1977 530i no start

[oakmountainguy]

Hi folks, new to the site and newish 530i owner. Having trouble starting my car. Before it started and ran but stalled after it warmed up. In the process of replacing the old coolant I spilled water along the drivers side of the engine. All of a sudden I get no pulse signal to the injectors. They received 12v when I turn the ignition but apparently they don't get grounded and thus don't pulse, hence no gas into cylinders and no start. But they were working correctly just minutes before I spilled water along the drivers side. I figured I shorted something so I shot the parts cannon at it and replaced the duel relay, the injection resistors and the ECU. No improvement. All fuses are good. I also get 12v to the ECU at the pins corresponding to the injectors. The only electrical bit I haven't replaced is the Bosh Drehzahlschalter tachometer/speed relay because I can't find any. Could this part be preventing me from getting pulse to the injectors? I don't really know what it does. Any help would be appreciated.

[Mike W.]

Welcome to the group, sorry about the reason though.

One thing you didn't mention is do you have spark? The ECU needs a signal from the distributor to pulse the injectors. I know you said drivers side, but odd things happen sometimes. Pull the cap and take a look. Then, cap off, ignition on, pull the coil lead to the cap off, position it next to, but not on ground, and rock the rotor back and forth. With a 6 cylinder engine there's usually enough movement in the centrifugal mechanism to trigger the pulse from the dist to the coil.

[oakmountainguy]

Thanks for the reply Mike. I verified I'm getting spark. Tested two ways. First I used a spark plug tester and second I pulled wires and connected an extra spark plug and grounded it. Saw spark in both tests. I assume if I'm getting spark then the distributor is working correctly, but maybe I'm wrong about that.

Rob

[528i-1981]

If you're getting spark, and assuming the coil is OK and you're not getting a weak yellow spark, how's your fuel pressure? You might have previously stalled when the thermo-time switch shut off the cold start valve. You probably know this already, but with the engine off you can check fuel pump operaiton by moving hte AFM vane with a screwdriver, it's audible. Installing a fuel pressure gauge is a very helpful diagnostic tool, I mounted one on the main supply line at the firewall. I think spec is 2.5 bar or 36 psi.

I don't really see how this would be related to your spilled water, but maybe it's not related?

[oakmountainguy]

Thanks Eric. I verified I have sufficient fuel pressure and strong spark. Still can't figure out why the injectors are not getting a signal to fire. They receive 12v power when ignition is on but never get a signal from the ECU to fire.

Rob
1977 530i

[Mike W.]

I'm still thinking, well, maybe guessing, it's the ECU not seeing ignition pulsing. So maybe ohm things out between the dist and the ECU plug.

[oakmountainguy]

Thanks Mike. I adjusted the distributor a bit and the car started up. I don't understand why it being out of time would prevent the ECU from firing the injectors but I'm not that familiar with distributor systems. Anyway, now it will idle for 5 minutes, then start misfiring and a few minutes later it just dies. Any ideas why it stalls after warming up?

[Mike W.]

Sounds like a dist issue, timing won't affect injector firing. Assuming you have the original points and condenser, I'd throw a new set of points and condenser at it. If the points or the contact block are worn it will affect timing and if the points are bad enough it could even prevent electrical contact as it warms.

[oakmountainguy]

Thanks Mike. The distributor has one of these Pertronix electrical ignition systems installed - another thing I'm unfamiliar with. Does anyone know if the Pertronix kit replaces the standard pulse generator in these distributors. I've come across some suggestions that a faulty pulse generator in the distributor could cause the engine to suddenly stall.

[Mike W.]

Originally 530s had a points and condenser distributor, so no pulse generator in it if it's the original body. Later 528i's used electronic ignition.

The Pertronix conversion has a pretty good reputation, but nothing's perfect either. Maybe check their website or give them a call about troubleshooting.