I'm new to the forum and am having real issues with my 760.
Yesterday (1/13/10) my wife was leaving home and got about a block away and the engine stopped and won't restart.

It was acting like it wasn't getting any spark so I first suspected a timing chain but in fact I found that it is firing. I removed the fuel line from the injector rail and found very little pressure and very little fuel when the engine is cranked. I suspected the fuel pump but found that both of them are working. I went ahead and changed the fuel filter and am getting MUCH better pressure at the rail but it still does not start. I also checked all of the fuses and they are fine. The one thing I couldn't find was a fuel pump relay. Is there one? Where is it? I ran the fuel pumps by ground a wire under the the dash and turning on the ignition. The pumps worked fine. Is it possible there's something else controlling the pumps that's faulty?

After looking on this forum last night I thought maybe the injectors were not firing so I disconnected the Mass Airflow Sensor and tried to start but with no luck.

It seems to me like the injectors are the problem..more precisely the system that controls the injectors. What else should I check? Could it be that the timing chain has jumped a cog? I determined that the the plugs are getting juice by hooking up a timing light and I got nice, steady flashing from all cylinders.

Anything else I'm missing. Oh, and now when I first crank the engine it seems to try to start but only for a nano-second.

Thanks in advance for you suggestions.

Dave

 

You need to check the fuel pressure. If it's not high enough it wont deliver enough fuel and it wont start.

There is also a fuel pressure regulator.

I think you may have a bad main fuel pump. It may be delivering some fuel but not enough pressure.

You should also check the MAF air tubing for holes. If I remember correctly, that motor is simular to the one in the '87 740GLE which is a 4 cylinder.

 

UPDATE:
So I was doing some electrical testing to make sure the main pump was really the culprit. I pulled the cover off of the relay and observed that it was operating properly. I pulled the #11 fuse and I still got fuel to the rail. Just for the heck of it I traded the #1 and #6 fuse and hit the starter. To my surprise the car started. So I turned it off and traded back the same two fuses. The car started just fine.

Bottom line I don't know what I did or what was the problem but it's running fine. Drove it to church today and haven't had any issues. I bought a main pump yesterday before I did some testing but I think I'll hold on to it for a week or so before I return it for a refund. Just in case.