soundengineer

iTrader: (16)

First off, I thank any of you who can help.


The basic bigger Picture
Daily Driven Car(I have a backup vehicle too) - 2001 Camaro Z28 - lots of race parts...getting faster by the mod...
State of Tennesse emissions is Visual check for Cats(gutted..LOL) and OBD2 readiness tests

I am planning on using the Holley EFI Dominator System on my car.
but I will still need the Stock PCM for OBD2 tests/emissions compliance

I know I can make the readiness tests pass with a little code editing...no big deal there for me.

What I need to know is what stuff does the stock PCM really need to see?
I'm not really sure what stuff has to show up for the OBD2 tests. I dont know if they check anything other than readiness tests.

I also want to know if my cruise control can be made to work without the stock PCM...trying to keep it, I take some long trips and it would be nice to still use it.

Also, the AC system... I'm planning on keeping it if I can, do I need the Stock PCM to control anything for the Air Conditioning? does the PCM control the clutch engaging or is it just a buffer device to "allow" it to engage when certain variables have been met.

I'd like to know if I can control the stock gauges with the Holley system as well.
not exactly sure which ones work straight up or with a PWM signal.
I can easily command a pwm from the holley Dominator
Obviously I can get Oil pressure straight up, and I can get Voltage the same...
Speedo/Tach/ECT/Fuel Gauge are the things I dont know about.


and lastly.. if I do need to split signals to the stock PCM(like Crank/Cam/vss/whatever... can I just tap the hot signal wire and split it to the stock PCM and leave the grounds and reference voltage to the Holley Dominator?

once again.. IF anybody can help...I am greatly Appreciative.

G-Body

iTrader: (4)

I think that the cruise should work without the PCM. The A/C clutch is completely controlled by the PCM. You might be able to pull all that out and use a compressor cycling switch from an 80`s GM and make it work but I`m not sure.

The speedo is looking for a 4000 pulse per mile square wave signal and the tach is a 4 cyl signal but I`m not sure about the rest of the gauges.

soundengineer

iTrader: (16)

does anybody know for certain if the cruise control works without the pcm?
and can anybody tell me what is needed to drive it without the pcm commanding it? mostly asking where the VSS signal has to go to to make it still work, or where it comes from to begin with(like does it come from the gauge cluster or from the vss directly or as I am trying to find out, maybe it does come from the pcm....)

I can still use the PCM for things it needs to control...(like AC)
I just need to know what makes the pcm realize the engine is actually running....even if its not controlling any of it..LOL

gofastwclass

iTrader: (2)

Cruise works off the speed control out from the PCM. I'm sure it could be "fooled" by the same signal used to run the speedo but the brake has a line going in the PCM which also shuts off cruise, disengages the torque converter, etc. All this would be easy to get around if one were determined. The transmission would need to be swapped for an older non-electronic variant or a manual if it isn't already...

G-Body is right about the AC.
Fans are both PCM controlled as are the gauges...

Sounds like you have an interesting dilemma. Good luck!

soundengineer

iTrader: (16)

at this point it sounds like my easy route is to let the stock PCM control the AC....
fans can be controlled by the Holley Dominator...no problem there...might just be easier to let the LS1 pcm do it so I dont have to run new wires.

does the 99~02 gauge cluster use the data connection for the tach? or is it an actual tach signal going to it...

if it uses an actual tach signal, then I can send one from the Holley dominator and not have to worry about splitting the crank/cam signals to the LS1 pcm.

I know the Oil pressure is direct, and I assume that ECT/Fuel/Voltage is all thru the data connection from the LS1 pcm. am I correct?

soundengineer

iTrader: (16)

really the biggest questions become if the LS1 pcm needs the Crank or cam signals to think its running to control those extra things... or if it just assumes it is running and not relying on a specific signal to determine that.

does that make sense?
do I have to fool it into thinking its running by sending a running signal into it from an existing sensor..

I can easily just turn off all the codes in the pcm, set them all to no error reported, check the SES, it will pass all its tests and show no errors..

gofastwclass

iTrader: (2)

Hahahahahaha!!!!!!

Sorry this makes me laugh. I can just see you now "Problem, what problem Mr. Dmv there aren't any lights or codes..."

I know the PCM knows when the engine is running but I haven't a clue how. If the engine stalls it kills the fuel pump, stops the injectors and spark. I would assume it goes by crank / cam signals - but then it would want to fire the coils and injectors... Hmmm... too much thought for me at 1AM even though I'm still wired I should be sleeping.

soundengineer

iTrader: (16)

the dominator system will be controlling all of my fuel and spark...
so I'm not worried about the stock PCM at the moment..

I'm already considering keeping around a second harness or an adapter harness to run the stock pcm once a year when I have to go thru emissions...really its just an OBD2 test and a visual inspection for cats..
I went through last year with a big cam... the dude didnt care...he just connected his pcm checker and tested the gas cap for leaks..that was it...
its all automated... I just dont know what the computer test checks other than readiness tests and it looks for DTC's that are emissions related.

soundengineer

iTrader: (16)

and as far as I'm concerned.. as long as the PCM thinks its in control... it can shoot blanks to all of its sensor connections that wont exist anymore...LOL

Pro Stock John

iTrader: (34)

You should be able to piggyback the Dominator EFI with the stock PCM and gauges. If you are interested in going over your list of requirements I can check with someone at Holley. My email is john@motorsports-media.com.

I've run several aftermarket pcm's over the years, including a FAST e-Dist style early setup and then a BS3.

I think Holley's EFI setup is the best bang for the buck out there, is easier to start using for a first time user, it will control a 4L60E or 4L80E with adding another $ part, and they have a team providing tech support.

I've suggested to them that they create a DIY-driven FAQ on stuff like the right way to ground everything. It's usually grounding issues that are the big issue for aftermarket controllers, and then understanding open and closed loop.

flame

iTrader: (13)

The simplest thing would be to leave the stock pcm fully connected and feed only needed sensors into the aftermarket system.

To answer a couple of your questions though

The speed sensor is fed into the pcm and then from there is fed to the dash and cruise module. There is a cruise inhibit and cruise status to the pcm but I believe it should work without those.

In order for the pcm to know the engine is running it will need to see crank signal to have rpm. Not 100% sure but cam signal should not be required.

For the a/c to work properly it will need TPS signal to disengage the compressor at WOT, idle control to bring rpm up at idle, pressure sensor input, fan control should be left with the stock pcm to eliminate too high a/c pressure when stationary.

For gauges the 99+ gets all except oil pressure through class 2 serial data from the pcm. If you run a 98 cluster you have the option of feeding in the signals for tach, speedo, ect. The fuel gauge may require a segment swap.

If you need so more info feel free to pm