Just got a new 396 stroker installed in 94 camaro Z28 and it won't fire up. We have good fuel pressure,spark and power to the injectors.But no ground pulse at the injectors from the PCM.Any ideas on how to diagnose the PCM?I don't have any wiring diagrams so I don't know what controls the ground pulse from the PCM to the injectors.ANY HELP WOULD BE GREATLY APPRECIATED....Tirefryr

 

Maybe there is a fuse on the ground side for the injectors?

 

computer grounds the injectors.

 

Can somebody tell me what tells the ecu how to fire the injector?

 

The Opti low resolution pulse tells the PCM which cylinder is on the intake stroke. The PCM figures out the amount of fuel required, based on the MAF mass air flow, figures the pulse width required to supply that mass of fuel, then uses the cam position (and inferred crank position) to determine when to fire the injector, then supplies the ground to the correct injector in the correct sequence, at the correct number of cam rotation degrees, for the correct number of milliseconds. If the PCM detects a circuit fault on any of the 8 injector circuits, it sets DTC 18.

If the PCM can not find the low resolution pulse pattern, it shuts down the fuel system, including the pump and the injectors. Have you scanned the PCM for codes? If you see DTC 16, and you can show that it is an active code, you have found the problem.

Shoebox has the wiring diagrams for the 95 on his website. There are a few differences on the 94, but not many. His wiring diagrams should provide most of the info you need.

Bookmark Shoebox's website, because sooner or later you will need a lot of the info he has there:

Main page:
http://shbox.com/1/4th_gen_tech1.html

Wiring page (the PCM wiring is at the bottom of the list):
http://shbox.com/1/schematics_wiring.html

 

I don't have a scanner avalible at this time so I don't now if there is any codes. Where is the cam/crank sensor you mentioned? I don't think the ecu is bad I just think the ecu is not getting a signal from something to fire the injector... I'm going to do a resistance/voltage drop test on the wiring from the injectors to the ecu.. Any help would be appreciated..

 

The cam/crank position sensor is the optical module in the back 1/2 of the Optispark distributor. Check the harness connectors for the Opti to make sure you didn't damage a pin.

 

No damaged pins, would the opti mod. still cause the car to have spark but no fuel ground signal

 

As far as I know, when the PCM can not find the low resolution pulse pattern from the Opti, it shuts down the fuel system. What it does to the spark, I don't know. Using a scanner will tell you if that is the problem, because there will be a code for it.

 

o.k I got a scanner. Found at pin A at opti spark the low impedence pulse was spiked out at 5 volts, and returned to 0 volts. Also the injector pulse width would spike to ground once at first crank, then would have very tight/short pulses. Should the voltage be higher on low impedence pulse in order for the ecu the properly ground the injector?

 

I'm also not sure if the ecu is bad or the optispark...???

 

Valves to tight? Letting compression out.

 

Valve settings are good.