1979 Mercedes 450SLC help

[jwillans]

An appeal to the collective mechanical wisdom of the forum in support of getting my Father's 1979 Mercedes 450SLC running again having stood in the garage for the 25 years. The fuel pump was broken and has been replaced, the original after market one allowed the engine to be started and revved but made an almighty noise and my Father exchanged it for a Mercedes original part that Mercedes suggested was the right model for this vehicle. This was fitted and allowed the engine to be started, but as soon as it was revved the engine stalled. Thinking the pump was faulty, this was exchanged for another of the same model but with the same result. Any ideas on what might be going on / wrong? In case it is helpful, my Father suggested the aftermarket / noisy pump seemed to prime the engine before it started while the Mercedes pump doesn't seem to be doing this.

[Halitosis]

Sorry of absolutely no help on your technical question, but just to say my dad had a 450SLC (I think was the colour was "champagne" brown). Fabulous car and the fastest I've ever been on a road - speedo said 145mph, early 80s on the M25 (hard to imagine now)
Anyway - good luck with the fix and would love to see a photo or two

[JasonM]

Could be so many things, accumulator ? Fuel Injectors blocked? Dirty fuel tank and crap in the lines? I gather the K Jetronic is a bugger to set up correctly.

[jwillans]

Could be so many things, accumulator ? Fuel Injectors blocked? I gather the K Jetronic is a bugger to set up correctly.

Thanks. In this case why did the first pump work? Could it have been at a greater pressure than standard thereby overcoming any issues upstream such as the injectors?

[JasonM]

I really couldn't comment further Im afraid, It was just speculation.

[Captain Morgan]

Apologies if I have the wrong end of the stick but as it sounds like this has been sat for some time have you thought about some of the bigger challenges with reviving a old timer?

Nor Merc but this chap gives a good view into some of the challenges





I had a R107 for ten years so I hope you get it back to fine fettle

[JasonM]

^ I love his channel.

And If you haven’t seen Vice Grip Garage then you should, his revival episodes are incredible, and he’s got a great sense of humour.

[meridian]

This may just be a stuck air flow plate/ fuel distributor plunger, common fault- the round silver plate in the induction plenum chamber moves up and down under varying loads and pushes a plunger up inside the fuel distributor ,remove the dist block from its baseplate- do not dismantle this,just remove the 3 holding screws and turn this over in your hand. You will now see a shiny ball ended plunger that may well have stuck in place ,remove gently without burring,clean in solvent and make sure it moves freely in and out. This was the most common cause of idle but no rpm and they would stick after a short time if they had been stood and plunger moved to a new position. Easy and worthwhile check, any move after that will need you to own a fuel pressure gauge cos the system is very pressure orientated..The SL was my model when at Merc in the early eighties but I am a bit rusty now but do try this. If you go the pressure test route I seem to recall these pumps are regulated to around 6 bar or thereabouts, Good Luck.

[jwillans]

This may just be a stuck air flow plate/ fuel distributor plunger, common fault- the round silver plate in the induction plenum chamber moves up and down under varying loads and pushes a plunger up inside the fuel distributor ,remove the dist block from its baseplate- do not dismantle this,just remove the 3 holding screws and turn this over in your hand. You will now see a shiny ball ended plunger that may well have stuck in place ,remove gently without burring,clean in solvent and make sure it moves freely in and out. This was the most common cause of idle but no rpm and they would stick after a short time if they had been stood and plunger moved to a new position. Easy and worthwhile check, any move after that will need you to own a fuel pressure gauge cos the system is very pressure orientated..The SL was my model when at Merc in the early eighties but I am a bit rusty now but do try this. If you go the pressure test route I seem to recall these pumps are regulated to around 6 bar or thereabouts, Good Luck.

Many thanks - this is extremely helpful and have passed along to my Dad.

[lewie]

Really enjoyed that thanks

[adrianw]

^ I love his channel.

And If you haven’t seen Vice Grip Garage then you should, his revival episodes are incredible, and he’s got a great sense of humour.

I like him, that was a good video, snap on now do left handed hard drill bits to go with their easy out's

[spanner monkey]

Unless it’s already been replaced, It’d be worth changing the fuel filter as it may have collapsed internally .