280SL 1968 won't start.

[Thierry du Laos]

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]

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.

[ja17]

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.

[Thierry du Laos]

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]

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.

[ja17]

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......

[Thierry du Laos]

Thanks, I will have a look this weekend.

[Thierry du Laos]

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]

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.

[Thierry du Laos]

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]

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!

[mrfatboy]

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. 👍

[ja17]

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.

[Thierry du Laos]

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]

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

[Thierry du Laos]

Thank you, I will read and try to work on the car next Saturday.
Best

[Thierry du Laos]

Hi,
Should the rack move easily a few centimeters and return forward to its resting position on its own when the FIP is installed on the car?
Mine moves easily only less 1 mm...
I removed the check valves.
I punched to release the cylinders and plungers.
The car starts again but missing 2 or 3 cylinders.
I think stuff got stuck again inside.
But anyway the rack has never been moving freely.

I wonder if I understood correctly the system?
- The rack moves longitudinally, and rotates the gears to control the fuel flow.
The gears go up and down to limit the cylinder play?

If I am correct, when I tap the cylinder, it should rotate the gear and push or pull the rack longitudinally? Eventually they both (cylinder and gear) come back up with the spring pressure....
I can tap the plunger until it is in contact with the follower and camshaft .

Thanks in advance for the info, because I am stuck also!!

[Thierry du Laos]

Finally I removed the cylinders. One was very difficult to remove, but it looked like locked with something inside.
It was moving but it wouldn't come out.
After many tries it unlocked free and popped out.
And freed also the rack in the same time.
So I cleaned all, inspected, and tomorrow I will fit everything back and I am confident .

[ja17]

Post a picture of your progress if you can.

[Thierry du Laos]

I didn't make many pictures, just this one!!

And this Sunday I re installed all, and in the end the rack was not moving anymore, once again and the engine started but not enough fuel.
I removed all again, couldn't take the cylinders out, but got the rack freed. I can't understand!!!!!
Re installed the check valves etc... one by one to see if one number would be the one that locks the rack, but got everything back with the rack free. No understanding !!!!
I tried to start the engine, but no way, no explosion.
After that I stopped because my batterry charger died. So this week I will look for a new charger, and next weekend try again, and if you have comment, they are appreciated.

[Thierry du Laos]

Can anybody tell me what are the movements of the gears < > cylinders, given by the rack.....
I believe that the gears rotate, but what about the cylinders?
Do they rotate or slide vertical, to control the fuel volume in the chamber of the cylinders?

An other question is, could the thermostatic valve on top rear of the FIP, disturb the rack operations?
And can I remove it to check, with the FIP installed on the engine?

[mrfatboy]

An other question is, could the thermostatic valve on top rear of the FIP, disturb the rack operations?
And can I remove it to check, with the FIP installed on the engine?

The WRD (warm running device) which you are calling  the "thermostatc valve" pushes down a mechanism in the FIP which slides the rack back (toward rear of car. Leaner) to its operating temperature position.

Even if the WRD slide valve was stuck closed the rack should be able slide forward.

The rack should move freely at all times.

If you inserted the bolt in the front FIP access hole in a running car you would see the bolt move forward as you rev the engine and move back as it returns to idle.

[ja17]

The rotation of the pistons by the rack is what regulates the quantity of fuel. In addition the pistons move up and down (pushed by the camshaft below), and create fuel pressure to open the injectors.  The cylinders are stationary. They are indexed by a pin and must always be installed in their "pinned-in -place) position. If the pistons cannot move up and down or turn in their cylinders, then the rack will be stuck. If you have an early BBB go to pages 07-10/3 thru 07-10/9for a good description and some excellent illustrations and photos of the injection system.

[Shvegel]

Thierry du Laos,
I hope you kept all your cylinders in order?  They are matched to the pistons and the tolerances are extremely tight(Millionths of an inch).  If you didn't keep them in order start looking for another pump.  If you did keep them in order look for someone to rebuild what you have.  I know a fair bit about the inner workings of these pumps and you really are deep enough in where you can destroy the pump.

[Thierry du Laos]

Step by step I catch more and more the system.

Yes I have kept the order of the cylinders.
Unfortunatly I don't have what you call BBB.
Next weekend I will remove all again and have a better look with these infos.
Now that its been removed and cleaned, fortunatly it comes out easy.
What I meant by thermostatic valve is the kind of can on top. => Not the rear water thermostatic valve that opens or closes the air during starting.
In Laos, or around, I wouldn't give to anybody this FIP. I try what I can and if I cannot solve, I will send somewhere serious!! But I have to understand and make sure it is not a simple problem that I can do. Like CSS for eg.