fischpj

Hi all, I have a 1991 500SL and had to replace the fuel line running from the tank to the fuel pumps. Well, to be honest, life got in the way and the car sat for about 6 months before I could get back to her. Since I was replacing the fuel line I figured as long as I was there I'd replace the entire fuel pump/accumulator and filter assembly with new parts. I replaced the rotten fuel line from the tank (oh, what fun) as well as all of the other components. I reassembled everything and now have about 76 psi of fuel pressure when cranking, but the car will not start. If I use a splash of starting fluid the engine runs for a second or two. During normal cranking, which is strong and not labored, the car seems like it wants to start, I call it stumbling, it seems like a cylinder or two fire. I'll check the distributor caps later today weather permitting, but thinking that since the engine does run on the starting fluid I have good spark. The gas is fresh, since I had to drain the tank to replace the hose.

It seems like the fuel distributor may be "gummed" up after sitting for about six months. Could that be? Any thought or suggestions?

Thanks!

dolucasi

My car sat for 7 months while I was rebuilding the manual transmission/clutch. It would not start afterwards. The fuel in it was quality chevron fuel but still the fuel in the lines had already turned color and gummy. Thank fuel was better because I had put some conditioner in the tank but never started the car afterwards. I did the same treatment you did except when I changed out the fuel pumps and the strainer with new units, I completely flushed out the fuel by using my air compressor from the fuel pump pluming side. I lot is bad fuel came out from the accumulator which was removed.

After this, it took a bit of cranking the get the air out of the system but once it started no issues whatsoever. Car starts like it did before, quarter turn of the engine and it fires right up like it was new at 210K miles. A new battery even made it better because the battery was weak after it sat for 7 months and it did drain all the way down once.

So never overlook a weak battery after the car sitting. The system voltage drops way low when you crank on a weak battery. I have a voltmeter in the car and I see it was dropping below 10V during cranking. That is also a problem because the ignition system probably has a minimum voltage spec. Though your car seems to start with the starter fluid so this is not your culprit particularly.

So I would certainly advocate flushing out the fuel system.

vesiadog

Sounds like you need to go over the basics…
I would check fuel at the engine to make sure it is coming out.. make sure filter is in the proper direction … If it will run with a little gas I would not waste a lot of time looking into electrical but instead go over your work especially looking at the filter direction than check the output… if you are not confident in the quality pump it out with the fuel pump … good luck

fischpj

Dolucasi,

Thank you for your reply! Wow, it was a great idea blowing out the lines! Sadly, I wish I had done that before I put the car back on the ground. Your reply did get me thinking though... When I bled off the pressure from my fuel pressure gauge, via the bleeder valve on the gauge, I noticed lots of air bubbles in the clear plastic bleed line. I really didn't think much of it at the time. I'm guessing that there may be lots of air in the fuel lines, fuel filter and accumulator and the fuel pumps might not be purging the air out of them. I was under the impression that the fuel system would pass unused gas back into the tank, thereby bleeding the air automatically. Maybe my return line is clogged...?

I'm going to try jumpering the fuel pumps to run continuously for a few minutes while I use the pressure relief valve on the gauge to bleed the air and possible foul gas into a container.

Thanks again for your reply!

fischpj

vesiadog,

Thanks for your reply! I'll check the fuel flow as well when I'm purging the lines. If I messed up and put the filter in backwards, I'll be kicking myself for weeks...

vesiadog

Very easy to do in that situation with the small lines/pump etc.

fischpj

Update, I tried pulling the MAS out and it seems determined to stay in place. I turned the unlocking knob to "0" and it still won't budge. I do see/feel the knob assembly rising when I turn the knob. I tried forcing it a few times but gave up and resorted to plan B. Plan B consisted of turning on the key to position 2 and letting the pump prime the system. After it was primed I used the pressure relief valve in the gauge to bleed off the pressure and the gas in the system. After about 20 repetitions of this I got half of a quart sized jar full of brown-ish foul gas that smelled of varnish. I also got a lot of air initially, but seem to have bled that off. When I crank the engine it still stumbles but never catches.

I don't want to force out the MAS, since all of my plastic parts are beginning to fail...

What I took from this morning's experience is that I am indeed pumping "gas" into my FD. The gas that's in the lines is most definitely no longer viable. Has anyone had a stuck MAS issue? It would be ideal to jumper pins 7&8 and let the let the fuel pumps run and flush the fuel lines.

On a completely unrelated note, my right turn signal and the front and back marker lights are on. When I use the turn signal to turn right the lights stay on, as well as using the hazard button. The left lights flash as expected but the right stay on. I'm assuming this is unrelated, but wanted to relay it just in case.

Thoughts anyone?

dolucasi

Why are you trying to pull the MAS out? I would leave it alone.

I should add to my post that after I put my transmission/clutch back on after 7 months just like yours, the car just would not start.
I cranked a lot and one would think that would clear the lines but it did not.

And the only action I took after this was to first drain the tank. It was of yellowish color. Perhaps not the best fuel. And then I removed the pumps because they already had 90K miles on them and would need changing in the next ~20K miles anyway.

When I flushed the lines, I could capture all the fuel in the lines and in the FD even if partially and that fuel was a lot darker color.

After I flushed the fuel, and put fresh fuel in the tank it really was not that difficult to start. Because of the air in the system it struggled a bit and may have stalled once but eventually it started and did not die again.

So I would strongly advocate for flushing the system. At least you will see what that fuel looks like.

Also I assume you already drained the tank and put in new fuel. If you have not done so that is step one.
And when you do that you are already ready to hook up an air compressor or a break fluid hand pump (assuming you have one) and pressurize to 30-40psi and capture the fuel.

- Cheers!

fischpj

Thanks again! Yes, the tank was completely empty because I had to replace the fuel line running from the tank to the pumps. The gas has actually leaked out since the hose failed. I started off with good gas. The only bad gas I'm seeing is in the line to the FD. I just ran down to my Harbor Freight and bought a fluid transfer pump to attach to the input line on the FD in an attempt suck the bad gas from the fuel line. I was trying to pull the MAS so I could jumper the fuel pumps to run continuously. No worries, I should be able to draw most of the bad gas by sucking it from the line.

More news shortly...

fischpj

The suction approach was successful, I managed to draw another half jar of slightly less foul smelling gas out of the car. I was hoping that that was enough, but the car still stumbles and does not catch. There can't be that much fuel in the lines... I'm sure the gas tank as bone dry and that the gas I put in is clean fresh gas. I still get 70+ psi from the pumps and the car still starts for a moment with starting fluid. So, gas, spark and air all good...

Could the injectors have gotten clogged from the bad gas?

dolucasi

I think you have 2 paths.

(1) Remove the cold start valve and make sure it is spraying fuel for 2 seconds during cranking.

(2) Remove one injector and make sure it is spraying as you are cranking.

I would do (1) before the (2) because it is accessible in my M103, Not sure about your large engine.

I would say all injectors being clogged up is a very small probability for only sitting for months not years.

Where are you measuring the 70+ PSI? At the FD system pressure port?

fischpj

Dolucasi, thank you again for your reply! Checking the cold start valve was definitely going to be my next check, tomorrow. If that's working then I'll check the injector as you suggested. I had a Jag that had the same issues and the injector was the culprit, hoping that that's it, as it's an easy fix.

Yes, Im measuring about 76-78 psi at the FD pressure port.

fischpj

Progress...

I measured the voltage at the cold start valve (CSV) and saw 12V with the key in position 2. What I thought odd was that the voltage never dropped. I sat there with the key in position 2 for about 30 seconds, not cranking, and it never went to 0. I would of expected to see 12V during the period when the CSV was supposed to be operating and then drop to 0.

Next I removed the CSV from the manifold and kept the electrical and fuel line connected and placed the entire assembly in a jar. I'd expect to see fuel spray or residue in the jar when cranking, I saw nothing.

Then, I pulled out the CSV and found that there was indeed fuel in the line under pressure and I disconnected the input fuel line... I took the CSV to my work bench and put 12V on it and heard the distinctive clicking I'd expect to hear when energized. My next step was to blow through the CSV to see that fuel flow was not obstructed. It was not. I couldn't blow through the CSV when not energized and could when it was. So, I have a good CSV and fuel, and a bad taste in my mouth.

So... I'm guessing that the seemingly constant 12V to the CSV is an indication of an issue. That being said, if the CSV was energized all the time I'd expect to see lots of spray and there was none.

I'm thinking the 12V I see at the valve is of very low current and not actually energizing the CSV. I also took the opportunity to look around at all of the surrounding wiring and saw no signs to rodent or critter damage. I'm also wondering if the CSV matters to me since I'm in FL and the air temp this morning is low 70s. I would think the car should start, maybe with a bit more cranking.

Thoughts?

dolucasi

It sounds like you have multiple issues. The car would struggle to start without the CSV but everything in perfect condition it should start and keep running, the fact that you can start the car with starter fluid and can not keep it running indicates another issue.

Have you measured the voltages on this connector before crank, during crank and after crank with it unplugged as well? That could be an issue. Also what is the voltage with ignition on.

Also, make sure you have an MB or a KAE OVP and not a URO OVP. If you see a URO label on your OVP unplug it and toss it in the trash can immediately and get yourself an MB one.

I am currently rescuing a '88 5-speed W201-2.6L. It was doing strange things with the ignition off. Also had a 50mA drain. You guessed it. A URO OVP was the culprit. Replaced with a known good MB one and everything is back to normal.

Also whatever the brand look at the date code of your OVP. And let us know what that date is. It is stamped with ink on the side of the OVP.

fischpj

Yes, I had a voltmeter on the connector in an attempt to verify it was getting voltage and shutting down to 0V after a few seconds. Before cranking it was 12.5V (I still had my trickle charger connected), while cranking it was 10.8V and immediately after cranking it was 11.8V. Ignition on was the 12.5V previously mentioned. The over voltage protection relay/circuit is a Mercedes part made in Hungary, p/n 201 540 37 45, and the date code is 89 7236 000, I think that's the date code. No other numbers were present.

On another note, I'm going to need to put this project on hold for now. Sadly, life is getting in the way and I'm not going to be able to "tinker" for about three weeks. Thank you so much for your support. I'll be back ASAP.

fischpj

Hi all,

I'm finally back working on my R129. Sadly, life got in the way...

Before starting with the more exotic stuff I decided to disconnect the fuel line which connects to the cold start valve and see if there's good fuel flow, I know real basic stuff. I connected a rubber fuel line to the fitting which feeds in the cold start valve (CSV) and put the other end in a quart glass jar. I cranked the engine and saw that gas was indeed coming out of the CSV fuel line, roughly equivalent to the flow from a half open faucet. I was expecting a "squirt" of fuel as I was cranking, but I definitely got good flow. I did notice that the gas coming out was brown and smelled of varnish, aka bad gas. I'm amazed at this since there was not a drop of gas in the tank as I had to replace the fuel line from the tank to the pumps, and the fuel pumps, accumulator and filter are all brand new, I also put in five gallons of fresh gas. I did not blow out the fuel lines, since I had no good way of doing that at the time. I got about two to three quarts of bad gas out of the line before I stopped cranking the car. I'm confused why this could be. Is there some sort of auxiliary tank? I'd let the fuel pump run continuously by pulling the fuel pump controller and using a jumper, but I can't get it out of its socket... it seems stuck and I don't want to force it.

Any thoughts on why there's so much bad gas in the lines?

I'm thinking of using a hand pump to pull gas out of the CSV line, will that work without messing up the fuel distributor?

Thanks in advance for any suggestions and guidance.

vesiadog

Unless you replaced the tank … there is fuel in the tank . i would put 5 gallons in it and let the fuel pump .. run it out into a container… use it in a lawnmower …

dolucasi

If you add up all the lines, pumps, filter, FD, etc. it probably adds up to 2-3 quarts. I recall getting a couple of quarts when I blew it out a year ago and mine is a little old 2.6L inline 6.
Not too surprising.

BTW, way back, the numbers you quoted for the OVP was a serial code not a date code. If it is Mercedes, KAE or Siemens it will have a date code. Always know the born on date of your OVP. You will sleep better at night after you get your car running.

fischpj

Thanks, I'll go ahead and remove the 5 gallons I already put in and hope for the best. Is there some kind of additive thatI can put in to allow the bad gas, whatever will be left, to burn?

dolucasi

I think you were better off just using a hand pump or air compressor to blow bad fuel out in the first place but to answer your question I do not know any fluid that can recondition bad fuel but I'm no expert in that.

fischpj

I drained all of the old gas, via siphon through the CSV inlet. I then put five gallons of fresh fuel back in. I did manage to get the car to run for a few seconds using starter fluid longer than I had had it run before. I'm guessing there's still old-ish gas in the fuel distributor or some of the injectors may be partially or fully clogged. I'll look into cleaning the injectors...