Fuel injection help required

[cfm65@me.com]

Hi Guys,
My 250SL has been starting and running fine for a while. It has been standing for six months due to an extended visit abroad.
At the end of a recent 80 mile round trip it started cutting out and stopping. On further observation, it starts and runs fine for a while. After 5 to 10 minutes(I think it is temperature related)it stops and dies as if it has run out of fuel. It will also battle to start. After a few minutes of cooling, it will start up normally and after running beautifully for a while, it would stutter and stop again for no reason.
History,
Fuel injection pump restored by a local Bosch centre and specialists. New injectors, fuel pump, fuel pump filter and engine fuel filter. New Blue Bosch coil and 123 Dizzy. Car ran beautifully, started easily. Reasonable hot starts and but heavy on gas.
After the six months abroad the problem started.
Any suggestions will be much appreciated.
Regards
Chris

[MikeSimon]

Chris:

I will be very interested in the feedback to your question. I have exactly the same problem on my 280SL and that's why it was parked 20 years ago. Never got a definitive answer. Most guesses pointed to the electric fuel pump in the rear and restrictions of some kind due to debris/contamination.

[Iconic]

Mike, Do you still have the problem?
Chris, I had a problem that sounds the same. Fuel is dangerous and you should let someone else do this if you are not comfortable with it. My suggestion is to disconnect the RETURN fuel line at the fuel tank. The one that feeds back into the tank.
Measure the flow out of the fuel line. It should be a liter in 15 seconds. If dramatically less than that, you have found your problem.
You then need to work your way backward on the fuel line to find and remove the restriction. I replaced the metal line running back to the tank. There is quite a bit written about this. I'll look for links in a few minutes.

[Iconic]

Here's a couple of old threads:
https://www.sl113.org/forums/index.php?topic=10721.msg71193#msg71193

https://www.sl113.org/forums/index.php?topic=10887.msg72577#msg72577

It was fun reading part of the thread where I got to drive my car in 2009 for the first time without it dying on me.
Good luck !!

[MikeSimon]

I am currently working on getting the car back to run. Due to the long sitting period, I took the head off to look inside the motor and have to address several issues I found with the head. Other things I will do is replace the tank, e-fuel pump and the fuel lines. I got temporarily stuck because other projects interfered.
Hopefully by this summer, I can run the car and see how it is doing.

[ja17]

Yes, sounds like the classic "fuel delivery" problem. The fuel tank and its internal screen should be checked. Check the inside of the tank for debris and varnish. Check the intake screen on the intake of the electric fuel pump. Check the main fuel filter. Check the fuel pressure and volume. Check to make sure the fuel return line to the tank is clear.

[Shvegel]

Another thing to consider is you might have a winter blend of fuel in your tank.  These blends usually contain more Alcohol and aromatics and are less stable at high temperatures.

[cfm65@me.com]

Thank you Gents,
You inputs are much appreciated.
Please keep them coming and I will report back ASAP.
Regards
Chris
Cape Town
Ps. Shvegal, we don’t have winter here in the southern tip of Africa. Cold winter temps, at worst, will go down to about -10*C during the early morning and during the day warm up to +10*C or so. Very little snow on the highest mountains, if we are lucky.
However, your advice is still much appreciated,thanks. Chris

[MikeSimon]

One question I have with the suggested procedure to check the fuel flow. If you check the flow at the end of the supply line to the injection pump or right at the fuel filter, why is it important to disconnect the return line?

[cfm65@me.com]

Mike,
As I understand,  a return flow of around one litre/15 seconds, proves that the entire system operating pressure and fuel flow, is within designed limits. The problem is elsewhere.
Regards
Chris

[Pawel66]

Mike, if you check it at the end of the return line - you check the entire system for the flow. If the flow is weak, below, say, 0.6l per 15 seconds, you have to look for clogged place systematically. I, after flow at the end of return was pathetic, checked the flow on the hose from the fuel tank - that was ok, then I checked flow after the additional fuel filter on that hose - this one was bad. Additional fuel filter was clogged.

I think the pressure is related, but not necessarily the same tests will prove it is there.

[Iconic]

One question I have with the suggested procedure to check the fuel flow. If you check the flow at the end of the supply line to the injection pump or right at the fuel filter, why is it important to disconnect the return line?

Mike,
Well, if you measure flow somewhere else, and it is in spec, then you might wrongly conclude you have proper flow if you have a clog in the return line.
This whole idea is based on the idea that a larger amount of fuel must circulate to cool the Fuel Injection Pump (FIP). In fact, the engine only uses a very small fraction of that flow.
You check it at the return to tank, and if withing spec, then you know it is within spec for the entire circuit. If it is not too spec, then you found why your car dies unexpectedly (due to heat up and "vapor lock" (maybe) in the FIP.

[MikeSimon]

OK, I did not know that your are supposed to measure at the end of the return line. I thought you measure at the end of the supply line to the injection pump.
Do you do this with the engine running or off?

[Pawel66]

Just fuel pump running. Bob says you need to let it warm up for a few minutes. Good battery, certainly, required.

[BaronYoungman]

That is correct to check the fuel pump you're going to have to let it run for a couple minutes I have seen many pumps that originally start out running well but there is a short inside of the Armature and as the fuel pump heats up which it naturally does to an operating temperature it causes the Armature to short out and the fuel delivery to slow down. At a minimum you should run it for 3 minutes before checking the flow, but more the better. When I test have 4 cycles of 5 minutes , 10 minutes , 20 minutes and one hour at the end of each I  check flow rate.  I also may suggest that you have a clogged tank line had your fuel tank ever been recondition/ recoated? Sometimes because out tanks are set up diffently from most fuel tanks they are not coated right and clog or semi clog the line to which the flower pot will fill up from it sitting or from the fuel tank being very full and sloshing over into the flower pot but as you're running it drains down and does not fill back up due to impeded flow eventually causing fuel starvation.
Just my 2 cents Bob "Baron"  Youngman

[ja17]

You should also do the pressure check once again while the problem is occurring for more information.

[cfm65@me.com]

Hi Guys, report back.
To recap, the engine ran fine for about three months, before we went abroad for six months.
Checked return fuel flow at the tank, 15 seconds= less than half litre.
Gave it another 15 seconds. Total 30 seconds = less that a litre.
Checked delivery fuel supply just before front fuel filter. Slightly better but still less than a litre in 30 seconds.
Checked fuel supply at fuel pump = about a litre after 30 seconds( very similar) to the checks above.
Checked fuel pump and rear filter. They are still brand new as I fitted them a year ago and both clean inside, no gunk.
Drained the tank and found fuel also clean.
Checked battery voltage as well as voltage supply at the pump, both good at 12 volts.
The new pump is not an original Pagoda pump but a replacement Bosch, recommended by one of the usual SL parts vendors.
With the lockdown, I will not be able to have the pump checked by Bosch agents, for some time.
Stay safe guys.
Regards
Chris

[MikeSimon]

Bob: thanks for the remarks about the "armature". when I first had the problem, someone suggested that the e-pump was shutting down because of temperature. Several people then opposed that statement and said there was no such thing and the pump had no temperature related shut-off. The whole issue with my car definitely pointed to a temperature related problem as once the car stopped running, the running intervals would get shorter and the 'stop" intervals would get longer, like there was a "cool-off" time needed. My tank is not coated and the only problem the tank could have is rust and contamination inside. 

[Pawel66]

Checked fuel supply at fuel pump = about a litre after 30 seconds( very similar) to the checks above.
Checked fuel pump and rear filter. They are still brand new as I fitted them a year ago and both clean inside, no gunk.

If by the "rear filter" you mean the screen inside the fuel tank and it was clean - probably it may be the fuel pump.
Unless you had very little fuel in the tank. In such case the small window at the tank floor under return line at the flower pot wall might have been clogged. This is the fuel passage at low fuel level.

https://www.sl113.org/wiki/Fuel/Tank

[cfm65@me.com]

Hi Pawel,
Thanks for your reply, much appreciated.
No, the in-tank screen filter was checked and found clean, a few months ago.
I am talking about the rear filter, the one between the tank and the pump. Both the filter and pump are new units, fitted a while ago and both checked clean. The tank is above half full and the fuel vent system is working fine.
I also think it is a faulty or incorrect replacement fuel pump.
Regards
Chris

[Pawel66]

I see. So you also have an additional filter - they say it is a good idea, I have that too.

Good luck!

[cfm65@me.com]

Thanks,
Take care.
Chris