Hi

I'm having some hot start problems on my 85 W126 500 SEL Euro version, I'm getting what I believe to be vapour lock in the fuel lines, and hence fuel starvation causing excessive cranking under hot starting, and sometimes on cold starting if i've been on a long journey where the engine has fully warmed.
Once eventually started, I can hear bubbling in the fuel tank as if the vapour is getting purged from the lines.
Should my fuel pump run for a few seconds upon turning the ignition on? If not, is there a certain relay I can splice in to make this happen?
How do I know if my fuel accumulator is shot?

Kind Regards

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Ben

'85 500 SEL
'85 928S2
'88 560 SEC
'90 750i

Maybe one of the experts can chime in, but I thought for some of the older models MBZ actually specified in the manual to hold the gas pedal down part way when starting hot. I believe my 560SEL and my dad's 450SEL said this right in the manual. If you didn't step on the gas, the result was hard starting not unlike what you described...

Hope this helps.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Hi,

Thanks for the suggestion, I've tried holding down the accelerator pedal part way, full way, pumping etc with no joy.

Regards

__________________
Ben

'85 500 SEL
'85 928S2
'88 560 SEC
'90 750i

Ben12345

I bought an 85 380SE about 3 months ago, it has over 200K miles. Mine was hard to start hot until i got familiar with it's personality (and cleaned up a few things). This is what I did : cleaned the ICV with carb cleaner, cleaned the air intake (air flow) with carb cleaner. Then removed the injectors and cleaned them with carb cleaner and oiled the injector seals (since then I've replaced the seals). When the engine is hot, I crank and gently press the gas pedal at the same time. It works every time now. I believe one cause of difficult hot starts is leaking fuel injectors. They can dribble gas when they're not supposed to and experience a vacuum leak around the seals if they are old and hard. Hope this helps.

djb2000

hi
I have a 85 500sel that was acting up witrh problems like you stated.I was convinced that i had a pump,injector problem,until after reading thru the posts on hard starting. quits when running,no fuel , etc I noticed a common thread was check the fuel relay,(use the search button) in there I found a way to open the relay and check it,Mine was broken,I ordered a new one from fastlane (click on buyparts at top of page)for about 60 bucks ,installed it and a whole bunch of problems just went away like magic. My thanks to the guys who posted and phil at fastlane,
Cliff

Thanks for the suggestions... I'll try cleaning the injectors and ICV. It seems as if there is a slight misfire at idle when i'm running on petrol, so that could be the cause.
I've already tried the relay from my parts car (which started and ran fine) to no avail.
I just had my Inspection (passed fine BTW!) and the CO level was very low, onlt 0.12% when i'm allowed up to 4.5%. The examiner said that my mixture appears very lean, so maybe my fuel pump or filter could be clogged too, causing a lean mixture and hard starting.
I've taken the pump off my parts car, and ordered a new filter, so I can change those just in case.

Kind Regards

__________________
Ben

'85 500 SEL
'85 928S2
'88 560 SEC
'90 750i

DJB2000 - can you describe the procedures for cleaning the ICV (idle control valve)? My car sometimes stalls out when the engine is hot and I think this may be my woe with it. I have asked on several topics here before on how to clean it, but no one has yet stated how to do it. I know where it is, but I do not know what all I need to do to remove it. I am looking for "step by step" instructions. I cannot tell, but are their any electrical or fuel connections to it, or is it all vacuum? Thanks!
BTW- my car is a 1985 380SE as well.

I have not bothered reading the other replys, you have a bad fuel accumulator, or bad check valve. Thise dont realy go bad though. If you really want to know whats wrong this it, put some fuel gauges on it. But I am going to put money on it that its the accumulator.

In casse you don't where it is,it's under the car next to the fuel pump onm the 380-420-500 cars.drain the fuel tank first!!!.
pull the hose off the outlet side of the pump( replace that rubber hose !!) and you will see the check valve,it's a nipple on the pump.if you remopve it and blow air through the nipple in the direction oif flow it should let air through,it must not allow air back the other way.
If it is suspect,order a new one.
The fuel accumlator is easily checked,Start the car running and get it warm.
Turn the engine off, wait about an hour,then temporarily loosen the forward line on the fuel distributor,the pressure should spray out.( caution it's at 5 bar ,place loose rags to catch any fuel spray and put the cigarette out) If not the accumulator has gone.
In that case pull the line right out and remove the nipple into the distributor,it has small filter which will be full of bits of stuff from the accumulator.After you have fitted a new accumulator,check valve,and FILTER!,The line ,in this case must be connected to hose and led into a bucket.connect terminals 30 and 87 on the relay and turn on the key to pump fuel and clear out the line.about 3-4 liters does the trick.
emove you jumper from the relay and try the starter again,let the car get warm and see if the problem persists.

Guess not.....

on my 500 i don't even touch the pedal, starts fine hot or cold.

Thanks Mercmad for an excellent procedure, I'm hoping the accumulator is good, as it seems as if I can only get it from the benz dealer over here, none of my usual german car specialists carry them, so it'll be expensive!
The parts guy will probably end up telling me that I have to buy the whole assembly under the car, the pump, filter, accu etc...
I dont know what its like in the US with older Benz cars at the main stealer, but over here in the UK, they dont want to even try to help you.

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Ben

'85 500 SEL
'85 928S2
'88 560 SEC
'90 750i

You shoudn't need to buy the entire assembly because the pump/filter assemblies are seperate from the accumulator.on the later cars such as the 560 there are two pumps and in that case you can get robbed severly .
Try going to a breaker and buying an accumulator from any of the W126 cars, Including the 280SE/SEL or even a part from a W116 450SE ( the 6.9 even has the same bit ) .In any case, get under the car and replace all thosae rubber hoses,the climate in the UK is not conducive to long life on the hoses I notice( My local breaker gets lots of mercs here for wrecking from the UK...)
http://www.hitcity.com.au/GermanWreckingCo.info
Good luck!

Just thought i'd let everyone know what the answer was to my problem. After putting a new fuel filter on today with absolutely no change in starting, and still having poor running, I decided to 'tweak' the mixture screw. It was indeed running way too lean, I turned it just under one turn clockwise and now its excellent! Starts fine, idles great, and now I have power that I forgot I had before.

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Ben

'85 500 SEL
'85 928S2
'88 560 SEC
'90 750i

Did you "adjust " the screw before this problem arose?,If not,it's the spindle valve sticking in the fuel distributor.Later,if it happens again,you can disassemble the distributor and clean the spindle with brake clean.They get covered in varnish after a few years and become sticky resulting in the symptoms your car displayed,the air flow meter won't go up and down properly.
Nice result!!!