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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

Reply to
Mungo "two sheds" Toadfoot
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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

Reply to
User

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

Reply to
Mungo "two sheds" Toadfoot

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