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engine wont fire

  • stylesmerc
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25 Aug 2019 12:44 #219975 by stylesmerc
engine wont fire was created by stylesmerc
hi my name is Mehmet Kashif i have a 1975 Mercedes 450SL
just recently i had my ECU tested and a New Fuel pump and a New relay the car wont fire
any suggestions?
regards mehmet

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  • krissbay
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25 Aug 2019 13:08 #219976 by krissbay
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Hi Mehmet,

does the fuel pump actually work? When you turn the key before the point of ignition you should be able to hear it. Maybe the new relay is not working. Why was it actually replaced?
Did the engine fire before?

Chris

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25 Aug 2019 13:25 #219977 by stylesmerc
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This all started when i changed the spark plugs i turn the key don't hear the buz before start up so i had the ECU tested its working perfect then changed the fuel pump for a new one still wont fire now i changed the relay which i have changed three times still no buz no fire and the pump don't seem to get any power?
I'm scratching my head over this one

mem

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25 Aug 2019 13:38 #219978 by Rudiger
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Mehmet, check the small wire at the Batterie. Positive post.
Rudiger

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25 Aug 2019 13:43 - 25 Aug 2019 13:44 #219979 by krissbay
Replied by krissbay on topic engine wont fire
You could try to remove the relay and bridge the right pins on the socket to get power to the pumps. In my case it's pin 8 & 7, but I'm not sure if this is same for your early SL. If the pump is then still not running measre the current at the pump. Maybe you got a broken cable?
Another test would be: screw out one spark plug and see if it is wet, this would indicate that you got at least fuel coming but no ignition. Did you get the right spark plugs?
Last edit: 25 Aug 2019 13:44 by krissbay.

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25 Aug 2019 14:18 #219983 by stylesmerc
Replied by stylesmerc on topic engine wont fire
Checked the wire on the Positive post even clipped it and put on new contacts plus spark plugs are the same as the old ones i changed,
Is there any chance t could be the ignition key itself still no buzz when i turn the key.My relay has only five pins for the pump and when i turn key on pump not buzzing because i can touch it. Have missed any other relay? i even cleaned the relay contact points with contact cleaner?
regards mem

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25 Aug 2019 17:04 #220005 by Dr-DJet
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Merhaba Mehmet,

well it is the ECU that lets the fuel pump run via that relay.

Can you check on pin 19 of ECU whether it is set to ground for 2 seconds when you switch on ignition? Also whether there is 12V between pin 16 and pin 11 and pin 24 and pin 11 when you switch on ignition.

Before you do that measuring for too long: Remove pin 15 from ignition coil. Otherwise your coil and power resistors can burn.

Viele Schraubergrüße - best regards, Dr-DJet Volker, Admin und Betreiber dieser Webseite
Wir sehen uns bei Moseltour und Alpentour


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25 Aug 2019 18:15 #220010 by stylesmerc
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Merhaba Dr-Jet
I sent the ECU of to a Specialist AVILEC Ltd based in isle of wight
and ran a diagnostics and they said it ran 100% perfectly and it came back with all the test results which i have. I know its something simple
regards mehmet

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25 Aug 2019 18:29 #220011 by Dr-DJet
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Merhaba Mehmet,

I never heard of Avilec and a D-Jetronic ECU is something totally different than a modern ECU. It is analogue electronics from the 60s.

If you are so sure that your ECU works. you should follow wiring diagrams and test all components and connectors there. Fuel pump must run for 2 seconds after ignition is switched ON. There are only few compoentns involved as you can see here on my D-Jetronic web site: oldtimer.tips/de/downloads/download/3-wi...p-control-d-jetronic

Viele Schraubergrüße - best regards, Dr-DJet Volker, Admin und Betreiber dieser Webseite
Wir sehen uns bei Moseltour und Alpentour


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25 Aug 2019 18:46 #220012 by Dr-DJet
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Hi Mehmet,

just for curiosity: How many function blocks did Avilec verify on your ECU? I really wonder whether they know their business or whether they just resolder everything and claim it works.

A failure of fuel pump control in ECU is something that can even happen temporarily.

Viele Schraubergrüße - best regards, Dr-DJet Volker, Admin und Betreiber dieser Webseite
Wir sehen uns bei Moseltour und Alpentour


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25 Aug 2019 20:36 #220023 by stylesmerc
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hi DR-Djet
i found them on Car & Classic site, then i contacted them and they wanted my year and chassis Numbers.they tested on it and didnt need any work i just paid for postage . here is the what they have done
Attachments:

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25 Aug 2019 20:38 #220024 by stylesmerc
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hi DR Djet
and here is another file with it beening tested
kind regards mem

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25 Aug 2019 20:46 #220026 by stylesmerc
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HI Dr Djet some reason i cannot add the other files
regards mem

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25 Aug 2019 21:46 #220031 by Dr-DJet
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Hi Mehmet,

your ECU has about 15 function blocks which can be triggered and analyzed. You only wanted to know whether injection and fuel pump control works. That is what Avilec has checked. That was not a thorough test of all functions. But it tells you that the basics work.

However I tell you that I have seen fuel pump control working one time and not working next. That is why I recommend to check what pin 19 does. it is up to you whether you believe me or not or whether you vheck your wirings and relay according to my diagram.

Viele Schraubergrüße - best regards, Dr-DJet Volker, Admin und Betreiber dieser Webseite
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26 Aug 2019 12:59 #220075 by stylesmerc
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hi Dr-Djet
i will do i will check it all out step by step thank you for your time
Best regards mem

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