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C4 Computer functions

Old 05-11-2018, 07:27 AM
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Scarab1988
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Default C4 Computer functions

Good morning
Here are a couple of computer questions you might have experience with.
What functions exactly does the stock computer handle, and are those functions daisy chained together so if it doesn't have input from say the stock fuel injection throttle position sensor, the transmission won't work?
Is the stock computer on a '96 LT-1 set up so if you remove the stock fuel injection, and replace it with a stand alone aftermarket fuel injection like the Holley or Edelbrock all in one system, will the rest of the car still function properly?
Thank you
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Old 05-11-2018, 12:38 PM
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Originally Posted by Scarab1988 View Post
Good morning
Here are a couple of computer questions you might have experience with.
What functions exactly does the stock computer handle, and are those functions daisy chained together so if it doesn't have input from say the stock fuel injection throttle position sensor, the transmission won't work?
Is the stock computer on a '96 LT-1 set up so if you remove the stock fuel injection, and replace it with a stand alone aftermarket fuel injection like the Holley or Edelbrock all in one system, will the rest of the car still function properly?
Thank you
I'm pretty sure most of the kits out there for standalone ECMs would support everything as far as running the vehicle is concerned. Little stuff like the AC and TCC are usually supported.

Does your car have an electric transmission? I think that the 4l60e's are controlled by the ECM. If you have an electric transmission, you ought to try and find an ECM that will support that. Otherwise, a couple places make separate boxes for tranny control for the 4l60e. I don't know if the later C4s have the anti-theft handled by the ECM or not, but that might be a concern.

So as far as replacing the sensors and harness and dropping in a modern ECM, it should be fine, unless you've got an electric tranny, or the late C4s have the alarm stuff running off the ECM. The early C4s do not, when I swapped my ECM, there was no input for anti-theft, it is a separate module for me.
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Old 05-12-2018, 09:36 AM
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Scarab1988
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Default C4 Computer functions

Thank you Blaster. I believe I do have the 4L60E. Good to know you can get a separate controller for the transmission. It's seems odd there are so many component control variations within the C4 production run. Unfortunately I'm a machinist, not a computer scientist. A lot to learn on the computer driven parts. Again thank you for your input.
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Old 05-12-2018, 10:12 AM
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Originally Posted by Scarab1988 View Post
Thank you Blaster. I believe I do have the 4L60E. Good to know you can get a separate controller for the transmission. It's seems odd there are so many component control variations within the C4 production run. Unfortunately I'm a machinist, not a computer scientist. A lot to learn on the computer driven parts. Again thank you for your input.
Sure, no problem!
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Old 05-13-2018, 10:17 AM
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MatthewMiller
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I'm no expert here either, so take this FWIW. But I believe Blaster is correct generally. However, your dash displays depend in part on inputs from the stock PCM on a 1996. For example, without a speedo signal from the PCM (which it gets from the VSS in the transmission tailshaft), you lose the speedo, odo, and some other optional function (was it adjustable damping? I forget, because whatever it was my car doesn't have it). So that's one issue you'd need to overcome. Also, you'll lose your tach signal without the stock PCM. These are common issues that people who swap over to LS engines encounter, so there must be solutions to them.

Depending on your emissions requirements, you will have problems there too. Your car is OBD2 (the first year for them), and typical emissions inspections just have the PCM report to a scanner plugged into the ALDL port. The PCM diagnoses the car itself and tattles on itself, if you will. If you have to pass a plug-in scanner emissions test in your locale, then getting rid of the stock OBD2 PCM means it will flunk the test immediately - the scanner will know it doesn't have the right computer in the car. That will be a bigger issue to work around, if it applies to you.
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Old 05-13-2018, 11:01 AM
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I don't think there's advantage to going away from the factory efi. Is there a reason you are looking for aftermarket efi?
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Old 05-15-2018, 06:24 PM
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Scarab1988
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Default C4 Computer functions

Hi Matt and Kevova
Matt pretty much everything you mentioned is what I was afraid of . The good thing in my state ( Mass ), if a car is over 10 years old, it just goes thru a safety inspection, so no emissions.
Kevova, I like the stock EFI. I don't know if you have seen the other posts I wrote, but my plan is to build another motor with an additional 125 to 150 horsepower / torque, pull my stock numbers matching engine and transmission and pickle them and put them in a crate, and put the 450 +/- hp motor and a built 4L60E in the car and have some fun.
Nobody around here I've talked to knows how to make a higher output motor run with the stock computer, so they have suggested using one of the all in one self programming EFI setups.
I've built 7 - '69 Camaros back in the '70's and '80's , but that was way before you needed to use computers to run engines and transmissions.
Having recently bought my first Corvette , (last fall , '96 LT-1 automatic) and I'm getting back into building cars after a long time away from it.
Thank you for your advise and tech info.
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Old 05-15-2018, 06:39 PM
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The PCM is reflashed ( programmed) so a laptop is all that is required. Possibly someone will chime in with a local tuner. You zip code would help with that. You could cruise where the corvettes, camaro, and firebirds gather and possibly get a lead.

Last edited by Kevova; 05-15-2018 at 06:41 PM.
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Old 05-15-2018, 07:42 PM
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Having recently bought my first Corvette , (last fall , '96 LT-1 automatic) and I'm getting back into building cars after a long time away from it.
I am right in the middle of acquiring the parts to build a 425+ HP motor, and I will be sticking with the stock EFI, except for possibly going to a higher rated injector. I also have have a '96 LT1.

Saturday I am going to pick up a set of heads to send to LLoyd Elliott. There is debate/conflicting information about the heads that were put on '96's as to the casting nbrs. The later LT1 heads flowed slightly better but don't have the same amount of material as earlier ones for porting.

If you are going to stick with the stock computer, you are going to have to acquire a JET DST unit to be able to tune the computer if a local tuner doesn't have one. If they do, they will charge you for the VIN slot that tuning your car will take up.

The '96's are sort of b*stard children as far as tuning goes. It is the 1st year of OBDII in the Corvettes. If you don't have emissions to consider, you could swap the PCM out for a '95 model and that opens up tuning opportunities.

Without spending a LOT of money, the JET DST is the only unit out there for tuning a 1996.

Last edited by drcook; 05-15-2018 at 07:46 PM.
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Old 05-15-2018, 11:23 PM
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Originally Posted by drcook View Post
If you are going to stick with the stock computer, you are going to have to acquire a JET DST unit to be able to tune the computer if a local tuner doesn't have one. If they do, they will charge you for the VIN slot that tuning your car will take up.

The '96's are sort of b*stard children as far as tuning goes. It is the 1st year of OBDII in the Corvettes. If you don't have emissions to consider, you could swap the PCM out for a '95 model and that opens up tuning opportunities.

Without spending a LOT of money, the JET DST is the only unit out there for tuning a 1996.
All of the above is exactly how I would have replied. The stock PCM is very capable and very tunable, if you have the Jet software suite. The Jet DST program is functionally identical to Tunercat, which is made for the earlier PCMs. Tunercat is a lot cheaper to purchase, and is what you would use on a 94/95 computer. The other advantage to the earlier PCM and Tunercat is that you can buy a definition file for Tunercat that locks down the Block Learn Multiplier (BLM) function in open-loop (WOT) mode. This is a good thing, because the 96 PCM will "learn" and trim the fuel over time, even at WOT. Once you have tuned the car with a wide-band to a safe air:fuel ratio, you'd rather not have the PCM tweak that on its own. So if you don't need emissions compliance, I think I'd recommend the 94/95 PCM and Tunercat. It drops right in. That PCM is very, very similar to the OBD2 96 computer. You could call it "pre-OBD2," since it had the architecture and some of the functions of OBD. Anyway, the one thing you'll get is a periodic "sys" indication where your oil/coolant/voltage reads out on your dash display, but that doesn't hurt anything.

Either way, you can easily tune a stock-style PCM to accommodate the power you're looking to build. As a reference, my 96 LT4 is now a 396 with heavily ported heads (similar in flow to AFR 195 Comps), a cam with small duration but plenty of overlap, ported intake, long-tubes, bigger injectors, and a good exhaust. It probably makes ~420rwhp, and it's a bit faster than a C6 Z06 in a roll. It runs very well on either my tuned 96 PCM (for emissions inspection) or my tuned 95 PCM, no problems at all.

One place to start looking into all this is LT1 PCM Tuning. He has a useful guide posted up there. If you don't want to do this yourself, I believe he can work with you via email to at least get you in the ballpark. OTOH, I would also think that anyone local to you who is proficient with HP Tuners or other more modern tuning software should be able to work on your car with Tunercat or Jet DST.
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Old 05-16-2018, 02:35 AM
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It runs very well on either my tuned 96 PCM (for emissions inspection) or my tuned 95 PCM, no problems at all.
what did you need to change to run the 95 PCM? I have read the knock sensors in the block ?

OH, for the OP, you might need to try and track down a '96 LT4 knock sensor for the PCM, but the stock LT1 ks can be made to be less sensitive if you are going to run roller rockers
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Old 05-16-2018, 06:04 AM
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Scarab1988
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Default C4 Computer functions

JET DST and a PCM out of a '95 C4.
Does anyone know of a good source for a '95 C4 PCM ?
Is there a PCM model number or serial number I should be looking for ?
My zip code is 02537
I'll check out that LT-1 tuning link.
Thank you
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Old 05-16-2018, 07:53 AM
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Use the stock 1996 computer, it is more then capable of doing what you need. It is easy to tune, just use the JET software. The 1995 and 1994 computers are prone to locking up and when they lock up they are junk.
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Old 05-16-2018, 08:09 AM
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MatthewMiller
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Originally Posted by Scarab1988 View Post
JET DST and a PCM out of a '95 C4.
Does anyone know of a good source for a '95 C4 PCM ?
Is there a PCM model number or serial number I should be looking for ?
My zip code is 02537
I'll check out that LT-1 tuning link.
Thank you
Wait...to clarify, if you use a 94/95 PCM then you don't use the Jet software, you use Tunercat. You would only use Jet DST if you stick with your current 96 PCM.

If you decide to switch to the earlier PCM, I believe you can use any PCM from a 94/95 Corvette or F-body. You need to make sure it has the knock sensor module with it. To answer drcook's question, I didn't need to change knock sensors...BUT I should note that on my car the knock sensors are turned off in the calibration anyway. So I can't categorically say they are compatible. But as calibrated on my car (KS function turned off), I can literally swap PCMs in a couple minutes and drive again. It is literally plug-n-play.

I guess when I mentioned swapping over to the earlier computer, I forgot that the OP would have to actually buy one from somewhere. That said, I would probably go junkyard shopping for one from an F-body or Corvette. Still, it would be less hassle and possibly more cost effective to just keep the PCM he has and and tune it with Jet DST. Regarding the risk of ruining ("bricking") the PCM while tuning it, I believe either PCM is equally susceptible. They are basically the same computer, only the 96 PCM has the OBD2 diagnostic features enabled. But I don't think there is much difference in the actual hardware that would make the 96 less vulnerable than the 94/95. But I can't prove that for a fact. I'm open to being shown the error of my thinking on that point.

Last edited by MatthewMiller; 05-16-2018 at 08:10 AM.
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Old 05-16-2018, 11:05 AM
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drcook
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We have had the discussion about running Jet DST and the chances of "bricking" the PCM as you say. It is my belief that a person is better off sourcing a Windows XP laptop (32 bit WinXP) to connect to the car with. I run the software for looking at files on my Win 7 desktop and have figured out how to crash the software. 64 bit software probably is a bit risky to connect to the car with, however, some folks have said that they are working ok. You do have to run it under WinXP Compatibility Mode, System Pack 2.
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Old 05-16-2018, 11:13 AM
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Originally Posted by drcook View Post
We have had the discussion about running Jet DST and the chances of "bricking" the PCM as you say. It is my belief that a person is better off sourcing a Windows XP laptop (32 bit WinXP) to connect to the car with. I run the software for looking at files on my Win 7 desktop and have figured out how to crash the software. 64 bit software probably is a bit risky to connect to the car with, however, some folks have said that they are working ok. You do have to run it under WinXP Compatibility Mode, System Pack 2.
I agree completely. I run Jet (and will run Tunercat) on a dedicated XP laptop. I know that Jet DST will occasionally hang up and crash on my Windows 10 desktop. Granted, that's just the editing software, so it won't ruin the PCM. Jet Flash is the program that's used to read and flash the PCM, and I haven't tried it on a 64-bit machine. But I have no desire to find out the hard way, either!
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Old 05-17-2018, 01:03 AM
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For safety and stability I strongly recommend keeping the 96 pcm. I went through 3 pcm units on my 94 Firebird LT1. You can salvage a bricked 94/95 unit with a chipset programmer and skill with an iron.
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Old 05-17-2018, 12:43 PM
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Originally Posted by Scarab1988 View Post
JET DST and a PCM out of a '95 C4.
Does anyone know of a good source for a '95 C4 PCM ?
Is there a PCM model number or serial number I should be looking for ?
My zip code is 02537
I'll check out that LT-1 tuning link.
Thank you
The FBODY PCM is essentially the same. Different part number but runs $EE no problem. I'm actually using a fbody PCM in my '94.

-- Joe
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