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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53014
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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560 sec, drive it every day - great running car - parked it

Customer Question

560 sec
JA: Thanks. Can you give me any more details about your issue?
Customer: drive it every day - great running car - parked it 2 days ago - went to start and it would not run. only cranks -fuel pumps not coming on. no noise from pump or pressure. jumpered pin 7 and 8 on fuel relay - pumps run, tried to start but just cranks. replace relay with new - part numbers do not match - but books say it will work - but pumps won't come on. volts at 11 and 9 = 11.85, volts at 11 - 8 = 12..jumper 7 and 8 pumps run ==Fuse 1? do not see a fuse 1....
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Submitted: 7 months ago.
Category: Mercedes
Expert:  Marty replied 7 months ago.

Hi, have you tested for spark? Will it run on ether?

Customer: replied 7 months ago.
it has spark and no this is fuel injection a w126 5.6 560 sec
Expert:  Marty replied 7 months ago.

I know the car, do you mean no, it won't run on ether?

Customer: replied 7 months ago.
I have not sprayed ether to try and get it to start. when 7 and 8 are jumpered i have good pressure and can hear and feel the pumps come on.
Expert:  Marty replied 7 months ago.

That's fine but what you are saying doesn't make sense. It would be nice to know that it runs on ether so we can focus on just the fuel system. How are you testing to see if the new relay works? Are you cranking the motor while someone checks to see if the pumps are running?

Expert:  Marty replied 7 months ago.

Looks like I lost you. I'll check back in the AM if you want my help with this.

Customer: replied 7 months ago.
this is a 87 it runs on pump gas, 91 octane, Original equipment ....i have not sprayed "ether" - "quick start spray" to try and get the engine to run since it is fuel injected. - the new relay is tested by removal and a jumper from pins 7 and 8. This works and the pumps come on, and pressure is noticed at the injection manifold. It worksthe same as old relay. When ignition is turned on - car will not start, just cranks over.So we have -
1. jumper pumps - pumps come on = good pumps - the car should start at this point.
The jumpered pump would run all the time and they do but engine will not start. - why bad filter? it was running fine.2.New relay should be good - but pumps will not run when key is turned on - relay may not be comparable to old part.3. voltage readings indicate open wire.or bad F1 fuse.....I know of no other fuse in the fuel system..
Expert:  Marty replied 7 months ago.

You are replying as if you don't think I know the car. I grew up working on these cars. Your diagnosis is flawed because you don't know if it runs on ether. The fact that it is fuel injected has nothing to do with spraying ether. The fuel pumps only run for 2 seconds when turning the key on. You need to crank the motor to see if the pumps are running with the new relay. Since it doesn't run when you bypass the relay and according to you the car has good spark the only possibility is there is no fuel in the tank or one of the pumps is bad or neither of your relays are bad because you have not checked them while cranking the motor and the actual problem is a mechanical fault with the engine such as a jumped timing chain. If you knew that it ran on ether it would determine the direction of the diagnosis.

Customer: replied 7 months ago.
it doe not runs on "ether" - it runs on gasoline - USA grade "A" GAS - from a pump at the gas I have stated several times - GAS not Ether - GASOLINE original w126 parts. running on gas. not ether - not meth. not Natural gas. just plain gasoline....If they pumps are jumpered and the pumps run why is there not gas going to the injection manifold.bad filter? do both pumps need to be running. - seems like bad relay - needs to be changed with exact part number - but why will it not start if the pumps are running?
Customer: replied 7 months ago.
worst advice I have every had in 15 years of Mercedes work - rude - and not knowledgeable - would not recommend - since it appears he does not know what GASOLINE is - money wasted.
Customer: replied 7 months ago.
then....did i miss this?
you have worked on these all your life - then why do you answer - my diagnosis is wrong. when you do not know what GAS is?
Not from here - Arab?
Expert:  Marty replied 7 months ago.
You are obviously not understanding. Ether is a substitute for gasoline. You spray a little ether into the air intake to see if it will fire. It is a diagnostic step. When dealing with novices such as yourself it is a simple step that tells me if the ignition system is ok. You are making way too many assumptions in your thinking and I don't have the time or patience to educate you. Either follow my instructions to you or I will opt out and let someone else help you. I am not being rude, just to the point.