not stop you from pumping it. When air is being sucked in it sounds a little different than when you're pumping fuel. It should firm up a quite a bit when the secondary filter is full.

I'm not one for changing parts before I know exactly what has malfunctioned. In your case I'd suggest you crack an/the injection line(s) at the injectors and crank the engine to see if fuel is being delivered.

BTW, I noticed a significant difference in my 84SD when I changed that banjo bolt on the IP. Thanks again to Greazzer.

Scroll up this page and click on "Technical Information and Support." Then scroll down that page. Just below the second blue banner you'll find more help than you need with more material than you'll care to read. I think it's titled "DIY Links by Parts Category."

[barry12345]

Try a little wd40 down the intake with the air filter cover removed. You will need a helper to pre glow and cranking the engine at the end of the glow cycle.

Also there are two check valves in the lift pump. The clear hose you installed back draining may suggest they are not in the best of shape perhaps. Assuming the relief valve is not totally sealing.

Remember that you can substitute the lift pump by having someone there to keep activating the primer pump as you crank. The resistance building you felt as you primed up does indicate the relief valve is really not wide open either. You can close off the return line temporarily with no damage to anything if unsure.The lift pump is a constant pressure design.

I guess what am suggesting is to make sure the engine is just capable of firing up as well. Not running it with that questionable oiling issue.

I am wondering if the last owner played around with the injection pump as well or anything else. You might remove the vacuum hose from he injection pump as well. You just never know what someone else could have done. It may even be helpful if you could get the whole story from him.

In a way it sounds like a bad lift pump. Yet if you see fuel exiting the return fitting when cranking it is still good enough.

Reduced to basics. The engine was running when the pan was damaged. If bad enough to restrict the oil supply is the question. When you crank the engine does the oil pressure gauge go full up? . Then that episode would have no bearing on the fuel system. It is illogical for him to have been working on the fuel system with an oil supply issue.. So things do not really add up. Or at least to me. You have to keep this in mind.

You do not want to change that oil pan until you know the engine is good. Or as much as possible. You have to pull the block to do it. Although apparently some have managed it without doing that I understand. If you can get oil pressure while cranking testing first is the reasonable approach. I suspect it is present and he just drove the car until another unrelated problem developed perhaps.

Incidentally even ugly as sin these days I suppose. The 1985 and 1986 jetta turbo diesels where the best and simplest cars I ever owned. I put so many miles on an 85 I actually got sick of driving it. Yet if I came upon a a clean low milage unrusted example today I would probably pick it up.

[Vikingdad]

Originally Posted by barry12345

Try a little wd40 down the intake with the air filter cover removed. You will need a helper to pre glow and cranking the engine at the end of the glow cycle.

I have tried that to no avail. It needs more than just the WD40 I suppose. Or perhaps the WD40 is not remaining vapor trough the whole intake and turbo before entering the engine. It has to be vapor to ignite.

Also there are two check valves in the lift pump.

Where are these check valves located and can I access them to clean them or whatever? Or do I have to replace the lift pump as an assembly to address a leaking check valve(s)? Not inclined to replace parts that I am not relatively sure need replacement if you know what I mean. But if I can clean them out....

Also, the lift pump is of the "newer" variety, with the black primer rather than the white one that unscrews.

The clear hose you installed back draining may suggest they are not in the best of shape perhaps. Assuming the relief valve is not totally sealing.

I'll keep that in mind.

Remember that you can substitute the lift pump by having someone there to keep activating the primer pump as you crank. The resistance building you felt as you primed up does indicate the relief valve is really not wide open either. You can close off the return line temporarily with no damage to anything if unsure.The lift pump is a constant pressure design.

Does this mean that there should be static pressure in the system? (meaning when the engine is off, should there still be pressure in the pow pressure system)? Or does it just mean that there is a constant pressure while the engine is cranking/running? Is there a spec for the lift pump pressure that I can measure?

I guess what am suggesting is to make sure the engine is just capable of firing up as well. Not running it with that questionable oiling issue.

I will be replacing the damaged oil pan and sump before cranking it any more- with new oil and oil filter in place!

I am wondering if the last owner played around with the injection pump as well or anything else. You might remove the vacuum hose from he injection pump as well. You just never know what someone else could have done. It may even be helpful if you could get the whole story from him.

Previous owner has no clue. Good guy and all (heck, he gave me the car!) but he has no clue what the idiot did to his car.

Tell me why the vacuum hose on the IP would cause problems...?

In a way it sounds like a bad lift pump. Yet if you see fuel exiting the return fitting when cranking it is still good enough.

Reduced to basics. The engine was running when the pan was damaged. If bad enough to restrict the oil supply is the question. When you crank the engine does the oil pressure gauge go full up? . Then that episode would have no bearing on the fuel system. It is illogical for him to have been working on the fuel system with an oil supply issue.. So things do not really add up. Or at least to me. You have to keep this in mind.

The oil pressure gauge does not move when cranking. That is what led me to investigate that problem and I found the pan caved in. The damage was not so much as to break any of the aluminum parts to the oil pump in the pan, just destroyed the rubber sump pickup and screen.

You do not want to change that oil pan until you know the engine is good. Or as much as possible. You have to pull the block to do it. Although apparently some have managed it without doing that I understand. If you can get oil pressure while cranking testing first is the reasonable approach. I suspect it is present and he just drove the car until another unrelated problem developed perhaps.

I am pretty confident that the pan damage happened right around the time the car stopped running. There is no oil residue on the fragments of rock or on the gouges in the metal of the pan. Believe me, if there had been much run time on the car after the pan got damaged, it would have gotten oil residue on it.

Incidentally even ugly as sin these days I suppose. The 1985 and 1986 jetta turbo diesels where the best and simplest cars I ever owned. I put so many miles on an 85 I actually got sick of driving it. Yet if I came upon a a clean low milage unrusted example today I would probably pick it up.

I liked that Jetta and regret having sold it. I don't really care what a car looks like if it is reliable and gets good mileage.. I am not the vain sort. Hell, I drove a Peugeot 504 for Pete's sake! I have no pride.

[Mike D]

The first thing you need to know is; what is the condition of my engine?

Do a compression test, don't guess. From what you posted, you've never seen the car run, yes?

You're looking for a MINIMUM of 250 P.S.I. across the board. This is not a good reading (should be in the 300+ P.S.I. range) but can be expected for an engine which has sat idle for a long time.

Remember the rules for a 4 stroke run cycle. "Suck, SQUEEZE, bang, blow". The "squeeze" is the most important part of the diesel equation. If you can't compress the fuel mixture hard enough you won't get ignition.

[Diesel911]

I did not read all of the previous posts so this could be a repeat of info.

Pumping the Hand Primer only bleeds the Air out of the Fuel Supply System (which includes the Fuel Injection Pump Housing and the Fuel Pressure Relief/Overflow Valve).

However, if Air is trapped inside of the Fuel Injection (steel) Fuel Injection Lines (tubes) and the Injectors because Air compresses it moves very little and the Starter cranking needed to get the Air out is hard on the Starter and Better.

To allow the Air a way escape you need to loosen the Fuel Injection Line Nuts at the Injectors and crank the Engine till Fuel is coming out and then tighten up the Line Nuts.

If you loosen the outlet line at the Fuel Supply/Lift Pump when you crank the Engine does Fuel come out?

In order to install a Fuel Pressure Gauge even for a temp test you need to fabricate some fittings and even with a liquid filled Gauge the needle bounces around considerably.
There is few ways to keep that from happenig but you need to read up on it.

Repair Links
Fast navigation http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html
http://www.peachparts.com/shopforum/forumdisplay.php?f=82
http://www.peachparts.com/Wikka/DoItYourSelf

[Vikingdad]

Originally Posted by Diesel911

I did not read all of the previous posts so this could be a repeat of info.

Pumping the Hand Primer only bleeds the Air out of the Fuel Supply System (which includes the Fuel Injection Pump Housing and the Fuel Pressure Relief/Overflow Valve).

However, if Air is trapped inside of the Fuel Injection (steel) Fuel Injection Lines (tubes) and the Injectors because Air compresses it moves very little and the Starter cranking needed to get the Air out is hard on the Starter and Better.

To allow the Air a way escape you need to loosen the Fuel Injection Line Nuts at the Injectors and crank the Engine till Fuel is coming out and then tighten up the Line Nuts.

If you loosen the outlet line at the Fuel Supply/Lift Pump when you crank the Engine does Fuel come out?

In order to install a Fuel Pressure Gauge even for a temp test you need to fabricate some fittings and even with a liquid filled Gauge the needle bounces around considerably.
There is few ways to keep that from happenig but you need to read up on it.

I have tried bleeding the system to my wit's end but I am still getting air bubbles, so I think there is some air getting in somewhere. Worth noting though that I do not see any obvious fuel leaks anywhere. I am probably going to end up sobbing together a pressure gauge after I get all of the parts I have ordered installed on it. I think I have some banjo bolts that will help me out here. Good to know the gauge will bounce around some. That is helpful.

Repair Links
Fast navigation http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html
http://www.peachparts.com/shopforum/forumdisplay.php?f=82
http://www.peachparts.com/Wikka/DoItYourSelf

[funola]

Originally Posted by Vikingdad

I have tried bleeding the system to my wit's end but I am still getting air bubbles, so I think there is some air getting in somewhere. Worth noting though that I do not see any obvious fuel leaks anywhere. I am probably going to end up sobbing together a pressure gauge after I get all of the parts I have ordered installed on it. I think I have some banjo bolts that will help me out here. Good to know the gauge will bounce around some. That is helpful.

A common point of air entry in the W123 is a rusty pin hole in the metal fuel supply line under the car, always under the clamp, which often does not drip but lets in a lot of air because the line is under suction. Take a clamp off and have a look. It should not be damp.

[Vikingdad]

Originally Posted by Mike D

The first thing you need to know is; what is the condition of my engine?

Do a compression test, don't guess. From what you posted, you've never seen the car run, yes?

The car belonged to a neighbor friend of mine and I did see it run before it stopped, and it ran like a bandit, no smoke and no odd noise. Cranking compression sounds strong.

You're looking for a MINIMUM of 250 P.S.I. across the board. This is not a good reading (should be in the 300+ P.S.I. range) but can be expected for an engine which has sat idle for a long time.

Unfortunately I am not equipped with the tools to run a compression test, and I do not have the gauge for a diesel in any case (going through a divorce and the STBX wife will not let me have my tools. Long story.) I will, however, be running some more in depth testing if I can't get it running. In the meantime though I am pretty confident I can get it running first. Thanks for the compression thoughts though.

Remember the rules for a 4 stroke run cycle. "Suck, SQUEEZE, bang, blow". The "squeeze" is the most important part of the diesel equation. If you can't compress the fuel mixture hard enough you won't get ignition.

Well acquainted with these concepts, that you!

[Vikingdad]

Originally Posted by Clemson88

I'd start with a valve adjustment. If you read much here you'll come across this a lot.

I would agree but for the fact that his engine has only 200K on it and it was well maintained by the original owner who put the first 180K on it. It was also running very strong until it stopped. Valve adjustment will be one of the first things I do once I can get it running again.

Pressure will build in the lift pump as you pump the button on top but it will not stop you from pumping it. When air is being sucked in it sounds a little different than when you're pumping fuel. It should firm up a quite a bit when the secondary filter is full.

Thanks. This is helpful.

I'm not one for changing parts before I know exactly what has malfunctioned. In your case I'd suggest you crack an/the injection line(s) at the injectors and crank the engine to see if fuel is being delivered.

As a professional mechanic when a car got towed in that was not running the first (and I mean the very first) question I would ask the customer was "What did you do to try and get it running?" followed by "Was it running before you began working on it?"

Right now I am having to guess at what the previous idiot did to it and once I get that ironed out I can start trying to fix what failed.

I have cracked the fuel lines at the injectors and I get a meager amount of fuel but it looks like there are some air bubbles too- which leads me back to the possibility of air getting into the low pressure fuel supply system.

BTW, I noticed a significant difference in my 84SD when I changed that banjo bolt on the IP. Thanks again to Greazzer.

Scroll up this page and click on "Technical Information and Support." Then scroll down that page. Just below the second blue banner you'll find more help than you need with more material than you'll care to read. I think it's titled "DIY Links by Parts Category."

I have a new banjo bolt on order, should get here in a few days.

Thanks a bunch for your input!

[Maxbumpo]

Plug in the block heater for about thirty minutes prior to attempting to start.

I agree with loosening the hard fuel lines at the injectors, and then crank until you get fuel and tighten them back up. Usually the first injector to get fuel out the line is the one at the rear-most of the engine (#5 in your case).

If it still doesn't want to start, next step is a valve adjustment.

If the car is still stubborn, AND you get some reading of oil pressure on the gauge while cranking, then I recommend pull-starting the car with another vehicle. The procedure is in the owner's manual for how to do this properly.

[Vikingdad]

Originally Posted by Maxbumpo

Plug in the block heater for about thirty minutes prior to attempting to start.

No can do. Kight now it is sitting on a trailer out in a grove of oak trees on a remote part of the property where I live. No power to plug into. I am working as an actual shade-tree mechanic at the moment!

I agree with loosening the hard fuel lines at the injectors, and then crank until you get fuel and tighten them back up. Usually the first injector to get fuel out the line is the one at the rear-most of the engine (#5 in your case).

Good to know that #5 is typically first to et fuel. Does it go from back to front typically?

If it still doesn't want to start, next step is a valve adjustment.

God I hope to avoid that until after I get it running! I really do. Not that IO am unable or unwilling to do the valve adjustment it's just that I hope to have it running first.

If the car is still stubborn, AND you get some reading of oil pressure on the gauge while cranking, then I recommend pull-starting the car with another vehicle. The procedure is in the owner's manual for how to do this properly.

It is an automatic (all 300TD models are automatic I think). I would prefer a manual, but it is what it is.

Is there a way to bump-start an automatic MB that I don't know about?

[funola]

You said the car belonged to a neighbor and it ran well. Valves don't all of a sudden go out of adjustment so adjusting the valves is not a priority.

Did the engine run with a looped lift pump and if so for how long? Looping the lift pump may have damaged it due to lack of fuel cooling. I would take the output hose of the lift pump and stick it in a bottle and measure how much fuel is pumped out while cranking. If you are not getting any fuel output from the lift pump, rebuild it or get a replacement. I am not sure what the spec is but the the IP needs some minimum fuel pressure for the engine to start/ run. IP internal fuel pressure is a function of the IP fuel pressure relief banjo bolt (facing the block) and the lift pump.