Not exactly between the engine and battery, but battery negative and ECU earth terminals (I measured on terminals 2, 14 and 24). All were about 0.15 volts when ignition was on and jumped to over 0.5 volts when engine was running (due to increased return current). There is some extra resistance in the ECU earth wire bundle connection (Can't test yet because I don't know where the connection is).
And yes they did rebuild it, from the block up. The notes on the receipts state that after the dealer had plugged in a Tech 2, it showed various faults for both lambda sensors. They changed both sensors for original ones (I would guess without even measuring the old ones). This didn't help so they deemed it must be a fault in combustion. On to the next garage for a second opinion. They reached a similar conclusion after trying new lambdas and fitting an aftermarket MAF
. They then rebuilt the top of the engine. Didn't help so back to the dealer. They suspected that timing was off after the rebuild but it wasn't. ECU was sent for repair, no problems there. They tried new lambdas. Nope. On to the next garage. They again CHANGED THE LAMBDAS and fit new oem catalytic converters for a sum that makes me cry. Surprisingly it didn't work so the owner gave up and sold it as faulty. I'm sorry for the previous owner who had to pay for "the ride".
When I got the car, it ran poorly. It used insane amounts of petrol and was low on power. I started troubleshooting, changed the aftermarket MAF for a used genuine one, got a diagnostic tool and did basic maintenance. The diagnostic tool told me the same things Tech 2 told the dealer. It showed me that both lambdas were registering a lean mixture and errors 13, 73, 74 and 89 were registered. I measured the lambdas directly from the sensor itself and they both showed over 0.8 volts on warm engine idle, which means pretty rich. ECU diagnostic on the other hand stated that both lambdas output only about 0.3 volts. Then it was a few voltage drop measurements here and there to find the problem.
To be clear, the car runs perfectly now with the additional earth wires I put in myself. I just want to fix the old earth wiring to tidy up the engine bay. My questions are:
Where is the engine earth wire connected on the 2.5 V6 engine?
Where do the small brown wires from ECU earth terminals go?
Is the earth terminal below the battery the only main earth terminal for the car chassis?