Sounds like you are sucking air somewhere. I'd follow every inch of the suction line to the tank and try to find a weak point. (There could be more than one).

Good luck!

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I've repaired and replaced everything from the sender, tank, all the way to the pump. That governor is the only thing I haven't touched and I have no experience with it at all.

Since it can free rev without the load the injection pump governor is okay I suspect. You did mention hills though.

With your engine in general you do have to accelerate before the hills. At best otherwise you will just maintain the speed you hit the bottom of them at In high gear. Of course this depends on the grades of the hills you mention.

I am going to describe a common situation that others may agree with. Say I hit a hill with my manual transmission 240d and can maintain 60 mph. If I catch up to a slower car ahead of me that slows me down.

Usually I cannot regain any speed and will top that hill at pretty much at the speed that I was slowed down to.

In your case it may be the amount of fuel is not up to scratch under load conditions. Also a quick drip check of the timing is probably not a bad ideal as the mechanic obviously missed the linkage issue. That indicates to me at least he was not familiar enough with these engines as it is such a common issue. Most members will want to hear about how the car is on flat roads as we cannot factor hills in well with these engines.

Now I will describe a 240 of your vintage I looked at once. The owner told me it would not top 50 mph on the flat.. It occurred to me that others might find this interesting as well.

The car had an older electric fuel pump of the 4-6 pound type when I looked. Allowing for normal filter restriction it was possible the injection pump was not getting enough fuel under load conditions. It seemed fine under no load conditions. I suggested he recondition the lift pump or change it but not feed the engine with that older carb type electric fuel pump. I never checked back to see what if anything he ever did.

So in your case I would want to see the fuel pressure under load conditions in the base of the injection pump. It costs about fifteen dollars to get a liquid dampened 0-30 pound pressure gauge and to get it rigged up for a test. Guessing at this and that is frustrating and can be expensive. To myself you have a few things to do before really considering the injection pump itself even if it is a possibility.

It's slow when it's flat. The 'hills' I'm talking about are so minor that I never noticed it was an incline before. My other 240D has zero problems moving around here.

Once I'm at speed, everything's great. On the freeway at 70, I'll barely touch the accelerator and look down to see I'm approaching 80.

I replaced the shifter bushings before the car would start. I had to take the arms off the transmission to do it. It took several attempts to get them back where the lever was in the right place. With that, it's either in gear or not, right? Should have no bearing on performance?

You have 240d driving experience and that is great. Order of business in my mind is to now double check the mechanics injection pump timing. Using the drip method. I base this on your description of seeing black smoke in one thread under no load conditions. But revved up. Plus your obvious knowledge of what normal is in these rocket ships.

A seriously retarded injection timing could produce your issues I suspect. This should also be a pretty easy check if he got it right. Also this engine could idle quieter than the other if the timing was really retarded.

I still have reservations about that mechanic not spotting the linkage issue. You may have to get an old spare hard line from an auto wrecker or member to make up a drip tube.

Or I assume your mechanic had one? Or did he not? Just setting the injection pump by ear perhaps instead? Maybe you could borrow his? Ask him anyways because if he did not have one the injection pump timing is really very suspect. Plus you may have the answer before even checking if he does not.

I also find it hard to understand your mechanic giving you back the car in this condition. Read up in the archives about drip timing this injection pump if you do not know already. You are just checking his accuracy initially.

Remember to have a second person to keep pumping the primer pump as you check it though. The result of the timing being really still off could be poor lower end acceleration very easily. The effect of the retardation is also less I suspect once at the higher revolution end of the spectrum. Also if you had fuel starvation issues this is the point where It should present by decreased acceleration at the upward end. As that is a pretty high fuel demand situation.

I have two 123 240ds incidentally. There remain other possibilities of course but the injection pump timing is the primary symptomatic possibility right now. All things taken into consideration. It has to be checked.

I am wrong sometimes of course as well. Just not much sense looking elsewhere without verification of the pump timing first in my humble opinion. Based on your previous 240d driving experiences narrowing things down a lot. Also look at the bright side. At this point I see no probable indications at all the injection pump is problematic in itself. Earlier I was not as sure.

No normal or even one slightly abnormal 240d can make 80 MPH in any other gear than the top one except perhaps the ones with a rare five speed overdrive transmission. So you got the transmission arms right.

Part number appear correct. It matches for item 383 in the exploded drawing here

Further explanation of the pneumatic governor (and the mechanical governor that helps eliminate 'sawing' or surging idle) operation, testing procedures, and great pictures are also located here as well as here

Before ordering the part, make sure to inspect the diaphragm to make sure it is needed. It seems to be a bit pricy at the dealership.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Thanks for the confirmation Alec.

And Barry, thank you. I've had incredible experiences with this shop before. The owner is like an encyclopedia with the parts (when I can get a hold of him) and two of the other guys are really good as well. One guy rubs me the wrong way and is never very helpful.

But I digress. I'm only off one day a week that they're open, but I'm sure they would check the timing for free since they touched it last. He told me when I picked it up that they were blaming the old fuel. Now that it's all out, I think they should look at it again.

2 things I'm worried about that are going against me right now;

I have 240D experience (15 years), but not with this car, or any W115.

And the PO removed the fuel pump for a reason. He was going to replace it but ordered the newer one, so he put it back on. He said it leaked, and I assumed it was the primer. In any case, it is not leaking now.

So some time has passed. I've swapped the injectors and taken care of the idle issues, but still very slow. The shop continued to stress that the 115 is slower than the 123, until I told the owner that I timed 0-50 in 30 seconds on a slight downgrade.

He double checked the timing and told me it was good, but he thought of something else to try this morning. He didn't say what, and I have not heard from them yet.

As an aside for anyone who finds this, that part number for the diaphragm was not the correct one. I still have the original and it was fine

Yeah, I'd say the 115 is slower than the 123. It tends to be a little heavier depending on the accessories it has. The rated hp is slightly different too....5 hp or so.

If an automatic of course it is dramatically slower, and the 115 automatic performs differently than the 123 automatic, read slower. In fact the 115 first gear is so low if you use it you'll probably be slower in acceleration. I guess its for climbing very steep hills.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Still no word on the car...

I just don't understand it. Everything seems fine mechanically, it's just so slow it not driveable. Last time I tried to take it to work I had it floored in 3rd gear with the hazard lights on. The muscles in my leg started to spasm and I almost got run over by an 18 wheeler!

The fuel pump is timed the same way as the w123, right?

Starting to sound like fuel starvation. If the engine in neutral will rev up reasonably quickly from an idle. It requires a lot more fuel to do it under load when the car is attempting accelerating. It is almost irrelevant that it can maintain speed once there. It takes a lot less fuel to do so unless going seriously uphill.


I would take a ten dollar 0-30 pound liquid dampened harbor freight gauge. Plumb it in to read the base pressure of the injection pump and extend it to inside the cab or visable from there with the hood closed.


You stated the past owner got a new lift pump because of leakage. Yet apparently his replacement did not fit. You put his old one back on. Yet observe no leakage.


Could the past owner have meant too much leakage in the internal valves of the lift pump? Anyways with the gauge temporarily installed take the car for a very short drive. If you have no fuel pressure when trying to accelerate then you know where to look for the issue.


The gauge is not a waste of money anyways as it is also useful to get the fuel pressure adjusted to where it should be in these old cars or at least check that it is.


You almost cannot keep using paid for service even if you can locate someone really competent. Simply because it costs too much. Plus older cars in general will have more needs. On the other hand you can learn to do many things yourself with the support of a site like this one.


We also on this site have talked about adapting the newer injection pump onto these engines. The difficulty I believe has been providing a constant lubrication for the injection pumps. I think a tee at the oil pressure fitting if there is room on the 115s.


Or getting a feed fitting installed there somehow. Using a very small copper tube or one with a serious restriction from that point. Plus a fitting installed on the valve pan to allow the return oil should work okay.


The 115s seem to have more trouble with their injection pumps than the later ones. Otherwise I believe they are a direct fit. You may have governor issues but without knowing adequate fuel is available in the base of the injection pump you just do not know. Adaquate fuel is indicated by the fuel pressure present in there.


If you establish what the fuel pressure is you may get a much better ideal of what to do next. For example if the lift pump is weak it is cheap and easy to recondition. Until you get that pressure you are for all practical purposes at a dead end. Other than guessing and spending money counting on luck. If the engine picks up speed quickly from idle with no load is all the more reason to look at the fuel pressure.

You keep saying you think timing is right...

What is it timed to?

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Ok so the problem with the pump is only on cylinder 3. They said compression is 300 in all cylinders, and they tried a third set of injectors. I'll have to take a look at the pump. Hopefully it's just the delivery valve.

Glad to hear that you've gotten it narrowed down to one cylinder. I was going to suggest a rebuild of the lift pump, and would likely still recommend that, no harder than it is to do. The parts were readily available from my local Bosch shop, about $45 total. This included check valves, spring, washers, etc. There is a parts diagram around here somewhere. My Bosch guy (Metro Injector, Allentown, PA) only needed the number off of the side of the injection pump. It made a huge difference in the way the car ran, and it wasn't running so badly before. You will need a 30mm socket to finish the job.

Another real improvement came when I changed the diaphragm and seals associated with the governor. It wasn't as easy, but was well worth it. The hard part was reinserting the circlip without dropping it into the pump itself. Mine wasn't ripped, but had become porous and was allowing fuel to pass through it. I read where you've inspected yours. Mine was $80 from Bosch, and readily available.

Do you have the part number still? I think mine should be fine but the one I had ordered was too big.

I just took the delivery valve apart and there were metal shavings all over. I cleaned everything and stretched the spring, but now it got less power and I need to take it to work tomorrow.