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internal voltage wrong readings

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Hi all , i am midway through a GDI install , i have noticed that when i crank the engine the tuning software loses connection , if i connect a battery charger it cures the problem.

I have checked the internal voltage in runtime , 5v and 8v are spot on ,12 v is down at at 10.3 !! , the feed to the ecu is reading 12.6 -12.4 everywhere .

Any ideas guys . thanks in advance..


It's not uncommon to see the voltage drop during cranking due to the current draw from the starter motor and this can be enough to have the ECU shut down. This usually happens with a marginal battery or alternatively a marginal power feed from the battery to the starter. You may find that simply replacing the battery with a larger unit or using a heavier gauge feed to the starter may be all it takes. Make sure you pay attention to the earthing from the battery too as this is just as important as the power feed.

Hey Andre , thanks for the quick reply , the battery is a motorsport gel type and has been standing for a good while although brand new, all cables from battery are brand new 25mm2 with good termination etc , it maybe the battery just needs a good conditioning charge.

I am guessing even though the comms have dropped out the voltage will still be high enough to power the ecu for starting etc..

Cheers Keith

We had this issue recently with a Syvecs S8 on a Mk6 VW Golf. The battery had been relocated to the passengers compartment and would occasionally cause the ECU to drop out of comms during cranking. When this happened the ECU was shutting down as the voltage was dropping to about 8 volts and the engine wouldn't start. A jump pack directly connected to the starter motor fixed the problem. This indicated in this particular case that it was the wiring to the starter that was questionable.

Thanks Andre , i am nearly ready to start the vehicle in the next few days so will check back through all the connections etc.

Cheers Keith

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