tamatt27

I've got the '94 LT1/T56 in my '88 Trans Am. I finally got it to start and idle last weekend. It's very tempramental though. I've got to crank it and let off several times in order for the engine to start.
This weekend, the car wouldn't start at all. The computer's not grounding the injectors. I've ohm'd out all of the PCM grounds and they're all less than 1.5 Ohms, and all of the PCM Ignition and Battery voltages are getting 12V.
Is there any way for ya'll to tell me some reasons why the computer's not grounding the injectors? It's got a brand new opti, and cap and rotor. I've got the VATS, EGR, AIR, etc deleted.
The only thing I can think of is the PCM's bad? I've got a spare '96 OBD2 PCM. Can I hook that up and will it work enough to see if the injectors fire?

Pasky

Only thing I can think of is to check your wires matt, double check your injectors are getting power when the key is turned and that the plug for the injectors (think its red) is plugged all the way in.

tamatt27

The injectors are getting power. I hook to the other injector terminal and the computer's not giving the injectors a ground...I finally got my Fluke Multi-meter so I can do a lot more in-depth electrical diagnosis now.
I'm also wondering if I can check the opti connector and see which wire gives the computer the signal to fire....and I'll backprobe it and see if the optical sensor's giving out the signal.
Only other thing I can think of is the PCM.

JDBlaze85

one reason the PCM will not ground the injectors is if the PCM thinks you are stealing the car. Anti-theft system. Have you bypassed it? If you can, scan the PCM for anti-theft codes. There should be one if that is the problem.

tamatt27

Pasky deleted VATS from the computer. Whenever I use Datamaster on my laptop to hook into the PCM, it's never able to connect to it. I'm fairly certain that I hooked up the DLC correctly.

JDBlaze85

I would try to establish communication with the PCM first, to diagnose your problem more easily.

Pasky

Matt, are you connecting ground and serial data to the ALDL? If your not connecting to the pcm, something else is wrong. I bet it isn't turning on. For a fact datamaster and tunercat were working last time I was there, something got unplugged.

tamatt27

It may be my laptop. I'm going to hook up the '96 PCM and see if I can establish communications with it with my laptop.
Pasky you need to come up here again and hook up your laptop and see if you can communicate with it, lol.

tamatt27

Are there any sensors that are directly correlated with the computer to control the injector pulse? Other than the optical sensor in the optispark? I've got a brand new opti, and brand new cap and rotor. Is there a wire I can backprobe in the opti connector to see a certain voltage to check and see if the optical sensor is giving a signal?

tamatt27

Or does anyone else have any ideas on what the problem could be or what I could do to isolate the problem?

Injuneer

The PCM looks for the low resolution pulse from the Opti. If it can't "find" it for two crank revs, it shuts down the injectors and the fuel pump. Have you checked for the DTC for loss of low res pulse?

tamatt27

Can I backprobe the low res signal in the opti connector on the pass. side of the intake? Is there a particular voltage that it should send? It would it be PWM?

JDBlaze85

if you wanna do it like that......check these sensors and see if they are recieving their 5V reference from the PCM. MAP, TPS, CTS. with ignition on.

Pasky

Im willing to bet your PCM isn't even turning on matt. Im telling you. Wire in your fuel pump relay properly and you can diagnose all of this much faster. You keep putting it off, but if you get rid of the hardwire for the pump and just wire in the relay, you'll always be able to tell if the PCM is on.

tamatt27

The way I have the fuel pump wired, it's using the relay. The only thing I have done to it different, is that the 'Hot in Run' wire is wired to a 'Hot at all Times'. That only means that the fuel pump will come on when the battery's connected, for 2 seconds, then shut off when the computer doesn't read any RPM's. So whenever I crank it, I hear the fuel pump come on. Also whenever I disconnect some of the PCM connectors, and re connect them, I hear the fuel pump come on for a few seconds.
That tells me that computer's controling the fuel pump relay.
Like I said before, I checked and double checked all the PCM grounds and power sources...they're all as they should be.
Blaze, will the opti have a 5V reference that I can check? Also, is there a way I can check the low res signal coming from the opti, and see if the computer's getting that?