Voltage Drop Help

[another69]

The wiring is all fresh, and the starting circuit is probably overkill. No, I have never checked for heat after starting but I will along with the connections again. FWIW the motor is now an LS3, and the same issue (I now realize) was happening with the old SBC. Cranking amps for the Braille are listed at 750, but I will get it checked. The starter never struggles, always fires right up.
I looked online and though I'm not familiar with the voltage filter Polous sells dc regulators for about $5 that have the rated milliamp output and will take 3v-18v and convert to steady 12v. That should work in theory, but it is another component that could fail. Tiny too, smaller than a postage stamp.
Aeromotive suggested a momentary button to cycle the signal to the controller after the engine starts. That resets it, and should definitely work, but I was hoping for a more "automatic" way of doing it and I don't want to add another relay.

[nokones]

Kenny,

Double check the cranking timing in your Holley tune. You might have the timing set too high while cranking, which is hard on the starter.

Andrew

That was checked some time ago. I think my tuner set it at 15 degrees. A couple months ago I asked if we should set it lower and he said no and since I was still having the problem he did a data log on the cranking and we were seeing the voltage drop down to 9.5 bolts for that brief second. He is an advanced trained Holley tuner so I supported his decision to leave it at 15 degrees on the cranking timing.

[another69]

This question was for Kenny, but Looking at my Holley base spark table, the lowest RPM shown is 450. Timing is from 18 to 22 degrees Cranking RPM is lower than that, but I don't see a specific modifier for cranking retard. So I assume under 450 RPM timing is still 18 to 22?

[blitzer454]

A diode and cap may work depending on the Aeromotive fuel pump Speed Controller current draw and how long the voltage drops while the starter is cranking. You didn't specify which model pump controller you're using, but I looked at this one. It has a couple of leads for power. One is labeled BAT and the other PWR. If the dropout on the PWR rail is the one that is giving you problems then adding a cap and diode should work. According to the manual the PWR pin needs less than 5A, so finding a diode and cap to compensate for a short drop out should be doable. However if the problem is caused when the BAT terminal drops out then adding a cap and diode is not going to work.

[CarlC]

What fuel pump do you have in the car? I may have something that will work.

[another69]

fuel pump is an Aeromotive stealth 340. Pump controller is a #16306. If it matters, my tank is a Rick's that will accept a stock modern GM fuel pump.

[dhutton]

Been there done that with that pump controller. Not a very robust design in many ways. For a little more money you could have gone vaporworx with true pwm control.

Don

[59rah]

I had a similar issue on my LSX using a Holley ECU. It ended up being not grounding the engine directly to the negative battery terminal. I installed the ground wire and voltage drop went from 10-10.5V while cranking that would not allow the engine to spark or start (before the ground wire install) to above 11.5V, and the engine fired right up. I'd recommend installing a ground wire to the engine block and ensure everything is tight (positive and negative).

[nokones]

I have two grounds from the battery; one to the chassis near where the battery is located in the radio module well behind the passenger seat of my C4 Corvette, and one directly to the all aluminum block. There is also a ground strap from the chassis to the block. I just looked up the conductivity of aluminum and it says aluminum is only 61% conductive of copper. I wonder if the aluminum block could be creating a grounding issue. I think I will run a ground cable from the chassis directly to the starter mounting bolts and see if that will help with the voltage drops. I guess that can't hurt.

[another69]

Don- why do you say the controller is not robust? My tank allows me to go the vaporworx route in the future if needed.

I will take your advice about the grounds. I have a #2 power & ground but the ground attaches at the chassis.

[dhutton]

Don- why do you say the controller is not robust? My tank allows me to go the vaporworx route in the future if needed.

I will take your advice about the grounds. I have a #2 power & ground but the ground attaches at the chassis.

I found the setpoint seemed to drift around and at times it would reduce the pump voltage when the rpm was higher than the setpoint leading to poor operation. This controller is an open loop controller which is very crude in principle and apparently in execution of the hardware. I think it is sensitive to both temperature and supply voltage.

I’ve since installed several Vaporworx controllers and the difference is day and night. Works first time, every time. It is a true closed loop controller.

Don

[another69]

My tank is set up for vaporworx if I choose to go that route. For now the Aeromotive return style system with Brown & Miller hoses has been rock solid except for this minor issue. Plus the money I have in the fuel system, I hate to scrap it all over this.

[blitzer454]

well you could always try the cap/diode fix. it's pretty cheap to try. Attach as shown:

I would use a big electrolytic cap, something like 5600uF and a big diode to make connecting it to the existing wiring easier. That should give you at least 10ms before the voltage drops below 9V, assuming the PWR pin is only using around 1A.

[another69]

Blitzer454- That looks like it could be the solution I am looking for - thanks for posting! I'm not that familiar with 12v capacitors & diodes though. In your diagram I see the diode, but is the cap the 2 lines that resemble NO contacts? I just connect one side of it to ground and the other to 12v+? Any idea on the size or rating of capacitor I should be looking for?

[blitzer454]

Yes, the cap are the two lines and also note the plus sign which shows that the positive terminal of the cap needs to be connected to the PWR terminal. You will also want to place the cap close to the pump controller to minimize the length of wire from the cap to the PWR terminal. Also keep the ground wire of the cap as short as possible. The triangle part of the diode diagram is the anode and the line is the cathode. The diode package has a stripe around one end of the cylinder which represents the cathode terminal. I went to digikey.com and picked a couple of parts that would be suitable.

[another69]

Thanks for clearing that up and getting me part info. I'd say definitely worth a shot especially for that price!

[andrewb70]

This question was for Kenny, but Looking at my Holley base spark table, the lowest RPM shown is 450. Timing is from 18 to 22 degrees Cranking RPM is lower than that, but I don't see a specific modifier for cranking retard. So I assume under 450 RPM timing is still 18 to 22?

There isn't a cranking spark retard in the Holley. It's just not how it works. In the System ICF there is a value you enter for cranking advance. So while cranking that is the advance. Once the engine starts it reverts to the main spark table.

Andrew

[another69]

Andrew - I see it now, cranking advance is set at 15 degrees. How much lower do you think I could go?

[andrewb70]

Andrew - I see it now, cranking advance is set at 15 degrees. How much lower do you think I could go?

Play around with it and see what it likes. Mine is set at 13. You're not going to hurt it by setting it lower.

Andrew

[nokones]

Setting it lower, would it help?