W116 280 SEL not starting or idling

1973-1980 : 280S, 280SE, 280SEL, 300SD, 350SE, 350SEL, 450SE, 450SEL, 450SEL 6.9
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scottb116
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W116 280 SEL not starting or idling

Post by scottb116 » Tue 02 Feb, 2016 4:15 pm

hi
I'm new to Mercedes and need some help
my W116 doesn't want to start properly anymore
bought the car a month ago, put a new fuel pump, battery and fresh fuel and drove it home, parked it in the driveway all good, started it everyday for a week without a problem, just had to turn the key and it started.
was giving it a clean up and started to wash down the engine, after a minute it stalled and wouldn't re start, blew out with air, still no start, unless I poured fuel into it, then I had to rev it to run, wouldn't idle at all.
i did noticed the plug leads were badly chewed by rats and thought maybe that was the issue, after changing the plugs and leads it still no better, so then i drained the fuel tank replaced the furl filters and refilled with fresh fuel, still no start?
when it does start (with help) i really have to rev it, and after 30 seconds it starts to blow white thick smoke.

its only had a problem since i washed under the bonnet, but i didnt have the washer on it for very long?

thanks

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Re: W116 280 SEL not starting or idling

Post by CraigB » Tue 02 Feb, 2016 4:54 pm

Welcome. If it was running fine before, chances are it is something small.

I will cut straight to the white smoke because you rarely hear of this and it seems to always be the same thing. From memory it is that the transmission modulator diaphragm gets a hole in it and the vacuum from the manifold sucks it up, into the intake and burns it. Check your dipstick level. Or remove the vac line to it (its on the side of the trans) and see if it stops the white smoke. Not a difficult part to replace.

See what others say, but for the rest of it, my suggestion is not to play with adjustments etc. Let it dry out properly. Also you don't say what year it is - is it djet or kjet? djet could have water in injector wiresetc. computer wires. But i don't have great expertise with these. Sounds like you have crossed the ignition side of things off the list.
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Re: W116 280 SEL not starting or idling

Post by scottb116 » Tue 02 Feb, 2016 7:33 pm

It's a 12/78 , I think it's D jet
I know it will be something simple, I need to stop over thinking.

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Re: W116 280 SEL not starting or idling

Post by CraigB » Wed 03 Feb, 2016 9:21 pm

this is a good thread to check out - Chai has taken some great photos to locate those items.

viewtopic.php?f=13&t=21886
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Re: W116 280 SEL not starting or idling

Post by scottb116 » Fri 12 Feb, 2016 7:33 pm

I've just been playing around I bit more, and it's so close to starting.
But a few times it's done a big engine fart, a big puff of smoke, blows the dip stick out and oil comes out from the oil cap.
Do these have a PCV or something similar?

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Re: W116 280 SEL not starting or idling

Post by CraigB » Fri 12 Feb, 2016 7:44 pm

oh dear - combustion pressure into crankcase. Have you checked timing and your spark plug colour/wetness? I guess a backfire could do that? Did you check modulator etc?
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Chai
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Re: W116 280 SEL not starting or idling

Post by Chai » Fri 12 Feb, 2016 10:10 pm

Yes there is a positive crankcase ventilation (PCV) hose from the top of the overhead cam cover to the air filter housing.

The engine backfire ejects gas into the air-filter and the air pressure runs through the PCV hose and into the engine/crankcase - your air filter is acting as a muffler: easier for the air to go into the engine - and this pressure pops the dipstick out.
Chai
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scottb116
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Re: W116 280 SEL not starting or idling

Post by scottb116 » Sat 13 Feb, 2016 5:54 am

CraigB wrote:oh dear - combustion pressure into crankcase. Have you checked timing and your spark plug colour/wetness? I guess a backfire could do that? Did you check modulator etc?
Haven't checked timing yet.
(The Car was running fine when I bought it home, it's only after cleaning under the bonnet I've had the issue)
I changed the plugs and leads after the problem started, but I think I might pull them out and check them, the old plugs where very dirty and one was damaged.
What modulator do you mean?

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Re: W116 280 SEL not starting or idling

Post by scottb116 » Sat 13 Feb, 2016 7:26 am

CraigB wrote:oh dear - combustion pressure into crankcase. Have you checked timing and your spark plug colour/wetness? I guess a backfire could do that? Did you check modulator etc?
Haven't checked timing yet.
(The Car was running fine when I bought it home, it's only after cleaning under the bonnet I've had the issue)
I changed the plugs and leads after the problem started, but I think I might pull them out and check them, the old plugs where very dirty and one was damaged.
What modulator do you mean?

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Re: W116 280 SEL not starting or idling

Post by scottb116 » Sat 13 Feb, 2016 9:17 am

scottb116 wrote:It's a 12/78 , I think it's D jet
I know it will be something simple, I need to stop over thinking.
sorry, but its a 2/78 K jet

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Re: W116 280 SEL not starting or idling

Post by CraigB » Sat 13 Feb, 2016 10:34 am

sorry- penny just dropped for me - when you changed the leads you have swapped them around, or in the wrong holes in the cap. That precisely explains the backfire thing. Water in ignition etc might have started it but then when you changed those bits could have fixed but then in wrong order its a new problem. Firing order is on rocker cover from memory. Get the car on tdc with distributor cap off and then just work around making sure they are in the right order. And i reckon we have all got that wrong at least once in our lives!

White smoke is still a worry but if you get it running smooth, and still blows white smoke, I really do think that will be modulator - but it shouldn't stop it running.
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Re: W116 280 SEL not starting or idling

Post by scottb116 » Thu 07 Apr, 2016 1:48 pm

still not starting
removed all the leads and replaced them one by one
if I spray some carby cleaner in, it runs for about 10-20 seconds,but wont idle I need to rev it
checked the fuel distributer, there is fuel going into and out of it, I undone the injection lines on the fuel dist and fuel was coming out, one had a bit of crap in it.
ive run out of ideas, currently trying to track down an old retired in my town, but he's a busy man.

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Re: W116 280 SEL not starting or idling

Post by Scotty H » Mon 11 Apr, 2016 6:21 pm

Hi

I'm also having a few ongoing problems with the starting of my 280SEL also, now in daily use after the previous owner's lack of use.
We have done the warm up regulator (a reconditioned unit I'm told), all plugs/leads, and checked the pressures in the lines. It's a Kjet, and starts immediately then stalls, but will burble into life on the second or third key turn, roughly idle for a minute before taking off with the occasional pop. After about 2km all will be good.

Curiously, I was speaking to a customer today who did training on Kjets and advised to check/replace all vaccum lines, which may work for you. To solve the starting problems, the warm up regulator seems to be like coils - they work or not. It may be worth trying a second hand one. There seems to be one course of action - check everything!!!

Not much help I suppose but I do wish you luck - they are a beautiful car!

Scott

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Re: W116 280 SEL not starting or idling

Post by V8Finny » Mon 02 May, 2016 8:40 pm

Not wanting to idle, yet revs strongly, is often an indication of too much air (per fuel) at idle.

This can often be due to a simple vacuum leak. rubber hoses aren't that expensive.

Other suspect is Ignition.

You may have wetted a control box, etc that needs to be dried out completely before you will get distinct pulses of spark from the ignition, rather than the current bllaaaaaaahhhhhh of spark supply that you are experiencing.

Hope that helps.
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Re: W116 280 SEL not starting or idling

Post by scottb116 » Sun 28 Aug, 2016 8:43 pm

So, the car isn't starting
But I haven't really spent much time working on it
I had an old mechanic look at it, and he said it appeared to be flooding itself, we starting looking into the fuel issue, and then starter failed, so I walked away for a few weeks.
I've been getting it ready to pull the starter out,but there is so much dirt, mud, oil leaks and road grime under this car, it's a mess and the rats have had a feast on it.
Is there an easy way to get the starter out?

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Re: W116 280 SEL not starting or idling

Post by lewbear » Fri 06 Jan, 2017 2:52 am

scottb116 wrote:So, the car isn't starting
But I haven't really spent much time working on it
I had an old mechanic look at it, and he said it appeared to be flooding itself, we starting looking into the fuel issue, and then starter failed, so I walked away for a few weeks.
I've been getting it ready to pull the starter out,but there is so much dirt, mud, oil leaks and road grime under this car, it's a mess and the rats have had a feast on it.
Is there an easy way to get the starter out?

man sounds like a nightmare, did you ever get it sorted?
1977 W116 280SEL - Red, cream interior
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Re: W116 280 SEL not starting or idling

Post by scottb116 » Sat 28 Jan, 2017 9:52 am

still not going, i started pulling the starter motor out, then lost interest and busy with other stuff.

but i've made it my mission this year to get it going and back on the road. ( i might give it a heart transplant ????)

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Re: W116 280 SEL not starting or idling

Post by brother benz68 » Sat 30 Dec, 2017 1:24 pm

Hi, I see you are thinking of engine transplant as you are having trouble starting your car, with what you have said with the car flooding on startup can I suggest you please check your start up injector? this extra injector is suppose to run briefly on start up for rich mixture but can give trouble if it is leaking fuel into the engine. Easy things first - remove plug to cold start injector to establish faulty cold start valve, try to start with the plug off. Second thing is to check the injector isn't leaking. Best of luck.

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Re: W116 280 SEL not starting or idling

Post by Mercmad » Sun 31 Dec, 2017 9:24 am

As with any car, start at the very beginning. Check compression. Adjust the valves . Replace the fuel filter . Dump that 2 year old petrol and put 10 liters of newly bought petrol in the tank. Check the fuel pump fuse. Turn on the ignition , remove that blue wire from the air flap body and push the air flap down. The pump should then run and you should feel pressure as you push the flap down. No pressure + no pump. replace it. A holden VK(injected six) commodore is the same pump but cheaper at repco. replace the blue wire. Check the coil for voltage.
Put a spark plug in the coil lead at the distributor end , put the plug against the head and get someone to crank the engine. Got sparK ? OK. No spark? the grey ignition box has failed ($$$) .
Got spark? check timing by placing the damper on the front of the crank to "0" . that is either number 1 TDC or 180 degrees out. You can check by looking at the cam lobes of number one, they will be facing upwards.
Now put plug lead one onto the cap terminal where the rotor is pointing. in a clockwise direction, replace each lead in the firing order, 1,5,3,6,2,4 . But before replacing the cap back on the distributor, check between the rotor center and the outer edge of the arm with a multi meter, it should be 1.5 ohms resistance. An infinite reading indicates the rotor is shagged.
While you have the multimeter, undo the two coil leads and test the coil, there should 5k ohms roughly .Again,an infinite reading means a dud part. reconnect everything, check the green lead from the dist. to the grey ignition box . it MUST be in perfect condition as this acts as a resistor for the ignition.

So by now, you must have compression, the cam cover is back on. You have a proper supply of clean fuel , and you have spark to the correct order. With 13 volts in the battery it should start.

This is just the basic stuff. You may find rotten fuel lines, a dead fuel pump relay, a dead pump or a blocked tank filter or even a rusty tank . You might find a dead cylinder or the compression is simply too low to fire the petrol . Lots of things can stop an engine and these are no different to any other in that repsect.
BTW, the trans modulator is bolted to the right rear side of the gear box, looks like a oil guage sender with a rubber hose connecting it . Remove that push on hose and if trans fluid is obvious in the hose or modulator it's buggered.

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