First off I'd like to thank whunter for recently posting about the vac pump, and where the excess goes if there's a leak... defenitely gonna check that out... very cool.

Okay, now the problem:

1) I can barely start my '84 300TD. Foot to the floor cranking for like 20sec (more than that and I start to fear for my starter's life) and it finally goes just when I am convinced that I should stop now for the sake of my poor extremely hard to replace starter. Also, when I crack a line, fuel lethargically leaks out rather than spraying like it used to... but there is fuel.

2) Once it fires, but running cold, I really have to work the pedal to keep it going. If I let it down below about 1100rpm it runs really rough and below about 900 it just quits (this is with my foot in it a good deal mind you). When it is good and hot (after driving for over an hour), it is even harder to keep it running, necessitating almost 1/4-1/3 or more throttle to keep it running.

3) I installed a vacuum/pressure guage in the fuel inlet line just before the IP, was getting good pressure, but a really crazy oscillation of the needle (btw. 8 and 15 psi) in time with the engine. I.E.- 2000rpm = 2000 'wags' of the needle.

4) I eliminated the lift pump as a factor by removing it, taking the spring out, and putting it back on (to seal up the hole and keep my engine oil in) and I added an electronic solenoid fuel pump. I also modified the pressure valve on the IP return (using a .030 MIG tip no less... I'll tell you how if you really want to know). So with the restricted orifice on the IP return, there is about 10psi at the IP inlet, with fuel constantly flowing through. I know its not FSM spec but I know of quite a few who have done similar things with no adverse affects. DID NOT SOLVE THE PROBLEM-- oscillation of needle greatly diminished, but the car still won't run worth a *****. This work effectively eliminated the lift pump as a variable in the diagnosis.

5) Running down the road at normal throttle load and normal rpm (~2000 or more) it runs great, no smoke, no sputtering, good power, runs like a top.

6) Here's the kicker (and its a weird one): Running on veggie (yes I'm one of those guys) with a good system by any standards (140-180°F before IP, 190-220°F btw. IP and injectors w/ electric heaters) It RUNS GREAT AND IDLES FINE.... Also starts fine cold or hot

7) There is one way to make it idle on diesel... that is to crank the idle screw waaaay in... which defeats the governor so you better not touch the throttle or it runs away... a non-option fix if you ask me... plus when I switch to veggie it would run away.

Hypothesis: I think that my IP is not making enough pressure to push diesel through the injectors at low RPMs, but at higher RPMs, due to the higher speed of the injector plungers, it can sort of "bounce" the fuel through (sort of a hard mental image to communicate). With veggie, because it is slightly thicker than diesel (although only slightly at those temps), the IP can make more pressure at low RPMs, thereby popping the injectors, and thus allow it to idle. Am I even remotely accurate as to my knowledge of the injector pump?

Does this sound at all reasonable? Has anyone ever encountered an IP failure that had similar symptoms (minus the veggie use, probably)? Is there any way I can replace the plungers/sleeves (not really sure how these work) or any other part in the IP without removing it from the engine.. it looks like you could almost get to the guts of the actual individual pumps from the top through those 2 nuts on either side of the injector lines...? I am extremely confused here. I have a parts car sitting in the woods with a (formerly) running engine, so if all else fails I will swap that IP in this coming weekend.. but I really want to find out exactly what is wrong, and why, and if there is an easier/better, more reliable and more complete fix.

Anyone who has ever seen a dead IP, let me know what the symptoms were! Anyone who has ever seen anything like this let me know!

...in the mean time I will be looking up how to remove, install, and time the IP....

If I suspected what you did I would put an injector out in the open and see if it was spraying diesel at cranking rpms. That would perhaps either eliminate or give you some indication of what you suspect. I think a large shop would hook up a pressure gauge on the line but an injector spray test should indicate well enough. The only other variable I can think of is if you have two fuel supply systems and there is something drastically wrong in the diesel one. It must be fun to attempt to drive on diesel to say the least. I also want to mention that if water is in the fuel and processes through the pump we were always told it acted like fine sandpaper or a lapping compound. Could your alternative fuel have had had water in it? If you change pumps and continue with your vegatable based fuel you might want to incorporate a water separator in you fuel circuit. Not hard to do.

I have pretty much beat this one to death... checked and rechecked every single piece of hose and every hose clamp... changed filters, pressurized lines... everything tip-top.

HAHAHAHA you have no idea... 2 feet and a hand on the shifter lever... that shift from S up to N at a stoplight with one foot on the gas and one on the brake is a real blast.. but as much fun as it is I'd like to fix it...

I am absolutely positive that my veg oil didnt have any water in it. De-Watered at over 212°F. I am not so sure at all about my diesel. After I got back from my road trip, when I changed the filter, some of the most foul nasty, rust-colored, WATERY gunk I have ever seen came out. I drained the tank, but it seems that there wasnt much in there, some, not much.. and the tank screen was fine... there is still a bit in the prefilter (from the lines), but I think its all gone now.... could one tank of bad fuel really have fried my IP? If thats the case I'm gonna can the OEM DIESEL filter and put a water seperating one on it... For that matter, everyone should... serious design flaw if you ask me... I'm seriously questioning the practice of buying diesel fuel at a pump too... if that is what did it...

Take a look at Diesel Giant's purge page and using this modified pop bottle, make a temporary fuel tank. This should eliminate the tank and lines to the pre-filter or where ever you plumbed.
If this modification worked, you have 1. bad fuel 2. something in the line or tank. 3. ?????
I have seen vegie crud build up inside a line 'on the wall' till it let loose making a flap valve.
If this temp. tank does not work, keep going up stream. Only after checking flow to all injectors and doing the above, would I look to the IP.
I believe IP's should fail slowly or over a long period of time.
I assume you did not find the wonderful black crud in the per-filter, have added biocide & have done a water test on your alt. fuel and verified the tank strainer.
? Did the vehicle run ok on this batch of fuel before the problem raised it's ugly head?
?Did you 'bleed' the fuel lines at the nozzles?
Good luck and please post the results.

G'mornin',

If your delivery valves on your IP are gunked up and not seating.....may cause this sort of problem.....

With the engine running feel each of your fuel injector lines.....should be able to feel the injection........or take a long screwdriver, put the blade on an injector......put the handle against the bone just forward of your ear......should be able to hear the injection process.....

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

Unfortunatly he cannot get an idle to listen to those valves click. But probably no reason they would not be heard at cranking speed as well either. Yes he could have bad diesel fuel and that probably makes sense. So trying to run the car on a bottle with fresh fuel would be appropiate. I always try to stay away from buying diesel at low volume outlets. If that was the case here. They sometimes have nightmare fuel in their tanks. Glad also he was dewatering his vegatable oil. Also did not realise this problem only surfaced on the one tank of diesel. A bad tank of fuel is always possible. Usually you become aware of that particular problem as drivability problems arise shortly after refuelling. But he switched from vegatable oil back to diesel when the problem arose. That might be enough to cloud the issue in my opinion. The injector spray output test at lower cranking rpms I suggested would have meant nothing if fuel is bad. Other than making the fuel itself suspect perhaps. The viscosity of hot vegatable oil is too close to diesel to make that much difference probable.

How do I go about checking/cleaning/replacing my delivery valves? Is there a way I can check them with the IP in the car? What do the delivery valves do? Would stuck/worn delivery valves contribute to a decrease in injection pressure at low rpm?

Its a little hard to do the screwdriver method, not impossible with another person, but I would have to run the engine at 1200rpm or so... would I still be able to hear it do you think? What am I listening for? What could this possibly tell me? The car runs smooth enough at higher speeds that I think my injectors are okay... I could have them tested and matched for kicks but I would like to make sure they are bad (and it doesnt seem they are) before I go spending money on them, if there is something else I could do instead.

As I said before, I eliminated the lift pump and the fuel supply system to the IP as a culprit by installing electric fuel pumps and modifying the return pressure valve on the IP. This modification is a proven one and did not effect the problem whatsoever... its still there. This was effectively the same as running from a bottle because I put diesel fuel in my vegetable oil tank (completely separate from diesel system (different lines, filter) and tried to run it to no avail... There is one more thing I can check, and that is my switchover valves. I will do that as soon as possible. Possibly an air leak in one of the valves could cause this problem, but I doubt it because they are under PRESSURE 100% of the time, never vacuum, verified by the pressure guage I installed 4 inches before the IP inlet (the solenoid valves are before (upstream of) the gauge).

I seriously think that the problem is something in the IP, because I have eliminated the rest of the fuel system (except for the solenoids, which I will check shortly). Also, another forum member was having a similar problem, up and replaced his IP, and the problem went away. I do not want to take this route, because I actually want to figure out what, specifically, is wrong. If at all possible, I want to avoid removing, installing and timing an IP as well Whether it is the fuel switchover valves, delivery valves, the pumping elements, or what I don't know but I would sure like to find out for sure, and I am wondering how to go about that.

I am slowly but surely narrowing it down to individual components. If anyone knows what the delivery valves look like, how they work, where they are, and what happens if one fails, please let me know. Thanks for all the support.

I had a tank of bad fuel go through. I know this because I changed the filter and found some (1/2-3/4 full) really horrible gunky water in it. I drained the tank immediately after discovering this, and there wasnt a whole lot of nasty in it. It is quite possible that almost the entire tank of bad fuel went through the engine. I began noticing problems in Montana, checked the prefilter and saw no indication of anything amiss, so I just kept going. I was pulling a trailer so it is quite possible that I burned a whole tank of bad fuel without noticing. I did not notice any adverse performance, but with the engine maxed out like it was, pulling the trailer, I dont imagine I really would have. Could be that a little watery fuel = the straw that broke the back of my 370K mi inj. pump? I guess we'll see someday, but I would love to know more about those delivery valves first! Thanks again for all the help.

That nasty fuel was in the oil or diesel tank?

It may have sent some via the return during changeover to the other tank and contaminated it.

empty the diesel tank and check your tank screen if you haven't allready.

If it runs great on oil then i would rule out the injection pump.

My guess is some sludge clogging your tank screen on the diesel side.

If it is blocked you will suck in air from somewhere and cause those symptoms.

Also blow out both the suction and return lines on the diesel side when you disconnect them at the tank and remove the tank screen.

Steve

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85 300d in progress

sorry just noticed post three so the screen is good huh?

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85 300d in progress

put good diesel in your oil tank and see if it runs good.

if it does then your problem is related to the diesel side system not the fuel.

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85 300d in progress

ok i have and idear!! Bear with me. Ohm's law states that it takes one volt to push one amp thru one ohm of resistance. More resistors, less flow. Did you check your return circuit? 80% of the fuel going into the ip is for lubrication cooling and to heat the fuel tank. if that is restricted it would back up the whole system like a squirrel in a shower drain (don't ask, please.)
Just an idear.....

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I like cars.

excellent idea, but I already tried it. Used known good diesel, all tanks, filters, lines in the car are clear of bad fuel. Original batch of suspected bad fuel was in the diesel tank, not veg tank. It was diesel fuel from a pump no less (the bastards).

Another good idea, yet I have verified that it is goin through just fine because electric lift pumps are circulating and I can hear/see it come out the return in my veg tank, and I have tried running with returns switched both to veg and diesel, and feeds switched to both veg and diesel side, and every possible combination thereof (running #2 diesel fuel in each tank) The IP has all kinds of fuel all the time, no problems there.

I was wondering if some delivery valves are going bad, if that could be the culprit?? having a hard time seeing how, considering it runs good on veggie, but the hard start/no idle problem has been discussed elsewhere in relation to bad delivery valves..... maybe applies here?? Also, I know I ran watery fuel through. How do I check whether the IP still makes pressure? Should the inj. lines really spray out hard when cracked at the injector? I am really thinking about these delivery valves....

Rather than take the delivery valves apart and clean them. I suspect if engine will still run and idle on vegatable oil if they are okay. The function basically is reverse check valves. When the piston pushes the fuel into the injector line it flows by the valve. When the piston starts down the valve shuts holding the residual pressure if any and fuel in the line to the injector. Let someone give a second opinion on this before taking the delivery valves apart. As for your hypothisis, bottle feed that pump close in with vegatable oil. If injector sprays visably out of the block at cranking rpms fine. Now try the same test with diesel fuel. Or if easier forget removing the injector and see if the engine will run on vegatable oil normally from a supply close to the pump. Then duplicate it exactly using the diesel fuel. No one here likes to hear of a bad pump but of course it is possible. If nothing else this should clear any suspicions you have about the pump one way or another. You are doing a lot of elimination as you go along but could still be missing something depending on your level of experience. I always try to do tests that either absolutly condem or clear a component as I go along or the confusion overwhelms me because I am not a working mechanic. At this time either clear or condem that pump without changing it. Usually it is not the pump when suspected but there are exceptions. Just some suggestions and thoughs for your consideration. Without being present it is very hard for me to get a feel of what exactly is happening. Others with more ability will try to assist I know. Not to get mad or frustated is the first law of these situations. I think you know that already though. Unfortunatly there are no extra brains here. If there were they would be lonely.

Okay here's how I'm gonna do this: I have an '85 300TD in the woods, I know it runs because I drove it there (before I pulled the wheels, brakes, rotors, and all sorts of other goodies off it... best $600 investment I ever made, and I haven't even gotten into the engine yet ). I'm gonna pull the pump on that car this weekend, and order up one of those IP locking screws, an IP gasket, and fabricate some sort of a bar/clamp assembly to facilitate timing the IP using the millivolt method. Anything else required for an IP replacement? Then I'm gonna yank the suspect IP and put the known good IP in, and see if it runs... maybe even stick the suspect one on the parts car to block up the hole if I'm feeling especially kind towards the mercedes species. If problem persists then I take a sledge hammer and a cutting torch to the car... just kidding... or am I?