Q – I know this is an odd problem but I am at my wits end. I have a 58 Porsche and it will not crank reliably. I have replaced the starter, the battery, wire harness, and ignition switch but sometimes it still won’t crank. On a car this nice, it is very embarrassing. Got any ideas? I spent a ton of money on it already. Hans
A – Hans, you have fired the “parts cannon” at the problem. On the other hand, it feels good to know that all those parts are new. On an older Porsche, you probably needed all those parts. My guess is that the solenoid is not getting full voltage all the time. The cure may be simpler than you think.
The cause of the symptom can be definitively tested by a qualified auto electrician through “voltage drop testing”. The starter solenoid requires a strong electrical signal. If enough voltage is lost, the starter will not crank.
Many people install a relay as a quick fix or “band aid” rather than finding the problem. I endorse band aids as long as you know that they are band aids. Although this may cure the cranking symptom, it may not address dim headlights, headlights that pause between high and low beam, or slow turn signals. In addition, with excess voltage drop, the charging system may malfunction and overcharge or undercharge the battery. This can make a big mess of your trunk.
Problems I have found are incorrect or corroded ground straps, loose bolts to the ground strap, faulty main battery cable (it is quite long), sleazy emergency battery terminals, poor crimps, and old terminals. The key issue to remember that circuits which test OK for resitance or voltage may not carry current (load). I have been fooled (and embarrassed) by a brand new ground strap with a new bolt. Unfortunately, it was screwed into a rusty bracket redundantly bolted to the frame.
You can test continuity or excellent static voltage and it can all seem fine. But when you load the circuit, it may not cut the mustard. Loading the circuit and measuring actual voltage drop is the only way to know where the problem lies and confirming the repair.
I watched a technician replace a horn, clean the horn contacts and replace the terminals at both ends of the wire. And he spent a fair amount of time doing all this. Still the horn sounded sick. The wire looked fine but when the horn was honked, it lost 1.1 volts. With a new power wire, that beeper blasted with a voltage drop of only.03 volt. You decide, parts cannon or diagnosis? — MC