4

I have an '89 BMW 525i E34. When driven every day, the car is fine. It has trouble starting when it has stood for a while.

This car sat for a few years before I bought it. Even after the purchase, it was not my daily driver. For about a year now, it has been my daily driver.

The hour after shut off...

There is absolutely no way I can get that engine to start for at least an hour after I turn it off. The engine does not even attempt to turn when the key is turned.

After an hour (sometimes a little bit longer), the engine will turn on and I am able to drive. Immediately after start-up, it sounds like it's flooded and backfiring.

Sometimes, the engine feels a bit strained the whole time it is turned on, but it is not as bad as the initial start-up. This doesn't happen if it has stood for more than an hour.

One day after shut off...

If it is not driven for approximately one day, it has severe starting problems.

The car will initially start, but does not quite feel right: the engine sounds flooded, backfires, and jerks.

  1. Any tips or advice?
  2. Anyone else experience this problem?
  • If you press the gas pedal when starting, does it fire up better? – anonymous2 Oct 28 '16 at 11:28
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Probably a fuel delivery issue

It sounds basically like you're not getting sufficient fuel pressure on start. When you leave your car without starting for a while, the pressure drops, and the fuel pump is unable to bring the pressure up in one fell swoop.

I would recommend checking your fuel pressure. If you indeed are lacking fuel pressure, it could be a failing fuel pump, but it also could be a clogged fuel filter or a failing fuel regulator, which is integrated in the fuel filter.

2

If it is not even trying to turn over it is most likely an electrical problem ie either starter motor or battery.

If it sat for a long time without being used this could have damaged the battery so it may not be able to take a full charge any more.

Equally if there isn't enough voltage to fire the spark plugs this could cause a misfire although this may indicate that the battery is not the issue eg the alternator could be faulty or there may be an ignition fault which is draining the battery.

The first check is to try jump starting it or using an external battery, if that starts it ok then the battery is the main suspect.

Equally if you don't drive it much it could just be that the battery is nearly flat most of the time and just needs a full charge so it is also worth just giving it a full charge from a battery charger.

1

In fuel-injected systems, hot-start problems indicate that the fuel line is unable to maintain pressure.

This can also be one of the causes for cold start sputtering, as more fuel is demanded.

This could be due to a few things related to the fuel supply line, including:

  • a leaky fuel injector
  • excessive pressure drop across the fuel filter (indicating that it is clogged)
  • minute cracks in the fuel line which leak fuel when under pressure
  • a bad non-return valve in the fuel line which is allowing pressurized fuel to flow backwards

I would not suspect a failing fuel pump given the symptoms; even a weak fuel pump should be able to start up the vehicle under hot-start conditions.

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