Hi guys,

I'm a noob. I have a 1999 Camaro SS LS1 engine in a 1959 Chev Sedan Delivery.

I'm hearing what sounds like an electrical motor hum coming from the engine bay...my thought is something is wired up wrong so I need to find it and correct it. I can't pinpoint it, so I went and bought a mechanical stethescope.

After scoping all around the engine bay, I'm hearing the hum from within the engine when its powered off. It's not an exterior pump. I put the scope to all exterior items within reach, around the engine, and on it. Where I'm hearing the hum is on the throttle body, passenger side fuel injectors, and oil pan (???). The sound must be traveling through the block...

Is there anything inside the engine that could possibly be making a constant high pitch hum? My thought was since I heard it through the fuel supply, maybe it was the fuel pump. But there's nothing producing sound there when scoped.

Thank you in advance.

alanon

 

Did you check the alt? That's about the only electrical thing on the motor that could produce noise. Does the sound go away if you disconnect the battery?

 

I have not, but I will thank you. The sound does go away when the battery's disconnected.

I put the probe to other exterior items directly attached to the motor (somehow missed the alt), and the sound is carrying through all that I've touched. I'm hoping the source will be louder.

Will check the alternator this evening and let you know.

 

Thank you Happy Salesman -- the alternator is the source of the power draw.

More precisely, it turns out the exciter has power to it all the time (vs on ignition).

I think I need to close this thread and go the route of electronics help to see how to proceed.

It's a restomod with the LS1 in it; wiring wasn't done by me...get to trace everything down now. Thank you for pointing me in the right direction with looking at the alternator!

 

the IAC motor will also make some noise if things have gone wonky.

 

thank you truckdoug! I think I've found the problem, but will keep that in mind. Would it make noise when the vehicle is off?

 

The ECU is never 100% "OFF" and some relays and such if they stick can cause some weird stuff..

1. Fly by wire throttle body motor.
2. IAC valve.
3. Purge valves if solenoid activated.
4. Diode packs in the alternator with a bad diode.
5. Backfeeding from lighting systems into the engine power circuits.. (Shorts)

 

it's def the alternator. I actually cut the wire from the exciter off the alternator and put the battery back on...took care of it. Reconnected the wire, and sure enough...

needs to be run to a switched line, I think.

 

I believe the pcm is what energizes the exciter, so if that's staying on I would look into why the pcm is doing that. A switch would work, but I don't know if you may run into other issues down the road from that.

 

I think whoever did the orig wiring job wired it to a 'always on' wire...it's getting 12v fed to it. Not sure the PCM's connected to it...actually doubting it is.
Wiring diagrams show that pin# 15 or #61 should feed it. However nothing is on #15 and #61 has no power out of it in any state (key on, off, start, yada yada). So I'm a bit confused.

I figured this would move from internal engine to the PCM diagnostics group, but they disallowed the post. I moved over to the hardcore tech group hoping maybe I'd get an answer there on this type of problem. Not sure where to go with it overall.

 

http://www.lt1swap.com/2001_PCM_CONN_PINOUT.htm Here is the pcm pinout for the 99-2002 camaro/firebird. Pin 15 of the red connector is the generator(altenator) turn on signal.

 

If I remember correctly I thought the turn on signal was 8v not 12. In either case, you could just tie the turn on signal into the ignition circuit, so that way the alt turns on when ignition is on. Just have to be careful about leaving ignition on without the engine running, as I can't imagine that's good for the alt.

 

What if there is no wire coming out of the PCM on pin 15?

Beautiful -- thank you! Can I tap in to any switch power source, or only certain feeds (so I don't fry anything or burn out fuses and/or wiring)?

 

To be safe, I would use a relay instead of just pulling it straight off ignition. I'm not sure how much current the alternator wants for it to turn on, and wouldn't want it to start popping fuses or burning out circuits.

This way, you can safely tap into a large power source (such as the battery or the post on the fusebox) without worrying about drawing too much current. Just make sure to fuse it so if a short occurs your car is protected.

 

You can add that wire.

 

thank you guys!