Hi everyone

Something strange happened. 2 days ago I couldn't start my car in the morning. It will crank but not start. The day before it was fine. I tried again couple of times during the day with no luck. Battery is Ok and I have the tank half full. Giving up I called for a towtruck. The guy also tried and he too couldn't start it.

Car gets towed to my usual workshop. The next day car started right up fine in the morning. Car's still in the workshop and my mechanic can't figure it out. It been starting flawlessly since then at the workshop. He's keeping it a day more just to make sure.

I've had the RSR and fuel pump relay replaced recently. Power stage is new. Hall sensor a year old. Fuel filter few months back. Distributor and plug wires also relatively new.

So big question is where should I start looking? I hope I can pinpoint the problem before the car fails again on me.

Thanks a lot

Aslan
B230E ZF transmission 229k km

I have a 1985 745t with a b230ft, and from your description it sounds like the ignition system is pretty similar. Right now I have a similar erratic fault that I've been trying to trace.

The car will sometimes stall out, sometimes not start, sometimes would. Seemed to be related to sitting in direct sunlight and high humidity, but not sure. Battery is solid, car cranks really strong, just won't turn over at all. Under no start checked for fuel at rail and bone dry (ignition fault indicated).

For a better analsysis got it to my indy mechanic, also baffled but sure its either the coil or the hall effect sensor (he tested the other potential culprits. Since you replaced the hall sensor within the last year (new distributor?) I'd probably rule that out. Same for the FPRelay, don't know what an RPR is. I would suspect one of the following:

- Ignition Control Unit: (black parallel socket looking thing by the battery on the fender. It can be bad or loose, test it and/or tighten it down.

- Ignition Coil: coils don't fail often, but they CAN fail and produce faults exactly like a hall sensor (and like you're seeing). Unless this is the power stage? I never know what people are talking about when they refer to teh power stage... :)

- Bad Battery or Ground

- Fuel Pump: yeah, wierd but definitely possible its failinbg intermittently. Jump sockets 30 and 71/2 (? see faq) of fuel relay socket and pump should whir on, if not its got issues.

good luck,
rt

Interesting points. High humidity? My car was sitting outside on the lawn and it rained the night before. Something related maybe??

I will definitely have a look at the ignition coil and the fuel pump.
Ignition control unit? Hmm .. can't see anything matching the description. Prob in a different location. RPR was a typo, meant to be RSR (radio suppression relay)

Power stage is a shiny aluminium? thingy by the fender besides the air filter box.

Thanks for the tip and good luck to you in tracing your intermittent fault. Do let us know if you've managed to solve it.

Power stage would be the coil then I believe, that would make sense though people seem to use the term "power stage" to refer to individual parts (the coil) and the whole dist./coil/converted high voltage system for the plugs.

The Ignition Control Unit isn't really a control unit per se, or at least not in the sense one would logically think. Really it is just a harness with a black big connector that looks like an old female parallel cable (from a computer) connector that, at least on my 1985 745t, connects to a black item the size of three fingers that is bolted to the inside of the fender directly rear of the battery (driver's side).

From what I understand the connector itself can fail but a common fault is for it to get loose or have a bad connection to teh fender, which it uses for ground.

If the car is specifically sensitive to high humidity and/or high temperature (with the biggest reaction being on a really hot, really humid day) look at the coil or the hall sensor/distributor (I think you should have a hall sensor on the 89). From all my research those two items specifically have that kind of common failure reaction.

good luck,
rt

Usual suspects. Radio sup relay, fuel pump relay. Crank sensor, if B230E has that.

The B230E does have all of those except for the crank sensor which is replaced by the hall sensor.

Do you know whether these components can be tested eg measuring its resistance or voltage etc? Thanks

Swap the AC fan relay (identical) for the radio sup relay, you won't have a fan maybe, but that is your temporary spare relay. Resolder or get a spare fuel relay. Intermittent faults would be hard to pick up until they occur.