Voltage at alternator versus ScanMaster

[turbonatr]

Had this in the scan tool tech forum but didn't get any feedback...

How much of a voltage difference should there be between the back of the alternator and what the ScanMaster tells me? At idle, I have around 14.1v at the alternator while the SM is telling me between 12.6 and 13.3.

 

[Razor]

Scanmaster reads the ignition feed wire going to the ecm. Scanmaster reads through the aldl. So it doesnt read this voltage correctly.

I would say 1.5 difference

 

[TurboBuRick]

Had this in the scan tool tech forum but didn't get any feedback...

How much of a voltage difference should there be between the back of the alternator and what the ScanMaster tells me? At idle, I have around 14.1v at the alternator while the SM is telling me between 12.6 and 13.3.

Thats a pretty big spread. Do you have a bunch of add-ons connected to the fuse panel?

 

[turbonatr]

No add-ons.

The reading on the SM will fluctuate even at idle whereas voltage at the alternator stays pretty much rock solid. Under a load the SM is saying voltage drops under 12 volts. I've seen as low as 11.4 volts under a load before I lifted.

 

[Razor]

Wire from alternator travels to battery + post. From the battery post it goes to the starter. Starter through fusible links goes to fuse box. From fuse box through ignition switch back to fuse box. Then goes to ignition on computer. Thats 20 feet of thin wire with multiple connections in between. This is why there is voltage loss especially as the car gets older.

What does it matter what the scanmaster reads on your computer when the alternator is OK. This is why hot wire kits are sold for your injectors, fuel pumps, cooling fans, and ignition modules.

 

[TurboBuRick]

No add-ons.

The reading on the SM will fluctuate even at idle whereas voltage at the alternator stays pretty much rock solid. Under a load the SM is saying voltage drops under 12 volts. I've seen as low as 11.4 volts under a load before I lifted.

Try and compare readings with key on engine off. See if you still have the same spread.

Is the fuel pump hot wired?

 

[turbonatr]

Pump is hot wired.

Here is where things get interesting. I have a very rich condition with fuel pressure at 43psi line off, which is where Eric recommends the pressure as a starting point with his version 5.6 chips. The car will actually beltch black smoke at this fuel pressure and part throttle driving is virtually impossible. I have to have the fuel pressure set to 30psi line off in order to drive it. I was wondering if the voltage had anything to do with my low load, low boost rich condition or if it's simply a matter of the chip needing to be reburned leaner.

 

[turbonatr]

Key on engine off,

SM...11.3
Alt...12.26

 

[TurboBuRick]

Razor nailed it on the head. The old wiring is more than likley the cause. I can't see the low voltage causing your rich condition. That sounds more like a bad maf.

 

[turbonatr]

MAF is a reman GM unit. I had originally thought the MAF was the cause, too. I was getting a MAF code so I bought a "new" reman MAF. Rich condition continues.

Of course that doesn't mean the reman MAF is actually good...

 

[turbonatr]

I think it may be time to step up to an LS1 3.5" MAF. Even if that's not where my rich condition is coming from, a 3.5" MAF would be better for my combo than the smaller factory 3".

 

[Roger]

I replaced alt to bat wire with #4 & got an improvement in v.

 

[turbonatr]

Ordered an LS1 3.5" MAF, 4" to 3.5" reducer (I have a 4" MAF pipe) and a 3.5" K&N conical filter. Assuming my rich condition is from the reman 3" MAF, this should fix the problem. If the MAF isn't the issue, the 3.5" MAF is a better match to my combo anyway. Going to take a closer look at the wiring as well and upgrade as needed.

 

[Beamer]

This is why hot wire kits are sold for your injectors, fuel pumps, cooling fans, and ignition modules.

Hmmmmm....

Are there hot wires for our ignition modules? That may be a good idea to ensure we have full power for spark. I just have not heard of it. Also, is the injectors suspect to having a voltage low problem with drop through the old harnesses?

Just looking for some more info...

Mike

 

[Razor]

More of an issue with low imp injectors.

In the game of feet, its all about the inches. Every time you improve power to things that have demand, you have the chance to better a situation.