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Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 49542
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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380SL: MB..fuel system; wont start, put fuel..fuel pump relay

Customer Question

Fuel System Problem to 1985 MB 380SL: Have no pressure guages to test fuel system; won't start, put fuel down air.throttle and started momentarily. Replaced new fuel pump and filter, still will not start. Should I next attempt to buy and replace the fuel pump relay? It's getting expensive just guessing. What would be the fourth part in fuel system I should consider replacing, if any? Please Help!
Submitted: 5 years ago.
Category: Mercedes
Expert:  Marty replied 5 years ago.
HiCustomer what is the history of this problem? Has the car been sitting awhile?

Marty
Customer: replied 5 years ago.
It is not run "frequently", but I run it about once a week for the sake of battery. I parked it from a short run three days prior without incident. Then, on fourth day, I cranked without avail./start. i Tested by placing fuel down Intake. It tried to start. So I ordered what I suspected to be most common problem, fuel pump and filter. Still only cranked w/o starting. With difficulty, found fp relay behind glove box, but hard to remove. Am considering purchase of $100 fuel relay, but what else other than fuel distributor at engine could be faulty? And testing that would not be feasible. I understand that the Fuel Dist. is expensive to replace, hence I need your advice, Sir.
Expert:  Marty replied 5 years ago.
Ok, can you tell me if the fuel pump runs for 2 seconds when you turn the key on and does it also run while you are cranking the motor? You may need a helper to turn the key while you listen or feel for the pump operation in the back.
Customer: replied 5 years ago.
I am so sorry, but I am at work and away from the perpetrator. Can I go check in a couple of hours (lunchtime) and get back with you then? I will email you with the test in a few, if you wish, and to what address?, or should I keep this page open 'til then? Sorry to prolong...
Expert:  Marty replied 5 years ago.
No problem at all, but you'll need to reply back to this question. Take your time. I'll be around throughout the day.
Customer: replied 5 years ago.

Got results!!: (Tried twice)--No sense of power/vibration at pump when powered to Acc; no vibration when continue action to cranking. Felt quite dead to touch, so Negative on this part, Marty...PS Thanks for quick responses, but I am back at office and would have to check anything else on car in about 5 Hrs after work...What do you suggest?

Expert:  Marty replied 5 years ago.
Ok, do you have a voltmeter or test light?
Customer: replied 5 years ago.
yes,Sir. I can try, but let me know what to set the voltmeter to...I usually only use it to test continuity, rather than voltage values, etc., hence consider me illiterate on its application/usage. Roy,
Expert:  Marty replied 5 years ago.
Ok, we will need to remove the fuel pump relay and bypass it. We want to use a fused jumper wire and jump from terminal #7 to #8 in the relay connector. Your pump should run and you should be able to start the car. If it does then you will need to replace the relay. An inline fuse holder makes a good jumper wire. Let me know what you find.

Marty

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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 49542
Experience: Bosch Certified Master Tech. Over 35 years experience.
Marty and 2 other Mercedes Specialists are ready to help you
Customer: replied 5 years ago.

OK--and thank you for your time. I was reluctant to attempt replacement partly on cost and partly because of in-accesability. I cannot see the annotation "N-16/4" that Manual refers to, but I will try. If this jump is unsuccessful in starting engine, and before you go, what would be the next item to replace, in your opinion? One more question: there is a doo-hicke type cannister placed in line ABOVE the fuel filter (in rear) at pump unit. The manual says it is #52, a fuel reservoir? Should I conisider this as a "blocked" possibility? as well, or is it not critical to operation/function?

 

You say, let you Know; I will in a week or so, when I acquire the new fp relay (when tested, as you recommend. How might I send you the results, if you are interested in outcome? Thanks for your direction, Sir. XXXXX@XXXXXX.XXX XXX-XXX-XXXX

Customer: replied 5 years ago.
PS I feel you didn't get you monies worth...I am willing to increase fee originally agreed upon, if you need. Just let me know it you feel short-changed, Marty, as I do not operate that way! roy leyva
Expert:  Marty replied 5 years ago.
Hi Roy, you are probably referring to the fuel accumulator. It won't be your problem. It's job is to maintain pressure on the fuel system when the engine is turned off. A bad accumulator results in difficult hot restarts. We've got to get your fuel pump working first. Don't worry about losing me after you click accept, you can revisit this question at any time if you need more help.

Marty

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