450 SL in Denmark

Hi Peter,

how is ignition timing and dwell at 1500 and 3000 rpm? And what vacuum does your MPS see at idle?

Hi Volker,

Here are the readings
      
                         Idle           1500 rpm            3000 rpm
Dwell             30 dgr.          30 dgr.                 30 dgr.
Timing 1        5 ATDC
Timing 2                            15 dgr. BTDC       20 dgr. BTDC 
Vacuum 1       12,5 inHg (315 mmHg)
Vacuum 2       16 inHg (410 mmHg)

Timing advance is right on spec and so is dwell at idle, 1500 rpm and 300 rpm.

I have used two different vacuum gauges, and they show different results - see also pictures. I tend to rely mostly on the hand pump version, which is also the one showing the lowest reading. That reading is too low.

With a warm engine I also performed a smoke test to see if there are any obvious vacuum leaks. That did not show anything. No leaks. These tests tell me that my problem is probably not injection or ignition related, but rather mechanically related. Could be many things, such as piston rings, wrong valve clearence, etc. But it points towards a compression test and even better a leak-down test, correct? 

 

Best, Peter

Hi Peter,

that vacuum level is too low in idle - even if both pressure gauges are scrap. I use a class 1.0 100mm pressure gauge -1 to 0 Bar.

Either you have a vacuum leakage or piston rings or valves are the issue. You should have >500 mBar at idle. Your vacuum level also makes the MPS signal load to ECU where there is no load.

And yes you should do a pressure-loss test and buy a proper vacuum gauge.

Thanks, Volker. I agree. I have arranged that the car will go to the mechanic next Sunday where he will perform a leak-down test. I'll report back.

Best, Peter