Weird electrical issue. Please help

[bmxr152]

So i bought a 03 cobra finally after years of wanting one. So i brought it back to the shop, adjusted the pivot ball that was wrong for the t56 magnum and fixed a bunch of wiring with the battery relocation. So the problem that im having is that the speedo and tach go crazy when i do a wide open pull. Basically they die and then when i let of after a second they go back to normal. The car runs good still when this happens. Could this be a ground issue or maybe and bad alternator? I removed the WOT box that was installed too and still the same issue.

 

[Wings65288]

I remember having a similar issue. Not positive but thought it had something to do with the alternator not charging my battery enough in the upper RPM's, like past 5K rpms

 

[bmxr152]

Do you remember the voltage? I am seeing voltage drop to around 12.6 in the higher rpm range. it looks like it has some parts store crap alternator, but i dont want to throw a PA alternator at it if that is not the issue. Im on a stock lower with a 2.76 upper. Looks to be stock alternator pulley as well.

 

[DSG2003Mach1]

Do you remember the voltage? I am seeing voltage drop to around 12.6 in the higher rpm range. it looks like it has some parts store crap alternator, but i dont want to throw a PA alternator at it if that is not the issue. Im on a stock lower with a 2.76 upper. Looks to be stock alternator pulley as well.

If you're reading voltage through the OBD2 check the battery with a meter while it's idling and compare against the gauge. It's pretty standard for the gauge to read at least .3 lower than actual for some reason. Either way, 13 volts @ WOT is getting on the low side and pump volume can really start to fall off

 

[Roots-type]

If you're reading voltage through the OBD2 check the battery with a meter while it's idling and compare against the gauge. It's pretty standard for the gauge to read at least .3 lower than actual for some reason. Either way, 13 volts @ WOT is getting on the low side and pump volume can really start to fall off

All of this. Plus ignition loses out too which will highlight a weak coil that would normally work ok.

Mine actually reads .4-.5 lower through the obd2. Mid 13s and up is what you want though.

 

[Wings65288]

Mine was like 12.2 towards the top if I remember correctly

 

[bmxr152]

Mine was like 12.2 towards the top if I remember correctly

Did you have any issues with the cluster going all crazy?

 

[Wings65288]

Oh yeah the whole thing would have all the tachs simultaneously reset, like go to their max setting and all the way to 0. I've since upgraded alternators (unnecessary I THINK) and more importantly I had a trunk mount battery that was grounded to the THIN trunk metal. I've since taken it to the frame of the car AND added a few grounds to my engine block

 

[bmxr152]

Oh yeah the whole thing would have all the tachs simultaneously reset, like go to their max setting and all the way to 0. I've since upgraded alternators (unnecessary I THINK) and more importantly I had a trunk mount battery that was grounded to the THIN trunk metal. I've since taken it to the frame of the car AND added a few grounds to my engine block

Okay maybe I need to do that too. I have the battery in the trunk setup like that. Did you go to the rear frame area or all the way to the front?

 

[Wings65288]

Yeah just found a nice spot directly on the frame where a bolt had been removed. The bolt removed was somewhere near the rear passenger tire frame area. Just any bolt that's on the frame will do. There's a perfect spot on the passenger trunk side to run a thick 2 gauge black ground wire through this hole to the frame.

 

[bmxr152]

Well i fixed the issue with some extra ground cables from the battery in rear to the quad shock mount and one from the motor to the sway bar mount. I still have an alternator on the way since its a parts store one but all seems good now!

 

[BlckBox04]

I had the same issues. I put a 200amp alternator and a wiring upgrade and never had a problem since

 

[Wings65288]

Right on that's awesome. I think my tuner Malcolm was actually the one that pointed me in the right direction with all that. I haven't had it happen since either knock on wood.