| Author | Message | |||
     Bill Coburn Moderator Username: bill_coburn Post Number: 609 Registered: 4-2003 |
On a separate site I was attempting to explain the function of the fuel accumulator required for fuel injected engines. A hot engine requires considerable pressure of fuel to start, this is supplied by the accumulator. A cold engine uses a quite different system. The symptom is usually very hard if not impossible hot starting but when the engine cools down it will start immediately. The accumulator I believe is a sealed unit and not repairable. It is located beside the fuel pump on the left hand side of the car above the rear axle. After-market units are perfectly satisfactory and are usually supplied by auto tuning shops that service fuel injection systems!  | |||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 527 Registered: 9-2004 |
Bill you are on the right track ie pressure first. This is a posting that i put up on the RRBEW UK. K Jetronic Bosch. Remember the usual checks first. IE enough fuel correct charging rate cranking volts etc. To help with the poor hot starting first. The following component and order of testing may be of help 1. check the control pressure and warm up regulator. 2. " the system pressure and pressure regulator. 3. " accumulator. 4 " fuel pump,pump relay and fuel filter. 5 " cold start injector and thermotime switch. Note not a fixed time lag of 8 seconds continuous but heat and time related from 12 to zero seconds open contacts when working hot say 35c. 6 " metering head and control plunger. 7 " airflow sensor plate. 8 " injectors, yes they can leak puting out black smoke on start up. Control pressure hot 3.70 bar. System pressure 5.1 bar. Pressure drop after 20 mins 16 bar. Pump flow 90 lt/hr. After all this component testing first, it will take you to more common faults not listed. Bosch KE jetronic OBD later cars before the EOBD 2 introduction next maybe if time allows. | |||
| James Feller Experienced User Username: james_feller Post Number: 33 Registered: 5-2008 |
Hi Guys, Further to this, my EFI, Bosch K Jetronic is pretty good. But I note a few percularites with it. When engine cold, it requires only a brief turn of the key and it fires immediately and idles perfectly. This takes not even a second. I don't touch the accelerator as instruction book states. If I stop after a run and park and return to the the car, after say about 10 mintues or so, I turn the key and it again fires and catches without issue. Again I don't need to touch the accelerator. Now, here is my question, if I leave it warm for say an hour and return, I need to crank it for about 4-5 looong seconds. Once it catches its fine and smooth, it never stalls or idles rough, it just seems to take 'forever ' to actually catch when warm. The instruction manuals say to depress the accelerator while cranking a warm EFI motor to help it start. If I do this it does seem to prefer it. I have tried both pressing the accelerator and not, the old girl does prefer the accelerator pressed but still cranks for what seems 'ages' then catches, no problems. So for the question... is this normal? FYI, I have had warm up regulator rebuilt and also the fuel accumulator carbon cleaned or whatever they do to it. There is nothing wrong with the perfomance or idle it just seems to crank for a long time when warm and left for a little while... its normal yes? Cheers J | |||
| Peter Colwell Frequent User Username: peter_colwell Post Number: 61 Registered: 3-2005 |
What you describe is almost a text book account of a faulty accumulator. I had the same problem with a different older car, - from the Fatherland, but also KJetronic - and as soon as I started to describe the symptoms to my mechanic, he finsihed the sentence for me. A new accumulator fixed it. | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 1458 Registered: 4-2003 |
James, That is fairly normal. As a result, I have installed an override timer for the cold start thermal time switch (Turbo R Bosch KE2 Injection). I have set it to about 1 second, and it may be fine-tuned as required when first installed. I found that the thermal time switch fitted normally allows the cold start injector to activate for far too long, especially when the motor has cooled for a while but is still warm. The system works unchanged except that the 1 second override limits the injector's time to 1 second regardless of the motor's temperature. The cold start injector is inhibited by the thermal time switch as always when the motor is hot. The relay fits neatly beside the headlamp sequence relay, and the timer electronics and micro-potentiometer are encapsulated in the relay's socket. It all looks proper using the same Bosch relay as used throughout the rest of the car. The motor starts first kick hot, warm or cold. The 1-second limit setting works fine at all times on my car, and I have started the motor first kick at -25C many times. The timer needs only two wires in a sheath between it and the cold start injector to install. With the new sheath fixed to other looms with small cable ties, it all looks as if it were supposed to be there in the first place. By cutting the wire at the cold start injector plug and crimping a male and female spade connector at the break, installation is a snip. It may be returned to standard use without the new timer by simply unplugging the timer leads and connecting the inserted spade connectors to eachother. It's worth considering if you value your starter motor and flywheel/flexplate ring gear ! RT.  or with better resolution, click on this icon:
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| James Feller Experienced User Username: james_feller Post Number: 34 Registered: 5-2008 |
Thanks Guys, Peter, I may have confused you with my terminologies. When I talk of fuel accumulator I mean the hexagonal metal device ontop of the engine with the 8 little pipes coming out of it and going to the injectors. Jeepers I hope that's what it's called? At any rate this has been sent away for carbon cleaning while the guys did my rocker cover gaskets and top seals. While the guys were at it they removed the cold start regulator, which is very convienantly situated under the A/C compressor, and sent that away for rebuilding by some Bosch people. Richard for a layman like me, just so I have it clear, in these instances the car is swiching unnecessarily to its 'cold start' phase? yeah?It doesn't bother me as it seems fine I was just interested to see if this was fairly normal for mechanical fuel injection, which it seems it is. Peter you would not be talking about a lovely old 600 or 300 6.3 V8 Merc would you?? Both these 'fatherland' vehicles had K Jetronic EFI I believe. J | |||
| Peter Colwell Frequent User Username: peter_colwell Post Number: 62 Registered: 3-2005 |
James, the accumulator I meant was the cannister that holds fuel pressure when the engine is switched off. It looks a bit like an oil filter cannister. It is partnered with the fuel pump (rear) on my 450SEL. (Not 600 unfortunately, but very nice just the same). In my case the diaphragm was punctured, and the car started instantly hot or cold, but was difficult on a warm start, exactly as you describe. The device on the engine you mention is the fuel distributor, and is not an area I would go in to without good rea$on. All the best, I would put money on the accumulator being the problem. | |||
| James Feller Experienced User Username: james_feller Post Number: 35 Registered: 5-2008 |
ahhh I thought I may have mucked that up Peter. Yep the fuel distributor is what was carbon cleaned. Sorry I am no mechanic, just an interested classic car nut. :o) Ok, I'll put that on my list for its service later this year for the guys to have a look at and check it. As a matter of interest is the accumulator an earth shatteringly expensive item, in your 450, having this same style of EFI system do you remember what the item cost Peter? BTW, a 450 is a great motor! not quite a wonderful old 600 but still lovely nonetheless J | |||
| Peter Colwell Frequent User Username: peter_colwell Post Number: 63 Registered: 3-2005 |
No, the accumulator was not incredibly expensive, $145.50. |
