560SL hard cold start, ok when engine warm

[grigorean]

Hello to everyone.I have a big problem with my car.The car will not start when cold, only if I help it with starting spray.I must mention, that when it is cold the engine will run for 2 seconds and after that will shut off, that is why I must help it with spray, for 5 seconds, after that will run ok.The idle it is rough, economy indicator stays at 1/3 from minimum, and the acceleration is a little bit poor.

The car was involved in a big restoration process where the ignition system and fuel system was overhauled, also the engine was overhauled.
Before restoration, engine was running ok, but with some small problems caused by some air leaks

So, I have checked timming, and is all ok, I have checked ignition distributor timming, and is all ok, have checked compression and is all ok.Also the ignition coil, ignition distributor , ignition leads are new, crank position sensor checked internal resistence, signal with osciloscope when cranking, all seems ok.
Fuel pumps are new, fuel injectors are new, fuel pressure tested at fuel distributor and is all ok.Fuel distributor was replaced 2 years ago with one remanufactured by Bosch.
Injectors receive fuel, and spray in very good patern.
Have checked for intake air leaks, nothing found, checked using ISO octane.
Also have checked EHA, Throttle valve switch, Airflow sensor, coolant temperature sensors,and crankshaft position sensor

Really have no idea what to check next.Please help me if you have any idea.

[Frank Reiner]

g:

Suggest you try two things:
First, insure that the cold start injector is receiving fuel, and that the injector is being activated during the starting sequence (cranking & for 3-5 seconds after start).
Second, manually depress the air flow sensor plate ~ 3/4"-1" during cranking, while an assistant turns the key for you. This will provide additional fuel flow to the nozzles.

[grigorean]

Ok.Cold start injector was checked, I forgot to mention, it receives fuel, and also it spray fuel like it should, I checked this compared to the temperature.It is working fine.When I manually depress the airflow sensor plate while cranking, the engine have same problem...it has some combustion processes, for about 2 seconds, then cut out, even with the plate depressed.One more question about this....when it is cranking, the plate how much should drop? I have a circular space of 1-1.5mm, while is cranking.I ask because I think that maybe have some air leak which I could not test enough with ISO octane spray.I can show you in the link below how is starting with engine warm .

https://youtu.be/_cwfJdSgoVU

[Diseasel300]

I suspect you have a pretty large vacuum leak somewhere. The economy gauge should be sitting on the peg (or just off of it) at idle on the black end.

Have you checked spark? I only ask because I had a similar issue a few years ago and it turned out to be a loopy EZL, only found when it finally went belly up.

[grigorean]

I have checked spark.How I have checked...first all the sparkplugs out and well grounded, and when cranking all of them sparks...and second, one ignition cable, from cylinder 5 was disconected from its sparkplug, which I let in engine, and was connected a test sparkplug well grounded.I have started engine, it was running also for 2 seconds, then I must spray ISO Octane, and engine stay running, of course a little bit rough because one cylinder not working, but, spark was visible at the test sparkplug....so I guess I have a good ignition system....I don't know what else to check.This is how it starts when cold:

https://youtu.be/9IO6hgjgnRk

Have checked the sparkplug gap to be at 0.8 mm.It is possible to have spark, but from a worn ignition module, it's voltage to be low and not enough to burn fuel??
Since on the ignition system everything is new, except ignition module.

[meltedpanda]

what year? Does is have a Kjet system? PM me your email and I can send you a trouble shooting guide

[grigorean]

It is 1986, KE jetronic system.Engine M117.967.

[Frank Reiner]

Originally Posted by grigorean

Ok.Cold start injector was checked, I forgot to mention, it receives fuel, and also it spray fuel like it should, I checked this compared to the temperature.It is working fine.When I manually depress the airflow sensor plate while cranking, the engine have same problem...it has some combustion processes, for about 2 seconds, then cut out, even with the plate depressed.One more question about this....when it is cranking, the plate how much should drop? I have a circular space of 1-1.5mm, while is cranking.I ask because I think that maybe have some air leak which I could not test enough with ISO octane spray.I can show you in the link below how is starting with engine warm .

https://youtu.be/_cwfJdSgoVU

When cranking the sensor plate should deflect ~2-3mm, so yes, you may have some air leakage.

What is the condition of the spark plugs, rich (sooty), or lean (dry)?
From your descriptions of starting, we might expect lean.

Have you inspected the fuel strainer that is in the inlet fitting of the fuel distributor?
Is the fuel in the tank fresh, or has it been sitting while all the engine work was done?

[grigorean]

Seeing the condition of spark plug, I can say that the mixture is rich, and that is also a thing that push me to idea of air leak, because i need to run enough rich that engine will not stop when warm...the sensor plate is not deflecting so much...the gap that is created when is sucked down is some about 1-1,5 mm maximum.Fuel strainer is ok.Fuel tank was empty and cleaned, fuel in the tank is new, and when I was checking the fuel flow to fuel distributor I have seen that fuel is perfect clean, and fuel flow is exactly as specified in WIS, about 1 litre in 40 seconds.

[Frank Reiner]

Originally Posted by grigorean

Seeing the condition of spark plug, I can say that the mixture is rich, and that is also a thing that push me to idea of air leak, because i need to run enough rich that engine will not stop when warm...the sensor plate is not deflecting so much...the gap that is created when is sucked down is some about 1-1,5 mm maximum.Fuel strainer is ok.Fuel tank was empty and cleaned, fuel in the tank is new, and when I was checking the fuel flow to fuel distributor I have seen that fuel is perfect clean, and fuel flow is exactly as specified in WIS, about 1 litre in 40 seconds.

When the engine is warm, have you checked the mixture control duty cycle at the diagnostic connector? Pins 3 (ECU) & 2 (ground). When the duty cycle is correct, it will oscillate centered on 50% (45 deg if using a dwell meter).

What spark plugs are installed?

[Diseasel300]

Based on your videos, you look to be running pretty lean. I wouldn't call the "cold start" a "start" either. That's a stall.

In your earlier video, when you are blipping the throttle, you shouldn't be getting that hesitation/lag either. It's hard to tell from a video, but it sounds to be running a bit on the rough side as well.

You can test the theory. Dump a tablespoon or so of gas down the intake and try doing a cold start. If you get more than that sneeze you got in your cold-start video, you can bet you have a decent vacuum leak somewhere.

[grigorean]

I use NGK spark plugs.Duty cycle was checked, and the mixture adjusted to obtain that oscillation at 50%...In a few hours I will try to get out the intake to check again the gaskets for air leaks

[Frank Reiner]

Originally Posted by grigorean

I use NGK spark plugs.Duty cycle was checked, and the mixture adjusted to obtain that oscillation at 50%...In a few hours I will try to get out the intake to check again the gaskets for air leaks

My request was insufficiently specific. If you please, all the letters & numbers that are stamped into the shell of the spark plugs.

[grigorean]

Originally Posted by Frank Reiner

My request was insufficiently specific. If you please, all the letters & numbers that are stamped into the shell of the spark plugs.

W7DC is the type.

Thank you.

[grigorean]

I have made a smoke test and I found a small leak at the fitting from intake manifold to brake booster.I will fix it, but I dismantled the entire intake to be sure there is no other leak betwheen intake parts.I am not sure if that small leak can make the car to not start.
When other person is cranking, I was trying to depress the air plate a little, to see if the engine will run...and there was no change...that is why I am affraid that this small air leak will not solve the problem.Also, today I have checked the fuel system again, again checked system pressure, lower chamber pressure, injection valves are new, and when fuel pump is running, if I depress a little the air plate, I can hear the injectors scretching..so there is fuel in cylinder.

I am waiting for the intake manifold gaskets, and I will put back together all parts and test the cold start again.

But I am still thinking what else could be if this will not solve my problem

Thanks.