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Car voltage is low under load


I have a 2006 Suzuki XL7. I’m looking for on advice on what could be possibly wrong with it. The major issue is that it has a chirping noise. It also has voltage under 13 volts when it is under load but over 14 idol. The chirping noise is louder and happens faster when driving it. I have sprayed water on the belt, that did not change the squeaking. I also have replaced the battery and alternator. It still has low voltage and the same chirping. I appreciate any help anyone can give me!

I would advise changing the belt, since you already changed the alternator. The old “spray water on the belt” trick is not always conclusive.

There may be a bad connection in the charging circuit that is causing the low voltage. Use a meter to check the voltage on the main output lead at the alternator. If the voltage is still low at that point then something is going on with the charging system. Perhaps a problem with an external regulator if it has one. If the voltage is higher than 13.8 volts then you need to look for a faulty connection between the battery and the low voltage point. Measuring across the main alternator lead to the battery while a good load is on the system and the engine running around 1,500 RPM you should not see more .3 volts across the lead.

The harmonic balancer on the crankshaft may be slipping, the is a rubber bushing between the center hub and outer pulley. With a crayon mark a line on the balancer from the center to the outer pulley where the belts are driven, start the engine and after you hear the noise shut it off and see if the line has split.

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If you don’t have one, go buy a five buck automotive stethoscope. You should own one, anyhow. Idle the engine and touch the probe end to STATIONARY engine components BEING VERY CAREFUL NOT TO GET HURT. Don’t touch moving parts and don’t get any body parts or loose clothing or hair near moving parts!

Often times, bolted-on hubs of belt pulleys, tensioners, air conditioner clutches, etcetera, are stationary and can be very carefully probed. You are listening for any screamingly loud bearing sounds that would indicate a component that could be dragging down the belt speed.

P.S. I took a look at a serpentine belt diagram for that 2.7L engine. It appears there are 2 idlers, besides having a tensioner and there must be an A/C pulley, alternator (which was replaced), and power steering pulley (?). You will probably have to hold the stethoscope probe firmly to the stationary body of the power steering pump as I doubt there is a stationary nut.

Oooo…, I like this suggestion. Also, look at the harmonic balancer pulley while engine is idling. I’ve had them go bad and exhibit a visible wobble. Also, and probably obvious (it’s a balancer), the engine could have a little vibration/shaking that wasn’t present before the balancer went bad.

I have an update, I appreciate all the advice. I don’t know how to test the connection between the alternator and battery. But I did some investigating. When I started the car, it had a voltage of 12.2. I saw it built up to 12.4 when I looked back, I gave the car some gas and the voltage dropped to 12.25 but very quickly came back. I also noticed at this time the car was running just over 1k rpm. The car continued to slowly grow and in 6-7 minutes it reached 13.36 where the chirping stopped. The car a few seconds later reached 14.4 where it stopped. When I throttled the car at this point it was more resistant, it never dropped below 14.37, and the rpm was now just under 1k. The last thing I noticed was that the chirping would increase as I throttled the car.

Again thanks for any advice anyone can give me. Also, I can test the resistance from the alternator to the battery if someone can give me insight on that. Also is there any way I can surely test if it is the belt slipping or a pully chirping?

Sounds like a slipping belt to me. Change the belt and let me know if I’m wrong. No loss to you if I’m wrong as its over 10 years old. Be sure to look at all tensioners and puuleys as well.

Once the belt is off, rotate and rattle all the pulleys it ran over. If there is any graininess or play, that needs fixing. It’s hard to see a belt slip but shining a timing strobe light on it will disclose any irregularity in its speed.

With the engine off, try rotating the alternator pulley with a boxed end wrench or socket. The pulley should not slip except under a bunch of pressure.

The belt was replaced within the last couple years. I will try what you guys said and update you.

To check the alternator cable place the positive probe of the meter on the large output wire connection on the alternator, place the other meter probe on the positive battery post, which is tied to the alternator. Now you will read the voltage drop across that wire. From what you have been saying it seems that wire connection is okay. You should not see more than 0.3 volts across that wire if the connection is good.