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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 22744
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a mercedes 300SE 1989 that won't start . I have a good

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I have a mercedes 300SE 1989 that won't start . I have a good spark but no fuel at the injectors. I have fitted a second hand fuel distributer and fuel regulator and still nothing at the injectors. Before fitting the regulator I checked there was fuel arriving there and was immediately sprayed the minute the ignition was turned on.Previous to changing these parts I took the car to a Merc. dealer in France who wanted 3200:00 Euro's to fix it and supplied a Devi's which included a new regulator and distributer.
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Customer: replied 3 years ago.

I would like to remain waiting thank you. I would add that I have also replaced the fuel filter and there is no problem with the pump.

Thanks Geoff.


Ideally measure the pressure at the inlet to the main engine fuel distributor (should be 5 to 5.8bar) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

If this is OK then remove the rubber intake boot from the fuel distributor and then unscrew on the top of the unit find the central nut , pipe feed into the fuel distributor and push down on the aluminum plate under the rubber boot you should see the main fuel metering pin / needle rise up smoothly as you push down the plate, if its sticky or dirty then its possible this is getting stuck.

If this is OK then remove all the injectors but leave them connected to their fuel lines and put all into a clear container then turn the ignition on and (having replaced the central feed pipe nut) push down on the aluminum plate all the injectors should spray at once and look for ones that aren't spraying as much as the others - and replace or ultrasonically clean as required.

Cold starting and running on your car is controlled by the warm up regulator. If the car is hard to start when cold and does not run well until the car warms up the problem will most likely be a faulty warm up regulator. A fuel pressure test should be performed to confirm that the regulator is faulty. The control pressure through the regulator should be approximately 2 bar when the car is cold and the pressure should rise to above 3 bar as the car warms up. If the pressure is too high when the car is cold it will be very difficult to start and the car will run poorly until the engine warms up. The overall fuel mixture should also be checked and adjusted after the warm up regulator is checked or replaced.
Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 22744
Experience: BEng hons Mech engineering, in auto industry 22 years
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Customer: replied 3 years ago.

Thanks for the advice Matt. I have the correct fuel pressure and the injectors are all working. At the fist attempt to start the car it fired once and then nothing.I removed the plugs and they were soaked with petrol.Prior to me changing the fuel distributor the mercedes dealer had told me that they had adjusted the fueling as much as they could and that a new distributor would be required.Could it be that the fueling needs resetting professionally with the new distributor or should it not matter.

Thanks *****

Hello Geoff

the only adjustment that should be touched is the mixture screw on the side of the unit - hopefully nothing else has been tampered with as everyhting else should be left alone

if this doesn't help then its likely to be an issue with the fuel pressure ' warm up ' regulator this offsets the fuel pressure according to temperature
Customer: replied 3 years ago.

Thanks again car now fires but wont start. I will change the warm up regulator and hopefully it will start.

I have received an e mail from just answer to say I have asked for a refund.this is not the case as I am very pleased with the information you have given.If you have a problem getting your money get them to contact me and i will confirm.

Thanks Geoff Ellis.

P.S.Terrible with computers.

Hello Geoff

the question is showing no refund

so thanks for the rating