Warm starting drama...

[Andrew280SEL]

Hey guys
Ive had this problem a while but just wondering if anyone would have a good idea.
Whenever my 280 is warm, starting requires the acc pedal to be flat against the floor, as if it were flooded.
Is it something perhaps to with a valve or something, like the cold start valve which may be allowing excess fuel into the chambers after turning off? I hope I havnt answered my own question.
If I have, is it hard to replace yourself?

The car is fine afterwards, except a vacuum leak that needs fixing in the inlet manifold which gives a slightly choppy idle.

[Andrew280SEL]

Thanks Patrick

I'll give it a go when i get the chance, as im still on my L's and dont drive it very often.

Now, it does always start first time perfectly when its cold. Would it do that if it has the problem you speak of? I have also noticed when its warm that if i push the throttle in about a quarter of the way before i turn the key, and keep it there it will kick a lot sooner, sometimes even first time. Of course, if it doesnt itll keep turning over until I floor it.

[Andrew280SEL]

Ok Thanks

Again I will try your method you mentioned earlier when i get the chance, just to cover all grounds.

But I do know my idle isnt helping. I pretty much need to keep my foot on throttle a bit along with the brake to keep it running normally. So ill need to get that fixed too. Speeding up the idle for the moment, will suffice i think so it keeps running when standing.

[Nutz]

Do you have black smoke out the tailpipe or a strong raw fuel smell at any time,warm or cold ?

[WGB]

My 450 (same system with less injectors) with K-jet got harder and harder to start when hot until I replaced the supplementary air valve and replaced the (missing) under bonnet insulation.

If the pressure testing does not show a problem the supplementary air-valve should be easy to remove and test in some hot water.

It will need a new gasket to replace if OK and some coolant may spill.

In a 450 it lives in the water jacketed part of the inlet manifold at the front of the engine.

It has a small bellows thermostat connected to a throttle slide like you find in the carburetor of a motorcycle and closes as the engine warms up. If it stays open and the idle is set with the engine not fully hot it will cause poor hot starting  starting and poor hot idling which will steadily get worse as the engine gets hotter.

The picture below shows a view into the slides of two auxillary air valves sitting in a cup of boiling water. The old one on the left is still partially open while the new one on the right is fully closed.



The new valve cost about $250 (I think) from M-B Spares in Canberra about three years ago.

Bill

[koan]

The picture below shows a view into the slides of two auxillary air valves sitting in a cup of boiling water. The old one on the left is still partially open while the new one on the right is fully closed.

Both the auxiliary air valves pictured look like they need some attention with a hammer!

If the 450 uses the same valve as the 6.9, the part numbers in the Bosch K-Jetronic book are the same, it should have one stepped piece at the top, in the pictures they both look like they have two.

After many years of heat cycling and spring pressure the middle piece works itself out, it should look like this in profile:

                                                                              ________
           __________                                          __|________|__
    ___|__________|___    NOT THIS     ____|_____________|___
   |                                  |                          |                                        |
   |                                  |                          |                                        |

The fix is to take a hammer and a block of wood and tap the top bit down until the center piece is flush with the outer piece.

The idle speed will probably need adjusting after this.

(hope my ascii art makes it - it looks OK in preview)

koan

[WGB]

New one works perfectly and was out of a new packet.

Bill

[Andrew280SEL]

Thanks again. This is good info. Hope it will help me when I FINALLY get to drive it this weekend. At the moment shes wrapped up in the shed.

Do you have black smoke out the tailpipe or a strong raw fuel smell at any time,warm or cold ?

Well theres no smoke at all, but there is the fuel smell. But we put that down to it running rich, which it is at the moment. But boy it is strong! Could there be another reason for it?

[Nutz]

Your cold start injector sounds like it's not closing which will cause hard hot starts by flooding the engine until residual fuel pressure drops below 45psi (3bar).Also the fuel injectors should be checked as well.

[Andrew280SEL]

Hi again.

I tried the repressureizing (excuse spelling!) by putting it in Drive and turning the ignition key to Start, but I didnt hear the fuel pump go. Which I thought It would as even when the car is going, and i stand outside of it I can hear its distictive noise. Is it possible this technique doesnt work on Mechanical models?

But in any case I did notice that if I start it straight after shutting it off it kicks first time. But if I wait say 10 mins it requires a bit of pedal to start properly.
So it does seem to point towards pressure but I dont know.
Any ideas