450 SL in Denmark

Hi,

following mail arrived today and I will ttry to answer here:

Peter schrieb: I hope you are doing well. I take the liberty to reach out to you directly as a last resort before I have to surrender and send the car to the shop. But I totally understand if you cannot be bothered - you surely have many other things to do and tonnes of people like me writing to you all the time and you have already helped me a lot. But here goes: At idle:The engine runs fine at idle. Perhaps a bit rough when cold, but after a few minutes of warming up it is very smooth. The ECU idle potentiometer is set to the leanest position. If I click 4-5 times to make it richer the engine begins to miss and “puffs” out of the exhaust pipe. All connectors plugged in (temp sensor I and II and throttle switch)When going into D and setting off from 0 km/h it almost dies and I need to be very gentle on the throttle to get it moving. Once reaching 50-60 km/h it begins to even out and does almost pull as it should. Not a perfect linear pull, but better than starting from 0 km/h.  Disconnecting throttle switchI have tried to disconnect the throttle switch and as expected, it barely idles. Almost stalls. When I put it into D, it dies. I cannot even make it move - not even if I go very gently on the throttle. Disconnecting air temperature sensor (and with throttle switch back in)When disconnecting the air temp. sensor the engine almost behaves like it should. Fine idle and pulls away from 0 km/h without having to go easy on the throttle. Pulls very nicely all the way up and with a linear curve. Maybe not running 100%, but quite close. Pre-requisites

• Timing and dwell is exactly where it should be
• New plugs (NGK BP5ES)
• Fuel pressure is 2 bar and is stable when I rev the engine - also when putting the car into D. Have not checked it while driving (accelerating) because I do not know how to route the extended fuel hose out of the engine bay without it being bent or crushed by the hood
• Checked for vacuum leaks via brake cleaner and have found nothing - have not used smoke, though
• Have pulled off throttle housing and cleaned the TPS 
• New (never used and in Bosch original package) engine temp sensor installed 

Hi Peter,

please check first of all whether you have a vacuum of 500 to 600 mBar at MPS hose at idle. From what Then check whether all injectors tick by touching them - you will feel it. Then please verify ignition timing at idle and that you have correct ECU matching your MPS.

Hi Peter,

are you sure that ECU rheostat is at lean and not at rich position ? What sounds so strange is that with disconnected air temp sensor car uns well. That means 20% more fuel.

Hi Volker,

Just checked vaccum with this device and at shows around 180 mBar at idle.  

All injectors are clicking regularly and in an even pattern. Timing is according to spec.

ECU rheostat is turn all the way counter-clockwise (towards the left-hand-side). When I turn it clock-wise it begins to miss-fire (at least it sounds like that) after 3-4 clicks.

Hi Peter,
the device you use doesn't show values in mBar but in mmHg and inHg.

What did it show?

Regards
Norbert

Hi Norbert,

Please see the picture - now with an arrow indicating the level of vaccum at idle.

 

Hi Peter,

I read 160 mm Hg which means 210 mBar. Far too little for idle. Should be 500 to 600 mBar.

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

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