Cranks but no start, injectors not operating

What inputs to the 1995 Buick Riviera PCM (Powertrain Control Module) would prevent the PCM from operating the injectors (assuming the PCM is not defective). I can operate the injectors by disconnecting the PCM connector and shorting the injector wires to ground one at a time. The “fuel control” signal from the ICM (Ignition Control Module) to the PCM is present (clean 5 volt square wave, 3 pulses/rev). Spark plugs are firing. Can I conclude the PCM is defective?

It does seem like the PCM may be trouble going from what you say. I assume you have checked for any codes and if you have verified that all the power connections to the PCM are present then I think replacing the PCM will solve the trouble. Good troubleshooting.


Does your ignition key have a chip resistor in it?

Is the security lamp illuminated during cranking?

Is your fuel pump running and developing pressure?

You need to get a diagnostic chart for a “engine cranks but won’t run”, it gives step by step instructions for diagnosing this condition. The end result of some testing is the replacement of the PCM but there are diagnostic steps to follow before replacing it.

There could be a shorted injector that took out a quad driver in the PCM resulting in the no start condition. This will require replacing the shorted injector and PCM. If you replace the PCM with out replacing the injector you will short out the new PCM.

Get the problem diagnosed before installing parts.

Thanks for all 3 responses, I’ll try to answer the questions as briefly as possible.
Responding to Cougar:
My code reader says the car computer is not responding
Responding to TwinTurbo
The ignition key does have a resistor chip.
The security lamp does not come on.
?Service Engine Soon? light is on
The fuel pressure is 42 psi (holds when pump quits) which is in the desired range for my VIN (has a 1).
Responding to willey
I have both the original (thick) Riviera service manuals and have followed the “engine cranks but won’t run” as far as I can (manual relies heavily on the GM Tech 1 tool). All I have is a code reader (right now, car computer will not communicate), Fluke multimeter, and a 2 trace oscilloscope so I’m limited to voltage, amperage, continuity, and resistance measurements.
There are some electrical abnormalities which I thought could be dealt with later but your comments and re-reading charts A1 and A3 in the service book lead me to think I better check all power and ground connections, primarily to the PCM. All testing is being done with a new battery installed. The known electrical abnormalities are:
(1) Both radiator cooling fans come on as soon as the ignition is turned on (is this an indication of bad coolant temp sensor and would that shut down injectors?).
(2) The warning chime for when the door is open and key in ignition is very soft and "wimpy? sounding.
(3) Hazard flasher dash light stays “on” very, very weakly (not blinking) when battery is connected, brighter when key is turned on. Hazard flashers and indicator light work OK otherwise.
(4) Climate control system is just displaying 3 dashes on the display, hvac blower starts when ignition turned on.
What resistance should the injectors have if injectors are not shorted? Each injector would ?click? as I grounded each on the disconnected PCM red connector. How many amps should a good injector draw?
If the PCM receives good ?fuel control? signal, does any other input to the PCM make it decide to stop firing the injectors?

The ‘Service Engine Soon’ light will remain on as long as the car is not running. But, you may still have codes that may help. Your car probably has an ODB-II style test port, but still an ODB-I system that requires a special code reader. The ODB-II code reader will not work. '94 an '95 GMs were bad for this. Until you can get the codes read, your shooting blind.

Thanks for your response…my code reader (AUTOXRAY EZ-READ 2000)is compatible with the 95 Riviera (requires a special cable) and it has worked on this car (my daughter’s) in the past and works on my wife’s 95 Riviera.

Someone who actually responds to questions!! I need a moment to compose myself…

The good news is, it’s not the security system since the lamp is not lit and you also have fuel pressure which VATS/PASSKEY disables if it doesn’t see the chip resistor.

My code reader says the car computer is not responding
(2) The warning chime for when the door is open and key in ignition is very soft and "wimpy? sounding.
(3) Hazard flasher dash light stays “on” very, very weakly (not blinking) when battery is connected, brighter when key is turned on. Hazard flashers and indicator light work OK otherwise

It sounds like you have either a bad main power connection or something is seriously dragging down the bus voltage. What does your battery voltage read with the ignition off and then with the key set to RUN? Measure the voltage on the wire terminals, not the battery terminals and post back with your results.

Not having a GM scanner can make diagnosing the problem very difficult. The problem is if you don’t follow the diagnostic steps you might miss something that gives you the wrong diagnosis and you end up replacing the wrong part.

The resistance spec for the injectors is 14.3-14.7 ohms at 68 degrees.

Bases upon your electrical indications, I would lean towards a bad connection or switch somewhere. I bet if you figure out why your flashers are dim, then bright when you turn on your ignition, you’ll get to the root of the problem.

Something like could have better troubleshooting charts than the factory manual. It doesn’t rely so heavily on using the Tech 1 scan tool. The alldata charts, probably, show how to check across the PCM for quad driver operation, AND, what other inputs have to be present to enable the drivers.
GM cars do turn on the engine fan(s) when the OBD tester is connecter is connected to the cars OBD port. Why? Good question.
The OBD test port should have a 12(?) volt terminal, and a communications terminal. Use a wiring diagram to follow those wires to the engine computer.

In your first reply to our questions you stated that the hazard lights are dim and get brighter when the key is turned on. This may mean you have a bad ground. I suggest you clean the ground connections from the battery to the chassis of the car. You may want to use your meter to check for bad ground connections using the negative battery post as the reference.

Since the PCM isn’t responding it is most important to make sure all power and ground connections to it have been verified to be ok. After checking the grounding I would do that next before anything else.

Sorry I disappeared for a couple of days…had to put new calipers and pads on my 2002 Buick PA. Will start checking power and ground connections on the Riviera. Thanks again for all the suggestions/comments, may get to the bottom of this yet!