Author Topic: 280SL 1968 won't start.  (Read 503 times)

Thierry du Laos

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280SL 1968 won't start.
« on: January 07, 2019, 06:34:06 »
Hi, my car had problems to start 4 months ago, and when she started, she ran on 4 cylinders. I had to go abroad 2 months, but when i came back she won't start anymore.
Ignition is correct, but when I open an injector line and crank, there is no fuel coming.
When I disconect the fuel line at inlet of the fuel injection pump the fuel comes out.
When I disconnect at the outlet of the injection pump, there is fuel also.
So I wonder what happens in the injection pump?
At the back of the injection pump there is two big solenoids. I believe there is one to open the fuel at start, but what is the second one for?
When I put 12 Volts at the upper one, I can hear it is moving!
Any suggestion?
How do these two solenoids work?
Thanks.

mrfatboy

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Re: 280SL 1968 won't start.
« Reply #1 on: January 07, 2019, 11:31:12 »
It sounds like some of your injection pump plungers are stuck.  I will let the pros chime in here to tell you how to test and fix since I have not done it before. You can also search on how to do the procedure on this forum.

The upper solenoid is the fuel enrichment solenoid. It always activates when the key is turned when starting. 

The lower solenoid is the fuel cut off solenoid that I believe activates when in 3rd or 4th gear AND when the throttle is not depressed. There is a microswitch on the left side firewall connected to the throttle linkage that detects no throttle.



1969 280sl (Aug 1968 build)
Signal Red
4 Speed

ja17

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Re: 280SL 1968 won't start.
« Reply #2 on: January 07, 2019, 17:55:42 »
Hello Thierry,

If you have spark on time, fuel supply with adequate pressure and volume, and compression, your engine will star. A fresh set of spark plugs is a good and inexpensive place to begin, check fuel pressure and volume also.  You can check to make sure your injection pump is free by moving the rack back and forth, it should move freely. Yes the lower solenoid is a fuel shut-off emission device. If it is activated when the engine is off, the engine will not start. You can temporarily dis-connect it with no consequence.
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

Thierry du Laos

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Re: 280SL 1968 won't start.
« Reply #3 on: January 10, 2019, 04:52:17 »
Thanks for these great informations.
There is spark and I put a new set of spark plugs in when I finished to rebuild the car, not long ago.
I will check the lower solenoid this weekend. I just checked the upper one, so far.
And a scily question is: How do you move the rack? Is it through the control lever ( that is connected to the external control linkage)?

mrfatboy

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Re: 280SL 1968 won't start.
« Reply #4 on: January 10, 2019, 05:31:25 »
On the front of the pump (pointing to radiator) there is a black rubber cap that is covering the rack access hole.  You may or may not have the cap after all these years.

You can insert a 5mm bolt (memory?) into the access hole and screw it in. From there you should be able to push and pull the rack easily if it is moving freely.  The bolt should be about 30mm in length or so.
« Last Edit: January 10, 2019, 05:55:39 by mrfatboy »
1969 280sl (Aug 1968 build)
Signal Red
4 Speed

ja17

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Re: 280SL 1968 won't start.
« Reply #5 on: January 10, 2019, 06:15:03 »
Replace the spark plugs anyway. It's an inexpensive investment and may save hours of time. If the old ones are still good save them for future use. Not all IP racks have the  threaded hole on the end. You can still feel the rack move slightly when the accelerator linkage is depressed all the way and released. You can also push it back through the access and feel it spring back slightly. Review some of the old posts on the IP rack. Here is a pic with some info......
« Last Edit: January 10, 2019, 06:40:58 by ja17 »
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

Thierry du Laos

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Re: 280SL 1968 won't start.
« Reply #6 on: January 11, 2019, 03:06:28 »
Thanks, I will have a look this weekend.

Thierry du Laos

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Re: 280SL 1968 won't start.
« Reply #7 on: January 13, 2019, 04:12:50 »
Hi,
I had a try on the rack but it didn't move!
After inserting a screw in the rack (5mm) and pulled hard, screwing a nut. I could give it a little play. Approx >1 mm.
And the engine can start again, but not so good, like missing fuel.
My questions now are:
- What is the normal free play? 1 mm, more?
- Has anybody got a section of the pump to explain how its built inside?
- Shall I damage something if I pull more on the rack?
Thanks for the help.


Pawel66

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Re: 280SL 1968 won't start.
« Reply #8 on: January 13, 2019, 10:55:08 »
Thierry,

Just to give you a quick reference so that you find information on what you ask about:

Technical Manual
https://www.sl113.org/wiki/Fuel/Injection


In this thread you will find more specific info on how the pistons work in FIP
https://www.sl113.org/forums/index.php?topic=27193.msg194937#msg194937

You may want to study these.

Please wait for experts to respond, but to give you some quick answer before the experts chime in: it sounds like the rack in your FIP is stuck. It should move more quite easily and it should return forward to its resting position on its own.

In essence the pistons in FIP move up and down and also back and forth around their axis. These movements are related to movement of cam shaft and this rack (through levers). If this rack is stuck it usually means that one or more of the pistons are stuck.

If you go through forum you will see that some Members worked their way out of the stuck rack/piston situation by means of slowly and patiently cleaning and flushing the mechanism and gently putting it in motion. Others would send the FIP to be checked/rebuilt.

If I were you I would refrain from forcing the rack movement until you get advise from experienced Members.

As per my best knowledge, the rack can get stuck due to mechanical damage but also due to long period of non-usage.
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

Thierry du Laos

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Re: 280SL 1968 won't start.
« Reply #9 on: January 13, 2019, 12:59:28 »
Děkuji Pawel.
I will go through these documents.
I worked for 3 years some 30 years ago, in Ruzinie airport with CSA!!
Nice country and people, and not too many tourist at that time..
Best
Thierry

Pawel66

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Re: 280SL 1968 won't start.
« Reply #10 on: January 13, 2019, 13:56:00 »
Thierry, I am at the Ruzine twice a week! The airport has been re-built about 15-17 years ago.
I fly from Prague to Warsaw, where I live. Usually LOT, sometimes CSA... You get a free wafer bar in LOT...
Czech people are great indeed! Very polite, good engineers. Country is beautiful wherever you go!

The town of Prague and the country were completely diferent than now even 15-20 years ago - massive change occured.

Humongous amount of tourists in Prague all year round these days! Crowds!
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

mrfatboy

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Re: 280SL 1968 won't start.
« Reply #11 on: January 13, 2019, 20:14:30 »
Thierry,

You are in luck.  It just so happens I have an old R20 pump on the bench.

Inserting the 5mm screw in the front rack access hole and pulling it out yielded ~10.5mm in travel. Pushing it in from its resting position was ~8.25mm.

These numbers can be slightly different depending on how the pump is tuned.

The rack should feel like it is spring loaded and should always return easily to its resting  position after pushing and pulling. When moving rack it should glide effortlessly. 👍
1969 280sl (Aug 1968 build)
Signal Red
4 Speed

ja17

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Re: 280SL 1968 won't start.
« Reply #12 on: January 14, 2019, 01:17:37 »
Other factors which effect the rack position and movement are; temperature/position of WRD, altitude (barometric compensator), accelerator lever position and engine rpms when running.
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

Thierry du Laos

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Re: 280SL 1968 won't start.
« Reply #13 on: January 14, 2019, 05:06:12 »
Mrfatboy,
Mine is not moving that much and I am not going to push or pull anymore now because I don't know, following your infos, if the rack is in front or back!!
I understand that I have to remove from the top and find what is preventing the rack from moving.
One more question:
- By removing the 6 assies on the top, is it going to modify the calibration of the pump in any way?
Fro background, I had the car for 2 months  July-August parked (Rainy season in our tropical region). Then in September I started the car to move her but she was running on 4 cylinders. I had her stopped again for more than month, and she wouldn't start anymore after that. Now she just started and ran by moving a little the rack.
So I suspect corrosion from water ingress? Hopefully superficial corrosion????
Let's see when I can remove the injector's fuel lines. I have to make the good wrench for that.
Thanks.

mrfatboy

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Re: 280SL 1968 won't start.
« Reply #14 on: January 14, 2019, 20:54:22 »
There is a lot of great info regarding stuck racks on this forum.  Use the search function for "stuck rack" or google "site:sl113.org stuck rack".

Here is an oldie but goodie from ja17 as just an example :)


https://www.sl113.org/forums/index.php?topic=886.0
1969 280sl (Aug 1968 build)
Signal Red
4 Speed

Thierry du Laos

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Re: 280SL 1968 won't start.
« Reply #15 on: January 15, 2019, 05:52:09 »
Thank you, I will read and try to work on the car next Saturday.
Best