Low Voltage + P1135

[Adamdmc]

Maybe I'm just paranoid, but I always get the fault code when it drops down to 13.6vdc. I guess that time will tell.

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[19963.4lsr5]

Maybe I'm just paranoid, but I always get the fault code when it drops down to 3.6vdc. I guess that time will tell.

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On a hot summer day I’ve seen 13.5 on my rig with the 80a Alt. Normally with this 80a Alt, the lowest I seen is 13.6 to 13.8.

The one I have on now is a 70a with an aftermarket VR and diode block. Plus a smaller pulley to spin it faster at idle.

I installed a DC amp meter temporarily when I sped up the Alt to track any improvement.

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[Adamdmc]

But is this normal for 45 degrees outside and running less than 7 miles (10 min)? I need to be able to trust it for 2000 mile 36hr round-trip runs from SC to MASS.

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[19963.4lsr5]

Your 13.5v was under what conditions?

If you have an automatic and you seen 13.5v in gear with your foot on the brake idling at 600rpm with lights and your heater on that is normal.

The factory Alt can only push 40a at 600rpm.

I’m pretty sure the low end spec is 13.5v in the FSM......


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[19963.4lsr5]

The charging specs are at 2000rpm.

13.9-15.1 at 2000rpm at 77f.

13.5-14.3 at 2000rpm at 239f.

The temps are underhood temps not ambient temps.

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[Adamdmc]

Thanks for the data. I always prefer to speak with data, otherwise it is mere speculation or theory. I'm going to watch it for a day or two and see what happens.

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[19963.4lsr5]

Thanks for the data. I always prefer to speak with data, otherwise it is mere speculation or theory. I'm going to watch it for a day or two and see what happens.

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I usually don’t speculate[emoji57]


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[Adamdmc]

Ok, so maybe I don't have an alternator problem any longer, but I still feel like something isn't right. I just drove 100miles of interstate and voltage read 14.0-14.4 the whole way. Once I get off the hwy and stop at a red light voltage starts dropping. Rolled window down and it dropped to 13.5 then slowly down from there. Is it possible that my battery isn't holding properly? Nothing else was running, like blower motor or auxiliary items plugged in.

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[19963.4lsr5]

My rig only uses 13a to run with nothing on but the radio.

Look for a bad battery connection

Measure battery post voltage while someone rolls down the window.

What rpm were you idling at when you put the window down and seen 13.5v.

A bad diode will cause reduced voltage at lower rpm. When I lost a diode I had a loud whining when I would turn on anything. It would barely push 12.9v just running the engine at idle.


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[19963.4lsr5]

Where were you reading the voltage from?

The cig lighter is not a good voltage source.....


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[alumarine]

At idle the voltage can drop.
And as 19963.4lsr5 said, best to measure voltage at the battery.
Have you done a load test on the battery?

 

[19963.4lsr5]

Hot idle at 650rpm voltage stays at 14.1v putting down the window.


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[Adamdmc]

Let me start by saying thank you all for all of the great information that you have shared. It has been truly helpful. However, I still suspect that the battery is on its way out. I'm still getting the P1130 and P1135 codes when the voltage drops, and only then. On top of that it started turning over longer before the engine starts, and now making a slight grinding noise while turning over. So, yes possibly the starter is also starting to go, but I need to make sure the power is sufficient before addressing the starter. I drive about 50k miles a year up and down the East Coast on marathon style trips that can sometimes be up to 2000 miles in less than 36 hours. So what batteries out the will stand up to that kind of abuse? Looking for quality with good specs.

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[Bad Luck]

Let me start by saying thank you all for all of the great information that you have shared. It has been truly helpful. However, I still suspect that the battery is on its way out. I'm still getting the P1130 and P1135 codes when the voltage drops, and only then. On top of that it started turning over longer before the engine starts, and now making a slight grinding noise while turning over. So, yes possibly the starter is also starting to go, but I need to make sure the power is sufficient before addressing the starter. I drive about 50k miles a year up and down the East Coast on marathon style trips that can sometimes be up to 2000 miles in less than 36 hours. So what batteries out the will stand up to that kind of abuse? Looking for quality with good specs.

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I prefer to use a lead acid battery in vehicles that came factory with it. I've got a factory sized battery from O'Reillys. https://www.oreillyauto.com/detail/...tery-group-size-24f-24r/24rext/4742480?pos=15

 

[19963.4lsr5]

I just put a interstate MTP-24F in

750cca and 130RC.

It tested at 770cca with my MidTronics tester.


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