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  #1  
Old 07-02-2011, 08:42 AM
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Question General Fuel System Questions and Diagnosis Help

I've been spending the last few months trying to track down a long crank start problem in my m110 280CE. Being new to gassers has made this more difficult as I'm learning about what each component does as I question whether or not it is functioning.

The problem: after sitting for a long time (over night, after work, etc.), my car takes a full second to maybe 3 full seconds to turn over. It cranks just fine but won't catch and start. Sometimes when it does catch, it's a little "stumbly." Doesn't matter if it's a cold morning, warm morning, cold engine, or warm engine, it does the same thing.

Here's what I have done: New last year: ignition pick up assembly, ignition control module, coil. New this year: fuel pump, fuel filter, all under car fuel lines, plugs, wires, cap, rotor, fuel accumulator, fuel pump relay, all new injectors, sleeves, holders, rings, and just yesterday, a new cold start injector. I've also gutted the vacuum system and paired it down to the basics. Works great, no leaks anywhere, all good.

The problem still exists. My next plan of attack was to replace the thermo-time switch as I can only guess that it might not be signaling my cold start injector. However, this problem exists on the hottest days in a hot parking lot after work as well...

Basically, I need to know what the difference between a fuel damper and a fuel pressure regulator are. Does my car have both? Should I try replacing either or them? Both?

Should I be looking into the vacuum connections/system of the WUR? I don't want to go near the internals of that thing though, not nearly enough mechanical experience to consider it. Maybe the vacuum connections under there are loose or dried out? The car lived in Arizona, I've had to replace a lot of plastic and rubber.

The air slide valve appears to be working just fine as well. Half turns on the white plastic screw bring my idle speed up and down just fine, no problems there.

I'm also using high octane fuel. I was using SUNOCO's Ultra93 at the beginning of the summer after she came out of storage. I've since switched down to their Premium 91 octane. I just read, however, that high octane can cause a difficult start. Should I just try out the mid Plus 89? I really like the response and quite engine I get from the high octane though, but I could try it if that's the issue here. Does anyone know what Mercedes originally suggested? This is the low compression m110.

Any thoughts? I know this has been a long read but I'd really appreciate the help and would love to hear from the more experienced. Thanks for the help.

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  #2  
Old 07-02-2011, 12:39 PM
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you need to look at things besides the dartboard and replacing parts. it SOUNDS like too much fuel. can't really tell from here, i can't see the car.
but, i would open all the flaps that are the airflowmeter, throttlebody-been a awhile since i've looked at a 110 motor-and see if anything's wet with fuel. i would also start it when cold, let it stumble and clear, then pull the plugs. they may be wet. i would look at the control pressure when cold, it may be too low when cold, allowing extra fuel. i wonder what brand parts you used for the cap, rotor, plugs, wires and coil. had bosch wires give me problems out of the box. had bosch platinums give me problems on cold starts. had non bosch caps and rotors do the same. never seen a non bosch coil on a bosch car, but i would imagine it might cause problems. i also wonder if you got the correct bosch injectors. if they leak while resting, that cause the same overfueling stumble.

all that being said, i see you replaced the accumulator. i had a 450sl that would do the same thing due to a leaking accum. replaced the old accum with a new 1 and the stumble went away. it sounded like it was too much fuel, but testing proved the accum. was leaking, diverting too much fuel back to the tank, making it lean. never seen it before or since. maybe the new 1 is bad already? if so, it will leak out the vent line while running-not supposed to.

go to this site-

http://handbook.w116.org/matrix6.htm

it has all the testing info you need, along with which tools to use for fuel pressure tests-very important on a kjet car. good luck, chuck.
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Old 07-02-2011, 01:47 PM
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i buy only bosch or mercedes stuff for replacement parts, unless it's not entirely necessary (plastic bits, vacuum stuff, etc.). the plugs are non-resistor bosch plugs i found on-line. the correct, original equipment ones.

i get all my parts from either fastlane, ********, or performance mercedes. all of them have been dead on when it comes to VIN # parts breaks and equipment that fits. any questions i had i talked to a person before ordering the part so i'm confident that the parts that have gone in are correct.

i agree with you that it sounds like an over-fueling issue. i've been following this list of troubleshooting: http://w123gassers.smfforfree2.com/index.php/topic,8.0.html as well as using that site for a complete manual as well. thermo time switch was next on the list and then he suggested moving on to the WUR and the airflow sensor and control plunger, all of which i'm not too excited about as a shade tree guy. also not sure about all that system testing. took a quick look but looks greek to me.

any other ideas?
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Old 07-02-2011, 04:21 PM
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if it sounds like too much fuel, then why care about the thermal timer? if it works, then the cold star injector works and that means more fuel. the thermal timers's job is to tell the csi WHEN to fire and for how long. if it doesn't, and you are really getting too much fuel, fix that first and then deal with what might not be working, especially when you have the 116wsm to test the thermal timer and cold start injector, along with the other parts. stop throwing darts and use the info provided. it might have been cheaper. i honestly hope that the parts replaced were for other reasons and not chasing this problem. glad to see you bought the correct parts, i just hope for the correct reasons. good luck, chuck.
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Old 07-02-2011, 06:38 PM
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i know, i know.... i understand what you're saying. some parts were replaced as needed, some were replaced chasing this problem. spend a little money, learn a lot about how the car works, not too bad of a trade off, just annoying when i can't figure out the problem.

i'll get to testing the components i guess. the desire to replace the thermo time switch comes from the idea that it might be broken and sending messed up signals to the cold start valve. is this misguided in some way?

anyone know anything about the low compression/high octane fuel issue? is that something i should spend my time thinking about?

what about the difference between the damper and the pressure regulator? should i sniff around in this direction at all?
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Old 07-02-2011, 08:53 PM
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when thermal timers fail, in my experience, they FAIL to turn on the csi. i've not seen 1 do the other. testing it would prove it out.

110 motors, and all mbs in the states require 91 octane or higher, otherwise detonation will take place.

as far as the question about the damper and regulator, the damper just dampens the pressure pulses. has no bearing on rich or lean. there are 2 regulators involved in kjet, 1 in the fuel dist and the control press. regulator itself. you need to read the book as to whether the 1 in the fuel dist has any bearing on the problem. the control press. regulator can. pressure testing, as in the book, will prove this out. good luck, chuck.
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Old 10-25-2011, 09:51 PM
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I don't know if you ever got this situation fixed but I had the same issue last year. Finally switched out my fuel pressure regulator and that did the trick.

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