Bouncing ammeter

[dewsky]

Ok guys....I installed a Sniper EFI on my 360. Got her running and now when it's running the ammeter is bouncing from nothing (middle) to full right and back and forth. when first started it was not doing this but started after a few minutes. I have disconnected the ballast resistor from the system and wonder if that could have anything to do with it. Also, the wiring for the distributor is still there, but the box is unplugged (Put a Holley Hyperspark system on it.). Any Ideas?

 

[67Dart273]

Boy you need to get this fixed PRONTO especially when dealing with electronics. There are number of things that can cause this

No particular order

VR voltage/ ground loop problems
Problems within the alternator
Problems / loose / bad connections in the wiring harness
In rare cases a bad VR

Bad connections in the charge path to the battery. If you have bypassed the ammeter, that might simplify finding it. suspect the major component path in a stocker. Read the MAD bypass article and pay attention to the diagram posted there:

Catalog

The major points to suspect are ANY connection in that path from the alternator to the battery, EVERY terminal and connection

Alternator. Several problems there, including bad brush contact, worn/ sticky brushes, and a stator which has vibrated it's insulation off and is shorting between turns

Grounding VR harness path: Check and improve VR grounding. Check connector at VR and at alternator brushes, make sure they are tight and in good condition.

IF YOU HAVE A TRUNK MOUNT BATTERY suspect that some wiring glitch there is a gotcha, including both hot and ground sides

 

[67Dart273]

Is the ammeter fairly rhythmic or completely random and erratic?

 

[Dana67Dart]

You might be taxing the alternator with the added electronics

From a search on current draw of a sniper.

 

[dewsky]

Is the ammeter fairly rhythmic or completely random and erratic?

It’s pretty rhythmic.

 

[Mattax]

You can solve it.
The ammeter is in the battery output/charge wire.
Full right points to 40 amps Charge. (it could be more than 40 amps but thats the max the meter shows)

There should be nothing attached between the battery positive and the ammeter.
But if you have attached anything the draws power in between or at the ammeter or the battery positive terminal, then check those additions.
Also be sure the starter cable isn't shorting to ground.

 

[Mattax]

The standard factory wiring strategy is not really appropriate for an EFI system. It makes a number of assumptions based on low power needs at starting and idle. EFI has high current demands (pump and injectors) all the time.

My suggestion is to look over your wiring and come up something you are comfortable with doing.
Find the electrical needs of the pump and injectors. These will be in Watts, or amps at some specified voltage.

There are at least two approaches that would handle the loads reasonably well.
1. Connect the alternator output directly to the battery positive.
+ use a maxi-fuse or fusible link in that line.
+ install a voltmeter to monitor the electrical system while running. One that plugs into the lighter socket could suffice termporarily.
- With this arrangement the ammeter will no longer show battery charging and disharging. it will show flow through that line when its the shortest path to something.
>A diagram of a more solid way to do this with an auxilery box and relay here. <

2. Connect all of the new loads to the alternator. A relay could be used so its powered in start and run.
+ use fuses or breakers in the connections
+ ammeter still shows charging and discharging
+ adding a voltmeter, even one in the lighter plug would be a good addition to let you monitor if the system is performing as it should.
- With this arrangement, during start power for the EFI still has long route. If the EFI needs during start are real high, say 20 amps or more, over time weak points in the original wiring may cause you problems.
- If the EFI electronics are sensitive to alternator output noise and need the battery to soak it up.
>The second and third diagrams here show ways to do this with an auxilery box and relay . <

 

[67Dart273]

It’s pretty rhythmic.

That might indicate more of a "loop" problem. FIRST thing to do is attempt to determine if you have a voltage drop problem. Tell me some more about the wiring, AKA is this factory, aftermarket, been replaced, repaired, chopped up, etc?

WHAT HAPPENS in a stock system with typical voltage drop problems:

The drop in the ignition circuit supplies the VR. This can be say, a bad connection in the bulkhead connector, the ignition switch contacts, the switch connector, etc. OR IN the output circuit in the ammeter/ bulkhead connectors part of the circuit

This can form a sort of "loop" that when the VR commands charge, the voltage comes up and the resistance in the circuit can cause a glitch in the way the VR senses. The voltage comes up, the VR starts to back back down, the voltage goes down, the VR wants more charge voltage, and it just repeats.

Things like VR grounding to battery neg, the bulkhead connectors, etc all need to be checked

Try running a BIG wire (or 2 or 3 no10 wires in parallel) direct from alternator to the battery. If that settles down the system you are on the right track.

IT IS RARE but this can also be caused by a bad VR