fuel pump only comes on sometimes

[SALS450SLS]

hi all i have a 1980 450sl almost finished with the restoration , since i bought the car when i turn the key on the fuel pump comes on most of the time , sometimes i have to turn the ign on off a few times to get it to go on and start. i replaced the black fuel pump relay and still have the intermitten problem any help please ? replaced fuel pump also, when it dosent work the relay dosent even click cold it be a faulty ign switch
thanks sal

[450slcguy]

Similar issue

I also have a '80 450(slc). I rarely hear the fuel pump activate when the key is turned. Irregardless, the car always starts immediatly on first key turn. I've often wondered why I don't hear anything. Once in awhile, I do hear it activate before starting, but rarely.

I've been thinking this could this be related to the high idle problem I've been fighting a losing battle with for close to a year. Possibly related?

Any thoughts out there on what is going on? The fuel pump, filter, relay, and pressure regulator have all been replaced in the last 3000-4000 miles with OEM parts.

[Deltacom]

Originally Posted by SALS450SLS

hi all i have a 1980 450sl almost finished with the restoration , since i bought the car when i turn the key on the fuel pump comes on most of the time , sometimes i have to turn the ign on off a few times to get it to go on and start. i replaced the black fuel pump relay and still have the intermitten problem any help please ? replaced fuel pump also, when it dosent work the relay dosent even click cold it be a faulty ign switch
thanks sal

SALS450SLS
Your issues seems to be more to do with the fuel accumulator loss of pressure that prevents engine starting due to fuel low pressure triggering the disconnection of the fuel pump relay that will disconnect the pump if the engine does not start.

Originally Posted by 450slcguy

Similar issue

I also have a '80 450(slc). I rarely hear the fuel pump activate when the key is turned. Irregardless, the car always starts immediatly on first key turn. I've often wondered why I don't hear anything. Once in awhile, I do hear it activate before starting, but rarely.

I've been thinking this could this be related to the high idle problem I've been fighting a losing battle with for close to a year. Possibly related?

Any thoughts out there on what is going on? The fuel pump, filter, relay, and pressure regulator have all been replaced in the last 3000-4000 miles with OEM parts.

450slcguy
Your high idle problem may well be a defective auxiliary air valve.
SEE THESE POSTS relating to similar problems you have. It may help.

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[450slcguy]

Originally Posted by Deltacom

SALS450SLS
450slcguy
Your high idle problem may well be a defective auxiliary air valve.

Been there, done that. But thanks anyway.

[SALS450SLS]

Originally Posted by SALS450SLS

hi all i have a 1980 450sl almost finished with the restoration , since i bought the car when i turn the key on the fuel pump comes on most of the time , sometimes i have to turn the ign on off a few times to get it to go on and start. i replaced the black fuel pump relay and still have the intermitten problem any help please ? replaced fuel pump also, when it dosent work the relay dosent even click cold it be a faulty ign switch
thanks sal

should the fuel pump come on at ign for a few seconds then it goes off ,every time or not?

[SALS450SLS]

Hi all 1980 450sl replaced servo i had a 102 used a 104 inside is the same guts. Replaced inside ac pushbutton controls ,Ran the car for a bit but only blew hot from the defrost, moving themp wheel the same only hot thumb wheel didnt respond, put in a new amp box under glove box dash , everything but the center blower worked hi, lo, bylevel ,only difference the blower was faster in def mode ,it workd for 5 min then it went back to def only . Took out the amp opened it , transistor fried??
The other thing that dosent work is the door locks vacume?
Also when i start cold the car races for 5 min,then slowly coming down ??

Thanks sal

[SALS450SLS]

1980 450sl

[SALS450SLS]

could a bad hot water pump the one next to the servo burn a ac amplifier out

[nobby]

I'm not really sure what you want. Your posts are very hard to read and I can't quite make out if you are making statements or asking questions.
Lots of smart people here willing to help.
Help them help you.