Possible bad lift pump SDL - PeachParts Mercedes-Benz Forum

cmac2012 · #1 07-13-2017, 03:02 AM

Drove home just fine Tuesday night - 40 miles - and then Wed AM would not start. It would sputter, sometimes turn over a couple times then die. So I'm guessing I have glow plugs but insufficient/no fuel. Couple of small details, fuel was sorta low when I left for home but I didn't think I'd see the idiot light and I don't recall it coming on. I happened to read this thread where a few people said that they get better performance on a full tank:

http://www.peachparts.com/shopforum/diesel-discussion/168353-300sdl-faster-when-fuel-tank-filled.html

Who knows.

In post #3 was the opinion that removing the fuel cap to relieve any vacuum can help make life easier on the lift pump. Coincidentally, I put in two gallons of dino diesel just in case I spaced the idiot light. And when I pulled the cap, there was, in fact, a strong inhale. Seems like there would be something in place to cope with that.

My question here, my E30's have a procedure to jump the fuel pump relay so you can check the pumps for sound. But the lift pump is mechanical I'm guessing. I need to finally get that service manual CD. I'm too green with this engine. Don't know what I'm looking at half the time. And I'm not finding a really good troubleshooting guide.

I recently received the viton fuel O-ring kit from Squiggle Dog but have yet to install anything. Still waiting for the 36 point socket to arrive. Going to install all new fuel filters as well.

oldsinner111 · #2 07-13-2017, 04:20 AM

i had vac in my w126 i would losing the cap. i used bio and it cleared up.

cmac2012 · #3 07-13-2017, 06:03 AM

Biodiesel? I'm using HPR now, which is similar of course.

Another thing I forget to mention, I'm thinking I shouldn't run it down so close to empty. My E30s have an intank pump that need, or want anyway at least a quarter of a tank to be happy. Don't know if that's an issue here. No intank pump anyway.

barry12345 · #4 07-13-2017, 10:23 AM

I am not sure by your description. Sounds like you may have a blocked vent line from the fuel tank. The strong whoosh when you removed the fuel cap to me makes it a possibility.

cmac2012 · #5 07-13-2017, 12:11 PM

^ Good advice, I'll look into it. The more I look at this and think about it, I need to check the injection pump relay. There must be some info somewhere about jumping it.

Maxbumpo · #6 07-13-2017, 12:56 PM

The problem you need to fix first is the clogged fuel tank vent valve. Don't make this more complicated than it is. Usually you can simply clean out the mud / spider nest or whatever and restore function.

The only test I would recommend is to try starting the car with the fuel tank cap off. Any attempt to test / diagnose the IP or the lift pump is futile in the best case and may become very expensive in the worst case.

dieselbenz1 · #7 07-13-2017, 12:58 PM

No fuel pump relay its a mechanical lift pump immediately down line of your primary fuel filter. Is your primary fuel filter full of fuel?

cmac2012 · #8 07-13-2017, 02:03 PM

Yes, I quickly realized that error of thinking - what else could it be but a mechanical pump with that shape. I don't know if the main injection pump has a fuel pump relay as they are commonly known. After all, this is not some tiny pump about as big as a tomato paste can such I used to change out in my Bimmers. That is the sweet fantasy- happened twice with my E30s: pop in a new relay and good to go.

I'll get two new filters, I should have done this weeks ago, oh well, it ran great, but I'll do it now. And I'll fill the new filter before putting it on. But your suggestion to look is a good one and I will definitely investigate when I pull the old one off.

I really doubt that I ran the tank dry. I'm in the habit of glancing at the temp, oil pressure, and tach readings every few minutes or more, I'd have noticed the idiot light for fuel. Plus, when I left for home Tuesday night, the needle was between the imaginary 1/8 and 1/4 tank levels. In addition, it ran fine until I got home and then wouldn't start the next morning. The chances of hitting exact empty at my door are slim. And finally, I put two gallons of dino in from a fuel can on Wednesday morning, it took the gauge back into well visible range, about where it had been Tuesday night, I doubt two gallons would show that visibly on a completely empty tank.

I like this car but many times when I've looked at the engine I have to admit to myself that I know damn little about it. Jeez I miss my E30 Bentley manual. I got the Haynes 124 manual thinking I'd at least have some OM603 info - it's pretty lean, less impressive than even the average Haynes manual. Haven't seen the Benz Bentley manual.
I need to get the 300SDL factory manual, I forget where to order it from.

Squiggle Dog · #9 07-13-2017, 02:16 PM

If you get a whoosh sound when you remove the fuel cap, you definitely have a clogged fuel tank vent which will cause power issues. Usually it's at the flared plastic fitting under the car. You'll want to snake something like a wire or pipe cleaner up there and get it unclogged. You can also used compressed air, but there is a risk of whatever is clogging the line to go inside the tank.

Also, if you replace the O-rings in the lift pump it should restore the performance and that will rule out another possible problem.

Diseasel300 · #10 07-13-2017, 03:07 PM

Was the Whoosh you got from the fuel tank positive or negative pressure? IE are you 100% sure it sucked air IN? It's not uncommon for them to blow air OUT. There is a vent with a bell shaped valve under the car near the differential that controls pressure in the tank. It will maintain ~1PSI of positive pressure in the tank, but should maintain 0 vacuum. If you have a vacuum in the tank, you likely have a blocked vent line or a failed valve.

There are no electronics or electric components in the fuel delivery system of the OM603 engine. It is 100% purely mechanical. If you bled the system dry, push the pedal to the floor (and hold it there) and crank in 15-20 second bursts with 2-3 minute rests. After 2-3 crank bursts, it should fire up and run. It'll do this on a completely dry fuel system too (empty filters, empty rack, empty lines).

If you did in fact pull a vacuum on the tank, your lift pump is in healthy condition, otherwise it would have stalled out long before pulling a vacuum. They're far more reliable and long lasting than people make them out to be.

cmac2012 · #11 07-14-2017, 02:51 AM

Quote:

Originally Posted by Squiggle Dog

If you get a whoosh sound when you remove the fuel cap, you definitely have a clogged fuel tank vent which will cause power issues. Usually it's at the flared plastic fitting under the car. You'll want to snake something like a wire or pipe cleaner up there and get it unclogged. You can also used compressed air, but there is a risk of whatever is clogging the line to go inside the tank.

Also, if you replace the O-rings in the lift pump it should restore the performance and that will rule out another possible problem.

I'll look for that fitting.

I just picked up my O-ring kit at my mail-box, thanks for that. I have a box at a UPS store, pretty handy, all of the mail order buys I make are waiting safely for me when I make it down there, had probably been sitting for several days.

I'll put most of those in in the next few days.

cmac2012 · #12 07-14-2017, 03:30 AM

Quote:

Originally Posted by Diseasel300

Was the Whoosh you got from the fuel tank positive or negative pressure? IE are you 100% sure it sucked air IN? It's not uncommon for them to blow air OUT. There is a vent with a bell shaped valve under the car near the differential that controls pressure in the tank. It will maintain ~1PSI of positive pressure in the tank, but should maintain 0 vacuum. If you have a vacuum in the tank, you likely have a blocked vent line or a failed valve.

There are no electronics or electric components in the fuel delivery system of the OM603 engine. It is 100% purely mechanical. If you bled the system dry, push the pedal to the floor (and hold it there) and crank in 15-20 second bursts with 2-3 minute rests. After 2-3 crank bursts, it should fire up and run. It'll do this on a completely dry fuel system too (empty filters, empty rack, empty lines).

If you did in fact pull a vacuum on the tank, your lift pump is in healthy condition, otherwise it would have stalled out long before pulling a vacuum. They're far more reliable and long lasting than people make them out to be.

I'm pretty sure it was negative pressure. It's a good question, I had to play it back in my head. Pretty sure I recall that I had to pull gently to get it off, then heard the whoosh. There was no pushing outward sensation, pretty sure.

Re the no electronics, I'll be damned. Like I said, I really don't know that much about it yet, THAT was something you'd think I would have known. So does the lift pump do it all? Create residual pressure in the injection pump I mean? Looking at it I can imagine that the injection pump has its own power take-off somewhere in there.

This is actually very good news for me. My last 14 or so years have seen two BMW E30s as daily drivers. I took the first one from 214K to 440K (still running), the second only got about 50K on it before I was rearended hard. Anyway, nice cars but one PITA is two electric fuel pumps, one in the tank and on inline, one the underside in front of the left rear wheel. Both of them spendy in OEM (around $300 ea) and when the intank pump goes, not long before the inline will and it starts to whine loudly for a while. Twice I was stranded with dead inline pumps, the second time years after the first. I was prepared and swapped in a spare on the side of the highway up in Oregon. Not the most pleasant job with gas everywhere. I found aftermarket units that will work well enough, but the dreaded pump whine is always around the corner.

Diseasel300 · #13 07-14-2017, 10:16 AM

Quote:

Originally Posted by cmac2012

I'm pretty sure it was negative pressure. It's a good question, I had to play it back in my head. Pretty sure I recall that I had to pull gently to get it off, then heard the whoosh. There was no pushing outward sensation, pretty sure.

Re the no electronics, I'll be damned. Like I said, I really don't know that much about it yet, THAT was something you'd think I would have known. So does the lift pump do it all? Create residual pressure in the injection pump I mean? Looking at it I can imagine that the injection pump has its own power take-off somewhere in there.

I ask about the pressure issue because it can be hard to tell. The 1/2-1PSI of positive pressure that can build in the tank can be alarming, but it's normal. Negative pressure is not normal.

The lift pump is the sole fuel circulator in the fuel supply system. It draws fuel from the tank, fills the fuel filter, fills the fuel rack, and maintains pressure in the system against the overflow valve on the back of the IP. Fuel delivery to the injectors is drawn from the fuel rack and pumped by the high pressure elements in the IP. The only electronic gizmos involved in fuel delivery are the overboost switch (which cuts off boost pressure to the ALDA if boost goes too high) and the EDS solenoid which maintains idle speed. The car can and will run with both of those systems bypassed.

Father Of Giants · #14 07-14-2017, 10:47 AM

Quote:

Originally Posted by Diseasel300

I ask about the pressure issue because it can be hard to tell. The 1/2-1PSI of positive pressure that can build in the tank can be alarming, but it's normal. Negative pressure is not normal.

The lift pump is the sole fuel circulator in the fuel supply system. It draws fuel from the tank, fills the fuel filter, fills the fuel rack, and maintains pressure in the system against the overflow valve on the back of the IP. Fuel delivery to the injectors is drawn from the fuel rack and pumped by the high pressure elements in the IP. The only electronic gizmos involved in fuel delivery are the overboost switch (which cuts off boost pressure to the ALDA if boost goes too high) and the EDS solenoid which maintains idle speed. The car can and will run with both of those systems bypassed.

So the lift pump is literally a fuel pump? Is there a fuel pump in the tank of the 300SDL?

Diseasel300 · #15 07-14-2017, 10:49 AM

The lift pump is the ONLY pump in the system. There is no other fuel pump anywhere in the car, the lift pump is it! Very much like an old carbureted car.