Need help with fuel delivery

[rgafitanu@gmail.com]

First to moderators, please do not kick this post to W11x subforum. Yes, I do have a W111 but it has a 230 engine from an SL and I need the expertise of the SL people. That's why I subscribe as a full member to the Pagoda forum without owning an SL.
My problems started maybe a couple of months ago after driving over 30 minutes and usually at high rpm. The engine would lose power and if coasting or coming to a stop it would stall. It would start immediately but the power loss and stall would persist. After cooling everything would go back to normal, for another 30 minutes.
I spent hours reading the forums posts. I verified the "flower pot" return issue by filling the tank and eliminated it. I found the distributor points to have, one a crater and the other one a deposit and replaced them, changed through red and blue distributors until I reverted to the original combination and 39 degrees dwell angle. The problem is still there.
I moved to fuel, I checked fuel delivery at the CSV and on the return line at the tank and found to be about 40 sec/ltr. I pulled a spark plug and it was charred light brown so fuel starvation? I quickly concluded that the fuel filter was clogged. It was indeed brown from rust deposits and I changed it.
The problem didn't go away, 40 seconds at the CSV. I concluded that the pump is letting go of the ghost so I bought a generic 140 GPH 14 PSI pump.
Replaced the pump, still 40 seconds at the CSV.
Bought another fuel pressure gauge, 15 seconds at the pump, 40 at the CSV. I disconnected the fuel line before the filter pot and got maybe 30 seconds. I blew compressed air in the line from fuel pump to filter pump forwards and backwards, I wasn't happy so I checked the integrity of the fuel line under the car. I found a serious strangulation probably from a smart technician that placed the lift pad under the fuel lines. I cut off the flattened part and replaced with rubber hose, progress. 15 seconds at the fuel line before the filter, still 40 seconds at the CSV. Frustrated I realize that the original pump may be OK, I put it back and put a new fuel filter.
At the CSV 10 PSI, 15 PSI with the return line clamped but 40 sec/ltr consistently. At least I know that the pump and the overflow valve after the IP are OK.
Logic tells me that the filter + filter pot + the tee + CSV fuel line could be the culprit.
I could remove the filter from the circuit and try it again but the filter is supposed to be there even if I would put another inline filter somewhere. The original filter is designed for flow and pressure to be there before the IP.
From reading all these posts, I am concerned that vapor lock due to insufficient flow is the cause for power loss and stall.
I can insert a tee at the CSV and plumb the fuel pressure gauge inside the car to read the pressure when the power loss occurs although I'm not sure if vapor lock in the IP would show as a pressure drop upstream of the IP in the CSV.
Anybody has any ideas?
Thank you.

[Naj ✝︎]

Going by my experience with my first 230 SL, I eventually found that the return line to the flower pot inside the tank was completely clogged up with rust particles from an internally rusted return line.
In your case, it would seem that it may be partially clogged.
You could try to run a wire thru the return inlet to see how far it goes.

hope this helps

naj

[ja17]

Also, there is a check valve/regulator built in the return fitting of the IP make sure it is working correctly. I like to have a fuel pressure gauge installed when the problem occurs. If the pressure drops off just before the problem is happening you have a clue.

[Tyler S]

First of all you will never get 1-L in 15 sec at the CSV with the Injection pump still in the circuit. Most of your fuel is going through the Injection pump and back to the tank. The CSV line is also a smaller diameter so it is a restriction. So I think you are OK there. .... If you can plumb your pressure gauge into the return line just AFTER the injection pump, you should see almost no reading. If you see anything say over 1 or 2 PSI, You have a restricted return line somewhere as Naj pointed out. This can indeed cause a vapor lock issue. Is it possible there is another crimped (return) line near the one you repaired? Start there and report back.
Tyler

[Benz Dr.]

I usually check after the fuel damper and look for 1 liter in 15 seconds at that point. If I have good volume there then I try to blow some compressed air through the return line going back to the tank. Use a rag around your air wand or you could end up with a face full of gas if the line is plugged.
Remove the fuel cap from the tank so any pressure is released - another way to get fueled. If you can hear air bubbling up through the fuel in  the tank that's a fairly good sign that the return lines are open. You should have very little blow back at your air wand or the return line could be partly blocked. Remove the short fuel hose at the tank and try blowing back to the front of the car. It should be easy to blow through.
You can try to blow into the tank but the same safety rules apply.
 If the return line inside of the fuel tank is plugged you might be able to clear it out using a battery operated hand drill and a bass guitar string kind of like a roto rooter. Flatten the end of the bass guitar string so it will bite in better and feed it into the pipe slowly or it may jam on you. ( excuse the pun )

 I use a low E string so that it has some weight to it. Of course, you would want to empty the fuel tank first. The string should be able to follow the contours of the return line. Or, you can get the tank boiled out. I have no faith in the various coatings out there. Some of them can come off and present you with a bigger mess than you started with.   




 

[rgafitanu@gmail.com]

Thank you all for the help.
There is something that I forgot to mention. When I was chasing the flower pot and the possibility of it being starved of fuel I removed the fuel sender and I inserted a snake camera in the flower pot (not being aligned with the sender hole). I had maybe 2 gal of gas, 1" level and I switched the pump on but I couldn't see fuel starving or a jet flow from the return. I set the tablet to record and I drove the car for 10 minutes. I didn't get any power loss symptoms but I didn't want to force it by risking driving at 4000 rpm with an open tank and snake camera sticking out of it. I got back and reviewed the clip and I could not see any level change that would be suspect one way or another. Just the usual sloshing from braking/accelerating. I don't know if should have seen anything.
Joe, I believe that the check valve in the IP output fitting is working right. I had it out and I could move it with my finger, it also allows some flow all the time to eliminate bubbles (I could blow air in the opposite direction, very small though). Also the pressure with unrestricted return was 10 PSI and with return clamped was 15 PSI which means that the check valve opens at 10 PSI.
Tyler, you are right, I was suspecting the smaller CSV line and the tee to create some obstruction. I misinterpreted the BBB with their CSV picture. The spec clearly indicate to measure output right after the IP check valve. I will do that this weekend. Great idea to measure the pressure there to "flush" out an obstructed return line.
Benz Dr., I intend to swap the fuel tank this weekend. I have a donor W108 that a member sold to me for the 3.69 rear axle (my best move so far) and as a bonus it had a good tank (same for my W111). My tank has a leak somewhere and I can fill only about 16 gal. I had the donor tank filled with 21 gal of vinegar for a week for cleaning, I will blow some air to make sure the return line is OK and mount it.
I will post results.

Radu

[Benz Dr.]

I had a 111 coupe for a while and it would drive great as long as I stayed at highway speeds. If I slowed down while driving through town it would stall and not restart. After a half hour of cooling down it would restart no problem and drive as usual until I slowed down again. It was the fuel pump and once I changed it the problem went away. My conclusion was that the pump stayed cool while driving at speed but once I slowed down there wasn't enough air flowing under the car to keep it cooled off. There is also the problem with extra heat in the engine bay while driving at slower speeds in city traffic and there's a greater possibility that vapor lock can start to factor in. So, while the problem was the fuel pump, ( tall style ) the lessened fuel volume from a hot pump along with heat in the engine bay conspired to kill my fuel flow. Fuel volume is your friend on these old cars. The more you stay within the optimum running parameters the more that fuel will cool  your entire delivery system.

     

[rgafitanu@gmail.com]

So this weekend I started by checking the fuel flow after the IP. It wasn't good. I took out the fitting with the check valve and it got better to 30 sec/ltr. Then I remembered that the BBB indicates to have more than half a tank when checking the output. I had only 5 gal so I concluded everything is OK. I drained and removed the tank, blew air in the intake and return of the replacement tank and mounted it. I put 5 gal start the car, after 10 minutes it stalls. I take the filter out and replace it, start the car, it stalls after 10 minutes. I take it out for a drive, within 1/2 mile it stalls again, this time at a stop sign uphill, I barely get it started to get back. This smells like a starving flower pot.
Next day I add 5 gal, so now there are almost 10 gal hoping that it would be above the flower pot wall. I check the pressure at the CSV with power to the pump and I get only 8 PSI. I start the car, it stalls after 10 minutes. I start it again and I read the pressure at the CSV, 6 PSI and dropping. At 4 PSI it stalls (no surprise there).
I am thinking to replace the pump with the generic pump to eliminate the pump as a cause. Logic points to the replacement tank since this is the component that was replaced before the stalling. I just hate siphoning 10 gal. I think I will put the endoscope camera again in the flower pot to see what is going on before taking down the tank.
Frustrating, I blew air through the entire return line with no obstruction, I blew air in the tank through both lines (Almost blew up the tank, forgot to take the cap off). One theory is that the intake in the tank is getting clogged since I get only 8 PSI??? Maybe they reversed the intake and return lines on the W108? The intake is at the bottom and return on top on mine and in BBB.

Radu

[rgafitanu@gmail.com]

I am loosing it. I went home for lunch and I took the fuel sender out to check the flower pot. It was completely immersed in fuel. I started the car but I couldn't see anything. And the car didn't stall anymore, it ran for about 30 minutes until I had to leave.
I will continue to run it to see if the problem is still there. Now I am suspecting the pump. If it does it again I will remove it and clean the intake screen. That's the only thing that I didn't clean/replace/blow.

[Benz Dr.]

I find the most frustrating time is just before you figure out what was wrong. Kind of like finding something in the last place you looked - of course you quit looking; you found it.

[Tyler S]

So the car ran well with the fuel sending unit removed? That points to a blocked vent line for the tank. Pressure or vacuum can build up in the tank and cause fueling issues. When the thing stalls out, remove your gas cap and make sure you dont get a big hiss of air flow. If you do, blocked vent line somewhere.

[rgafitanu@gmail.com]

Tyler, you bring an interesting point: vent line. When I got home in the evening I started it again and it was running for about 30 minutes so I tightened the fuel sender to take it out for a spin. Of course in 10 minutes it started to loose power. I brought it back, hooked the gauge to CSV and of course 6 PSI and dropping until stall. I started drinking.
I don't remember when I measured previously 6 PSI if I had the cap on or if it stalled before with the cap off to rule out a vent line. I prefer it to be a vent line. I will check the pressure again with the cap off to see if it goes back up to 10 PSI. If not I will replace the fuel pump with the ebay pump.

[Tyler S]

If your vent line is not the issue, One last thing to rule out before you condemn the pump is to make sure you have battery voltage at the pump when its acting up. A connector somewhere or fuse with high resistance will drop the voltage to the pump.

[rgafitanu@gmail.com]

I switched the pump with the cap off and got the same 6 PSI, so it was not the vent line. I put the ebay pump and got 9 PSI and if I clamp the return I get an increase over 11 PSI. The pump must have a relief valve that kicks in. But I went out without any problems. Today I will try longer trips. I will also plumb the pressure gauge inside so I could monitor it.
This would be the third time I am rebuilding this pump, something is leaking or the propeller has to much room, the first time I had a thicker o-ring at the bottom plate and it wouldn't make any pressure. I also get several drops of gas through the pump vent, I remember the bellows bushing was quite compressed so I have to stretch it. Or the brushes, it looses pressure over time.

[Tyler S]

Is this the long style pump? BenzDr mentioned in another post that the long style pumps are very tricky to rebuild and there is not a very good success rate with them maintaining good pressure after rebuilding. You may want to just leave your aftermarket pump on and call it "fixed" for a while. Then come back to it later with a newer short style pump. They are a bit easier to find and easier to rebuild.

[rgafitanu@gmail.com]

Yes, it is the tall pump and when I was rebuilding it there were 2 problems. The locating/driving washer had a crack in it which eventually split the washer. I was hoping that it would be held together inside the bellows bottom face recess by the c-clip. Also the bellows seal was quite compressed and although it wasn't leaking I am not sure I stretched it enough. I will see when I will open it if it can be salvaged, I can laser cut a locating washer at a local shop.
For the time being I am leaving the ebay pump in there and I am plumbing the pressure gauge from the CSV to inside.
What sucks is that I lost the auction of a tall pump a few days ago on ebay Germany. It sold for $130 but I got confused in the German translation. I am thinking to get a more powerful pump, there are some inline pumps with 75PSI. The overflow valve would open at 10 PSI but at least the volume would be solid for high rpm needs and to prevent vapor lock.

[Tyler S]

Dont use that 75 psi pump. Those are designed for returnless GDI (gasoline direct injection) systems. You will end up with fuel in your crankcase from the pump overcoming your oil pressure. The relief valve can only handle so much. There are others on here that have used different pumps. Maybe they can chime in or try the search for aftermarket pump to see what has worked for others.

[mbzse]

Dont use that 75 psi pump.../..

In addition, you will ruin your injection (FI) pump. Higher fuel pressure than what the original factory electric feed pump gives destroys the oil film inside the FI pump, severe wear will occur with time.
/Hans in Sweden
.

[Benz Dr.]

What you need is a high volume low pressure pump. Roughly 4 liters in one minute ( 1 US gallon ) at 10 PSI is actually quite a bit of volume at low pressure. This is how this system was designed and it's what you would want to stay with. I'm fairly sure that you would end up blowing every fuel hose in the system unless you changed to high pressure fuel injection hoses so it doesn't seem like the answer to me.

 You need about 10 PSI to make they system work but some pumps will put out 15 PSI. I haven't seen this myself but I'm told they exist........... 

[rgafitanu@gmail.com]

Thank you all for the advice. I will stay in specs. I tubed yesterday the pressure gauge inside and I took it for ride at night on sleet, 75 mph on the highway. The pressure stayed solid at 8 PSI. I was hoping for closer to 10 PSI but maybe the extra tees and length of tube or the cheap Advance Auto gauge contributed for the 1 PSI drop from the measurement at CSV.
I took the tall pump apart. The locating washer was in its place but the intake screen looks dark brown and the check valve is not holding (see pictures). I will ultrasound the screen and the valve and see what I get. While I'm at it I will measure the locating washer and have a few laser cut.

[ja17]

Yes, you need more fuel pressure. A lot of cars hold around 14-15 at higher rpms. When it drops below 9 psi, all sorts of strange problems occur.

[rgafitanu@gmail.com]

Here it is the screen after an ultrasound bath. The check valve fitting works well too, so I will put back the pump and see the pressure. I am thinking that if the pressure is 9 or 8 PSI but it gets to 13 or more with the return clamped then the cause is the overflow valve in the IP outlet fitting, right?

[Tyler S]

That screen looks much better. Could have been part of the issue. Along with the check valve not fully opening...
Yes pressure should increase with the return line clamped off. The releif valve has a metal spring inside that could have become weak causing a lower pressure BUT it would be a consistant reading. Not the pressure drop you were getting when the car would stall.
Also when you clamp the return line the pressure should go up immediately. If it takes a while to creep up, thats a sign of a worn pump.

[rgafitanu@gmail.com]

I got the tall pump back in showing a solid 10 PSI at the pump outlet and before the filter. Delivery is 15 min/ltr right at the pump and about 20 after the IP. I was hoping the pump would push more right at its outlet but there is some leakage (not to outside), I'm not sure why the technical manual says to install the impeller in the same orientation, it looks symmetrical to me and I forgot how it was mounted anyway. The car runs very good and the inside pressure gauge shows a solid 9.5 to 10.5 PSI. It actually varies with electrical loads I can see it dropping 0.5 PSI with he turn signal.
Anyway the car starts cold and hot very well, I was suspecting the injector lines check valves to leak. I guess I have to readjust the idle vacuum and the air/fuel ratio, I messed with them trying to sort this out. I should probably retard the timing a few degrees especially after I changed to a 3.27 rear diff, I can hear some knocking under load sometimes.
I guess my lesson is fuel pressure and volume is crucial so I am going to leave the pressure gauge piped in.

[Tyler S]

Yes the impeller vanes have a slight arch on them. A bit of a quadrilateral shape to prevent cavitation when the vane rotates over the inlet port. You can usually see which way to install it back in the pump by looking at the wear marks as compared to the housing.
Make sure your battery is healthy and your charging system is putting out. A half psi drop with one turn signal seems a bit much.