I currently have a 1973 250 CE in for repairs it has a W114 engine and I am unable to find any service manuals for this particular car. It has a Bosch Electronic Fuel Injection System as standard and I can find no reference to this EFI system anywhere.

When it arrived I was told that the battery was faulty and as this is a show car that was not hard to believe. I could then start the car but after fitting a new battery it got worse still until I'm currently at the stage of only being able to keep the motor running for a few seconds.

I'm sure it is an electrical problem and something to do with a relay for the fuel system but as I can find no technical details at all about this particular setup I do not know what relays do what. To make matters worse I am unable to locate any mechanics who have detailed knowledge of this type of setup. The general layout of the car is normal but the EFI system is totally different to the latter models.

Can anyone advise me where I can obtain any technical data on this car or a service manual that covers the fitted Bosch EFI system and a wiring Digram? Even the actual model of the Bosh Fuel Injection system would be of help as I could then get the proper Bosch manual.

Of course all the normal channels for service manuals insist that this car should have Carbs or Mechanical Fuel Injection but Mercedes insists that it is as original with the EFI but are unable to tell me the model of the EFI system.

Col

The system is D-jet. The "D" stands for druck, pressure in German. The system is basically the same as used on the earliest V8s. There will be trigger points in the base of the distributor that fire injectors in groups of three. Volvo 164e had similar system and maybe the same points. There also was a BMW that used the system (also very rare). The Volvo is the common 6cyl version, although if you need trigger points the four cyl versions used in VW, Volvo, and 914 Porsche 1.7 and 2.0l may be a fit.

Since you refered to the battery a good place to start is the positive battery cable. In all the MB versions the main power lead was attached to the positive lead. The wire was not incorporated into the cars wiring harness and if you follow it, it will lead you to the EFI relay (controller relay). Once powered up the fuel pump ran for 1 sec and died unless the car was cranked.

The injectors are feed side controlled unlike modern injectors that are controlled on the ground side. A most usefull characteristic is the operation of the acceleration enrichment system built into thye throttle switch. If you turn the car on with the engine off and move the throttle to full throttle slowly you will hear the group of injectors, currently engaged by the trigger points, fire twenty times. This is always the first step to see if the controller is functioning. It also can be used to verify the trigger points, somewhat.

The points often get stiff with time and don't close fast enough to reopen the next go round. Sort of like floating valves.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

This is a Euro spec car. D-jet was not used in the US, although it might have been in Canada, that's why you get the info you get. No mechanical injection in the W114 chassis, either.

Fuel pump should run about 1 sec when ignition switched on and when starter is engaged or engine running. Fuel injectors must click when cranking even if it doesn't start.

Sounds to me like it's running on the cold start valve only -- fires, dies, does it again for a while, then eventually won't even sputter -- let is sit a while and it will again start briefly. That means no injection.

You can test the trigger points with an ohmeter if you pull the dizzy -- which I would on principle to clean the trigger points with brake parts cleaner. Make sure whatever you use doesn't contain methylene chloride or it will melt the plastic covers on the points and possibly the rubbing blocks, too! Flush out all the oil and verify that the points make contact as the dizzy turns. the oil will prevent them opening and closing cold, no effect hot. Worn rubbing blocks will require new points.

Another spot to check is the ground for the injectors and control box -- not sure where it is on the W114 chassis, but it's on the right side firewall on the W108. Big nest of brown wires, and if the connection is corroded, no injection.

If the car hasn't been driven for quite a while, drain some gas and check condition -- if it reeks of stale gas, drain it all out and replace with fresh and jumper the fuel pump relay (can't tell you the location unless it's on the ECU bracket, in which case it will be the bottom relay) and let it run a while to flush all the goo out. With any luck, it will run then.

Pete

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

After much mucking around it turned out to the the engine management module but the injectors where opening and being triggered but only at cranking speeds anything greater and it was just running on the cold start injector.

Of course after testing the injectors where actually opening I then resorted to basic electrical things like ignition switch, points and replacing the injector points in the distributer all to no avail. If I shorted out the fuel pump relay it would at least idle as long as I wanted it to but of course it wouldn't come off the idle and certainly was underivable. My best guess is that the owner jump started this car and damaged the control unit. Now that it is drivable all I have to do is build a new Transistorized Ignition Module and clean up the mess that I've made.

But thanks for the data as I will certainly get a Bosch Manual for the Injection system which is so much like the latter units but has different relay points. What I found confusing at first was the lack of any transistorized ignition module but on closer inspection I found it hidden between the battery holder and the front of the car. Incidental the car was an AU delivered unit so that is probably why there is so little data about it.

Thanks

Col Luck

Certainly sounds like fouled trigger points -- if the electronic fuel injection computer operates the injectors at idle, it should also operate at speed, transistors are usually either bad or not, no intermediate conditions!

Pull the trigger points if you haven't and examine them. Might be hard to get new ones (or expensive), but it sounds as if they are not working.

Also check the play on the distributor shaft bushings -- if there considerable wear, the shaft may be pushing over so far that the points don't open and close!

The engine rpm data is provided by the trigger points, so if they won't work above idle, the fuel pump will shut off.....

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

The trigger points where one of the first things that I changed as I've had problems with them previously. I then changed the electronic part of the ignition switch as I was unsure that it was working properly I've also had a few of those go west over the years although I've only had to replace 2 from a Mercedes.

The whole thing was beginning to get to me as while the injection system is not one of those "Black Arts" to me this one just is different and without a wiring diagram I was unsure exactly what relay did what. Add to that there are 3 relays connected that actually fed nothing other than a wire that ended in a spade connector and a few other minor things like about half a mile of wiring that did absolutely nothing and has since been removed. Then the fact that there was a Kettering Ignition system fitted was more that a bit confusing. I eventually found the Transistorized Ignition Module well hidden in front of the battery tray and about half a inch away from the front of the car so it started to begin to make more sense even though I could not find any wires exiting from the loom that should have feed the coil with the trigger impulses and there where certainly none cut off. Short of removing all the loom covering it will be almost in possible to find where the wire has disappeared to. Also there is no power getting to the Ignition Module and I can not find where it has been disconnected so my original feeling was that something had gone wrong with the ignition switch particular as there is a heavy weight hanging off the key ring.

But just to make matters even better all the low pressure power steering hoses had been replaced with water hose which was in the process of dissolving and spreading hot ATF all over the engine bay. It was anything but clean and not at all what I had expected from the previous times I've seen this car. With all the oil that had been spread around both the injector trigger points and the ignition points where first replacement musts but the injectors where opening or at least getting a signal at cranking speeds although I'll admit that I never got a chance to actually test as to weather they where working when the engine was running for the short spells. I'm in agreement with a previous poster and agree that the engine was only running on the Cold Start Injector . But with a good clean up new power steering hoses and the engine management module changed it's working and is even drivable now. I've temporally replaced the engine management module with one from a 115 280 SE and while it looks the same on the outside it's totally different on the inside hopefully it has a lot more capacitance built in so it will not be as susceptible to alternator ripples in future.

About 10 years ago I escaped from working on the then new fuel injection units as I actually wanted to work on a Mini Cooper S rather than work on something easier to repair so then I knew it was time to give it all away. But other than the occasional Classic Mercedes which was first brought to me by my Uncle and then some of his friends I do not touch cars any more, but in all honestly I just love working on these old Mercedes as they where just so far ahead of their time and generally are a real pleasure to play with as I do not consider this to be work. Currently I have several of these for my own "Play Toys" but mostly they are of the twin cam variety with EFI. I find them so much easier to play with than the carburetter models.

Those along with a 408 2.2 Lt 4 cylinder fitted out as a mobile home are my current stable of "Play Toys" and I suppose I just have to add my 1982 900 SS Ducati into that group as well but I've had that since new and only run up 17,000 K on it so I do not get to play with that one much.

Col

I may be wrong, but I seem to remember seeing a wiring diagram for either the 250CE or 280E/CE W114 which showed the D-Jet ECU still with 4 outputs to the injectors as for the V8 versions. On these 6-cyl versions I seem to remember 2 of the injectors each with their own output and the other 4 injectors sharing the outher 2 outputs (in pairs like the V8). This would suggest the 6-cyl versions would still have 4 trigger points like the V8. Does my memory serve me correctly or am I imagining seeing this?

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

On the 6's the injectors fire in two lots of three. If I remember correctly the V8's did it in 2 lots of 4.

I really wish I still had that Bosch book that got washed away in a flood and was impossible to replace. That was in January 1974 and I've been trying to get another copy ever since. Of course we didn't appreciate that book as it was given to us and when we wanted another one they where no longer available but it was amassing just how much it got used.

Col

V8s are 4 lots of two.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

well now, having spent several hours learning about my car i have made some not so nice discoveries.plenty of testing and measuring has me convinced that the computer is at least half dead.turning on egnition,pump runs,injectors click when pressing excelerator.turning to start i may get a fire or short run.cold start injector does not come on,some argue its too warm,i think the only thing stopping it is no power at the relay when engine is cranking. injectors are not getting any power when i have run engine on hot wired cold start injector.all other probes ,sencors and and trigger points seem to function as designed.might be heading up the garden path since the info has come out of a v12 jag workshop manual.it is also bosch and physical appearance plus values stamped on items are identical to my car.
i have tried to locate another computer and have found one out of a 1973 250ce,same engine,but the last three figures of the part number are different.006 compared to mine 004.
this is where it becomes interesting again since jet another wrecker is of the opinion both are incorrect for that car and should end in 024 or 025. both cars are 114's. please someone tell me it doesnt matter and the 006 is just fine.out of a running car and well priced.
another question is the ignition.the unit under the battery doesnt hook up to anything anymore and i have normal points and coil ignition.doesnt bother me at this stage as at least i have spark.

was/am in a bit of a hurry and forgot a couple of points.when i had the engine running of the coldstart injector i wanted to measure the signal to the trigger points.i had a weak(maybe .5 volt)signal between ctr.and and one side and nothing between ctr. and the other side.does this seem right?
must go once again,thanks for listening.

If the injectors click while cranking, the computer is fine. If you have an ocsilloscope, you should be getting about 7 ms injection pulses. If the injetors are dead and the fuel pump cuts out when in the run position, the ignition wiring or the ignition switch is shot -- this may be related to a butcher job on the transisitor box for the ignition.

You must also verify that you actually have the fuel pump running and producing pressure. When these sit for any length of time, they get stuck. Can be freed up, but if fuel delivery is poor, it won't start.

The cold start valve usually will only operate below freezing. It's operated via a thermo time switch in the manifold (or somewhere) that senses engine temp, and a relay that is switched by the computer.

Replace the ignition with a Crane or Pertronix unit, they work better. Verify that the ignition wiring is correct around the resistors and that you actually have juice to the points, else it won't go due to lack of spark!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Well as you asked for it, it doesn't matter! I've used Engine Management Modules from the 2.8 Lt Twin Cams on a 250 Single cam without a problem.

There is one thing to look at on the left hand side under the dash there should be a group of brown wires which go to earth make sure that these are actually earthing and have not corroded as that will give you exactly what you are describing.

For a run around I got a Pug in for repairs and was told that after he drove through some water it stopped. As the fuel pump was not running it seemed a good place to start so I changed that no improvement then it was suggested that a relay under the dash might be faulty and as there is no way of testing except to change it a new expensive relay was brought but again no difference. I even by this time had disconnected the fuel filter just to make sure that it wasn't blocked and building up pressure in the filter and stopping the fuel pump from running. Well after listening to the owners description of how it happened I gave up and started on the normal diagnostic things and found a bad earth for the fuel pump inside the boot.

Apparently the car had been running badly for quite some time {of course I wasn't told this} and when there is no solid earth provided for the fuel pump it sends out a brief pulse of power and if nothing happens the management module shuts down the fuel pump which explained why I was not showing any power present at the fuel pump.

Go over all the earth points pull them apart clean them up and then try again.

As for the Cold Start Injector even in Darwin it doesn't get hot enough for it not to run at least on startup so I would look very closely at the relay which controls it but only after cleaning every earth point you can find and making sure that it is actually earthing. I take it that the Ignition Module is working as you said you had it running on the Cold Start Injector but new points never hurt. And while you are at it check the cam chain as well. They are a pain but do quite often need changing and are not all that expensive provided you stay clear of Mercedes and buy from

http://www.mbspares.com.au/default.asp?d=18036&p=16933

In Canberra. They are quite helpful the last cam chain I brought from them cost me about $80.00 AU freighted to me overnight. They should also be able to help you with a engine control module as well but I would go over every earth point that you can find before taking that step. Most of the troubles in any EFI car relates to earthing problems and I've seen many a mechanic replace some very expensive items with no result only to find a bad earth point at some out of the way place.

Provided the Box looks the same and has the same connector it will work although the Auto Transmission may change at different points in the speed range depending on just how highly stressed the engine for that model that the module came out of is.

If you have to change any electronic parts remember to disconnect the battery first and grab some metal part of the car to bring yourself to the same potential as the chassis that way you will avoid Static Damage which is another killer of these electronic components.

Have you checked the points on the side of the distributer as if these are sticking or have lost their spring tension they will not be sending the signal to open the main injectors as well.

I hope that is of some help to you just post again if you need to know anything else.

Just as an after thought a lot of the Power Steering return hoses are replaced with water hose which reacts with the ATF and makes a real mess under the bonnet so if this is the case replace the return hose with the proper Oil Hose and clean down everything in the engine bay before the ATF begins attacking all of the rubber parts like the relay isolation washers which are very hard to get.

Col