450 SL in Denmark

Hi Peter,

check hose from manifold to MPS for leakage and if okay, let someone do a smoke and a pressure loss test on your engine. That will tell where manifold leaks and if engine pulls enough vacuum.

PLEASE EVERYONE FORGIVE ME if I anser slowly right now. I have family issues to sort out with elderly family members.

Here’s a update. I’ve had the engine smoke tested in order to ascertain if there is a vacuum leak. That was not the case, i.e. the engine is tight. After having had the engine wiring harness inspected, it appears that the wiring of several injectors were not well and were exposed down to the bare kobber and in some instances they were so close to each other that it caused disturbance in the signalling. In addition, the wiring of the air temp. plug was in so bad a shape that it is doubtful how much signal and how good a quality signal has been sent to the ECU. 

All injector wires and air temp wires have been temporarily “fixed” so the engine now runs and probably will run for a while. I have known for a while that the engine harness was not in a good state and now, there is no doubt I need to change it out for a new one. That will be a winter project. For now, I am just happy to have the car back in a running state where I can enjoy it for the next couple of months before the Danish autumn kicks in.

Best, Peter

Hi Peter,

well it is good to know that you found your problems. Be aware that you need receptacles with special width 2,8x0,5mm and not standard 2,8x0,8mm ! You can read in chapter 10 of my compendium.

Hi Volker,

As usual with my car, things have a habit of developing quite rapidly. I drove a longer ride earlier this week and for the first 10-15 km. the engine ran beautifully, but then gradually began to miss and run rough to an extent where it stalled. As I stood there on the side of the road, I unscrewed the fuel filler cap and petrol spilled out from the filler neck and on to the ground. The tank was only 3/4 full and despite that, the level of fuel was at the very edge of the filler neck. 

After having the engine cool down a bit I unscrewed the fuel filler cap and unplugged the air temp sensor (otherwise, the engine would not run when put into gear) and then I limped home. I have had the car towed to an experienced mechanic who has experience with D-jet systems. He has been tinkering with the issue for the past couple of days and has tried to re-construct my experience, i.e. car running good when cold and during warm-up but once it gets really warm it begins to run rough. By then he measured CO, and recorded 0.1-0.2%, which is practically nothing. 

He has another 450 SL (D-jet) and has taken the ECU from that car and connected it to my car and performed the same exact exercise (cold start, warm-up and really warm operating temperature) and now the car performs as it should. His suspicion is that the ECU "mis-interprets" the signals from either or both of the temperature sensors and makes the mixture way too lean, once the engine gets warm.

Have you experienced this before and does it sound like a plausible explanation? - and in case the ECU has gone bad - can you then perhaps give it a go on fixing it?

Best, Peter

Hi Peter,

no that is a new fault for me. And I also do not understand why fuel should stand in tank neck when tank is only filled 3/4. Did your mechanic check whether there is dirt in tank that collects there? That sounds like your problem.

Hi Volker,

my own theory is that there is something wrong with my tank ventilation which causes too high a vacuum in the tank. This vacuum prevents the fuel from properly flowing through the fuel delivery system. The engine problem only shows when the car has been run for a while, i.e. when the pump has been running for a good while, thus allowing fuel and air/fumes to circulate in the system.

Does that sound sensible?

best, Peter