LFX Wiring
 

I never found anybody who posted their wiring, so I thought I would post how I wired my car and compare notes with those who have an LFX up and running. It took quite a bit of research from a set of 2012 Camaro manuals and taking notes from some of guys on this forum. My car currently starts although it seems to take at least a couple of tries. I think it's fuel related at this time. Just to get it started I disabled VATS and quite a few other DTC codes related to anti-theft, communications to another subsystem and emissions, so you will need something or someone who can edit the software. I have EFI Live.

Some background on my build, it's a 99 NB and the engine is an LFX out of a 2012 Camaro that was an automatic car. The ECU I am currently running is the original one that came with the engine so it is for an auto, but it is now mated to a 2013 Camaro manual transmission.

So, on to the wiring. It really came down to two large connectors where you tie all your inputs: "Fuse Block X50a Underhood X3" and "X102 Wiring Harness to Forward Lamp Harness" (These are GM names for the connectors). The schematic I have shows where I applied the ignition 12v and battery 12v. I used one gigantic relay with it's own battery connection for the ignition 12V since the fuse ratings adds up to over 100amps. It's up to you how you want to do that part. Just as a word of caution, don't just hack off those connectors without marking what pin they go to. I think all pink/black is ignition 12v, but I don't know if they are all interchangeable. That's why I listed at least one point the wire went to (most of them go to more devices than what I have drawn in the schematic). I did that in case you did what I did and hacked the connector off thinking I would just use the color coding to figure it out until I realized there are multiple wires with the same color. Keep in mind, my car is not road worthy yet, so things like the reverse connection from the transmission is not hooked up yet. Some day, I hope my emissions and ac stuff is working, but first things first.

The starter motor stuff mostly bypasses the Camaro ECU and is all the miata wiring. I found out this week the ECU does not need a Park/Neutral signal or the Brake signal to start. Another side note, you need to plug off the purge valve if you're not going to use it or you may have a gigantic air leak into the manifold.

not sure where my edited pictures went

Thanks for posting this info, it will definitely come in handy!

Anybody use this schematic? Just curious. My car started once upon a time and I haven't been able to get it start again even with another ECU. I noticed I have no reference 5v anywhere, so I'm thinking there is something else I missed in disabling some of the codes.

E39 / E39a ecu is very sensitive when it comes to battery voltage - it'll crank over fine, but if the voltage is too low it won't turn on the injectors. A lithium battery jump pack has turned out to be really useful especially in cold weather, with the ECU commanding only 13.8v from the alternator, leaving the battery a little undercharged. Not a problem in the stock-ish camaro configuration, but with the remote battery of the miata, it's a little marginal.

Thanks for the tip. I did notice my cranking voltage going from about 12.8 to 10V.

What alternator are you guys running? I've tried the one that came with my motor (2015) and a junkyard one from 2010 and I still only have 12v when running and the battery is barely charging like the alternator isnt being excited into charge mode. Any tips?

The problem isn't the alternator, it's the ECU - partly why v8r recommends the e39 instead of the e39a. In a camaro the BCM monitors voltage sends that data to the ECM which then produces a 128hz square wave to the alternator for voltage control.

There's two inputs into the denso alternator - field and lamp if memory serves. The e39 will enable the lamp input, but the e39a won't (also: note I'm not speaking authoritatively here, just what I understand). With the lamp enabled the ECM will output 13.8v - which is less than optimal for battery charge.

I made a 555 circuit to produce the square wave and threw it into our car and it did.. nothing. I suspect I might've blown up that field input by putting 12v to it when I was originally troubleshooting it (the 128hz is 5v). We've got another alternator to try on, but that's been on the backburner. I think (again, not authoritative here) the lamp can be excited by a 1/4watt resistor (390? ohm?) to 12v (edit: Looks like I'm wrong about this. Don't do this.) - which'll at least get you 13.8v, but having the car on a float charger in the garage and a jumper box in the trunk has been beneficial if not optimal.

https://www.motor.com/magazine-summa...arging-system/

https://gearsmagazine.com/magazine/a...tem-diagnosis/

Note: looks like I might've made a mistake on the field enable there with the 1/4 watt resistor suggestion, that's for the other GM alternator stuff.

Huh.. after doing some more reading, I think I might've accidentally put my PWM signal on the F terminal instead of the L terminal. I didn't realize it before, but the F terminal is a feedback signal from the alternator to the PCM.

https://www.motor.com/magazine-summa...september2015/

Seems to imply that if you disconnect the L terminal from the ECM, the alternator might self excite and default to 13.8v?

Excellent info in that link, and your theory is right.:bigtu:
I disconnected the 2 wire plug and fired the car up and immediately got a huge bump in voltage to almost 14v!! I put a multimeter on the output terminal of the alt and got a reading of 13.9VDC. Previously I never saw more than 12.1VDC. I'm not sure if the alt will melt down or the battery will boil (I have an AGM actually) but I'l be testing it out extensively tomorrow.
Man I hope this dumb thing solves the issue.

Adam

I don't think we have to worry too much about boiling, it's more of an undercharge issue with ours. 13.8 is enough to keep the battery cranking the engine, but because of the E39's sensitivity to voltage, it won't turn on the injectors with a low voltage batt - further exacerbated by the long power cables. When I get a moment I'll see if I can get the 555 circuit thrown back on the Lamp input instead of the Field - we really need the batt voltage to be 14.2

A follow-up:I did 400 miles and a 12run autocross on Sunday with no issue, got no misfires as I had been getting prior to this fix. I also drove with seat heaters on as well as headlights and no issues. Voltage stayed at 13.8 or 9 all day through the 19 hours of use.

Adam

Nice, I'll pass the info onto v8r. I tried my circuit again last night and no joy, gonna swap the alt and try again.

So you guys just disconnected the 2 wire alternator plug on the back of it and everything was all good after that?

Seems to have worked for me. I have a consistent 13.8V. While I'd like 14+V I've now put a couple thousand miles on my car like this and never need the battery charger anymore.
It'd sure be great is someone else has a 14V fix but until then, unplugging seems to keep the car running

I'm still working on the alternator controller, but so far no joy. Did replace the alternator in ours (well, sorta - got another one off ebay for cheap that turned out to not spin freely, pulled the regulator out of it and swapped it into our old housing) and it's been behaving better - but summer temperatures make the battery flow juice more readily, so I'm not sure if that has solved all our ills.

Taking apart the regulator - I don't think it's fully digital. I thought it's just using the 128hz control signal to feed an RC smoothing to op-amp, but I measured 40-180ma current at varying pulsewidths (and opamps are supposed to be high impedance). The output signal is documented as a hall, but I can't seem to pull a signal off it unless it's barely self exciting, and the output is 12v 202hz.. course these are bench results on my "busted" regulator so it may all be off.. I need to build my circuit with higher current capabilities and maybe snag another reg out of the junkyard. Analog isn't my forte, just know enough to be dangerous, so if anyone has a better idea...

I'm nearly done with my ND LFX conversion, I wanted to use the donor engines fuse box,
I'm pretty average with wiring lol, how would i do this using the stock block?

Very interesting to me as I have a 2013 LFX and a 6L50e in my 1966 Chevelle and I have the same charge issue. I currently have nothing connected to the alternator plug.
i have been daily driving mine for awhile and it hasn’t let me down but I know the 13.8v isn’t correct.
I’ll follow this in hopes that one of you comes up with a solution. You are all far smarter than I.
https://cimg3.ibsrv.net/gimg/www.mia...539477f35.jpeg
In and running well.
https://cimg4.ibsrv.net/gimg/www.mia...3c0c694de.jpeg
My daily driver

Heh - I'd think not swapping in a V8 would be sacrilege, but I dig it. What's the gas mileage like? I suspect it won't be a huge issue for you, since you've got a much shorter battery cable (miata battery is in the trunk, so ~15ft of battery cable if memory serves). As for the alternator controller.. too many irons in the fire, but I do intend on getting back around to it.