Strange issue I have picked up in my data this year. My voltage during a run used to be flat at 14.8V. I installed an efi system this winter, which is really the only change, and now the data looks like a sine wave going from 14.8v to 15.9 volts with a frequency of about .2 seconds. It ONLY happens during a run. From the time it goes WOT to when the rpm drop below 6500. Then it goes flat like it always has been.
Anyone ever seen this? It has to be coming from the alternator.

My VAT has the capability of detecting weak/bad diodes. Via bar graph. It's an older Snap on unit.
AC wave detectable when you do a bench.You can still have a good working output and have leakage.
Any alt that had more than 15.8 on a 12 normally got replaced. Those were the recommendations from Sun Electronics Corp. You have a rebuilder around you for a bench?.

This message has been edited. Last edited by: TD3550,

Well the good news is I think your alternator is large enough to keep it fully charged during a run. It does sound like your alternator (Regulator?) is going bad. I have never noticed anything like that on my logger but it did tell me when my alternator quit charging.

Rebuilders are getting hard to find anymore! I may be able to get my wife to drop it off at one the next county over.
Would like to figure out what body this thing is and just get a new primary and use the other as a backup if I can get it fixed. Any good way to identify an alternator?

Here is a link to my wholesaler. The units i normally get from DB Electrical are truck units.

Ref Point. Single and 3's

https://www.dbelectrical.com/a...utomotive/chevrolet/

That looks familiar, and I think it is the one that is in the car now. Not sure what is wrong with the alternator, but it sure hasn't seen that many runs to have failed.

could it be injector pulse related

quote:

Originally posted by rusty:
could it be injector pulse related

I thought of that. But the frequency doesn't change through the pass. If it were injector related, the frequency should get faster. It's almost like once the rpm reaches a certain threshold, the regulator loses control and the voltage bounces.
or
Something is goofy with the Racepak reading.
Really strange is that you can't see this movement on the injection ECU data. It's flat. How can that be?
I have a new alternator on the way. Will see what that does.

What is the sample rate of the EFI datalogger? If it is a newer Holley setup, set it to 100 samples per second.

quote:

Originally posted by Mike Beck:
What is the sample rate of the EFI datalogger? If it is a newer Holley setup, set it to 100 samples per second.

20 ms. Its a megasquirt ms3 pro/u

How is the alternator wired? Are the main ECU power and grounds direct to the battery? How is the rest of the car grounded?

EFI’s are very specific as to how each circuit is grounded.

Only system I have had issues with showing noise on the data logs is FAST XFI with XIM and RacePak...

Alternator large ground cable to block, and from that connection to the battery. Hot wire I believe right to the battery side of the main switch.

I have a ground block connected to the battery, and the ecu and about everything gets grounded to that.

I put in a new East Coast Auto Electric alternator last night. We will see if this changes anything. The sine wave started this year, and everything was the same as last except for the efi.

The wave doesn't seem like noise. It is such a clearly defined sine wave at the same frequency and amplitude that it is hard to call it noise.

I also put a solid state relay between the ecu and the air shifter solenoid. Hopefully that will eliminate the brief shut off I see when the shifter is triggered. I used an msd relay, and I have to say that thing is really handy.

Alternator fixed it. Flat as a pancake now

By chance, was it a Delco 10SI unit?

Well the size is the super mini by ECAE. The one I replaced was not a Delco branded unit if that's what you are asking. But it is the super mini size. Sorry I'm not very knowledgeable about the terminology of the styles.