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Cold start/initial idle

Started by zedster, 19 February 2009, 12:19 PM

zedster

Ok guys, I just recently found a great Mercedes cert mechanic and he got my 1979 450 SEL running after sitting for 3 to 3 1/2 years. I am sure he will figure this out because he is real good and says the car is definitely not done but I just wanted to throw this out there for your guys input. When you go to start the car after it has been sitting overnight it takes 3 to 4 tries to get it started. Then once it is started the idle goes way up and then back down to a point where the car is about to die. It then (about 4 times) will idle high and back down but not to a point where it is about to die. Once its running and warms up she runs great! Any starts after that and she is warm the car will start up no problem.

What has been done on the car recently:

First trip of mechanic
Replaced battery
New fuel pump (reason it was not running)
New fuel filter
New fuel line from tank to pump (damper cage)
Drained the gas tank of about 5 gallons of really bad gas
Changed the oil and filter
Filled the gas tank with Super Unleaded (92 octane) and some injector cleaner
Added about 2 quarts of transmission fluid (was low)
Added about a gallon of water to radiator

Second trip
Replaced a hose from the engine to the brake booster (old one was Mikey Moused)
Replaced the Power Steering filter and added fluid

Third trip (I brought the car to my mechanic)
Replaced Power Steering fluid
Replaced Radiator coolant
Replaced thermostat (Wrong thermostat was in the car and he found the sensor going to the instrument temp gauge is bad)
Replaced brake fluid
Replaced differential fluid
Replaced Transmission fluid and torque converter

I have used about 3/4 of the tank of gas I filled up with. Sorry so long but my curiosity is killing me.  :o

Bill

1979 450 SEL "Spinne Blaue"

scraf

Cold start valve? ( I'm no mechanic, but I saw that mentioned on another forum today )

koan

Quote from: zedster on 19 February 2009, 12:19 PM

When you go to start the car after it has been sitting overnight it takes 3 to 4 tries to get it started.


That's because the fuel pressure has leaked away. Any number of causes, leaking fuel accumulator, fuel pump check valve (new one should have come with the pump), primary pressure regulator, cold start valve or fuel distributor.

To check the diagnosis next time you do a cold start, pressurise the fuel system first, select "R" or "D" and turn the key to start for 10 secs, then try a proper start.

Quote

Then once it is started the idle goes way up and then back down to a point where the car is about to die. It then (about 4 times) will idle high and back down but not to a point where it is about to die.


Not sure about this one, 6.9's have a "coasting boost valve", I assume 450s have one as well. One of its functions is to prevent stalling if the revs drop too low, maybe yours is a bit enthusiastic. Could try disconnecting and plugging the two large hoses that connect to the valve.

Look in the library for your engine to identify the parts.

Check the obvious things like ignition advance and if vacuum advance is working.

koan
Boogity, Boogity, Boogity, Amen!

Big_Richard

Quote from: koan on 19 February 2009, 03:22 PM

Not sure about this one, 6.9's have a "coasting boost valve", I assume 450s have one as well. One of its functions is to prevent stalling if the revs drop too low, maybe yours is a bit enthusiastic. Could try disconnecting and plugging the two large hoses that connect to the valve.


Isn't this device only fitted to emission controlled engines ?

Mine was cactus internally so i removed it completely and plugged both connections. runs perfectly without out, but i dint have the air pump either.



Nutz

Incorrect cold control pressure may be the result of it 'hunting' at idle, which affects the control plungers (located below the fuel distributor) ability to deliver adequate fuel to the injectors when the engine is cold.

zedster

Thanks for all the input guys, I will keep you posted.
1979 450 SEL "Spinne Blaue"

koan

Quote from: Patrick Bateman on 19 February 2009, 04:50 PM

Isn't this device only fitted to emission controlled engines ?


It is fitted to emission engines and I think non emission engines as well, I assume a '79 US 450 would have one.

As its name suggests it adds extra air when coasting with closed throttle to reduce emissions, it also causes an increase in idle RPM for a few seconds after starting. Hmm, I may have confused this last function with the dashpot on some carb engines that aims to prevent stalling.

Quote

Mine was cactus internally so i removed it completely and plugged both connections. runs perfectly without out, but i dint have the air pump either.


Mine never did much either, now I have better manifold vacuum after the valve job it now works as it should.

I've noticed diagrams of this valve in early MB books show the in and out air black arrows pointing in the opposite way compared to later books.

Did your car ever have an air pump?

koan
Boogity, Boogity, Boogity, Amen!

TJ 450

The deceleration air valve is only on K-Jetronic modes with air injection and EGR, according to my knowledge.

Does your new brake booster line have a check valve installed?

Was this problem happening before any of the work?

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

zedster

Quote from: TJ 450 on 20 February 2009, 04:28 AM

Does your new brake booster line have a check valve installed?

Was this problem happening before any of the work?

Tim

Yes, the new brake booster line has a check valve. The car runs a lot better with the new line then the old. You would have to give it gas at stop signs to prevent it from dying with the old hose.

I do not remember it doing this over 3 years ago. I saw that cold start valve on ebay which is what got me thinking.

Bill
1979 450 SEL "Spinne Blaue"

zedster

My mechanic finally looked at the car when its cold. He said it is the cold start valve or sensor, I can't remember which. I did notice that the car will start the first time if I turn the key to make the buzzers sound for about 10-15 seconds then start it (thanks koan). My mechanic wants to do a tune up (plugs, cap, rotor, wires, and timing) first before replacing the cold start. He checked the rotor and cap in front of me and said they didn't look too good. I also watched him use some type of meter on the spark plug wires and said the readings were high.

Bill
1979 450 SEL "Spinne Blaue"

zedster

#10
My car got a tuneup today (wires, plugs, cap, rotor, and timing set) I could not believe how much quieter the engine was when I picked it up. My mechanic said the Autolite plugs were pretty bad and gapped wrong (he replaced them with Bosch). All plugs he said could be unscrewed by hand  :-[ #8 plug he said was another story and was stripped. He got the new one in and said hes 80% sure it will be okay. He said the timing was way off. I took the car for a spin and noticed the idle was pretty low but the car had more get up and go! When in park the car idles around 750 RPM. When the car is in drive and at a stop signs it is around 500 RPM and feels like its going to stall. I will have him adjust this (he showed me how) after I get my emissions test.

When setting the timing he said 2 vacuum lines just broke apart they were so bad. He replaced them with temporary ones and will replace these next week.

I will check the cold start tomorrow night. I hope it is better. Before the tuneup turning the key and waiting for the buzzers to stop then starting has seemed to help out a lot.

Bill
1979 450 SEL "Spinne Blaue"

zedster

OK, my car runs a lot better now and it starts up on the first try.  ;D It was not the cold start valve. Several vacuum lines were either connected to each other or to the wrong place. A lot of vacuum lines needed to be replaced because when they were touched they would just crumble. The 2 parts listed in this thread were replaced Part number needed and the idle control valve (where you adjust idle by turning a white screw with a screwdriver) was taken out and cleaned up. The idle could not even be adjusted before this! Air/fuel mixture was also adjusted. A vacuum leak in my brake booster was found. Just recently my battery kept going dead and this was traced to the AC Servo. I kept reading bad things about them and now it too needs to be replaced. It is currently disconnected. It is like driving a completely different car now, it actually has POWER!
1979 450 SEL "Spinne Blaue"