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1989 BMW 325 Starter Problem

This has been a great car and a blast to drive…trouble now is that it won’t start occasionally. Turns over like a charm just doesn’t ‘kick in’. It has happened after a brief stop (15 minutes) in a shop and also after it has been sitting for 6 hours. Nothing special going on weather wise…once in damp weather once in sunny 58 degrees. This also only seems to happen randomly every 20 or 30 starts. My mechanic is baffled and of course so am I.

Corrosion? Solenoid? Gremlins?

That year had many problems with the secondary ignition wires (big problems with coil wire), but don’t replace parts just because I say they commonly fail, test things. You say it turns over fine so this rules out the first 2 of your ideas.

An intermittent can be hard to diagnose and I assume the reason your mechanic is baffled is because he hasn’t been able to have the car in hand while it’s acting up?

For a first step it needs to be narrowed down to what is missing; fuel or spark. Without knowing that it’s almost impossible to even narrow the causes down.

You might consider doing this. Purchase an aftermarket fuel pressure gauge, mount it on the fuel rail (easy to do), and leave it in place. When the car acts up quickly note if fuel pressure is present on the gauge. That will at least give you a starting point for solving this problem.

If and when you ever decide to sell the BMW remove the fuel pressure gauge and save it for the next vehicle you buy.

If I had to make some very wild guesses here, I’d say (in no particular order) the ignition switch, ignition module, or the fuel pump. Those Bosch fuel pumps really take a beating and they can be a hit and miss affair. If that’s the original pump I’m surprised it’s made it this far.

These are some very helpful suggestions…I will head over to my NAPA store this morning and give this fuel pressure gauge test a shot. It is VERY intermittent and you are correct…it is pretty hard for even an experienced BMW mechanic to narrow this down without it acting up in his presence.

Not familiar with your car, so this is an Auto Mechanics 101 generic answer.

Before you buy a fuel gauge, when it fails to start, can you hear the fuel pump spin up for a couple of seconds when you turn the key to the On position?

If not, check the wiring diagram for a fuel pump relay. Find it and see if the fuel pump spins up if you short around it.

If the pump spins and the car starts when you bypass the relay, you are on the right track but you have still not found the problem. Look at the wiring diagram. Something needs to tell the fuel pump relay when the engine is not running so it shuts off in the event of an accident. Figure out if that is a power or a ground signal, and supply the needed signal to the fuel pump relay. Wait till it fails again, then get in there with your jumper wire and supply the needed signal to the relay. If it does not start, the relay is bad, if it does start, the problem lies in the more expensive hardware that controls the ignition.

Remember, all this assumes that you don’t hear the pump spin up when you turn the key on. If you hear it, check the fuel pressure, but the next focus will be on the ignition.