Is the cold start injector getting voltage? Is it spraying? You can pull it out of the intake manifold, position it over a container and start the car cold. It should spray a fine mist of fuel.

 

If you know that at least one of these two CSVs is good, in other words, if the other car had no starting problems, you can easily check for voltage between both terminals of the pulled off CSV connector while the cold engine is being cranked.

If the cold start problem is not caused by the CSV or missing voltage to it, I suggest to test the fuel system’s "holding pressure". There might be a pressure drop caused by leaky fuel pump’s check valves, accumulator, pressure regulator, control plunger’s axial seal ring, injector(s) or other leaks … also the CSV could be leaky, which, of course, is highly unlikely in your case if your other car did not have starting problems with it.

Best wishes for 2017 to everybody!

H.D.

 

Hi Tom,

After some thinking here, I'm with HD, GT, & 281 regarding the 'fuel pressure' angle... but with a slightly different take..

When you said that the engine cold starts straight away with the throttle depressed.. yet has issues with the closed throttle, I believe what is likely happening is that one or more injectors may be leaking fuel drips when the car is shut off after a drive..

If so, it would follow that there would be less fuel volume/less pressure available in the 'system' initially as H.G. alluded to.. and that fuel could be both pooled in the intake or saturating the carbon on the backside of an intake valve or two causing a 'momentary' over rich mixture... which.. when the throttle is opened would almost certainly clear (as you describe)....

Additionally, in there was no difference with the swapped out cold start injecto(s).. my thought is that both are likely to be found OK.

Good Luck man & a Happy New Year..

Breakfast time now..

MBL

 

If the “holding pressure” drop is caused by leaky injectors, what MBL says, can indeed happen.

Talking about those “carbon deposits” on the backside of intake valves, and in the last part of intake ports … these are often the reason when the engine has to be started 2 or 3 times before it stays running, because the first injected fuel is (partly) absorbed by these (dry) carbon deposits. ... If the engine shows that behavior, don’t start to replace fuel pressure holding parts like check valves, accumulator, injectors etc., instead do a fuel pressure test first ! … it may not be fuel pressure related. :wink_2:

H.D.

 

My indy MB mechanic tested the fuel pressure last Summer and said it was good.

It looks like I will get a chance tomorrow to disconnect the cold start valve and test the voltage and spray (if in fact it sprays). I also have the parts on hand to replace the Thermo valve along with its' seal ring so I will install them tomorrow.

Does anyone know if I will lose coolant when I remove the Thermo valve? I am unable to find the correct torque for the Thermo valve. Does anyone know that value?

I have new gaskets for the cold start valve. Should I apply gasket sealant?

 

My indy MB mechanic tested the fuel pressure last Summer and said it was good. ...

And since when has it been necessary to “depress the pedal all the way to the floor before turning the key” in order to get the engine started?

 

Okay … the CSV seems to work well.

In that case, and since you’re not completely sure whether the cold start problems started before the fuel pressure test was done or vice versa, I suggest another fuel pressure test. If the engine behaves well under all running conditions at operating temperature, a 30+ minutes lasting “holding pressure” test after the hot engine has been switched off is all that is needed.
Although, since your mechanic is probably familiar with the KE-Jetronic, I’d let him first test the lower chamber pressure including acceleration enrichment test at a simulated coolant temperature of 20°C … he probably knows what that means. If he uses proper CIS fuel pressure test equipment, that takes a few extra minutes.

H.D.

 

I gave the pressurized system more than an hour and I did not see any leaks. I disconnected the CSV fuel line at the fuel distributor and gasoline was under pressure. Everything is put back together and I ran the car for 30 minutes to reach operating temperature. No leaks and everything sounds good.

Looks like another fuel pressure test will be needed for the lower chamber. Does anyone have that test equipment for sale and/or recommend a good brand that will fit the W126 fuel connections? Doing another smoke test might also be appropriate.

January and February are not my favorite months here in Iowa so this project may sit for the next few months.

 

I gave the pressurized system more than an hour and I did not see any leaks. I disconnected the CSV fuel line at the fuel distributor and gasoline was under pressure. ...

It’s not about the question whether there is residual pressure after the system has been pressurized … it’s about the question to what level the pressure drops when the hot engine is switched off and at what level it still is 30 minutes later.
Besides, like checking the duty cycle, testing the fuel pressure (system ~, lower chamber ~, holding ~), is a standard procedure for troubleshooting the KE-Jetronic and a lot easier than people usually think. Complete fuel pressure tests, also covering acceleration enrichment and overrun cut-off, can be done within less than an hour (passively observing the manometer during the ‘holding pressure’ test taking most of that time) ... and they can supply a lot of information about many KE-Jetronic components.

I agree with MBL about ethanol. Especially if the car isn’t used much, ethanol containing fuel can be problematic with the time. Not only can it increase carbon deposit forming, but it also bears risks for KE-Jetronic components.
And these carbon deposits on the backside of the intake valves and in the intake ports are not only often the reason for starting problems … also the engine’s running behavior, particularly at idle, can be affected. The mixture of atomized fuel and air passing metalic bright surfaces is more homogeneous compared to it passing carbon clad surfaces.

And not only does the engine consume more fuel if it contains ethanol in order to deliver the same performance due to its lower energy content, but also Lambda control requires a richer air/fuel mixture. With non-ethanol fuel the stoichiometric mixture is about 14.7:1 … with pure ethanol it’s about 9:1. … If this leads to thinking, that that must have an influence on the duty cycle … you’re right! :wink_2:

I talked in more detail about several things regarding ethanol containing fuel’s effect on the KE-Jetronic (including its effect on the duty cycle) in this thread:
http://www.benzworld.org/forums/w12.../forums/w126-s-se-sec-sel-sd/2720049-ke-jetronic-lambda-control-duty-cycle.html

H.D.

 

Hi Good Morning H.D. ,

I shouldn't think there would be hardly any rest pressure in the system after sitting say… 6 or 8 hours or for that matter.. overnight for the COLD start..

Re: ethanol. My thoughts were definitely USA~centric on that one.. as thats about all we can get here over the last umpty-ump years.. decades.

You wrote the KE-Jetronic 'bible' in that post of yours last year.. a very impressive BenzWorld contribution man.. Well done.

Happy New Year,

MBL

An earlier parallel thought on starts & general drivability:

In my view, our W126 cars, though excellent vehicles, cannot hope to possess the same engine smoothness and flexibility as a new premium (fill in the blank here) automobile / SUV of today.

That said, I'll take my SEC over a modern something anytime.. Heck, I am only 14 years into its ownership and appreciation so far..

 

Hi MBL,

... I shouldn't think there would be hardly any rest pressure in the system after sitting say… 6 or 8 hours or for that matter.. overnight ...

”hardly any” … me neither.

Regarding ethanol: In case of fuel containing more than 5% ethanol I generally recommend to use a suitable fuel additive.

Thank you for your compliment regarding “KE-Jetronic ‘bible’” … lol … But it’s actually just about the KE-Jetronic’s “Lambda control” and its adjustment … there’s a lot more to say about the KE-Jetronic than that.

... I'll take my SEC over a modern something anytime...

Yeah ... the SEC is undoubtedly a timelessly elegant classic. ... As I said earlier, my 300CE is the only Mercedes of that era I currently have. Both my wife and I really enjoy driving it ... makes us always aware of the nice panoramic view it overs compared to modern cars in which the side window’s lower edge is at a much higher position in relation to the sitting position. And its engine still has its nice typical inline six's smoothness.

H.D.