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

Hi Volker et al,

Here are the test results of a compression test. I've enclosed a photo as well, but will table it out here:

Cyl. 1 ==> 10 bar and spark plug looks fine
Cyl. 2 ==> 10 bar but spark plug looks a bit fouled (rich)
Cyl. 3 ==> 11 bar and spark plugs looks fine
Cyl. 4 ==> 10 bar and spark plug looks fine
Cyl. 5 ==> 10,5 bar but spark plug looks a bit fouled (rich)
Cyl. 6 ==> 11 bar and spark plug looks fine
Cyl. 7 ==> 11 bar and spark plug looks fine
Cyl. 8 ==> 10,5 bar but spark plug looks a bit fouled (rich)

It cannot be faulty trigger points as the fouled spark plugs do not sit in the correct groups.

I'm surprised about the compression levels as this is supposed to be a low-compression US-spec engine. Is this normal?

Is the next logic place to look the injectors themselves? I've already made a pressure test and the fuel pressure only drops 0.2 bar after 20 minutes and that is OK. Could it still be that these injectors are stuck open?

What now?

Best, Peter