Starting Issue, 1974 280 SE

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.

MBGraham wrote: 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.

Graham, that is an interesting hint. I am not fond of the Bosch 0 580 464 999 as it is for 4 Bar and has a maximum pressure of 8 bar. This Nissan pump looks like the Bosch pump. Do you have flow and pressure data for it?

Regarding Pertronix: In my eyes it makes no sense that Carl changes more things than necessary. If he has a stron spark when his car does not start, Pertronix will not change it. No need to replace a functioning ignition module.

Now Carl we are curious whether you will notice a pressure deviation when car is not starting. If that is okay, injector spray test will let you know whether injectors are working well. Then finally you have to verify correct ignition timing. All that an engine need to start is: Air, spark and fuel.

Volker wrote: Graham, that is an interesting hint. I am not fond of the Bosch 0 580 464 999 as it is for 4 Bar and has a maximum pressure of 8 bar. This Nissan pump looks like the Bosch pump. Do you have flow and pressure data for it?

No data, but I do have one new in box. It appears identical to Bosch. There are many in use on Mercedes and Volvos it seems. The company that made them was bought by Bosch at one time. They then discontinued manufacture. But there is still new stock available, mostly on eBay from Nissan dealers.

Regarding Pertronix: In my eyes it makes no sense that Carl changes more things than necessary. If he has a strong spark when his car does not start, Pertronix will not change it. No need to replace a functioning ignition module.

It is hard to discern whether a spark is strong or not. Pertronix eliminates problems caused by distributor shaft wobble at low rpm. Carl already swapped ignition module for a working one, so probably no need to bypass existing unless it has a wiring or other fault.

All that an engine need to start is: Air, spark and fuel.

If only it was that simple

Volker wrote: Hi Carl,

welcome from down under! Of course English is no problem and you are welcome to write in that language. This seems to be the months of failing MB M110s. I am impressed how much you have done so far. I have read your history of pain (and maybe should do again carefully) and understand that you only have cold start problems and that you do have a strong spark while it will not start. I also read that you have thoroughly tested everything on your car. On the fly 4 things come to my mind:

1. How is fuel pressure on cold car when it does not start? Also 2.1 Bar?
2. Did you do my spray test by letting all 6 injectors spray into glasses with cold engine?
3. Story reminds me of a 350SLC. When really cold it would start but then run maximum 40 km/h. Warm it would go well till 160 km/h and then start to stutter a little bit. In the end it was the rpm based ignition timing adjustment in ignition distributor. Old fat had made it stick when cold. I could only see that when I hooked the car to my igntion tester after a cold night in my workhop.
4. What could also cause this is a leaking injector or cold start valve. It would more or less drown cylinder in fuel and it would take long starting to get rid of it. Should be more than 1 injector.

Hi Volker,

Thank you for the reply!

1. Yes, fuel pressure remains at 2.1 bar during cold cranking and at all other times.
2. Yes, I have done a spray test for all 7 injectors.
3. Yes, have plotted ignition advance curve, it is correct.
4. With regards to the leaking injector, i do not believe this to be the case. I did remove the plugs and inspected the top of the piston crowns after sitting for one night and could see no evidence of fuel dipping from the injectors. I also attempted to start the car with the ECU removed but with the ignition system connected figuring that the engine may fire a revolution or two with any fuel in the combustion chambers, it didn't.

Remember however, that once the engine has finally started, it runs fine. This is my biggest frustration, the fact that there are no running issues, fuel consumption is good and it consumes almost no oil. (Note, the is a small "Stutter" if I snap the throttle wide open from idle, but my friends 280 SE also does this, except his car starts first time .

MBGraham wrote: This is a tricky one! Cold start in Australia is probably not that cold!

Question - Do you have the starting problem when you first start car in morning? The subsequent starting problems after 30 min sound like the common hot start problems. They are caused by fuel that gets hot after sitting for 20-30 min under hot hood (bonnet) and then flashes to mixture of vapour and liquid through injectors causing overly lean mixture.

One simple test to add to your data bank would be to blow through the fuel return line to make sure that fuel is free to return to the tank from the fuel pressure regulator/damper. If that line was blocked, pump might overheat fuel because it has nowhere to go at low engine speeds.

Is the pump an original D-jet type pump? The flow seems a little low. Should be ~2L/min.

Volker - I too had the centrifugal weights in my distributor seize up. Since then, I always check timing at 3000rpm (which for my NA V-8 is about 27 BTDC.) The 6 cylinder would of course be different.

Hi Graham,

Yes, the starting issue is occurring under all conditions except if the engine has been run for more than 30 seconds and restarted WITHIN 30 minutes. Any other condition will entail hard starting.

Thank you for the tip about the return line. I have not tested this function.

I think pump flow is OK according to factory data.

nordfisch wrote: Hi Carl,
a Warm welcome from me, too.
As Volker mentioned before, you did almost everything one could do to solve the problems.

This is really a great task for us, too...
Your engine looks as being new, not as rotten as many other car-owners have problems with.

Now, some more ideas from me:
- What about the engine / body grounds? I once owned a W115 that had thick, round wires soldered in at the connectors screwed to the body. This soldered connections had broken and failed from time to time.
- Did you replace any connectors of the wiring harness by new ones? There are connectors being sold with wrong dimensions that don't give reliable contact. Look at the compendium, wiring harness.
- Maybe the injection at your car doesn't get the starting voltage directly from the ignition lock or the starting relais, but from an extra contact at the starter. At Opel-cars (I know better) this function failed sometimes because of contacting problems inside the magnetic switch at the starter (Opel has Bosch-Starters installed, too...)

What you could do more to identify the problem?
- replace the temp sensors by fixed value resistors, both sensors about 300 Ohm would signal 'normal condition' to the ECU. Simple 1/4 Watt-resistors will do.
- when installing LEDs with dropping resistors directly at the injectors you can control their firing under normal operating condition. A resistor with 100 Ohm did the job for me, using a white LED. You must try out the direction of the LEDs- seems once wasn't cared about the direction of these connectors when mounting the harnesses.

My ideas, so far... I will send you a PM regarding a favor you could do to me...

Regards
Norbert

Thank you Norbert,

I have the PM, please give me a few days to reply.

1. I have not tested to wiring loom grounds. Is there one specifically I should look at?

2. No, I have not changed any connectors, and in fact, I have removed and replaced the engine wiring loom, just to check.

3. Let me check the wiring and look for the starter contact if applicable.

4. That is a good idea to check the sensors with fixed value resistors, I will try this, and thank you also for the LED tip.