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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.

Reply to
Tony Gist
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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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T> After a journey (only has to be around 15 miles) the 740 can be a right

Reply to
Bruce Pick

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.

Reply to
Mike F

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

Reply to
Bruce Burrus

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