About 1500mi ago my '84 300TD started running rough on diesel at low rpm (below 1500), and stalling at Idle and when in gear. I first tried adjusting the idle screw, but in order to achieve a smooth idle, I had to adjust it too high for the tranny, so I backed it back down. Then I tried adjusting the valves (they were fine), gutting the ALDA, and blocking off the EGR (ball bearing method) and this briefly solved my power problems (and then some , but not the idle problem. The car will not start when hot (above 40°C), and will only start cold with ~10-15sec of cranking with my foot to the floor. Over the last 200mi I have noticed a reduction of power at driving speed. I also tried messing with the rack damper screw on the back of the IP... no effect whatsoever. Here's the catch: it runs like a dream on veggie... Idle is fine, perfect even, shifts into gear nicely, gobs of power on the highway and accelerating from a stop, just wont run worth a ***** on diesel. Here are some of my hypothetical ideas as to why it wont run right:

1) Injectors (one or more leaking or not spraying right) I have never checked them so this might be a start?

2) Rack damper screw (do these things go bad? how do I tell?)

3) Timing.. dont really know much about this, I have heard that due to veggie's high cetane value (near 60) that you can mess with the timing and have them run fine... could my injection timing (I'm guessing this would be start of delivery) somehow come out of adjustment so badly that it wont run on diesel but will run on veggie? How do I go about fixing this?

4) IP bad? Should I pull my IP and have someone who knows bosch IPs look at it? The fact that it runs great on veggie makes me think that this is not the case.

5) Bad lift pump? I am planning on installing a vacuum/pressure guage right before the IP soon, this should tell me whether this is the case.

These are the only things I can think of, seeing as i am almost 100% certain all my valves are switching correctly, and there are no air leaks on the diesel side. Advice from anyone familiar with this sort of problem, timing issues, injector issues, IP issues, would be greatly appreciated.

If it runs perfect on veggie, and crap on diesel than you know several things.

Your IP is fine.

Your injectors are fine.

Your timing and valve clearance is fine.

Your Rack Dampener pin is fine (although it wouldnt hurt to get the updated version.)

My guess is that there is some problem with your conversion.

Could you explain how your system works? Do you use the stock lift pump for both fuels or just diesel? What pump powers the veggie side of things?

My guess would be either a problem with the diesel side of the conversion or a bad lift pump or whatever pump you use for diesel. You may even being experiencing something as simple as bad fuel... Hows that pre-filter look?

How long has this been going on?

Sounds like an easy fix

Here is how my WVO system works on the diesel side (the path a particle of diesel fuel would take as it goes throught the system):

diesel tank > 6 port solenoid > stock lift pump > 6 port solenoid (again) > stock diesel filter > 3 port solenoid > IP > 3 port solenoid > diesel tank

here is how it works on the veggie side (the path a particle of veggie would take as it goes through the system):

WVO tank > 6 port solenoid > stock lift pump > 6 port solenoid (again) > Heat Exchanger > veggie filter > 3 port solenoid > IP > 3 port solenoid > WVO tank

to clear things up, the fuel system uses the stock lift pump on both fuels, and the 6 port and the first 3 port are wired to operate together, and the second 3 port (the one after the IP) is on a seperate switch for purging. Essentially, instead of buying 2 lift pumps and removing the stock one, I just bought a 6-port and set it up to run both fuels on the stock one. I don't think the problem is with the conversion because except for the fuel going through the solenoids, the diesel side of the system is basically stock. The only difference is that I T-ed the low pressure injector return lines into the IP return before the 3 port. I have checked and double-checked all my connections and I am pretty damn sure that there isn't an air leak anywhere.

I really think it could be the IP... something tells me that the fact that I have to floor it to start on diesel suggests that it is an injection problem, not a pre-IP problem... I know the IP is designed to operate with positive pressure, if the lift pump is bad could this problem happen? Although, the fact that it runs on veggie just fine pretty much eliminates this as an option.

In conclusion, I really really don't think there are any problems with the fuel system before the IP.

Your right,because you use the stock mechanical lift pump for both fuels, that eliminates this pump from being the problem.

Although I disagree with how you think the IP is the problem. There is no reasonable answer to it running fine on veggie and crap on diesel and it being a problem with the IP. These IP's are tough, I highly doubt that this is where the problem lies.

How long have you had these symptoms?

What does your pre-filter look like? is there black crap in it?

How long has it been since you filled up your diesel tank?

My money is on bad fuel causing your problem... Check it out. It could also be your tank strainer, or a plugged vent.

Try putting some diesel fuel in your veggie oil tank and see how it runs. I cant see how you could have a inj pump problem but still run fine on veggie oil. The part of the injector pump that controls idle speed and all fuel settings for that matter doesnt see any of the fuel it runs on. It's lubricated by the engine oil.
If the engine runs fine with diesel in the veggie oil tank start looking at the supply system

Why not try getting some new, fresh, clean, known good diesel fuel and put it in a small tank (like an old apple juice container or something) then hook up the fuel lines (diesel side of course) Bleed out the air with the primer pump and see how it runs.

Never checked the tank strainer, could be it. There is some black particulate stuff in my prefilter, but not a whole lot. I have run 4 tanks of diesel through it since the problem began (road trip pulling a trailer), so I'm pretty sure it isnt bad fuel. I have also run a whole lot of lucas (like half a quart or more in each tank) and some howes meaner diesel cleaner in these tanks of fuel (just in case).

So, it appears the IP works, right? What about timing? Could the timing be an issue (veg cetane = something like 60, diesel = 40ish), therefore, if the timing was off wouldnt the veg run but the diesel not? My veg tank is full now, but I'll try running on a can of diesel to see if its the tank screen or vent. However, I don't think it is because I can still lay a healthy cloud of black smoke when I hop on it, and the power at speed was decent until quite recently (literally the last 200mi of my trip) If there was a fuel supply problem, wouldnt it be worse at higher load? Also, I think it is a diesel FUEL specific problem, because I have to wait a little while after I switch the feed over to veggie for it to run right, i.e the diesel has to circulate out of the pump. If it were a clogged screen somewhere the problem should stop right when I flick the switch (thereby releasing the vacuum), right?

The DIY method for start of delivery timing seems kind of hokey to me (pump the hand pump and look for about 1 drop per second), is there a better way to do it? Is there something I'm missing? Would a worn rack damper screw cause these symptoms?

Sorry, I didnt see your replied last night.

Anyway, just because you have had 4 tanks through the car of diesel doesnt mean that oyu dont have bad fuel.

Are you buying your diesel in the same place?

There could be algus or fungae ( I never remember which grows in diesel ) that is growing in the diesel tank and causing your symtoms... these seems most likely because of having a small about of black stuff in your pre-filter.

I would try replacing both filters and running some known good fuel through it to see what happens.

I would have a hard time believing that your IP is not timed correctly since it runs so well on veggie. I really do not think the engine should run so much differently on different fuels, even if it is not timed right.

Dont worry about timing until youve tried running the engine on known good diesel.

I forgot to mention...

In my experience, the rack dampener pin/screw only affects the idle.

I dont think the rack dampener is something you should be worried by or messing with currently.

Okay. I messed with it some more today, and here is the current info. I can get it to idle on diesel. The problem is, I have to turn the idle adjustment screw on the side of the pump housing up so far that if I were ever to step on the accelerator, the RPMS would go up and up and up and run away (ask me how I know . With the idle adjusted so far up, if I put it in gear with my foot on the brake, it stalls on the spot, my guess would be due to the vacuum valve on the top of the IP being out of adjustment due to the high idle adjustment. I am at a total loss as to what to do. And to answer your question about fuel, I am almost completely sure that bad fuel is not the problem. The fuel in the prefilter looks good, and I bought the fuel at a few different locations on Rt. 90 between Iowa and Vermont. The black things I mentioned were just grit. The fuel filters were all replaced in Jackson, WY.

To recap:

1) when the idle screw is set to run at an acceptable idle, the engine goes nuts when I touch the accelerator (sort of a "sticky" IP situation?)

2) The car stalls when I put it in gear when it is adjusted to this idle setting (not really a problem because it should fix itself once I fix whatever is causing my bad idle problems)

3) I am about as sure as sure can be that my fuel is good.

soo, my question to all who can help is what the hell is going on with my IP?
Thanks for any input.

Greasy beast, I'm sure you've got a bad IP. I had exactly the same problem. Was very surprised to see two others (you and Pat Cain)with this problem of running great on veggie but not idling and very hard starting and power loss while on diesel. Pat said his problem was solved by replacing the IP. My symptoms started happening after running a tank of veggie that had probable water contamination. The problem was not air in lines or plugged lines/filters as one would at first think. I tried timing the IP, set valves and valve timing, etc. Replace the IP with a junkyard one and problem was instantly fixed. Power was back, idled like it used to on both diesel and oil and started just fine ever when hot and on diesel. Old IP had damage to ALL cylinders probably because of water injestion and was not pumping proper pressure when on diesel but with thicker WVO worked fine. Very hard problem to diagnose but I am 100% sure if you try that old IP you have in the junker out back the problem will be fixed. Now I've got to find a way to make sure no water is in that WVO as it seems to kill the IP right quick!

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'84 300SD, '87 300SDL, '81 300SD

I just ordered delivery valve seals and I'm gonna rebuild the delivery valves before I go ahead and pull the pump. To me it seems that bad delivery valve seating/seals *could maybe* cause this problem, because injector lines would possibly leak low viscosity fuel back into the IP plungers between injections at low RPMs.. I.E. in the time between injection on #1 and then back to injection on #1 @ idle rpm, thicker fuel would not be able to leak back through bad seal in this amount of time... Also seems to make sense (to me at least) that the injectors require greater throttle position with thin fuel to pop and maintain idle, just an idea.. maybe it works maybe it doesnt, will post when I switch them out... if it doesn't work I have a brand new-sealed set of delivery valves for my replacement pump.

Sounds like a worthwhile try but I still think it's the IP. Your problem is EXACTLY what mine was. I just got back from the injection pump shop and the guys told me that the plungers and barrels were bad. He showed me the plungers. With the naked eye they looked fine. With a magnifying glass you could see many small scratches or lines that he called scoring. He said that when the engine was warm and with the thinner diesel, these scoring marks allowed fuel to leak by which prevented IP from making enough pressure to pop the injectors. Especially at idle with the lower volume of fuel. When cold or with thicker WVO, it couldn't bypass through the scoring and would run great. Let us know what you find.

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'84 300SD, '87 300SDL, '81 300SD

i have the same problem with my 1983 300sd.... power decrease especially going up hill.... so i got tired of it today... pulled over... left the kids siting inside the car.... changed the fuel filters (2 minutes) and was back on the road with full power again......

always start with your fuel filters..... always start with the simple and work to the complex.... dont just run to the complex first......

been over this a million times, believe me if it was the simple I would have already had it licked. Its a problem specific to idle. Car has good power except wont hold idle (i.e. not fuel restriction).