740 Hot Start problem

After a journey (only has to be around 15 miles) the 740 can be a right
pig to get started again. It will crank obver OK but not fire. Perhaps
after 10 - 20 times at trying to get it started it will fire-up and run
perfectly OK. The problem is *very* intermittent - perhaps once every two
weeks it will play up for a day or two.

When the ignition key is turned the petrol pump hums away for about 1.5
seconds and I can feel the fuel injection relay click when I put my finger
on it. But it just doesn't fire up.

Are their some *simple* procedures that I can follow to try and track the
problem down? Or is it a case of replacing bits on the off-chance? If so,
would the first candidate be the fuel injection relay?

Thanks for any advice.

 

One of the two fuel pumps could be underperforming - producing
insufficient pressure. A shop can test for that. Or possibly,
borderline low pressure combined with borderline failure of fuel
injectors (less likely, but also possible).

Could possibly be vapor lock. This used to be more of a problem, before
modern fuel pumps and all the newer anti-pollution fuel venting and
routing methods. Vapor lock can happen in warm weather, something about
fuel turning to vapor inside the lines and thus not pumping.

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That could be the problem. Also there maybe (depending on year) a
couple of black relays under the hood, one powers the injectors, the
other the aux fan. Swap them if possible and see if the problem goes
away.

Also the fuel system needs to remain pressurized while the engine is
still warm. There is a check valve in the fuel pump to keep the
pressure in the lines. This often fails, and sometimes it's the fuel
pressure regulator. However I've never seen or heard of this failure
being intermittent.
--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

I just had the same problem with my wife's 90' model 740 GLE. The only
exception is it would do it sometimes when it was cold too. It turned out to
be the injector power supply relay. That relay is under the hood somewhere.
I'm sure someone in this group can tell you exactly where it is. I had to
take it to a shop for them to run a fault trace to find this problem. But
your description of your problem does sound very much like what we were
experiencing.

Bruce Burrus