'73 450 SL electronic fuel injection

Isdyldan

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Hi - I have common rail electronic fuel injection on a '73 450 SL engine which I have been trying to start for a while now. Does anyone know how this works please? The fuel comes into the rail via two small dome things (one after the other) with some sort of regulating bolts on top. I assume that these are for regulating the pressure in the rail. If I turn the ignition on, I get a 'wiz' from the fuel pump & pressure builds up in the fuel lines. For some reason no fuel comes out of the return pipe back to the tank, so I assume that no fuel is getting into the rail? Maybe the 'dome things' are adjusted wrongly? Does anyone have any experience with this type of system please?
 

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Within 1 or 2 days I will have the complete set up papers for the k injection
 

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it`s the dreaded d-jetronic actually, terrible things.

the original poster will have to furnish us with a little more info. do the injectors `click` when listened to through the shaft of a screwdriver? have you got a good spark? the 2x fuel regulators rarely give trouble unless water has been through the system or it has been left empty for a while. potential injection problems are the points in the bottom of the distributor - not the ones beneath the distributor cap, fuel pressure (pump or filters), injectors, ecu power supply, perished vac pipe to the manifold sensor, throttle body position sensor and many many more. check that spark and injector pulsing first.
 

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it`s the dreaded d-jetronic actually, terrible things.

the original poster will have to furnish us with a little more info. do the injectors `click` when listened to through the shaft of a screwdriver? have you got a good spark? the 2x fuel regulators rarely give trouble unless water has been through the system or it has been left empty for a while. potential injection problems are the points in the bottom of the distributor - not the ones beneath the distributor cap, fuel pressure (pump or filters), injectors, ecu power supply, perished vac pipe to the manifold sensor, throttle body position sensor and many many more. check that spark and injector pulsing first.



Even on this set up,,there will be no fuel going back to the tank as it should be cut off with no pulse,,like the newer systems
 

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Remove the pressure regulators from the fuel rail & see if any fuel is passing through them.Fuel pressure should be approx 2 bar (just under 30 psi give or take).
 
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Blimey, it sounds much more complicated than I thought! Fuel is seeping from the adjusting bolts on the fuel regulators. I'll have to investigate all your suggestions. I'm going away for a weeks hols, so will unfortunately have to wait to do any actual testing, but would be great if I can get an understanding of what does what. I understood that the injectors spayed constantly on this system as long as the crank sensor was sensing that the engine was turning. Maybe this is wrong?
 

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Blimey, it sounds much more complicated than I thought! Fuel is seeping from the adjusting bolts on the fuel regulators. I'll have to investigate all your suggestions. I'm going away for a weeks hols, so will unfortunately have to wait to do any actual testing, but would be great if I can get an understanding of what does what. I understood that the injectors spayed constantly on this system as long as the crank sensor was sensing that the engine was turning. Maybe this is wrong?

no your injectors are sequencially firing, being timed by those points in the bottom of the distributor. later injection was the cis method (continuous injection system). how have you got the regulators leaking?? they are way down the list of usual supects and i would leave well alone, have you listened to the injectors to hear them clicking yet? screwdriver method as listed above. your ecu is mounted somewhere in the n/s footwell area, fuel pump and filter under the back end, manifold vacuum sensor on bulkhead at end of pipe, throttle valve sensor on throttle body, cold start injector at front of fuel rail, the injectors and rail you have found, points as i said and that`s about it from memory but it`s been a while........
 

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Maybe the 'dome things' are adjusted wrongly?

they probably are now!! :D never had to adjust a regulator. rust in the fuel system from tank condensation is common - have you checked the filter? have you taken a fuel pipe off the cold start injector to check for fuel delivery? good luck.
 

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If the fuel is leaking through the adjuster 'bolts' it sounds as if the diapragms have split.If this is the case then the rubber could be acting like a reed valve & stopping the fuel from flowing through the fuel rails.
 
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Isdyldan

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Hi All,

I'm not sure if the flow and return pipes from the pump/tank are round the right way. (the car came to me in a dismantled state you see). Should the regulators be after the rail on the way back to the return pipe, or is the fuel pumped into the regulators first please?
I'll need to get someone to help me check the injectors for 'clicking' (someone to crank while I listen).
Thanks.
 

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Yes the fuel goes into the regulator first then comes out and back to the tank
 
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Isdyldan

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Thanks, that's what I thought, but how does the rail become pressurised then please? Wouldn't the fuel simply flow off back to the tank? Appologies if my fundamental undersatnding of the workings is non existant!
 

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This article in D-Jetronic fuel injection may be of help:


Troubleshooting D Jetronic.

No start and fuel pump not working;

1)Test the fuse,relay,wiring and fuel pump.



No start and fuel pump working;

1)Test the main relay and power from ECU.Ensure there is a good ground from ECU terminal #11 to ground.
2)If the ignition system has a good spark,good power supply,ground to the ECU and continuity at the trigger points(cover this later) and injectors fail to pulse,
replace the ECU.

Starts when cold and dies when the key is released;

1)Trigger points in distributor lack continuity.When the engine starts,it is starting off of the cold start injector and as you release the key,the cold start injector shuts off.

Stalls when engine is cold;

1)Inspect the auxillary air valve.When the engine is cold,remove the hose on the intake side of auxillary air valve and let air to be drawn into it.If the engine speed increases greatly,replace the auxillary air valve.
2)Temperature sensor 2 is also critical to cold operation.

Misfire or unstable idle;

1)Ensure that the ignition system is in good shape and also the intake is in good order.These need to be confirmed first as they are more likely to cause this problem.
2)Inspect the circuits and sensors of temperature sensor 1 and 2 and continuity through both sides of trigger points.
3)Inspect the vacumm hose that goes between the pressure sensor and the intake manifold.It should have no kinks and not collapse with vacumm present.
4)If all the above check out,do an injector flow test.

Misfire while driving;

1)Ensure that the ignition system is in good shape and also the intake is in good order.
2)Do a fuel pressure and volume test.
3)If the fuel pressure is constant,test temperature sensor 2,pressure sensor and throttle switch circuits.

Power is suffering;

1)Ensure that the ignition system is in good shape and also the intake is in good order.
2)Most likely this is due to low fuel pressure.Do a fuel pressure-volume test and pay close attention for loss of pressure.
3)If correct,test the circuits of the pressure sensor and temperature sensor 2.If these meet specs,do an injector flow test.
4)If everything checks out,repeat this test.

Stalls when you decelerate;

1)Ensure that the ignition system is in good shape
and also the intake is in good order.
2)Inspect the hoses and wiring for good contact.
3)Check your throttle stop adjustment and curb idle RPM's.

Smokes and runs rough;

1)Ensure that the ignition system is in good shape and also the intake is in good order.
2)Do a fuel pressure and volume test.
3)Inspect the circuits of the temperature sensor 2,trigger points, pressure sensor and injectors If they check out fine, do a injector flow test.

Misfire under Load;

1)Ensure that the ignition system is in good shape and also the intake is in good order.
2)Do a fuel pressure-volume test.
3)Inspect the circuits of temperature sensor 2, pressure sensor,trigger points and injectors.
4)If the above are good,do an injector flow test.

Trailer hitching;

1)Ensure that the ignition system is in good shape and also the intake is in good order.
2)Do a fuel pressure-volume test.
3)Inspect the circuits of temperature sensor 2, pressure sensor,trigger points and injectors.
4)If the above are good,do an injector flow test.
5)Check the throttle switch.

Idle speed too high;

1)Ensure that the ignition system is in good shape and also the intake is in good order.
2)Check and adjust the throttle stop and curb idle speed.

Idle speed too low;

1)Ensure that the ignition system is in good shape and also the intake is in good order.
2)Check and adjust the throttle stop and curb idle


Testing the D Jetronic Components


Main relay;

1)There should be 12 volts at pin # 24 of the ECU.

2)If not,check for 12 volts at pin # 24 of the relay.

3)If 12 volts is not present at the relay but it clicks,replace with a new relay.

4)If there is 12 volts at pin # 24 of the relay,repair
# 24 wire between relay and ECU.

5)If the relay does not click,inspect the wire from the main relay pin # 45 to ground.

6)If the ground is good and 12 volts at relay pin # 38 when the engine is cranked,replace the main relay.


Trigger points;

1)With the engine not running and ECU harness disconnected from the ECU,check the resistance between ECU harness 12 and 21,then from 12 to 22.One should show a low resistance and the other should show an open circuit.

2)Rotate the engine 360 degrees and check the resistance.They should have an opposite reading now.

3)If not,perform the same test at the trigger points themselves.This will tell you if it a component or wiring fault.


Temperature sensor 1

1)With the engine not running and the ECU harness disconnected from the ECU,connect an ohmmeter between ECU harness pin # 1 and 13.At an ambient temperature
the reading should be 200 ohms.

2)If the resistance is well above 200 ohms,check resistance at the sensor itself to determine if it is a component or wiring fault.

3)Check resistance of all the terminals to chassis ground.There should always be an open circuit.


Temperature sensor 2

1)With the engine not running and the ECU harness disconnected from the ECU,check the resistance between harness terminal 23 and ground.The resistance should be 2000 ohms at ambient temperature.

2)If the engine is near operating temperature,the resistance should be below 1000 ohms.


Throttle switch

1)Test the throttle switch with the key on,engine off.

2)Slowly open the throttle,and as it opens the injectors should alternately click.You should hear 20 evenly spaced clicks.

3)If this is not met,place a 0.016 in.(0.4mm)feeler gauge between the throttle stop and throttle stop screw.Connect a voltmeter to terminal 17 of the throttle switch.The voltmeter should show voltage while the ignition key is in the on position.Remove the feeler gauge and the voltmeter should show no voltage now.

4)If this fails,loosen the screws and rotate the switch until it meets these requirements.

5)If they can not be met and voltage is always present no matter where you position, replace the throttle switch.

6)If the voltmeter reads no voltage,ensure voltage is being supplied to the switch.If so,replace the throttle switch.

7)If no clicks are heard while performing test 1 and 2,check wire numbers 20,17,14 and 9 for continuity end for end from the ECU to throttle switch.


Pressure sensor

1)With the engine not running and the ECU harness disconnected from ECU,check the resistance from ECU harness terminal # 7 to 15.Should be 90 ohms and then check the resistance between # 8 and 10.Should be 350 ohms.If this is not met,test the sensor itself.

2)on occasion,the sensor resistance will check out,but will not hold vacumm.Using a hand held vacumm pump perform this test again (step #1)


Injector circuit

1)With the engine not running and the ECU harness disconnected from ECU,check resistance of ECU harness pins # 3,4,5,and 6.All should have less than 25 ohms.

2)If the resistance is greatly higher or lower than 25 ohms,test the injector itself.

3)If the injectors pass,repair the wiring harness.
 

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With the engine not running,,the fuel supply to the pump stop,,the only way to get continuous operation is to remove the relay and bridge pins 7 and 8
 

Alex Crow

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there should not be a fuel return!!

the fuel goes through the two pipe regulator first, then through th three pipe one and into the fuel rail - no return.

some explanation of the pipes being used or pictures would help.
 
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Isdyldan

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Hi - I'm not sure if this photo is clear enough to see, but you can make up the too pipes top right near the battery, one going to the regulators (2 pipe first then 3 pipe as you say), and there is a pipe going to the other from the fuel rail bottom right/middle.
 

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osc

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Your Mercedes
1971 450SL; 1989 911 3.2 Carrera Targa; 1999 BMW 728i
I have a 1971 450sl and have also had problems with it so i have learned a lot about the d-jetronic system.

First I can confirm there is a fuel return line and there should be a flow of fuel back to the tank. The system is based on constant fuel pressure, controlled by the regulator and the extra flows back into the tank.

From the beginning, the fuel comes via a stainer in the tank into the prefilter then into the pump, then normal inline fuel filter. This fuel line appears in your engine bay and is the one that is towards the front of the car.

The fuel directly feeds both fuel rails (and the cold start device) then the output from the rails goes into the fuel pressure regulator (FPR; 2 input lines, 1 output) then into the fuel damper and finally into the return line. You need to connect a pressure gauge anywhere before the FPR to check that you have about 28-32 psi which is about 2 bar. Note that i've had to increase my pressure to about 3 bar to get it running right (i will put up a post about this soon). My FPR also started to leak from the screw when i adjusted it so you will need to get a new one do to bosch direct, merc charge a fortune)

I am sure I can help you fix this so get in touch and I can talk you through a diagnosis, then you can post up the answer to help any others with the similar issues.

If anyone knows about the intimate details of d-jetronic and fine tuning the system then please get in touch.
 

Alex Crow

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on second thoughts, osc is quite right!! sorry for any confusion.

on a separate point, does that large dia manifold vacuum pipe connect to the manifold pressure sensor? (large aluminium electronic component on inner wing near battery) the vacuum comes from the rear of the manifold.

how much fun the d-jetronic is. common problems are idle switch adjusted wrongly on throttle body, engine surges up/down. points going all open circuit in distributor, usually clean up ok. perished vacuum hose to the mps. stuck or u/s injectors. millions of very dangerous fuel leaks from perished pipes. damaged and brittle wiring. u/s air or coolant temp sensors, runs very very rich! also all the usual corrosion in fuel system related troubles.

as i said before i have never had to adjust a fuel regulator, i wonder what other problems you are masking osc. you have found the mixture adjuster on the ecu?
 
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Isdyldan

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Hi, I have the flow & return the right way, and there is a fair amount of pressure as fuel squirted everywhere when I pulled the pipe off (including my face!). The regulators are not leaking now - only when connected the wrong way round and fed from the pump. There is 'ticking' from the injectors when the engine is cranked. There is a spark at the plugs and the timing has been statically set to TDC, although the ballast resistors are not in the circuit - there is 12V to the +ve of the coil and the -ve is connected directly via a wire to the points. I'm not sure how this is supposed to be connected, but assumed this should work? I know this would damage the coil if run for more than a few seconds, but figure I would cross one bridge at a time. It did fire up for half a second yesterday, but not even a sign of starting today.
 

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1971 450SL; 1989 911 3.2 Carrera Targa; 1999 BMW 728i
One of your ballast resisters needs to be wired in series with the coil positive because these cars have a 8V coil.

The other resister is wired in with the electronics from the Ignition Control Unit (smal box with 4 coloured wires mounted under the front wing).

I traced the wires from the Haynes Book - do you have access to this?
 


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