Engine started..coughed, shuttered and then died under load.
 

Hello,

My car is a 1978 W116 300SD with the 5CYL 617.950. I've done a lot of reading on this site and have learned quite a bit.

Here's what happened to me this morning. I just did a valve adjustment yesterday and found several were tight. After adjusting all valves to spec..I took the car out and it ran even better than normal.

This morning I was taking my in-laws to the airport and I fired up the Benz, and let it run for a minute. As we came to the bottom of the driveway, (inclined) I placed it into LOW to get moving and it started to get jerky, sputter and finally quite after moving about two feet. I tried to crank it again and while it wanted to catch...no joy.

This has caught me by surprise...the car ran great the day before. Am I correct in assuming it's a fuel issue? The GP light came on, and the car fired right up this morning as usual. Plenty of fuel (over 1/2) and I just changed the primary and secondary fuel filters about two months ago.

I did notice today that when I went to see if I could use the primer pump to see of I had some issue with the filter not having enough fuel in it, It's the old style and it didn't do anything but go up and down..and never seemed to make any suction.

Please let me know what else I should be trying.

Thanks,
Mike
Duke1

did the car restart after it quit? could be air in the lines or a sign of a fuel delivery issue... Hard to say

Sounds like a fuel issue, or something happened during/due to the valve adjustment. You may have bumped something when working on the valves. Check all lines and hoses.

it's sometimes hard to tell with the hand pump if it's pumping or not, unless you start out pumping air. do you hear any buzzing sound from the filter area when you are pumping? it could be many many things that caused the stall. try removing the fuel filler cap, and the oil filler cap and see if it starts normally and report back.

Empty fuel tank?

hmm, it's also possible the fuel lines are reversed, and at 1/2 tank or so, with the car sitting at an odd angle, you may have sucked air from the tank...

Gents,

VSTECH-No I hear nothing when I pump it, nor do I feel any resistance. It just goes up and down. I'll try the two caps and get back today.

PAWOSD- I was very careful about not knocking anything..but your right..one of my thoughts is that I bumped something loose. I went through all my hoses connections around where I was, and I saw nothing loose.

AQUATICEDGE- No the car never did re-start...you can tell it wants to..but it has not started again.

KERRY- I was going to be quite upset with myself if I ran it out of fuel..but it had a little less than half a tank the day before and I put five more gallons in before I began to troubleshoot.

The only thing I might not have already mentioned is I cracked open my 19mm return banjo nut on the primary fuel filter and had my wife crank the engine. I got some bubbles and then some fuel dripped out. I tightened it back down but still no start. My gut tells me fuel...could my fuel pump have died?

Thanks,
Mike

Yes, your fuel pump could have failed.

Well, your IP is your fuel pump, there's a lift pump/manual Primer. my guess would be that you've got air int he system somewhere, as someone suggested, possible park at an odd angle or maybe the primer handle buggering up... It's hard to say. pump the handle about 100 times and see if it starts

VSTECH- I removed the fuel filler cap with no success. I'm open to more suggestions...but I keep thinking it's a fuel lift pump. The manual primer does nothing and I've pumped that sucker till my fingers hurt.

The way it stalled on me this morning sure seems like fuel starvation. I'd love to hear more.

Thanks

Well, if the primers not doing anything about moving fuel, I'd replace it, Take your main filter off and see how much fuel is in it, if it's slightly empty fill it back up and see if your car'll start. Keep the accelerator pedal to the floor until it starts.

I would use a container of diesel hooked to the input line at the lift pump and held high up for a gravity feed to see if it runs under those conditions. If it does, it shows your lift pump (which is your fuel pump in the traditional sense of fuel pump) is bad.
Does fuel flow out of the line from the tank when you remove it from the primary fuel filter? You could also remove the return line and see if you have fuel running out when you try to start the car.

I'll try those things tomorrow and get back to you.

Thanks

Another thing to check, open your Gas cap, try running with it off, if there's a Whooshing noise you have a Vent issue

I wanted to post the latest findings.

I wanted to make sure that I wasn't missing a GP issue...so I tested those per the MB tech manual..and all is good.

I then wanted to try one more time on the primer pump, so I went at it again. I swear I must have pumped that thing at least five or six hundred pumps with nothing.

I was following the MB manual on "burping" the IP so I wouldn't have any air in their....I noticed that in the tube from the IP to the primary filter had lots of bubbles and wouldn't fill beyond half way. I then checked my primary fuel filter by taking it off and saw that it was only half full. I filled it back up and tried again...no luck.

I noticed a sheen from under my vehicle. It struck me today that I've seen the same sheen for a couple of weeks now and didn't know what it was. I'm pretty sure it's fuel that's been leaking from my fuel/lift pump. I then noticed today upon closer inspection that the engine mount right below my lift pump has a small puddle of fuel on it.

So I'm thinking that with my primer pump not working and fuel puddling below my lift pump...that it's gone south on me. I ordered a new one and we'll see what happens.

I'll post my results.

Thanks
Mike

We need a more detailed hypothesis as to where that fuel is leaking from. I'm not real familiar with the lift pump but I'm thinking that the only possible places for the fuel to leak is either from the primer pump or from the fitting where the fuel line attaches to the pump. Is there another place it can leak? It could be that the line from the primary fuel filter to the lift pump is bad and the lift pump is sucking in air rather than fuel. I can't remember another instance on this forum where the lift pump failed and the indication of that failure was a leak. Can anyone else recollect such a case?

Kerry,

I'm probably not describing the part correctly, and I am a newbie at this. The manual primer pump is attached to a small device which has two feed lines on it. This is then bolted onto the side of the IP with three 10mm nuts.

My primer pump is shot, and I was told, or I thought I read some where that this could also mean that the fuel or lift pump was on the way as well, or could be.

I'm thinking that it's leaking, as I've never touched it since I've had it and up until recently, it's worked without incident. Putting all the pieces together, I now know that it must have been leaking for at least a week or two as of the sheen on my driveway which I talked about in the last post.

When I placed my hand underneath the fuel pump, I felt several large drops of fuel that had attached themselves. This location is close to the drivers side engine mount, I assume that it dripped from the fuel pump to the engine mount.

I usually drive this car to work as my DD, but my thought....and it might not hold water...is that with the extra weight of two more people and their luggage in the car, going up my hill by my driveway was too much for a weak pump and it sputtered out on me.

Maybe it's a stretch...I don't know. I'm always open to your thoughts.

Thanks,
Mike

I think the leak is the cause of the problem. The issue is: Where is the leak coming from? I'm not aware of how the pump itself can leak. Does anyone know if it can?

The manual primer pump can leak if it is not locked tight enough. I have to use pliers to lock the primer pump on my car.

:eek:
I'd be scared of breaking the plastic handle with pliers!

He hasn't mentioned a leak while he's pumping so it doesn't seem like it's the primer pump.

Yes it can break. Just be careful. Some 116s have metal handles.

My primer pump has the off white plastic handle. It as well as the fuel pump look original to the vehicle.

I just got my new BOSCH fuel pump with the new style primer pump and when I pushed down on the primer pump handle..it moved some air. I really did need a new one. I'll report back tomorrow on how it works (or not).

Mike

Gents,

I just wanted to post back with my results. I got the old pump off and the new one installed in no time. Really was fairly easy...just took my time so I didn't lose any of the nuts and washers.

Once I got the new one on, it was time to pump and purge the system per the MB tech manual.

I had to crank it awhile...but it finally caught and runs well. I noticed that when I just began to push down on the accelerator there isn't a hesitation now like there was before...that might just be my imagination.

Anyway, I want to thank you all for giving me your expert advice. I hope this post helps someone.

If anyone has any questions in the future..feel free to PM me.

Happy New Year to you all,
Mike

Good news. Can you do any forensic analysis to figure out exactly what the problem was? Where was it leaking?

Kerry,

My gut tells me that if I had just replaced the primer pump I would have been OK. I didn't want to take the chance and be out a DD so I decided to do the fuel pump as well.

My guess would be that the primer pump was the cause of my air leak and then when I couldn't purge the air like I was suppose to, I ran into the above mentioned problem.

I did notice and I can post some pics that the old pump had some wearing (striations) in the metal "ears" that hold the "lobe" that goes around inside the fuel pump. The new one did not have these marks. Otherwise the old pump looked good.

My curiosity is now demanding that I get a new primer pump and place it on the removed old fuel pump and see if that will move the same air as the new pump. If so, I have a "spare".

I never could locate the leak, but again, my thinking is that it was the primer pump seal/gasket went out. I've checked several times now that I've run it at speed for while, and I don't see any more fuel, and when I check the whole pump with my hand, I don't feel any liquid. So here's hoping I got it.

Mike

That would be odd if that is the case. Usually what happens when the primer pump fails is that fuel comes out around the shaft when it is pumped. At least, that is what most people report. Since nothing was happening, it suggest a different problem or an unusual twist on the primer pump problem. Was the lift pump tight against the IP when you began to remove it or was it loose?

Did you screw the white knob (of the old primer pump) in clockwise after priming? If not, air will get in. You did not mention spilling lot's of fuel with the old primer pump, which is normal so the old pump may have been bad, or there was too much air in the system and it was not strong enough to push the air out first.

Kerry,

I did see some fuel around where the primer pump fits into the fuel pump. The pump was tight, and I do believe it was the original.

Funola-Yes the white knob was screwed down tight. I'm know the primer pump was bad, as it didn't move any fuel at all. Once I got the new one on, I removed all the air fairly quickly.

Since I've replaced it, no leaks and she runs well.

As an aside...I had to replace my battery today as all that cranking and it's cold here (teens to high 20) finished it off.

Mike

Here's a relevant post from someone with a lot of experience with the pumps:

http://www.peachparts.com/shopforum/2419328-post19.html

Lift pump failure is rare, but not unheard of.

Failure of the old style primer pumps is common. Usually a bad one will leak fuel when pumping.

The new style primer pump is vastly superior to the old style, especially when the system has run dry or sucked in air for whatever reason.