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

Hi,

I am not too sure that it is the same with the US fuel vapor evaporation system, but I do not hear air noises when I open my tank. Christian can surely tell more.

What I hear more often is that dirt collects in front of fuel sieve in tank when pump sucks out fuel. Then you can drive a while and dirt blocks fuel outflow. You sit and wait, in the meantime dirt dissolves in fuel again. Then engine runs suddenly as usual.

Hi Peter,
I think you should check what Volker wrote.

Just install a fuel pressure gauge instead of the cold start valve and let the pump run permanently for an extended time.
 
Regards
Norbert

...just diconnect  the ventilation line from valve near the rear axle and see if something is changing ! You can also check if the line to the gastank is free with compressed air !

Hi everybody,

Thank you for your valuable input. I have picked up the car today and have taken it for a longer run in order to try to replicate what happened the other day (petrol coming out of the filler neck, engine running rough, etc.). The mechanic has provisionally hooked up another ECU (0280 002 007), which is for a complete other engine, I know (3,5 L), but we did that in order to ascertain that it is not a clogged fuel filter, fuel tank strainer, vent system, etc. and the care is running again. It is not buttery smooth as I suspect that this provisional ECU makes the car run rich. This is also confirmed by a CO measurement. Fuel pressure is stable at 2 bar.

The tank vent system has been looked through and there is nothing clogged and after a good run there is now only a very subtle "swoosh" when I open the tank cap. Nothing is spilling out.

Could it really be the ECU? Something is indeed pointing in that direction.

Volker, is there any way for you to test my ECU if I send it to you? - and if it is indeed bad, do you have any good xxxx xxx 005 on your shelf that I can purchase?

Best, Peter

Hi Peter,

I have asked Christian to answer your question of fuel spilling out of tank neck as I am not too familiar with US tank evaporation system.

However it is for sure that this was not caused by your ECU. I recommend that you find that fault first and if it is found switch back to your original ECU to verify if all faults are gone. Of course I will further support the donor of flowers if your fault continues. And yes I have a proper ECU as well.

Hi Volker,

That sounds good. The theory of the mechanic is that because none or only a small amount of fuel was consumed by the engine, the vast majority of the fuel was sent back to the tank through the return line, thereby causing excessive turbulence in the tank.

I will go for an afternoon/evening drive and see what happens. As explained, the ventilation system, including the valve under the car has been checked.

Br. Peter

I went for a drive and both before, during and after the trip I took off the fuel cap and only heard a very subtle "swoosh". I have tried to upload small video clips. Seems pretty normal to me.

drive.google.com/file/d/1o7P1kuC1QLWPOhd.../view?usp=drive_link

drive.google.com/file/d/1mAB4zbcfWEfSpoo.../view?usp=drive_link

drive.google.com/file/d/1P5TAqJ5_sX3NaOS.../view?usp=drive_link

.

Well, here is an update on the almost ever lasting (same) problem. As a recap, the engine starts up fine and idles fine. There is an occasional miss here and there at idle. Once in gear it misses quite significantly and is difficult to get moving from 0-60 km/h. Once up to speed, it pulls nicely and evenly. Ocassionally, I experience that the engine is behaving normally and pulls as it should from 0 km/h, but then a day or two later, the same symptoms appear again. I feel I am chasing a ghost.

Here is what has been checked/replaced over the past several weeks:

• Fuel filter replaced
• Fuel strainer in fuel tank replaced
• New fuel hoses at fuel pump assembly
• Fuel venting system checked
• Fuel pressure OK
• Capacity check OK (1 L in 30 sec)
• New ignition points
• Dwell OK
• MAP sensor holding vacuum 
• Smoke test to check for vaccum leaks - my mechanic says there are no leaks
• Timing OK and the centrifugal mechanism is working as mechanical timing advance is working at 1,500 and 3,000 rpm
• When pulling the vacuum hose from the vacuum can at ignition distributor, the timing advances 5-7 degrees - so seems to work
• Tried to connect another working ECU - no difference
• All injectors are ticking steadily and evenly (although two injectors have "softer" pulses than others (have tried to switch them with other injectors to verify if it was the trigger points, but the "soft" pulsation followed along, so likely not trigger points)
• When I connect a T-piece to the MAP sensor and measure vacuum at warm idle I get steady-ish (perhaps sligtly fluctuating) 13-14 inHg or 340-350 mBar - that seems low. 
• When stepping on the throttle, the vacuum goes to 0 and then jumps to 20 inHg or 500 mBar - after that it settles again around 13-14 inHg. - I have inserted photo 

I am beginning to suspect that I might have a vacuum leak after all, even though my mechanic says that he has checked it and found nothing. What else can explain the low vaccum in the manifold?

Any thoughts?

Best, Peter

Hi Peter,

have you ever done a compression or better a pressure loss test on your engine. If piston rings or valves are not tight, you might also have low level of vacuum in manifold. That of course makes MPS to signal wrong load to ECU and enrich mixture. That would fit to low vacuum and problems in low rpm.

Also check all hoses connected to manifold whether they sit tight or loose.

Hi Volker,

Thank you. I will start by checking valve clearance. I have bought the correct wrench Hazet 329-4 on Kleinanzeige which will hopefully reach me when I'm in Hamburg next week.

The strange thing is that the behaviour of the engine is totally arbitrary. The other day it ran flawlessly across the speed range and during acceleration only to be totally unpredictable the next day where it did not want to accelerate but ran fine when up to speed. This afternoon, I just took it for a short trip to see how it behaved today and here it also missed and lacked power even when acceleration from 70 km/h onwards. This erratic behavoir makes it extremely difficult to diagnose the real underlying problem. I would suspect that if the rings are worn or the valves are out of adjustment or there is false air, then the symptoms would be the same all the time and dependent on load, speed, etc. and not erratic.

Best, Peter

Could the fact that I have two injectors whose pulses are softer, yet still regular, suggest that they are not providing enough fuel into the combustion chamber, hence leading to too low a manufold vaccum? I have not yet performed a volume and spray pattern test.

Hi Peter,

wrong injector pulses would affect mixture - meaning A/F ratio - but not vacuum level. Pistons moving down create vacuumwhen exhaust valves are closed and intake valves are open. If air can comes from another source, vacuum level will be low too.

So sealings under injector are a source, but injectors are not.

Well, I finally got around to pull the valve covers off - initially to adjust the valves. Before I got that far I went to check the timing chain. Here I discovered that the chain has either stretched or maybe even jumped a tooth as the timing marks on the cam do not line up with the TDC mark on the crank pulley. I think that I may have found the culprit of the low engine vacuum. It seems indeed that the valves and the pistons are not playing the same accord at the same time.

The first picture is of the RH cam with the crank pulley at TDC and where the timing marks do not line up. The second is the same place but with timing marks lining up at the cam but now the crank pulley is several degrees retarded.

Best, Peter