ScaryFast

Has anyone researched a good stand-alone EFI system for the LT1?

I'm fighting vainly with multiple problems in my '93, trying to make the stock fuel injection system work without half of the inputs, larger injectors, and an inability to communicate.

I need a very simple racing style system that works with the LT1. I don't want to have to worry about all of the things my current PCM is looking for, like inputs from the body computer, AIR system, or EGR.

Painless makes a harness and computer but it's only set up for stock motors. Mine is far from stock. Can I get away with any basic system? I'm guessing I need something that will work with the optispark signals as they are different than a "normal" distributer ignition. I'd be happy to use the stock harness or purchase one with the computer, and I want to be able to adjust timing, fuel / air, etc.

Ideas?

Otherwise I'm stuck arguing with my stock computer (VATS disable methods are NOT very effective!) or going >gasp< carb'd

And I know how you guys feel about carbing a sub-500 hp LT1

500hp

You could look into getting your chip ('93 PROM) programmed to run in open loop for your specific mods/engine combo. TPIS has done this on special combos that don't require part throttle fuel economy and emission requirements (okay for the street, but sucks gas on the highway).

FD2BLK

I made my own harness for my 84 using the stock LT1 harness that came with the motor and I had none of the stuff you are refering to, no airpump, EGR or input from anything other then the ECM and the following sensors (O2's, IAT, TPS, KS's and MAF). I have done a little work while tuning my 94 and could easily do away with the O2's and KS's and even the MAF if I wanted). Many racers will run the car in Open loop and just disable the codes and a lot of the F-body croud by passes the knock sensors because of false knock. Who ever did your chip should be able to disable all of the emisions and any of the features i mentioned above you want out.



Here is a shot of the LT1 in the 84

Baldturbofreak

any of the major standalones work with the Lt1. BS3, fast, XFI, it all about what feature/$$ you need and want to spend. In either case do yourself a favor and get Wideband feedback. If your a crafty DIY guy www.msefi.com you can build your own for less than 200 bucks

ScaryFast

That's basically where I am now, Alvin did the chip and removed most of that stuff. I didn't think about having him remove the knock sensor input, that would have been genius.

It doesn't solve the elusive problem of why I can't communicate with the damn thing. A stand alone system would have it's own software (I would hope, anyway) and be a helluva lot simpler to change. To make changes to mine I need to purchase the chip burning HW and a bunch of EEPROM's.

FD2BLK

You don't have to do the Ks's via tuning you can just use a resistor to feed the ECM a no knock signal. As far as your communications problem I don't know what to tell you other then follow the helms procedure it should tell you what the problem is. Maybe it is time to drop $100 and bring the car to the dealer and have them see what your communications problems are. Look at it this way, a new EFi system could be having the same problem as what you are having. A simpler fix maybe to look at an F-body ECM or to wire an aldl directly to the ECM. The reason I say this is that I know the F-body ECM for the 95 OBDI does not need the CCM to communicate to data master. The F-body has no CCM and neither did my 84. Looking at my 92/93 corvette wiring I see that the serial data goes to the CCM then to pin "G" of the ALDL but is also parallel to pin "M" of the aldl connector. The reason I mention this is that looking at the AKM data cable web site I think you are looking at pin "M" with the data cable correct? If so you may want to check the connection with the CCM and the Heater A/C programmer disconnected. If the wires are parallel like the drawing then possibly the CCM or heater control is dragging down the signal to the CCM. I would also use a meter and check the resistance between pin D4/D5 ECM to pin M on the ALDL, pin D20 ECM to pin B ALDL (Diag enable) and check to ensure a good ground is present on pin A of the ALDL.

FD2BLK

Have to love the internet. After reading your post I did a quick search and found that the F-body and Y-body use the same ECM so the only difernce is the wiring. Because you are only going to use this as a track car I would look into by-passing the CCM and wire the ECM serial data the same as the F-body. Here is a link to the GM diagram for the 1993 F-body, scroll down to the 1993 Firebird LT1 and down load the diagram.

http://home.att.net/~subzero350/

RED92LT1

Check out the Mega Squirt. Very inexpensive, totally PC tuneable and loaded with options.

These systems are running on some pretty fast cars!

http://www.megasquirt.info

ScaryFast

I can't actually wire the car like the F-body until I can verify that I no longer need the CCM "security disable" input to the ECM. Of course I can't check this until the car runs. However, the ECM should still communicate without the CCM so my next step is to unplug the CCM and see what happens. Monday I tapped directly into the pin at the ECM to eliminate any vehicle wiring continuity issues, however, if that line is being grounded or is noisy it still might interfere. I should try cutting the line right at the ECM and wire directly to my ALDL cable...I just hate to cut and splice too many times or I'll be causing more problems in the future.

Unfortunately, it's friggin' cold here now so I can only work on it in short periods before my hands go numb and I have to go back inside...

FD2BLK

[QUOTE=ScaryFast]I can't actually wire the car like the F-body until I can verify that I no longer need the CCM "security disable" input to the ECM.[QUOTE]


You can probably have your tuner disable the VATS in the ECM. If it was a 94/95 I know you can. On my 84 I had the VATS disabled and it worked fine. If you get it to talk with the CCM disconnected you will not be able to start the car without either the CCM input, a VATS disable box, or the ECM programed for VATS disable. I know you already are aware of this but I just thought I would throw it out there. I noticed the F-body only uses D4 for the serial data so if you may keep that in mind whan atampting to direct wire it. Also does your data cable get power from the ALDL?

ScaryFast

Yeah, I've heard you can do that, any idea what the resistor values are? They aren't listed in Helms.


There is no way I can take it to a dealer. They're going to look at it and say "no way." Look at the photos of the interior. They're not going to be interested due to supposed liability of working on this car...not to mention what they'd charge me just to try.


That's a good point regarding stand alone. I have plenty of experience with more modern serial communication protocols, which makes this one so frustrating, it should be easy to figure out such a simple system yet there is no plausible explanation as to why it won't work! I am a sore loser, I really want to figure this out and make it run, regardless of whether I keep stock EFI or not. But I'm running out of ideas.



All of the data lines on the vette are tied together (CCM, ECM, EBTCM, and another one, I don't have my schematic here). Pin M is all I need to communicate, and gnd if using a tech tool. I simply plug the pin from the cable directly into pin M.

Do you have the schematic for the AKM cable? I'm wondering why it's $90 when I can get the PCB from them for $10 and the components from Radio Shack for another $3. I'm starting to wonder if my cable is not correct, but I don't want to spend $90 to find out that it's fine.

I've checked the continuity of the wire from the ALDL plug to the ECM and it's fine. I don't remember having that diagnostic enable pin. I'll have to look at my pinout again later. What does the ECM want there, ground?

ScaryFast

It's done, but the VATS system is a very tricky thing...None of the VATS disable boxes worked as there is a secondary line from the CCM (security disable) that needs a pulse to ground (not a constant ground, mind you!). I used the equivilant resistance to eliminate the pass-key part when I originally removed my interior. But that's not all...

My point is that even though it's supposedly removed from the PROM, I'm not going to remove the CCM until the car is running and I can verify with certainty.


I would be so elated to see communications on the data line that the car never has to run again!

It has separate wires tied to ignition and ground. I hardwired them and checked voltages at the cable's PCB. They're working.

FD2BLK

True but I have built a couple of ALDL boxes in the past and always needed +12 VDC and ground. I built the one in the digram below to work with a freinds TBI truck and free scan
http://cable.invisibill.net/


The schematic is here. I think a big part of the cost with Andrews cables are the OBDxx pig tails.

http://www.akmcables.com/aldlif.jpg


I don't think it is used when you are hooking the serial cable to it but I was wanting you to check and see if it is shorted to ground. It is also refered to as Mode select and I seem to remember somthing about and diagnostics but I have never. Here is are some links with some good info that may help

http://www.akmcables.com/aldl.htm
http://cable.invisibill.net/
http://www.akmcables.com/assembly.htm

As far as the VATS I understand what you are saying and I can not speak to the 92/93 ECM but I know the 94/95 F-body ECM does not need the CCM because I ran it in my 84 and never had the CCM or a VATS box of any sort.

ScaryFast

Update - unplugged CCM with no change.

I do have the diagnostic enable pin, it's used to check codes with the SES light of the dash. Forgot about that. Supposedly with the 93 I don't need to jumper it to gnd while communicating, but just to confirm I tried with and without. Nada.

I'm going to build a new cable tomorrow. It's unlikely, but I suppose it's possible that something happened to mine. I don't know what else to do...and of course TTS tech support is gone all week.

FD2BLK

Did you build your last cable? If so on the DB 9 you used pin 3 for transmit, pin 2 for Rcv, and pin 5 for ground? The reason i ask is a lot of people get a DB9 confused with a DB 25 and xmt and rcv are reversed.

ScaryFast

No, I bought one from ALDLcables.com before I realized that it was so simple to make one. I'll pay close attention when I make the new one. I can't verify which pin is which because they solder a PCB to the connector. I wonder if I stuck two small pieces of wire into it and manually swapped the two pins if I might get lucky.

Do you know what the differences are between the two transistor type and the ones that use the MAX232 IC? Do the newer cars need the specialized circuit to operate?

FD2BLK

I doubt they reversed the pins but the reason for the MAX232 as far as i know is because some ECM's didn't like the transister ones and it was a little cleaner package. The AKM cable I have gets its power from the Laptop as far as I know. So when you build your own dont forget the power and ground. If you get jamed up and can't get it to work let me know and I can lend you my cable. You will just have to use jumper wires from the DB 25 to your ALDL since I have the OBDII connector.

ScaryFast

From what I can tell (mostly from AKM's site) the 232 version is for the newer cars. I'll build and try this cable, if it still doesn't work I'll take you up on your offer.

How about offering some garage space, too. It just got damn cold up here!

Thanks for the continued help. I am determined to get this thing talking.

Alvin

So I take it your still having problems?!?!

Have you contacted the guys who build your cable? Theyoften have quick and easy fixes as they see compatablilty issues between laptops and cables all day long.

Once you can get data from the pcm its very easy for us to go back and clean it up if need be.



I would urge you not to go with a aftermarket fuel injection without meeting someone local with it and have them show you the ropes. In the past few weeks I have either done or redone cars that guys put fast on thinking that was the solve all problem. 2 of them wouldn't even crank and the other two would foul the plugs out or about cut off when you give it gas. I see this all the time, people think that DFI or aftermaket EFI is the easiest way to tune and they get way in over there heads way too fast.. They are lucky often if they can even get the things to crank.. you see with a stock EFI system you are starting off with a excellent base right from GM. With Fast you don't have a base to go on.. and if you do it will be generic as hell like a SBC base etc..

ScaryFast

Yup. Before I sent you the ECM I simply had the PCM not supported error. Now I've taken a step backward, and it won't even recognize that a cable is plugged in. I've been unsuccessful in getting tech support from ALDLcables so I'm using other means.

I'm also building my own to try based on research online.

This has to be a set up issue if you were able to communicate with the ECM in your shop. It doesn't appear to be with my laptop (I've used 3 with different configs), leaving the vehicle wiring and the cable. The stand alone system is a last resort.