Very looong cranking but runs well? - Mercedes-Benz Forum
 
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post #1 of 9 (permalink) Old 08-14-2019, 01:44 AM Thread Starter
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Very looong cranking but runs well?

Hi

Have just been trying to work through the fuel system of my 1978 280 SLC (euro) and progress is good. I just recently posted about some vacuum lines on my WUR and that has solved the cold running issues mostly which is very good! I have had a bit of search but nothing seems to come up related to this?

The only problem I have now is that to get the engine started there is a little bit of a procedure.

When you start the engine either hot or cold (slightly better when it has been used in the last few hours) you have one chance when it first turns over for the engine to catch and then it'll start very nicely, if you catch this all is good. If this doesn't work then you will need to crank for around 10 seconds (throttle fully depressed) with no signs of life, after that the engine then splutters a bit and roars into life.

I've never not been able to start this way but I feel that it cannot be good for the starter (also slightly embarrassing, man with the fancy car can't get it started properly).

A bit stumped on this one, so before I go and start randomly replacing fuel system parts would be great to get some opinions!

One other thing, when the engine is idling it will run smoothly but every couple of seconds it sounds like it misses a beat. I am not sure if this is related.

I have already replaced - Fuel pump, fuel accumulator, fuel filter, spark plugs, spark plug wires, new battery and have cleaned all of the injectors.

(Also just went to replace my gear linkage bushing because I thought the shifter was a bit wobbly, turns out I had none in there! The old ones had decayed so much they had completely fallen out. Shifter feels much smoother and more satisfying now!)
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post #2 of 9 (permalink) Old 08-14-2019, 03:21 AM
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Hi Chester, this sounds like the cold start valve (which injects additional fuel when the coolant temp is below 15deg C) might be malfunctioning (i.e. not spraying enough fuel) or the thermostat that controls it is not working (i.e. it reads the coolant temp higher than it actually is). I've had this happen on my 450 SL but in reverse, i.e. the thermostat was reading the coolant temp as lower than it was and spraying too much fuel, thus flooding the engine. To troubleshoot have a look here, whilst it's for a V8 I imagine it's fairly similar for the straight six. https://www.benzworld.org/forums/r-c...tarting-7.html
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post #3 of 9 (permalink) Old 08-14-2019, 06:48 PM
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You should check the fuel pressure accumulator below the fuel tank.

Rick
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post #4 of 9 (permalink) Old 08-15-2019, 03:03 AM Thread Starter
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I have changed the accumulator, so I am hoping that it works alright.

I will have a look at the cold start valve, any particular way to test?
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post #5 of 9 (permalink) Old 08-15-2019, 03:15 AM
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Chester, look at my post above with the link to the "cranking but not starting" thread.
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post #6 of 9 (permalink) Old Yesterday, 04:52 AM Thread Starter
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Originally Posted by miko1aj View Post
Chester, look at my post above with the link to the "cranking but not starting" thread.
Ooo this was an interesting read. So just to summarise, your cold start valve was injecting too much fuel when the engine was cold. This meant it flooded? And the temperature switch was responsible for this?

This would explain why I need to hold the throttle down at 100%.

I will have a check of those resistance values you quoted
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post #7 of 9 (permalink) Old Today, 04:03 AM
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Originally Posted by Chester123 View Post
Ooo this was an interesting read. So just to summarise, your cold start valve was injecting too much fuel when the engine was cold. This meant it flooded? And the temperature switch was responsible for this?

This would explain why I need to hold the throttle down at 100%.

I will have a check of those resistance values you quoted
Quick test is if you pull the CSV valve plug and it starts well.
Though this does not rule out the possibility that the CSV is stuck open but this can be checked by pulling the valve out.
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post #8 of 9 (permalink) Old Today, 05:33 AM
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[QUOTE=Chester123;17867898

So just to summarise, your cold start valve was injecting too much fuel when the engine was cold. This meant it flooded? And the temperature switch was responsible for this?

This would explain why I need to hold the throttle down at 100%.

I will have a check of those resistance values you quoted[/QUOTE]

Yes precisely - a vicious circle. Try what Djenka suggested, disconnect the csv, point it into a jar, crank the car and see if she fires up. If she does without any hassle than you're down to CSV or the thermoswktch that controls it.
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post #9 of 9 (permalink) Old Today, 05:34 AM
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Also the resistance I quoted was specific to M117 and the values might be different for straight six - you'd need to checj in WIS.
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