Starting Issue, 1974 280 SE

MBGraham wrote:

Volker wrote: Hi Graham,

fuel flow from pump is correct with 1.5 l / min. Original spec for 0 580 464 005 is 750cm³ in 30 seconds. Anyhow if fuel flow is too low you would see too little fuel pressure when car does not start. That is why I asked the fuel pressure on cold car not willing to start.

Volker, you are correct that 1.5l/min is the RATED capacity at 12V and 2bar using n-heptane. Bosch say to use their numbers just as a general guide. In practice with gasoline and higher actual voltage, Djet pumps including my own have higher capacity. So that is why I said 2L/min. Back when Djets first came out, Bosch ran training programs for mechanics and in those the troubleshooting section said AT LEAST 1L/30sec. dl.dropboxusercontent.com/u/54783344/efi330.JPG

Fuel pressure is set by the fuel pressure regulator, not the pump capacity. Even if pump only put out 1L/min, pressure would be the same so long as fuel was being recycled via FPR.

Of course, during starting the engine only needs a small amount of fuel. Most is returned to tank. Low flow would not be a factor. But it could be an indication of pump condition. For example, a malfunctioning internal relief valve that is built into Djet pumps could be spilling fuel back to the suction. Unless car has a full time pressure read out, changes in fuel pressure may not be noticed.

By the way, we have found that the Nissan 280Z pump is essentially the same pump, but was made in Japan. Still available new on eBay at times: www.thezstore.com/page/TZS/PROD/11-3063 . Less expensive and direct fit compared with new Bosch replacement Djet pump.

By the way Carl. Despite this discussion of fuel pumps, I suspect Norbert is more on track that you may have an electrical problem in either the injection or ignition system. If it was my car, I would be tempted to put in a Pertronix points replacement and even perhaps bypass the ignition module (switchgear). They are pretty cheap. And then do as Volker suggested - pull fuel rails and watch injectors discharge into jars during a morning cold start.

Graham thanks for the tip re: the Pertronix. The problem I have with such modifications is twofold:

1. The cars ran perfectly when they were new so I expect mine to be the same! I know this can be a pipe dream with a 42 year old car, but in my case, my car has only done 113,000kms.

2. I am afraid also that I am an originality freak, I know it's old, I just expect it to work!

Volker wrote: Hi Carl,

I recommend you install a fuel hose into fuel line above injectors via T-distributor, Connect it to a manometer and let it hang out onto the windshield Then you can fix it there with tape and watch your fuel pressure during start and ride.

If it does never deviate, then there is no problem with your pump.

Volker I have done this test and the pressure does not deviate a fraction from 2.1bar.

Thanks to everyone!

My plans is the following:

1. Re-do injector test as per Volker's procedure.
2. Check wiring loom ground connections.
3. Check wiring loom in relation to the starter.
4. Substitute fixed value resistors in place of temperature sensor I + II
5. Try a third ECU.
6. Check return fuel line and damper in supply line.

If the above turns up nothing:

7. Set car on fire and move on.

Hi Carl,

if fuel pressure in fuel line is always 2.1 Bar, there is no need to check 6. Fuel pressure would increase if return line was blocked. And if fuel pump would not deliver enough fuel it would sink. I had the case where it would sink to 1.8 Bar after stopping fuel pump and then sink slowly. It turned out that I had a leaking injector.

However don't do 7. even if I understand your frustration.

I thought I had posted a reply, but somehow it did not show up:
Briefly:
- I would check return line regardless - blockage in swirl pot is a common problem especially if car has not been driven regularly
- Check ground resistance from ECU plug ground (with ecu disconnected) to body nearby. That should check total ground circuit. Then check each circuit from ECU plug as outlined in MB shop manuals. Maybe do cold and then warm. Problem is sometimes IN harness.
- Check all connectors. Sometimes terminals get pushed back inside.

carl888 wrote: ...
6. Check return fuel line and damper in supply line.
...

Hi,
just noticed this.

The damper is situated in the return line, not in the supply line.
I still don't know why (my car doesn't have a damper at all), but that's how it has to be.
Might be of relevance???


Part of the message is hidden for the guests. Please log in or register to see it.

Regards
Norbert