SOLVED**350SL cold start problems

Hello everyone

first of all, many greetings for all the best in the New Year.
Last week I tried to start my SL350 but without success.
Air temperature was about 10°C ( not so cold ) but the car attempted to start with a very low idle and then dies.
Even if I tried to push on the pedal, the engine stops.
In these days, I made the following checks :

- Wiring checks--> all was ok except for the following value that are slightly different from the normal:
MAP sensor resistor primary winding --> 76,7 OHM ( Normal 80-120 )
Injectors resistance --> 1,7 OHM instead of 1,2 OHM

- Cold start valve ---> I tested the spray come, not the duration

-Power signal to ECU --> ok

- Fuel pump pressure --> 2 BAR during crancking

- Trigger contacts signal --> ok

- Fuel lines have been all renewed this year

- Wiring harness connectors and rubber sleeve are new

- I also did a visual inspection of the rotor cap and distributor that shown some signs of carbon deposit but not so bad

After these checks I was able to start the engine but the cold idle remains low; anyway I was able to drive the car outside of the garage.
At normal operating temperature the car runs great and the idle speed is about 750 rpm

Today I tried to restart it but without success, the problem remains the same ( low idle and engine stalls )

Now I've the AAV in my hands and I checked the function by heating the probe with hot air; it seems to work fine.
The piston goes up when hot and return down when cold.

At this point I don't know what to do

I hope that someone can help me

Regards

Alessandro

Welcome, Alessandro to the forum!

The measurements you made are not spectatual.

Does the AAV open when cold or is it clogged?

Low RPMs means there is not enough air...

Regards
Norbert

Hi Alessandro,

I would normally also suggest an auxiliary air valve AAV failure. But I am hesitant as you describe that pushing the pedal does not let the car run as well when it is cold.An AAV opens a bypass to throttle and is nothing else than opening throttle a bit. So if it was AAV, opening throttle by foot should solve the problem.

I once had a case where ignition caused such a problem. When distributor was cold, 350 SLC would hardly run 40 km/h. But when it was warm, it would run like normally. That was hanging centrifugal weights in distributor. I only saw it when I left the car in my cold garage and directly hooked it up to my ignition oscilloscope next mornung. I swapped distributor and it was gone. Later I disassembled that one and cleaned and retuned it son my ignition distributor test stand and it worked again.

Another issue could be a broken engine temp sensor. Engine needs a lot more fuel while running cold.

Hello everyone

Thanks for you reply
I checked the AAV and I found that blowing air from the inlet side ( at room ambient temperature ) it flows normally from the outside so I can assume that it is ok
When the temperature rise, the piston moves upward and closed the air flow ( in realty not at 100 % since a little amount of air still flows through )
The only thing I found strange on the bottom of the valve is that the ring that retains the bulb in position appears like to be partially missing ( maybe corroded )
My idea is to try to start the engine without connecting the AAV hose and see if something changes.
About the engine temperature sensor, does exist a procedure to check it ?

Regards

Alessandro

Hi Alessandro,

I have seen few AAvs which had such a corrosion. The danger is that coolant could then pass through AAV into manifold. And residuals of coolant will finally make the piston in AAV stuck. Afterwards it is very difficult to take AAV apart without destroying it.

For coolant temperature sensor readmy my Checklist .

You should ignore my guess about distributor. It is my hottest guess.

Hello
after some test finally I dismantled the injector valves and tested the spray cone and injected fuel quantity.
The spray come seems to be ok but I found the following discrepancies on the injected quantity :

#1 : 2,0 cc
#2 : 2,2 cc
#3 : 2,6 cc
#4 : 2,4 cc
#5 : 2,6 cc
#6 : 2,6 cc
#7 : 2,4 cc
#8 : 2,4 cc

Now my idea is that the difficult cold start could be caused by a partially blocked injector so I'll proceed with an ultrasonic cleaning.
After dismantling the injector I also found that the injector sleeve are damaged so I think that another problem could be an air leak from them.
Unfortunately the item A1160780083 seems to be unavailable from MB
Do you have any suggestion ?

Thanks and best regards

Alessandro

Hi Alessandro,

it is clear that your injectors are clogged and you should get them cleaned. But that should affect your engine run more when your enigne is warm than cold.

Sealings A1160780073 are available at Daimler for 1,80€ .

Hello Volker
The sealing A1160780073 have been already replaced.
The problem is that my injector requires the sleeve A1160780083 and the seal A1160780773 ( these one are still available ) otherwise it will be impossible to keep them in position.
I've understand that there are 2 different injector style, one that has a sealing item A1160780473 and another one that needs a plastic sleeve A1160780083 plus the green seal A1160780773
My injectors are the type that needs the plastic sleeve but it seems to be unavailable.
Do you've any suggestion to replace it ?

Best regards

Alessandro

Hi Alessandro,
the sleeves are called `pintle caps`. No problem to buy them.

Regards
Norbert

Hi Alessandro,

bot A1160780073 and A1160780773 are available. Not too sure why you would need both.

Hello Volker

Enclosed you’ll find some pictures of the parts I need
The left one ( brown color but it should be white when new ) is the item A1160780083 that isn’t available from Daimler
Do you know if it is possible to source it or replace with something else ?
Regards

Alessandro

Alessandro, try here.
Insulation, Injection Valve - Mercedes-Benz (116-078-00-83)
www.pelicanparts.com/More_Info/116078008...pn=116-078-00-83-MBZ

www.ebay.com/i/351093109337?chn=ps&norov...rEAQYAyABEgIEWPD_BwE

www.autohausaz.com/pn/1160780083

Good luck
Rudiger

Hello Rudiger

Thanks for your help.
I’ll check and keep you posted
Regards

Alessandro

Hi Alessandro,

sorry I mixed 0073 and 0083. 24 pieces of A1160780083 are left in Daimler. Try your local dealer whether he can check worldwide stocks of Daimler. Otherwise you should try to reuse them.

Hi Volker

good day.
I found 8 pcs in US.... thanks to ebay
In the meantime, yesterday I tried the only one injector I've cleaned using the ultrasonic device; when cranking the engine, no fuel comes from it
Then I tried to invert the injector with another one with the same result.
At this point, i tried to power the injector with a 3 volts battery and it doesn't give any sign of life.
After trying several times, it comes to life again; what could be happened ?
Is it possible that this is the cause of cold start difficult ?
Then I tried to install it again on the rail and cranking the engine I noticed that the fuel flow improves effectively ( I found more than 10 cc instead of 3,0 / 3,5 cc of the other injectors )
So I'll proceed with the cleaning of the other 7 injectors in order to see in the starting problem may be solved

Alessandro

Hi ALessandro,

yes injectors can clogg when they are not used. Best is to send them for an ANSU cleaning.

Dear Volker

good morning.
After very long time due to time waste waiting for some parts from US and the pandemics situation, finally I finished the job on my car :

replaced injector pintle caps
replaced injector sealing
replaced caps , rotor and all the spark plugs wires
cleaned the 8 injectors by ultrasonic machine

Now the car runs smooth and the CO value has been set at about 2,5

But I still have a problem with cold start because sometimes the engine starts with 7 cylinders

I suspect that the injector N.5 sometimes remain blocked so I think that best solution is to change it.
I found the Bosch part 0 280 150 009 that is for the Porsche 914 ( with yellow body ); from Internet search it seems that this p/n should be same as mine 0 280 150 034 with the only difference in the bent hose.
Do you think I can install it on my car changing the hose with a straight one ?

Best regards

Alessandro

Hi ALessandro,

yes but be aware that manufacturers have produced fake injectors with original numbers and sell them in the US.

Hello Volker
thanks for your email and for your warning about the fake parts .Enclosed you’ll find the picture of the item on eBay, what do you think about it ?
Alessandro

Edit Admin: Due to German law you violate copyright laws by taking a picture from ebay and attaching here

Hi Allessandro,

it looks original. As far as I can say from a picture.