Delayed start - a few turns of key to prime fuel - 1985 280SL
 

I have a new to me 1985 280SL and it often, but not always, has a delayed or hard start. It is like the fuel loses it prime and the lines are empty. Eventually if I floor the gas and keep cranking it will start or better yet if I turn key, not to ignition but to get fuel priming, turn back and then turn on again, then do it again it usually starts right up.

Any ideas? Is there something to check as to why it may be losing pressure? Is there a back flow valve or something?
Also I feel like I may have a slight gasoline smell in the trunk. Nothing major but I do feel like it might be there. I was under the car and didn't notice anything around the fuel pump or fuel filter that indicates and leaking there.

I have never replaced a fuel pump or a fuel filter on a car, I have on my old golf cart and a boat however.... So please keep in mind I am a novice but wiling and capable of learning.

Typically those symptoms are a leaking check valve. Not too familiar with your car but it’s usually screwed on the pump or filter. I’d definitely search around for that gas smell.. leak or cracked vent hose somewhere

Does it act this way when stone cold or only when warm/hot? 1985 is a transitional year, the older K-jet system didn't run the fuel pump unless the engine was rotating and did no pre-prime when the key was turned. It relied solely on the fuel accumulator for good starting. Symptoms of a failed accumulator are a slightly longer crank when cold, but extended cranking or failure to start when hot or heat soaked.

If it's always starting hard, it may be that the cold start injector isn't working or it may be that someone has messed with the fuel mixture adjustment on the fuel distributor and gotten it too rich or too lean.

I think it starts easiest when cold. When I notice it most is when it has been driven and then it sitting for a few minutes - like in or our of a store for instance. Then if I did not try the key a few times to run the fuel pump it would crank for a long time. It does always start though.

Is there a way to check the accumulator or is it more of a try to narrow the symptoms and then just try a new one?
I can see the accumulator and it appears easy to access. Any instructions on how to change it and will it dump a whole tank of gas on me if I loosen it up?

Also - part number if someone has it would be great just to confirm. My car is a 1985 280SL which is a Euro model M110 engine.

Someone mentioned a potential check valve - is that a possibility?

thanks again!

Classic symptom of a failed accumulator. The accumulator has a spring-loaded diaphragm in it to maintain pressure on the fuel system. When it fails (ruptures) the fuel pressure bleeds off and the remaining fuel in the distributor vaporizes and causes vapor lock. When mine did this it refused to start unless you let the engine cool long enough. If you went into a convenience store and back out, you were guaranteed to have a 15 min wait before it would restart again.

This is probably stupid but I’ve spend loads of time googling and searching and can’t find a walk through just lots of issues around bad accumulators.

I can get at this from behind but is gas going to leak all over and drain the tank? How to prevent that? Please share some tips on how best to replace these and the pump and filter for that matter.

Any tips would be greatly appreciated and while I am there I may just replace the pump too although the accumulator looks simpler so I may just do that- unless of course I bathe myself in gasoline accidentally.

The pump is K-Jet specific. I'd leave it alone. A generic will not cut it and the OE ones are expensive. The accumulator will leak out whatever gas is in the lines and in the canister. It won't drain the tank onto you. Prepare for a spill but not a flood. It's pretty straightforward how to replace the accumulator.

Ok thanks. I saw some Bosch and some Bosch look alikes that appear the same design as the one on there now- although mine could be 20 or 30 years old as it doesn’t look new for sure.

What about the fuel filter? Will changing that drain the gas tank? Mine is a Bosch and it doesn’t look old but if I’m under there I may change it anyhow.

It appears replacing the fuel pump itself would drain the tank- is that correct?

What is a "1985 280SL" ?

I'm subscribing to this thread because I have a 77 280SL in with start/running issues. When first brought in I sprayed a little starting fluid in air cleaner and it started up and idled out well until getting up to temp then shut down. It would bog down if given throttle during this time. Next I pinched off return line at tank and it started and would rev during throttle application. Then the return line split and started leaking. I've got a new filter/pump coming and will do smoke test on system over next few days. Will replace hoses as necessary. I've still got more troubleshooting to do.

Someone asked what a 1985 280sl is- it’s a Mercedes roadster. Not sure what that question means but if it as simple as it sounds the 280sl is a German model.

Back to my question-

If someone could please share what can be replaced without draining the tank that would be great. Also if there is a proper procedure to change the pump as well without draining the tank that would be great to know.
I am going to change the fuel accumulator and potentially the filter and pump too but want as few surprises as possible.

Thanks

The guy who asked is a known pot-stirrer.

Don't waste your time with the pump. They work or they don't. You'll be spending big bucks on a pump with no gain to show for it. The filter and accumulator can be changed without draining the tank. As I said in a previous post, expect a spill, the lines and contents of the filter/accumulator will drain out when you open them.

Per the Factory Service Manuals (FSM), and as a matter of practice, the large feed line from the tank is to be clamped off when doing any work that will involve opening of fuel lines further downstream in the area of the pump/filter/accumulator package.

Yes, search for threads started by me. A few years ago I started experiencing intermittent hard starting - long cranking times both hot and cold, which became more frequent as time passed.

I suspected the fuel accumulator and figured out an easy on-the-car test to determine if it had an internal leak that shorts fuel back to the fuel tank feed hose and prevents the buildup of system pressure.

It failed the test and a new accumulator solved the problem.

I did a destructive analysis of the failed accumulator and found cracks in the elastomeric diaphragm that caused the problem. I documented that in another thread I started a few month later with photos of the worn out, cracked diaphragm.

Duke

You mention clamping the large line. With what? Channel locks for instance? I would be afraid it would destroy the line or cause leaks but please advise.

Also- can someone please confirm the proper part number for a 1995 280sl?
Thank you