w 108 4.5 staring problem - Mercedes-Benz Forum

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post #1 of 17 (permalink) Old 11-07-2014, 11:01 AM Thread Starter
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Date registered: Feb 2013
Vehicle: Mercedes benz w 108 280 sel 4.5 1972 and ford explorer 2013
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w 108 4.5 staring problem

Guys I need help with my issue
I Have a starting problem with My W 108 4.5 72 model
the car start rough and engine works on 2 cylinders only.Before I was thinking its the Cold start where Hell is little bit cooler than the place I live.
cold start checked and cleaned by Bosch service centre and the Thermo time switch is also replace with new one (stupid advise of electrician).I checked all the wiring of injectors I made a continuity check with ECU all are fine the spark plugs have a handsome sparks the injectors are not working this after i pulled connector wire one by one there I noticed that 6 of them are not working.I checked all fuses and all fine .I can hear the fuel pump is working fuel pump is new hardly I used it for 2K km.the pressure regulator is replace recently to a new one.the manifold pressure sensor is good as it is not leaking after checking with vacuum pump.Air filter is new,fuel filter is also new.i removed the trigger points inside the distributor (on the side fixed with 2 screw) and they were clean,cleaned them with petrol then with Carburator cleaner and last blow it with air but the result is the same .i replaced the ECU with similar category but no change..!!!
and clues what would be the Problem i appreciate your help
Jamal
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post #2 of 17 (permalink) Old 11-07-2014, 11:03 AM Thread Starter
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Sorry for mis spelling its Starting and not Staring
cheers
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post #3 of 17 (permalink) Old 11-07-2014, 12:56 PM
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Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
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has the car been running fine and suddenly it only runs on two cylinders, or are you putting an old car back on the road after extended non-use?

I would start with isolating if it is the injector or the signal. Best way is to take one of the two injectors you know works and plug it into one of the pigtails for an injector you know is not working. If it works in the pigtail, it is the injector that is bad. If not, it is the signal.

You said you checked continuity back to the ECU. Did you also check continuity to ground for each injector?
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post #4 of 17 (permalink) Old 11-07-2014, 01:46 PM Thread Starter
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thanks TZ
the car was running and on use twice a week for last 19 months but has a problem of high consumption of fuel.
Will check the continuity to the ground in the morning .actually i drove the car 55 km to replace the transmission linkage pushing at one Garage as its located in an odd place since then started the car and was rough i thought it will be ok when it come warm but reached to temperature of 175 F And i realised that some thing not ok i left the car and checked from down to see if any wire is disconnected or any unusual but non,the kick down switch plug is plugged.since then i start checking one by one but no clues.
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post #5 of 17 (permalink) Old 11-07-2014, 03:55 PM
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trigger Points Ignition problems

Lots of thinks can Happen so rather then just throwing money at it do all the testing you can . Pull the fuel Line where it comes into the Cold start Valve
and attach a fuel pressure Gauge and start the car to check for about 28 Lbs pressure > is less or more adjust the pressure at the Pressure Regulator .
If Its close no problem from the Pressure .
*****************************************
Preferably with the motor somewhat warmed up but cold well work as well .
Remove the Cold start valve ( 2 5mm Allen head ) and connect the valve to the fuel line only . Turn on key "without starting motor" with the wire disconnected ( to cold start Valve ) to make sure no fuel is coming out.
if fuel comes out the valve is bad .
Start Motor to check for fuel coming out of Valve still with wire disconnected.
if fuel come out replace valve
**************
cold start Valve
hard to test when the motor is running so poorly but if your getting a lot of Rich Black smoke from exhaust this is a symptom.
**********************************
Trigger Points : I Believe your car has Trigger points > 4 sets of points in the bottom of the Distributor Body . also has 1 set of points in the top of the unit . ( they set at exactly 0.14 Thousands )
I would set the Timing mark at top dead center with the rotor pointing to number 1 spark plug wire . Remove the Distributor and have a magnet to not lose the retaining Allen head ( most likely ) retaining bolt and remove the Distributor . Remove ( slide out ) the Trigger points Plate to inspect everything . Clean Everything all up and blow dry with compressed Air.
To set the Trigger points is very tricky I suggest you have a expert do it or buy a tool to do the Job
Link to took : $22
www.kad-forum.de ? Thema anzeigen - Kontakteinschub "Gebiss" D-Jetronic warten und instandsetzen
You can test the Trigger points with a Continuity test . Are 5 Wires to the T. Points the center one is the Ground so Ground to one set and turn the Dist slowly around . you should see " Continuity" about half the way around open and Half away around Closed ( this is with the T. Points installed in the Dist Body. Make sure you slide the Plate in firmly and tighten the retaining screws tight . Plate may shift around a bit so if not working try moving it a bit and re tighten it .
A Very good chance this is what is wrong with your car as the Rubbing blocks wear down so the points do not open enough ( read the tool info to enplane )
**************
Dirt Film : if your Engine Bay is dirty on the Drivers side front around the Resistors , coil , Distributor , ICM Unit , all those wire , Coil Wire this well cause the Ignition to fail very often . Fix any oil Leaks around this area and don't forget the Power steering pump and lines .
Hope this helps
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Last edited by aluminum; 11-07-2014 at 04:19 PM. Reason: Mispelling
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post #6 of 17 (permalink) Old 11-09-2014, 08:58 AM
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Also Check for cracks in Vaccum pipe going to MPS unit on the bulkhead .clean connector pins as well.
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post #7 of 17 (permalink) Old 11-10-2014, 11:38 PM Thread Starter
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W 108 starting Problem

Thanks Guys and also thank you Aluminium
I found out what was the problem and it is as follows
The Trigger points inside the Dist.
i actually removed the Dist. and also removed the trigger points cleaned all the good way.Put it back but no starting .again I took it out and looked very carefully and I noticed that the points spring at the very end where the wires are welded beneath that there is an INSULATING NIP with a height of 0.9mm only one point has this and the rest is missing ,i used a magnifier and look individually and could see that they are Damaged and Broken so I used a cigarette box hard paper and cut 3 square pieces 3 mm x 3 mm and the same from PET bottles and stick them with super glue and waited to dry and now had 3 new insulators ,i inserted them where they are supposed to be put back every thing adjust the timing,and here all firing .
I appreciate all who send me clues and solution and i followed them
cheers my dears
(By The way Aluminium i contacted the Guy in Germany and he is very nice and friendly and bought from him the trigger point adjusting tool)
:beerc hugr:: beerchugr:
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post #8 of 17 (permalink) Old 11-11-2014, 12:40 AM
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Good diagnoses!
Can we have contact source for point adjusting tool
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post #9 of 17 (permalink) Old 11-11-2014, 05:23 AM Thread Starter
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hello
here is the Link for the trigger point adjusting tool
the Guy name is Norbert Fischer
www.kad-forum.de ? Thema anzeigen - Kontakteinschub "Gebiss" D-Jetronic warten und instandsetzen
cheers
it is also there on the reply of aluminium
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post #10 of 17 (permalink) Old 11-11-2014, 07:30 AM
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i use a old bad distributor housing that i cut to view the trigger pointes and use this as a tool . the advantage of this , compered to the german tool , is that i can use a ohm meter , and spin the shaft and double check each contact for proper operation .
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