MB R107 SL280 1981 fails to start

[Shaun Fielder]

Hello everyone,
I am the sad owner of the above car, for 2 years I have been trying to fire her up but to no avail.
The story so far fuel system cleaned including tank, new filter, injectors and pump. New plugs, battery, dizzy cap and leads. Cold start function checked and working, spark at all plugs.
A local MB specialist had the car for 6 months siad he thought it could be a problem with the wireing and redundant alarm system but never got round to fixing it . At my wits end now located near Wrexham any help would be greatly recived? Thank you

 

[LostKiwi]

Ok back to basics.
1. Do you have compression?
2. Is the valve timing correct?
3. Is the ignition timing correct?
4. Are all the plug leads in the correct places?
5. Do you get fuel on the plugs when trying to start?
6. Will it fire if you fire ezi-start down the inlet?

 

[Shaun Fielder]

Thank you for your quick response to answer your questions:
1. Yes average 120-140 psi
2.Timing correct
3.Timing correct
4.Yes all leads correct (no back firing)
5.Yes plugs wet
6 Tried easy start no luck.

 

[LostKiwi]

Thank you for your quick response to answer your questions:
1. Yes average 120-140 psi
2.Timing correct
3.Timing correct
4.Yes all leads correct (no back firing)
5.Yes plugs wet
6 Tried easy start no luck.

120 to 140 is on the low side - i would expect 150 to 165. Still it should be enough.
How did you check the timing?

Does it even try to fire?

 

[Shaun Fielder]

Checked the timing static by memory think it was 8 degrees.
We did get it to fire on the last attempt but then the starter failed, just had that overhauled and new solenoid.
Mechanic suggested the fuel pump was not maintaining pressure could be that the aftermarket immobiliser is cutting electric supply to fuel pump so that was my next test.
Early start tomorrow but thanks for your suggestions so far.
Shaun

 

[Brian23]

Hi I had this problem with my wife's SLK and Television, he is sadly missed, said it was the k40 relay in which the square peg solder needs renewing. I took it off, re-soldered it and never a problem since. Hope this helps or maybe this car doesn't have one. Brian

 

[LostKiwi]

I don't think this is fuel related as ezi-start would make it fire. If it won't start with ezi-start (or even try to) that suggest a problem with ignition.
Are you sure you don't have the timing 180 degrees out?

 

[ajlsl600]

does that thing have electronic ignition or condensor .points?

 

[Shaun Fielder]

does that thing have electronic ignition or condensor .points?

Thanks for your suggestions so far to answer some questions:
I have checked for timing removed dizzy and turned 180 degrees to no avail.
The 1981 sl 280 has electronic ignition so no points to fiddle with.
Will double check conections to all relays as Brian suggests.
Will be trying her again at the weekend and report back.
Thank you so far

 

[LostKiwi]

Take off the cam cover. Assuming the firing order is 1-5-3-6-2-4 turn the engine by hand in the normal direction of rotation until number 6 exhaust valve closes and the inlet valve starts to open. At that point number 1 should be preparing to fire. Check the rotor is pointing to number one lead in the cap. Also check the marking of the crank pulley. It should be near TDC.
If that all checks out get a timing light and check dynamic timing using the strobe light. If you don't get pulses it means you aren't getting spark.

 

[ajlsl600]

Take off the cam cover. Assuming the firing order is 1-5-3-6-2-4 turn the engine by hand in the normal direction of rotation until number 6 exhaust valve closes and the inlet valve starts to open. At that point number 1 should be preparing to fire. Check the rotor is pointing to number one lead in the cap. Also check the marking of the crank pulley. It should be near TDC.
If that all checks out get a timing light and check dynamic timing using the strobe light. If you don't get pulses it means you aren't getting spark.

has that dizzy cap got a spring loaded centre carbon contact

 

[Brian23]

Hi I

Hi I had this problem with my wife's SLK and Television, he is sadly missed, said it was the k40 relay in which the square peg solder needs renewing. I took it off, re-soldered it and never a problem since. Hope this helps or maybe this car doesn't have one. Brian

I think that I was a bit unclear. If your car has a K40 relay, the solder to the square peg on the circuit board fails, See photos. Common fault on old SLK's but I do not know if the SL has one,

 

[star]

No k40 relay, if plugs are wet, it will not start due to spark tracking down side of electrode. Remove plugs and let the cylinder air or blast with compressed air. Then fit new plugs, cleaning doesn’t always work once wet.

 

[Shaun Fielder]

Thanks Star. Pity I do not live near Reading .

 

[Shaun Fielder]

Had another go this weekend progress so far:
All timing checked double checked I had not got the dizzy 180 so took the camshaft cover all all seems ok valves opening and closing when they should.
Put a direct feed to the fuel pump and she tried to start run for a few seconds, think I may try some fresh fuel as this has been in the tank for a year now , had a similar problem with a Morris Minor stale fuel.