Starting problem - 1989 740 B230E

Hi,

Sometimes, when starting, the engine will catch briefly then die. Attempting
to restart involves about 10 seconds of turning over and about a third
throttle. During this time it sounds like the engine is only running on two
or three cylinders. When the third cylinder fires up the engine will run
roughly for a few seconds then the fourth cylinder joins in and it runs as
well as ever.

If I think it's likely that this will happen, usually when the engine has
run for a short while, is just barely warm, and has been turned off for a
while, I keep the starter winding, hear the initial catch and die, and then
the engine will start and run fine.

Sometimes when completely cold the engine will run roughly for a few seconds
and then either clear itself and run properly, or a rev to 200-ish rpm will
make it run properly. Other times it will start and run fine.

Any ideas?

There has been a fault with the day-running lights which was down to a bad
earth so is is possible that this could also be a bad earth on the cold
start injector, auxiliary air valve etc.? I seem to recall a multiple earth
connector on the side of the engine bay (it's dark and I'm not looking
now!); would this be where most of the important (i.e. engine-related) earth
connections for the car, apart from the battery of course, end up?

Si

 

It's not likely that the programming for your car will ever allow the
cold start valve to operate. If it does however it only fires when the
starter is engaged.

Your problem sounds as if you are losing fuel pressure. You'll have to
hang a gauge in the system to eliminate the possible causes. You need to
know if the fuel pressure regulator, main fuel pump check valve, or
prepump hose or prepump itself are allowing the fuel pressure to drop.
It's also possible that the injectors themselves are not closing
completely on shut down and are dripping or the fuel pump relay is
intermittent and the pump isn't even running until the starter has been
spinning for a while. Instead of just starting the car immediately, try
cycling the key a few times and listen for the fuel pump to run for a
second or two to prime the fuel lines. If this cure the problem then
proceed back to the beginning of the paragraph.


If the above doesn't provide a solution then perhaps some ignition
maintenance is in order. It is possible that the coil is intermittent
and provides a weak spark when the trouble occurs, compounded by well
worn spark plugs or old wires, cap and rotor.

This general information. For a more specific response post the fuel
injection and ignition types. Depending on type there are additional
components that may be faulty.

Bob

 

Why's that? Is it just for extremely low temperatures?

Possibly, but more often than not it will start properly, straight away.

I haven't ever noticed the fuel pump running at all, to be honest.

It has a new coil, distributor cap and plugs.

I had a good look round the engine bay today and noticed that the braided
earth strap which runs from the bulkhead to one of the rocker cover bolts
(there are two - the other one disappears under the distributor somewhere)
had broken away from its connector, which couldn't have helped matters, so
that's now repaired. I hope, but doubt, that it caused the bad starting!

Si