thetoolbus2020

My girlfriend has recently picked up a 08 tC with 80k from her dad. he apparently replaced the motor a couple months ago and I have had nothing but issues from the car. This current issue has me completely stumped and looking for help / advise from anyone who may have an idea! At this point the car runs,
and idles as should, until I add any sort of load. Use turn signals, car will stall. Open sunroof, car will stall. Have even had it where if the turn signals are engaged the HVAC back lighting will flash at the same pace of the turn signal. The headlights will flash with the turn signals also when car is running prior to stalling

I also noticed today that the fuel pump seems to be a little more noisy than usual so diag into that will happen this week. It seems to surge when the turn signals are engaged while the engine is off but key on.

All fuses and relays are in proper working order. All grounds have been checked and double checked. Battery and alternator are both brand new and operating as should. I am completely stumped on this one.
No CEL. had SRS and ABS codes from other issues but those have been resolved with no further issues and still have stalling issues.

Any and all suggestions and help are greatly appreciated!

Added note is the car is 100% stock besides a Pioneer Head Unit.


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JakeAut0

I would get a decent scan tool so you can look at the data the ECM is receiving from the inputs and see if anything stands out as an issue.

Do they flash by turning off and on or, do they dim and then brighten?

thetoolbus2020

They dim and brighten with the flash of the turn signals. have checked data from two different Scan tools (Matco and Snapon) and neither show issues.
No Codes thrown either. did test today and fuel pressure is a little low..around 38/40 psi to the 44-50 required. but that wont cause electrical issues.

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JakeAut0

It seems like the issue is leading towards a charging system issue. I would test the alternator, new doesn't always mean it's good. The voltage regulator on the alternator could be faulty, this could cause an issue when the car demands a load. It could also potentially damage the battery. This is all speculation as I'm going off the info your giving me.

I would use a multimeter to check the battery voltage, make sure it is around 12.6 to 12.2. Then at idle check, it's at about 14 volts. Now, turn on a load or multiple loads and have someone watch the reading and see what happens.

I would also inspect all connections and wires going to and from the alternator

DannoXYZ

Time to measure voltages at various locations. Scanners are useless for this since ECM doesn't even know it's losing power, it just stops working. You need to have second regulated power-source, like 2nd battery that doesn't get used for anything. Then ECM can compare it's power line with this 2nd reference signal to determine if it's losing power, then trigger alarm code. Nope, no such failsafe circuitry exists.

So you gotta measure voltages manually like good mechanics have been doing for over 100-yrs... with multimeter.

1. measure power-supply line going into ECM. With key ON, then with engine running. What's voltages you measured.

2. then switch on turn-signals, use sunroof, etc. What's voltage going into ECM when these other devices turn on?


Most likely you have a short-circuit somewhere. By measuring voltages at various locations and comparing it to "what it should be" standards, we can narrow down area in wiring diagram for closer look.