I'm having trouble deciding which ECM to choose for my ls swap. The parameters:
'84 trans am - 15th anniversary model. 50,000 miles
5.3L engine. LC9 with 58x reluctor, VVT / DOD delete kits, and 220/114 cam
T56 transmission
gen iv plastic gas tank installed with grand am fuel sender

I probably should keep the original speedometer with milage. Even though this car won't be original, I'll look at that electric to mechanical speedometer adapter. Fuel gauge will be wire directly to fuel sender. 58x will create challenges with tachometer, oil pressure, and temperature.

I would like to use pocket's harness. What do y'all think? Should I use the lingenfelter 58x to 24x conversion module? Should I go with a 58x ECM, change the gas pedal, and try to figure out how to connect the tach, oil pressure, etc? I thought about the Holley HP EFI, but that won't solve my gauge problem. And if that Holley computer ever fried, it would be expensive to replace.

 

I see no advantage to the 4th gen plastic tank. Get a 3rd gen EFI tank.

Not really part of the PCM/ECM decision, but you included it in your list.

 

Plastic tank is already installed. It relates to the gauges as the fuel quantity signal won't come from the ecu.

 

A 3rd gen sender works just fine with a 3rd gen cluster. I don't see the point.

 

I do... plastic can not rust & contaminate your fuel.
Its also lighter & if I remember correctly it holds more fuel.


A third benefit is if you retain the factory venturi function in the fuel bucket, you can reliably run the car low on fuel without starvation. Something I could do with my 3rd gen tank, even with a stock engine when under 1/4 tank.

 

As for the ECM, I would base it on the type of throttle you plan to use.
Fly-by-wire or cable.


Just try to keep the sensors matched to the ECM for best compatibility.


The 58 tooth can be converted with a Lingenfelter box if you want to run the older 411 computer. Works well with my LS3.

 

Thanks Lonnie - that's good info. I saw that 90-irocdx3 used a lingenfelter converter with a harness from pocket. Two more questions:
-My trans am is an '84. Do any of the stock gauges get info from the ECU, or are they wired directly to a sensor? Some of the ford mustang forums discuss this for their LS swaps. There seems to be a guy who makes a custom gauge harness that is seperate from the stand-alone controller.

-I've read about some headaches with programing an LS ECM. Matching VIN numbers, security override, and a term called brick. Chevy performace sells a controller kit. I don't think I want the kit as their wiring harness is generic (not made specifically for my car). They do sell the ECM seperate. Is this ECM easier to work with since it doesn't have security features? Or can a good programmer modify a used ECM (411 computer / E38?) to do the same?
http://paceperformance.com/i-6255502...-19258270.html

Sorry for my ignorance. I just want to have a good plan before I go any further.

 

Gauges are wired (temp, oil & fuel level) directly.


Tach comes through PCM.


Any good programming software (EFI live or HP Tuners) can turn off the antitheft.
The VIN does not matter unless you are emissions compliant & the inspecting agency will be reading your PCM for emissions purposes. A good shop with unlimited software licensing should be able to program your existing VIN as well.

 

Right on all counts ^

Speedo is mechanical so a driver box such as cable-x will solve the issue

Dakota digital makes a tach/speedo box that converts the GMLAN signal the gen IV ECMs output for those to analog tach and standard 4000ppm speedo. They also sell their own driver box, so Id call them and explain what you're doing. They might have a simpler solution

Think Id pick the MSD atomic EFI over holley EFI if going aftermarket, but I dont see the benefit for this application

On the other hand, if you plan to tear the engine down, have a machine shop press a 24x reluctor on the crank to skip all these challenges

 

I did the LS3 with 411PCM & found some good & bad.


Good:
Cable throttle
Cheaper PCM
Cheaper wiring harness with no throttle pedal to purchase
Better support/knowledge base
Cheaper sensors/more commonly available used


Bad:
Less resolution on most PCM tables (most people may not even tune to this level)
Less friendly (potential tuning issues) using the 100mm late model MAF (something I would like)
need 58tooth conversion box or internal engine mods to use with newer engine.


Personally I'm still undecided which way I would go if I had to do it over.
Curiosity has the best of me now...
Looking back, I would have saved the cost of the converter box, but spent that on a throttle pedal.
I could have then downloaded a base LS3 tune & been at a very good starting point.

 

Swapping gen IV management is 100x more challenging than 24x stuff. The potential of the 58x systems is staggering, but the management freedom isnt nearly the same as the older 24x stuff which works fantastic for NA builds running under 7200RPM or thereabouts. Even for boost the 24x stuff works well in terms of stock management/tuning software so the gains for 58x arent big. Plus once you step to the 58x it becomes a lot more challenging to isolate and command feeds which means more confusing work for same result. The Holley advertises 58x control and I have ZERO clue on the Atomic stuff other than the occasional ad I catch for it so? Maybe some helpful info there.

Id drop the crank and swap to a 24x billet wheel and use an OEM 24 dbc set up or just buy the Holley and go.

 

here are a couple thoughts

- if you are willing to read up and would like to learn about tuning, i would consider the E38 / E67 58x type controllers... e38 works very well and more simple than e67
- these controllers are compact, easy to mount, and have great resolution and relatively cheap
- use of electronic throttle while more complex in some respects also eliminates IAC


as far as driving gauges it isn't a big deal, i have my original 85 iroc cluster with all standard gauges being driven. tach driven directly by ecu, temp from 98 ls 3 wire sender, oil pressure from standard 91 3rd gen sender, fuel sender as you noted already with plastic ls tank, and speedo by cable x box

hptuners has great support for gen III or gen IV ls ecus

 

I sold my 411 setup and changed to Holley HP. It's a wash on cost. I don't have to tune the car, no dyno time, and it will run great in a few minutes. And it doesn't care if you have Gen III or IV engine.

It does lack a few things though. It can't understand the T56 speedo and doesn't run reverse lockout unless you get really creative. And all the extra I/O gets used up doing basic functions. It's the price you pay if tuning isn't your thing.

 

Awesome responses. Thank you! Based on what I read, I'm leaning towards E38 with electric pedal and throttle body. LS1tech says E38 wires directly to pedal without tac module. I got my cam and vvt/dod delete kits from texas speed and performance. They offer a mail order tune. Since I'm using their recommended cam, I -should- be able to get a good tune from them. I don't have any other mods planned for a while. I'm going to be tinkering with the gauges no matter what I do, so it's not much of a factor. Feel free to offer any more advice.

 

I did a Texas Speed mail tune on a H\C\I 6.0L. It had their MS3 cam and ran like a champ. They'd seen a lot of engines on dyno just like mine so easy job for them in my case.

 

TSP package should work well, they do good work down there. The mail order tune will work decent and be safe but you should plan on road tuning in your a/f with a wide band once it's all up and running, its worth it. Idle and part throttle will be cake with the e38

 

Is Pocket still building harnesses? I'm about to ship my T56 tailhousing to a shop that adds a cable speedometer connection. I'll direct connect other gauges as well. E38 or 411 with lingenfelter... I'm flexible and ready to get my project moving again.

 

I run a 99 5.3 with the OEM ECM, 24x and Don't feel you really need the 58x. Also I use HP tuners pro and even with the regular HP Tuners you can adjust the tach output for basically any Pulse Per Rev. I use all speedhut gauges so Its even easier but theirs a High and Low value for the tach ouput that it uses in a formula to calculate PPR.

For what its worth:
High 6/low 6 is 2 PPR or 4cylinder output
high 3/low 3 is 4 PPR or 8cylinder output

I run my speedhut tach at 2 PPR and it works great.

If you don't need the stock gauges I recommend the GPS Speedo as you don't need to worry about a sender, gear changes, tire changes etc... satellites! Its the future baby! Just start it up and go.

 

Yes, PM me or email me direct for a faster response

 

Thanks - email sent.

 

Resolved.

 

UPS guy just showed with my 58x harness from speartech. I bought an intake with MAF from them too. I'll have to get an E38, pedal, and dbw throttle body. Speedometer will run off a cable connection I had installed on the T56.