I have a 1999 Trans Am that I just recently bought and it already has a HP Tuners tune on the car. I have plans on putting a ERL superdeck I block and later on installing a Procharger DSC1 on it. I know later on down the road when I get there I will need an aftermarket ECU and I was wanting to get the Holley EFI Dominator.

I have been reading up on aftermarket ECU's being piggybacked off the stock ECM like the BS3. Brian Macy from horsepowerconnection said that he could make a piggyback harness for the stock ECU on my car that will connect to the Holley EFI. I am hoping that this will allow the stock gauge cluster to work, control the alternator, and AC compressor as well.

My hopes of having that done is that when I go get the car smogged the smog tech will just connect to the ODB2 port and the stock ECU is still thinking it is running the motor and all will be good. Can anyone shed light on if this is true or not? If not how does everyone get their cars to pass emission with an aftermarket ECU?

 

While the system is can be piggybacked (there are certain precautions that must be taken) it still won't take away the stock PCM's view on the tune. That being said, the richer than normal tuning for WOT may cause a rich bank1/2 indicator setting the system to code. It would need to be cleared and get passed readyness to pass emissions.

 

Why do you think you need an aftermarket ECU with just a D1? The factory PCM will do everything you want it to do at that power level and more.

 

For one the tuners here aren't the best and the ones that are is like trying to get an appointment with Jesus. I don't want to keep paying $800 for a tune each time I do upgrades. By my calculation the car as it sits now definitely needs a tune ($800) then when I do get the 427 ERL superdeck I ($800) then when I get the Procharger kit ($800). So by my figures $2400 to hope that the tuner does a decent job in the short amount of time they give for tuning the car or just out right get a smart aftermarket efi that will constantly fine tune as you drive.

As far as electronics go that ecu is from 1999 it might as well be a packard bell 486 running my high dollar motor when I could have the new 2012 efi that is more along the lines of an i7 intel quad core processor.

 

You are mistaken on so many levels. Who is going to tune your new Holley Dominator system for you? It you think it's self tuning function is going to do it for you, I'm afraid you are going to be disappointed. I have been working it it on a new COPO Camaro race car. I can tell you it does not do that great a job.
Your stock PCM can do what you need, as Ed has already mentioned. If you go ahead and do this, somebody that knows what they are doing can program your factory PCM to not set codes, and report all your emissions flags as run and past.
$800.00? Damn! I have been working too cheap! LOL

 

Well that is sad to hear that the aftermarket ecus aren't as good as they make it seem. Those are the prices that the tuners here in vegas charge and from my experiences with them and other people in town the consensus is that we should drive to cali for someone that knows how to tune the right way. Guess I should just learn how to do it myself.

I have bought the Calibrated Success DVD and the tuning school beginning course. Is there any other courses or books I should buy to help me learn how to tune?

In all honest I would rather spend the money to learn something than to keep paying someone else to do it for me. I have no problem paying someone to teach me either.

 

With any EFI system, knowledge and experience are the keys to get the best tune you can for your particular application. Both you can aquire on your own car if you take your time and.learn as you go (with abit of help along the way)

Back to your question re: stock and aftetmarket ECU tuning. Factory PCMs are very powerfuland offer alot of tables that allow tune refinement. What they lack are realtime tuning capability and external controls (boost, water/meth traction etc). At minimum you should consider EFILive or HP Tuners and integrate a WBO2 sensor.

As for the Dominator EFI, its quite powerful, offers realtime tuning and I have to disagree but, the self tuning main fuel map works quite well. There are still tables that require tuning such as Accel Enrichment and cold start fueling but again, these are real time tunable with a fairly easy user interface.

 

I have HP Tuners already, I bought it when I had my GTO. It was stroked and turbocharged made 630hp and 650lb tq on 7psi when my turbochargers maxed out on a tune that I paid a professional to tune for $800 that when I left was still running a 10 AFR at idle.

My problem that I had with the stock ecu was the fact that it couldn't handle large injectors and once you hit a certain point you need a larger injector. With the LS2 at the time if you needed a larger injector like the 83lb hr injectors like I was using you needed a low impendence injector which meant I had to use an injector controller box. That isn't even mentioning the fact that the stock injector flow rate table would max out at I think it was 92 lb/hr. Which meant I couldn't even update the injector flow rate table because it was already below the injectors values that I needed to put in. I was told I then needed to scale tables by a percentage to compensate for the larger injectors. Which none of the books/courses that I have bought discuss how to do that and the people that do know how aren't willing to give up their knowledge (which I know I wouldn't either if it took me 20+yrs not to mention you are talking to a noob that will not get 90% of what you are trying to say).

I guess my problem was that I was trying to learn how to tune on a car that had been that modified was WAY over my head.

Is it worth it to keep the stock ecu and be forced later to scale tables once I am forced to run a larger injector that is beyond the scale of the injector flow rate table and loose bottom end resolution from scaling tables?

OR

Is it just better to start out with an aftermarket efi that doesn't have those types of limitations?

I would like some more input from the tuners that do this day in and day out and know ALL the short comings from both sides of the fence. I really don't want to get further down the road just to find out it would have been better to go with an aftermarket efi from the get go.

I do appreciate you guys that have responded with the insight you have provided already.

 

The LS2 uses the E40 computer and even some of the newer ECU'sto get around the injector limit you need to scale the tune. Some custom OS's will give room in the MAF G/sec (newer vehicles this is already lifted past the normal 512 limit) Go to HP tuners and look for scaling in theGen 4 section, that will give you a little insight.