reawakening a sleeper - PeachParts Mercedes-Benz Forum

#1 11-24-2006, 12:30 PM

Hello all please be gentle with me as this is my first post on forum.
I own a 108 bodyshell 280 3.5 which is a bit of a rareity in that it is still on its origonal back tyres(I swapped the front ones as they had gone threppeny bit shape with age) . The car has done 28,000 k's.
It had stood in a heated garage on the isle of man from 1971 untill my buying it in 98. it needed the injectors sorting then and a new mid zorst pipe then but drove fine for a year when I parked her up origionally for the winter.Seven years later(woops) I am waking her up again and so far have replaced the petrol pipe from the gas tank to the high pressure pump as it was perished. My question is when I turn on the ignition the pump runs each time for about 2 secs but is not getting gas to the injector manifold.
What am I missing please?. The fact that I cannot get a workshop manual here isnt helping me I know and I am more used to simple aero engines not antique electrics . Hopeing this post is not to aseine as I feel I must be missing somthing but as they say its only easy when you Know
Pip Pip Ian H

Tomguy · #2 11-24-2006, 05:36 PM

The pump should buzz for a brief period before cranking - 100% normal. This also typically pressurizes the injectors in full. Failure to do show may indicate:

1) Blocked fuel filter
2) Blocked or faulty fuel pressure regulator
3) Faulty fuel pump

#3 being least likely since you can hear it run - but the diaphraghm may still be shot in it. Check #'s 1 and 2 first. It sounds like one hell of a sweet ride, except that you'll absolutely NEED to flush EVERY fluid and replace EVERY rubber bit - fuel lines, radiator hoses, brake lines, subframe mounts, engine mounts, tires, etc etc....

meltedpanda · #3 11-25-2006, 10:01 AM

sounds like plugged lines or screens, try rigging up a temporary gas supply before the pump to see if she will turn over, be careful of sparks and such when using this method.
And of course all of what Tomguy mentions

plus - pictures of your baby

#4 11-25-2006, 12:15 PM

many thanks for the tips so far , two quick questions though .1. where is the pressure regulator. is it the bobbin sized assembly at the rear of the injector manifold or is that somthing else again?
2. where are the strainer gauzes that might get blocked. (I only ask as a few years ago I worked on a leapard moth aircraft and it took us about two days to find a hidden strainer in a pipe that was restricting the flow rate as partially blocked .I swear that only geoffery de-Havilland and his cat knew that damm strainer was hidden there!!)
When I get my digi cam back from the warrnty shop I will post a few pics
Pip Pip Ian Hogg

Tomguy · #5 11-25-2006, 01:47 PM

1) http://www.peachparts.com/shopforum/attachments/vintage-mercedes-forum/29559d1131938408-kick-down-switch-109-4-5-kickdown.jpg
The left silver part is the regulator. The right is the dampener. The kickdown switch is what's circled (ignore that)...

2) 1: in the tank (Main strainer, hex head visible on underside of tank). 2: Fuel filter. 3: Inside of each injector

There is a check valve in the fuel pump itself, as well as possibly a strainer (I don't recall).

Jengasan · #6 11-27-2006, 11:06 AM

Hello Ian, good to see another guy on here from the uk.

Something is dead (regulator/pump) or clogged (filters/lines) ! Just as a matter of interest how did you check for fuel at the rails ? i.e. which connection did you take off ?

Cheers

Jengasan

#7 11-28-2006, 06:26 AM

Hello . I JUST CRACKED THE FUEL RAIL OFF FOUR OF THE INJECTORS, and as they say dry as a witches nipple!!!
Its our big flying trade show in birmingham this weekend so it will be next week before my liver has recovered enough to tackle the old girl with the advice you gents have given me so far.
Pip Pip. Ian H

#8 12-13-2006, 01:13 PM

Hi chaps back again after another day fettling the old girl.
Hotwired the fuel pump after checking fuel was getting to it and after about 10 secs got a pressurised common rail. SFSG.
However when I reattached the power supply and turned the ignition on I got the usual 2 secs of pumpr unning but on cranking no firing at all.
Wev'e got a big fat spark so ign is ok.
So questions for you lads if you can help.
What pressure should the common rail run at?
Where is the sender that senses the rail pressure drop and energises the pump?
So I dont eat the ecu or my multimeter how do I check im getting a command pulse to the injectors?
And finally five of the injectors are weeping gas from the interface between the metal body and the steel top(dried out I guess) are they a servicable component and if so any idea where i can get them done in Blighty?
Just a final note to say how impressed I am with the caliber of discussion and info on this forum.
Promise pics shortly
Pip Pip Ian H

Tomguy · #9 12-13-2006, 05:10 PM

1) Pressure should be about 28PSI.
2) The pump is energized all the time AFAIK, and the pressure regulators are what keep the system in check (excess pressure/fuel is sent back to the tank)
3) Disconnect all the injectors. Put a 12v lightbulb on each line while cranking, a light indicates a pulse. don't use a headlight, a 5w lamp will work fine.
4) Replace all the injector rubber hoses with EFI-rated hose. You'll need 8 clamps to do the bottom half of these since the factory uses the brass crimping you dont have a tool to duplicate.

david s poole · #10 12-13-2006, 05:54 PM

hi ian,born in coventry myself now in dallas texas by way of sydney aust[stopped off for 23yrs]your car is old d jetronic and the injectors are fired by trigger points in the bottom of the dizzy.they are prob filthy.now you also have check valve in fuel pump and when you turn key on pump will only operate for 2-3secs.cranking the starter does not keep pump operating so you have to have enough fuel in the rail to start.then pump will activate again.you will need to remove distributor to access the trigger points.by the way the injectors are fired by 4vdc.good luck

Jengasan · #11 12-19-2006, 11:50 AM

Ian

I just found this thread again. I've had all my injectors done recently so if you're still looking for a source for repair in the UK let me know.

Cheers

Jengasan

Jengasan · #12 12-19-2006, 11:59 AM

Ian

I thought I was going to have to hunt for this but I found it pretty quick, go to and call them.

http://www.injectorcleaning.co.uk/

I had all 8 of mine cleaned, new pintle caps fitted and the baskets replaced as well as new hoses and clips. The results were pretty impressive, though I had actually done it as a safety measure (35 year old high pressure hoses).

You'll need new injector seals too but don't worry MB still have them and they are not (strangely enough) expensive. Just watch you don't lose anything down an injector port which taking them out etc. I'll share my experiences there if you are going to change them out without removing the heads

Good luck

Jengasan

P.P.S I have the complete MB printed service manual for the w108

#13 12-20-2006, 08:42 AM

thanks for the tips so far hopefully in the next week or so ill check out the injector circuit
have a good christmass all
Pip Pip Ian H

mercmad6.3 · #14 12-27-2006, 06:42 AM

Hi Ian,with aircraft experise you must know you ned to start from the Fuel tank ...
under the tank you will see a round bung in the center.Remove that and you find a filter built into the bung,get it ultrasonically cleaned because after sitting for so long the tank will be; 1/ rusty inside. 2/ full of noxious varnish. Both situations call for the tank to be dropped and cleaned out.Because these cars are so common I usually just buy a tank from the wreckers and get it cleaned then put the sorted item into the car.
There are two pipes running from the tank.
the large one is fuel to the pump.The small one is the fuel return from the injection.push a peice of mig wire down the small line to make 100% sure it is clear .They CAN and Do rust up for some strange reason.
With your tank clean you must replace all those hoses on the pump.
If you pull the pump remove it with all those fittings etc in one lump, replace the filter!!!!!.
The pressure Accumulator can be seen clearly once you realise you are not looking at the pump or the filter..

.
Once all that is taken care of you now and you have 11.5 volts minimum to the pump you can go to the next stage.
Remove the rubber line to the cold start injector.Thats the injector on the left front of the intake manifold.
Connect a pressure guage to that line so you can test the fuel pressure.
It must 28-30 PSI constantly .
The pressure regulator is on the rear of the manifold.
There is a an adjustment nut on the top.
If you have more pressure than that you have a blockage between the engine and the tank.If you cleaned the tank properly you shouldn't have this problem though.
What you must remember is that the injection will NOT work properly if the air cleaner is off the engine.
Once you are sure you have fuel pressure sorted,reconnect the fuel line to the injector then undo the injector and aim it into a small clear container.
Get an assistant to crank the engine and if the injection ECU is OK the injector will spray fuel into the container.

As you have spark,but no fire ,I would say that you don't have sufficient pressure to start the engine because it will fire on the cold start injector alone.
Try pouring a quantity of fuel down the intake.If it fires then you have narrowed down the fualts to low pressure.

cth350 · #15 12-27-2006, 06:53 AM

Ian,

You can get a CD of the service manual in the US for about 30$ plus shipping.
Last I saw, they didn't ship oveseas though. However, you might be able to get it directly in the UK these days. Ask your local benz dealer. If that doesn't work, one of us in the states can get it for you.

-CTH

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