So after 9 days it was time for the workshop to take a look. When I came to the car that morning it started fine – and engine running normal. What? So 2 weeks earlier I had a dead battery and last week the engine felt like running on 3 cylinders. And now it just decided to repair itself. Anyhow I drove to the workshop. Bertil was very busy and had hardly time to listen to my story that morning. I told my story and asked him to check any plausible clause for the strange problems I’ve had – and asked him to change the battery cables on both poles. Just in case.
I collected the car the day after. Battery cables were just fine. What Bertil found was that the main ground cable (earth-lead, “stomkabel”) between engine and body was loose. He made a new and re-fitted it. I’ve heard about that cable before but never checked it. It is crucial for the engine as it can provide ground for things like generator, starter-engine and essentially (in my last case) for the sparks generated at the plugs. With a faulty cable any of the three can potentially go wrong – fully or partly. Here’s an image from the workshop manual. It should be found far down below the battery above the exhaust – connecting the bell-housing (“sprängkåpa”) to the chassi.
Now, that cable have probably been loose:ish for some time. So what has it to do with an empty battery and an engine that lost 40-50% of its power? Here’s my explanation:
Empty battery: though I’ve been measuring 14V+ over the battery with engine running, the generator failed to deliver enough current for the charging. The volt-meter doesnt require any current (really) so the lack of Amperes passes unnoticed. Another possibility is that sometimes – but not always – it has not been 14V+ when engine running – and I have failed to notice the charging lamp. Either way, the car has been running on battery charge eventually emptying it during this spring.
Powerless engine: without proper grounding for the engine the sparks wont ignite the fuel/air mixture as it should. Also accounting to a certain smell of fuel which I hadent noticed before. The loose cable was affecting the grounding un-regularly so (just a guess) every 3rd or 4th spark went bad whereas the other were ok.
A nice side effect is that my usually quite un-stable idle (around 800-850 rpm) has now become rock steady. Most likely caused by the varying ground condition caused by the cable.
This explanation may sound like bleeding obvious to some, but it wasnt to me. Here’s a shot of the culprit and the solution, much in the same position as above. The metallic tube below is my single exhaust pipe. The spiraled tube is the oil temp sender and the transparant tube in the foreground is drainage to an air inlet. Bottom of Engine to the right in faint red – and cable bolted to the bell-housing.