Idle/Voltage drop, 2004 suburban 8.1L

[Kyle Leroy]

Hi all, new to the forum so I hope I'm posting in the right place.

 

Here's my issue, when in any gear, under any load at idle my voltage will drop from 14 to 13 and my RPM's from 700 to 500 and sometimes a little lower. No CEL or codes stored or pending.

 

Things I've tried:

 

-Cleaned MAF and intake

-Plugs and wires

-Had the auto parts store test the battery and alternator, both tested good

 

Soon to try:

 

-Clean all ground points (if anyone knows where they are located that would be great). It's from the the far north so it has some underbody rust issues.

- intake manifold gasket (does this line up with my issues?)

-smoke test for vacuum leaks

 

Please let me know if you know what the problem is or any direction I haven't already thought of would be greatly appreciated!

 

Kind Regards,

[Formulabruce]

Hi, Most people dont know that the A/C compressor will cause a load change and it can run during A/C cycles AND during a defrost cycle. ( YES it runs in the winter!) A Bad clutch kicking on will cause a significant load and V- ( drop)

put a real meter on the battery and test it under load conditions, then get a load tester ( auto zone) and hook it on the battery and see how good the system is .

Also a partially shorted battery can cause this

[Kyle Leroy]

Hi, Most people dont know that the A/C compressor will cause a load change and it can run during A/C cycles AND during a defrost cycle. ( YES it runs in the winter!) A Bad clutch kicking on will cause a significant load and V- ( drop)

put a real meter on the battery and test it under load conditions, then get a load tester ( auto zone) and hook it on the battery and see how good the system is .

Also a partially shorted battery can cause this

Thanks for your reply tho I've already done most of this, will test the short idea when I get off work. It doesn't matter what the load is, full or little. And with no codes to go on I'm lost at the moment. I'm going to clean the EGR valve and see if that helps. Any other ideas?

[davester]

how does the voltage vary at the alternator, both at idle and if you rev the motor, say to about 2K rpm?

[Kyle Leroy]

how does the voltage vary at the alternator, both at idle and if you rev the motor, say to about 2K rpm?

 

Thanks for the reply. The variance hardly registers at the alternator tho I have not tested it at 2000 RPM. What exactly will this tell you? It's a slight dip from say 14 volts to maybe 13.5 volts. And it's at the same time the idle drops by maybe 100 RPMs or less. Maybe it's nothing but I just like to have it a clean running motor. It does seem to idle a bit High because I am under the impression that it should idle at 500 and my tends to idle around 700.

[davester]

If the voltage varied at the alternator, then at least the voltage regulator in the alternator was bad. But since it's stable, but the voltage is varying elsewhere, it's either a significant load or faulty ground/power connections.

[Kyle Leroy]

You don't happen to know where all the ground points are?

[Kyle Leroy]

If the voltage varied at the alternator, then at least the voltage regulator in the alternator was bad. But since it's stable, but the voltage is varying elsewhere, it's either a significant load or faulty ground/power connections.

If it was a bad ground would it happen at other times other than just at idle.