Cant figure it out: Voltage drop when trying to start on AEM EMS (SR20)

[2_Liter_Turbo]

My new motor is having some electrical issues. S13 Redtop with AEM EMS (MAP), when running the starter, voltage drops to 9-10V area from about 13-14V when starter is not engaged. I tested the starter out of the car at a few auto parts stores (on their starter test benches), and I get about 14V @ 75amps. All grounds looks to be good, and tested all the grounds on the ECU itself. Hoping someone has ran into this before, and has some insight. Before new setup, car started on a flashed factory ECU, but did take a little work to get it to start. The AEM ECU wont start the car at 9-10V.

[anarchyperf]

Since your grounds look good. I'd suspect a weak battery

[2_Liter_Turbo]

Since your grounds look good. I'd suspect a weak battery

Thanks for the response,

We tried about 3 different batteries (one being brand new). The grounds that I can think of is the battery ground to the engine (with chassis in the middle), the small ones on the intake manifold, the one on the back of the cylinder head to firewall, and the one from the starter solenoid to the chassis. Am I forgetting any? All grounds in the ecu tested good as well.

[anarchyperf]

Have you had the car running with the AEM yet?

[2_Liter_Turbo]

Have you had the car running with the AEM yet?

I have not. The ecu was bought used locally from someone who went from an SR to an LS1. I bought it through a shop as well. I am not an ECU guy, so the shop that is doing my tune is having the issue of the AEM wanting to go into startup mode due to the voltage drop. It's only there while trying to start. Otherwise everything is fine, and the ecu powers on and talks to the laptop.

[anarchyperf]

Is your battery relocated? If so what gauge wire did you use? All contact points/ terminals clean?

[2_Liter_Turbo]

Battery is not relocated, it's a miata battery. Negative terminal is new, positive is clean and in good shape.

[anarchyperf]

The other batteries you tried also miata batteries?

[2_Liter_Turbo]

The other batteries you tried also miata batteries?

Size wise yes, lol. The new one was a gel cell type.

[anarchyperf]

I'd try a regular size battery. I had a similar problem when I ran one of those tiny batteries.

[2_Liter_Turbo]

I'll give it a shot. Is it possible it's the ECU? What about the starter (even though it tested good from multiple test benches)?

[2_Liter_Turbo]

Forgot to mention, we even tried having a battery booster box attached and we still got a drop. So i honestly don't think its the battery.

[Happy240sx]

If it is cranking, and the ecu does not drop it's connection due to low voltage, and you have "Start Sync" and your base .cal file is setup right for your car configuration... it should fire. Do you have all four of these things?

It's not uncommon to see a large voltage drop when trying to fire a car.

[2_Liter_Turbo]

It does not have "start sync" and I believe it is dropping the connection due to the low voltage during the starting circuit.

[Midtenn]

Have you gone through the full "first start up" section of the ECU setup process in the manual? Just because it was installed a similar car, it may need to be tweaked to your setup.

I know on my Miata, it takes a few turns of the motor for the ECU to sync with the CAS.

[2_Liter_Turbo]

I'm sure the shop has done it. They've done 100s of AEM setups, so I'm hoping they know their way around them, ha ha. Everything is pointing to the starter I think, so I need to figure out a way to load test it on a different car or something.

[silver350z05rb]

How about a failing alternator?

[2_Liter_Turbo]

OK, went over to a buddy's house and tested the starter on his SR car (tested his starter as well), and there was only about a .5V drop (normal) max between the three different tests I did on both starters (ground, power, and solenoid). So it's not the starter at all. I get the AEM trigger wheel on Monday, so after I get that installed, I'll see if we can get it started. I'm still out of ideas.

[Croustibat]

can you try turning your engine "by hand" (big wrench on the damper pulley) and compare it to another engine ? It may just be your engine has high compression and all. Your Vdrop does not surprise me at all, it is quite normal considering the current the starter has to draw. I sometimes go as low as 8V when my battery is weak. I do use a standard ECU though (with a nistune on it). Are you sure the engine is in good condition ?

[2_Liter_Turbo]

can you try turning your engine "by hand" (big wrench on the damper pulley) and compare it to another engine ? It may just be your engine has high compression and all. Your Vdrop does not surprise me at all, it is quite normal considering the current the starter has to draw. I sometimes go as low as 8V when my battery is weak. I do use a standard ECU though (with a nistune on it). Are you sure the engine is in good condition ?

The engine is new and rotates great. It has a tad more resistance due to the supertech valve springs, but it's not that noticable.

[Croustibat]

Not sure that is the valve springs effect, TBH. My point was just that: if it is harder to turn, the starter needs more power, and the more amps it draws, the lower the voltage will go. I am still surprised the ECU just dies because of that.

If you really want to rule out the voltage drop, try starting the car with 2 batteries : 1 dedicated to the starter (it is easy, the wiring is direct), the other one for the rest of the car. This way you should not have a voltage drop on your ECU. If it still is not starting, then it is not caused by the voltage drop. If it starts ... Then you are in for a world of electrical trouble.

[2_Liter_Turbo]

We got the car started today. The fuse for the ignition switch was corroded and basically fell apart when removed, and it needed the AEM CAS disc. Couple small bugs to work out now, and hoping to drive it home on Friday!

[anarchyperf]

Good find man! Things like that are the reason I (notso)painless wire all my cars lol

[inopsey]

We got the car started today. The fuse for the ignition switch was corroded and basically fell apart when removed, and it needed the AEM CAS disc. Couple small bugs to work out now, and hoping to drive it home on Friday!

did that fix the voltage drop?