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