Cleaning this up a bit, now that I have it running.

The configuration is as follows: 58x / 4x crank and cam in the engine. 58x / 4x holley harness. 58x to 24x lingenfelter conversion box. 24x / 1x OE ECU - P01 variant. The intent is to have the Holley run the engine, and the ECU to run the rest of the car.

I am splitting the Crank signal at the sensor, and I am splitting the cam signal at the sensor. One split goes to the Holley. The other split goes to the Lingenfelter, and then to the stock ECU. Running an extra temperature sensor in the passenger head, rear port, to give a signal to the stock ECU for fan control and for the dash. Oil pressure is going to the OE ECU and not the Holley, for the dash. Fuel pump is currently triggered off the Holley. It can be set up to run off the OE ECU also, but I found this easier when troubleshooting to have the Holley operate the fuel pump.

I'll see how this goes, as it's a work-in-progress, and I think that this will apply to pretty much any standalone system you want to use. I'm using Holley HP for my new engine management. The idea is to use the stock ECU to control the stuff it already controls and simply not the engine. Of note, I had to go back and add the cam sensor back in, so I have edited the pins below to make sure others do not accidentally remove the cam pins from the ECU. First, here is the pinout, and the trick is to focus on what you keep, not focus on what you remove:

Blue:
1-pcm ground - black
2-CKP 12V reference - Lt Green (Pin C on the crank sensor)
12-CKP signal - dk blue (Pin A on the crank sensor)
19-Ignition - pink
20-battery - orange
21-CKP Low Reference - Yellow/Black (Pin B on the crank sensor)
23-fuel level - gray
32-clutch switch - gray
34-Neutral Safety Switch (autos) -- orange/black
40-ground - black
42-cooling fan - Dk Green
46-Fuel Tank Pressure - Gray
57-Battery - orange
58-Serial Bus - Dk Green
61-Cam Position Sensor Low Reference Pin B - Pink/Black
70-Oil Level Switch - Brown (goes to oil pan level sensor)
73-Cam Position Sensor Signal Pin A - Brown/White
74-coolant temp sensor pin B - Yellow
79-Skip shift solenoid - gray or white (only keep if you want the feature)
80-Coolant Temp sensor pin A - black

Red:
1-PCM Ground - black
9-Fuel Pump Relay - Dk Green/White
10-Engine RPM signal to tach - White
15-exciter wire - Red (Goes to alternator)
20-VSS - Lt Green/Black
21-VSS - Purple/White
30-Fuel Enable - Dk Blue
33-Cooling fan - Dk Blue
39-Cam Position Sensor 12V Reference Pin C - Red
40-Ground - Black
44-Reverse Lockout - Lt Green
46-MIL - Brown/White
49-VSS Signal - Red (Out to ABS)
50-VSS Signal - Dk Green/White (Out to speedometer)
54-Fuel Level Signal - Purple
64-Fuel Tank Pressure - Dk Green


NOTES:

* Most of the internet says that you only need the crank sensor input for a piggyback to work. If you want the stock tach to work, you need the cam signal.
* If you set code P0341, you are not getting a cam signal, and the tach will not work. The rest of the car will function fine, but the tach will be dead. Disabling this code won't help, as this indicates the cam signal is missing altogether.
* You may end up setting a code P0342, which is cam signal low. If you set this code, the tach will quit working. If you disable this code in the tune, you will restore your tach. Weird, I know, but I turned it on and off multiple times, and it is very repeatable.

Notes on My Notes:
* I'm not saying the internet is wrong about every F body piggyback. I'm only saying that the added step of the Lingenfelter conversion box made it so that I needed all three wires on both crank and cam sensors. If you are not running a conversion box, you may get away with only the signals. But it's easier to not have to repin later, so until you have it working, I recommend leaving all wires intact for the crank and cam position sensors.

 

I found the best thing to do was to first remove all the pins from the PCM connector that were not going to be used. You have to remove all the factory loom, etc, and a lot of stuff is taped and braided together, so it's a job untangling. I had hoped I'd be able to simply pull on the un-needed sensors and the wires would pull through, but the insulations are all stuck together. You have to almost unbraid them and at times peel them apart. I DO NOT RECOMMEND CUTTING ANY WIRES AT THIS TIME. There are many duplicate colors, etc. It's far easier if you leave everything intact and slowly work it out. After you have pull out all the not-needed stuff and the pins are loose, you will need to cut some grounds and ignition wires. You'll find a spot in the harness where all the grounds seem to come together and the same for the pinks. Only cut what you need to cut to get rid of the connectors you won't be using - for example, the coils and injectors. The nice thing is that the wires are all formed to how they used to sit in the car after being baked into position for twenty years, so it's relatively easy to re-tape the harness back together. You still have to keep a map in your head of what goes where so you don't make any of the splits too short.

Here is what the harness looked like after removing all the stuff not needed to run the engine.


Here is about 2/3 of the crap that came out of the harness:


Here is how the harness looks after you start looming it together. The Jegs kit is really good TBH.



Here is a progress pic. You will note two exposed pink wires. I left those on purpose in case I need to tie into them for any reason. The power for those lines does not come from the PCM, but from connector C101.


Here is the completed harness. Kinda looks like the Hydra symbol. That was not intentional.


I'm waiting for the Tick Performance crank signal splitter, so I can send the crank signal to both the holley and the pcm. What will make this fun is I have a 58x crank, a 58x harness for holley, and a 24x stock P01 ECU. I will be retaining my lingenfelter box to convert the 58x to 24x.

The PCM sees CKP, so it thinks it's running the car, thereby managing all the other features of the car. I think I will need to split the VSS output also. I'm hoping I can get pin 49 to send VSS pulse wave to the holley at 4000 pulses per mile and the holley correctly interpret. If not, I'll have to split the VSS. In theory, this will allow the stock ECU to runt he car and let the holley run the motor. My plan is to run two coolant sensors, one on each head, and only run the oil pressure sensor to the car (not the holley).

If this works, I hope it helps others who might be thinking to tackle this and think it's beyond them. I figure I'm nervous also, but the worst that'll happen is it won't work and I'll have to get a screen for the dash. My goal is to be able to get the car running without dumping another grand into gauges, even if I have to go back in and do it later anyway.

 

Lot of work into all that! I assume you need stuff like the oil level, skip shift, coolant, etc. to prevent lights on the gauges from coming on. Why do you need the crank sensor?

 

If - and this is a big IF - I understand it correctly, the ECU needs to see the crank signal to know that the engine is running so that it will keep the fuel system running and also the cooling fans. Think about after you stall, the fuel pump shuts off. The cooling fans have different logic for running vs non running. As a side benefit, this gets the stock tach working.

yeah, the low oil light will be on as a nuisance light. The skip shift, I deleted. The reverse lockout though - it actually operates in reverse. I was going to just bypass it, remove it, and put a plug in, but decided if I can get the stock one to work for free, why not? The reverse lights themselves won't work unless you run something back from the transmission to the car's electrics. And I can get my fuel gauge working without running creative bypasses, etc. Also, think about evap. I had thought i'd just need to vent the gas tank, but now I can keep the purge system working as per stock.

 

Not sure I ever noticed the fuel pump dying after you stall, fair point! You mostly making the change to Holley for ease of tuning, HP gain, or drivability? Or all 3 lol.

 

I'm considering this route.i ordered the cp wire harness but it's still 5 weeks before they build it.

 

Thanks for sharing!

 

Thats what we typically do when we piggy back factory ecu in. In our C6 Z06 mile car with holley I made a small harness fir the E38 from scratch to make the car happy. Its way cleaner and all new wires vs trying to remove tons of wiring from the factory harness.

 

That makes sense. I think for a first-timer, it's easier to start with the factory harness to learn on. After doing one factory harness, I feel like I stand a better chance at doing a fully custom harness. Do you feel I got the pinouts right?

 

I agree its probably easier to modify a harness for most people. It took like 9 pages of diagrams to make the harness for the Z06. I didnt want to re-use 14 year wiring that had a ton of issues already was the main reason I made a new one. After doing it I like the results so we just started doing that on all of them.
Just by looking at your list I can't say for sure. I use the schematic and then make a list of what I need based on that but it looks like you have the main stuff covered.

 

The Holley harness comes with a fuel pump feed built in. In case there is an issue with my home-made harness, I'm running the fuel pump trigger from the holley on a small loom and gonna put a connector on it and run it up by C101 on the passenger fender. If I have to tap into the line to get the fuel pump running, I won't have much work to do at all. The only other real test will be making sure the cooling fans kick on properly. If they don't I will need to run another smaller loom over and find that trigger wire as well. Good news is, there is actually quite a lot of space to do all this with the main harness deleted. It's quite impressive how much space that thing was blocking.

 

Thanks for posting it's nice seeing stuff like this get posted to tech again. Bookmarked

 

Good stuff jake

 

I thought about doing this last year but ended up staying with the stock ECU due to life getting in the way and having no time to mess with it.

I know there's a company out now that sells a plug and play harness for our cars using Holley EFI and it actually has me interested in doing it again. I love wiring, but just don't have time for my car to be down for 6 months.

One question for you, any idea where you are going to mount the Holley ECU at? Are you leaving the stock PCM in it's original location?

 

It's current performance that has the harness. It's about 6 weeks of build time to get it .

A friend of mine mounted his holley in the kick panel on passenger side that we take off to get stock harness unplugged to pull motor. Fits nice and out of way there

 

I will be mounting the Ecu in the former heater core box. Stock Ecu in stock location. I looked at the CP harness. Figured it was worth a shot to try and possibly learn something. Worst case scenario I have to buy the harness, right?

 

Darth,

Do you know if the cruise control will still function when piggy backing the stock ECU?

i don't know if the pcm and/or bcm controls it.

 

I think so IF you leave those wires intact and the vacuum line. I didn't worry about it because I lack the vacuum to run cruise control.

 

I'd have to double check, but I don't remember it having a vacuum line going anywhere. My car has TCS, so it has two cables on the TB. I don't know if that is uses that for cruise or not.

 

On mine, the second cable goes to a vacuum diaphragm. Diaphragm is inside the dash. basically runs the throttle when cruise is enabled. The vacuum line that feeds the diaphragm is that little one in the back of the manifold. I think it also feeds the AC vent controls.