No Injector pulse

badwench · 3 Weeks Ago

95 Riviera 3.8 SC
Cranks but will not start

Like I have a new battery, new alternator, clean grounds, no error codes when I run a scan, The security light will be flashing when I get in car, after I put key in and turn to on the security is on solid for about 10 sec. and goes out--which from what I read is the way it should be. However when I crank the engine I have no pulse at the injector when checked with NOID light. I have 12V at each injector. I also have fire to plugs as indicated by the use of timing light. I also have 40+ PSI at fuel rail. I read that this car did not have the security relearn but I tried anyway with no luck. I also have made a splice with resisters = to the key. However I have not tried to use it as not sure which wires to splice. Being 6 ft + and 200 lbs + it is hard to see anything under the dash.
I Just need to find more on the injector pulse circuit.

Thanks for any help

Larry Schramm · 3 Weeks Ago

Do you have a tech 1 or 2 scanner? One of the things that might be bad is the crank shaft sensor behind the crank pulley. Without a crank signal, the injectors will not fire. With a scanner you should be able to see a crankshaft revolutions.

badwench · 3 Weeks Ago

Thanks Larry for the speedy reply.
Not sure what you mean by Tech 1 or Tech 2. I have a Actron Super Auto Scanner which will check OBD 1 or OBD 2 systems. Although the 95 Rivera has a OBD 2 connector it is actually a OBD 1 system. As for the CPS check I did not look at data for that but will today. However based on what I know it is my understanding that the crank signal is used both for the injector operation and plug firing. Being I have fire on all plugs as checked with timing light I doubt that is cause. But will check with scanner today--will let you know. About to drive me nuts.
Again thanks

mercman86 · 3 Weeks Ago

With a bad crank sensor, you will still get spark, but it wont be sparking at the correct time or the correct cylinder. However, like larry explained the injectors will not pulse. I would take a look at that cps.

badwench · 3 Weeks Ago

Just went and checked, have no error codes and did not find the crankshaft revolutions info when I checked data part. But then again, this scanner is a new toy for me and I may be overlooking the crank revolution one. Reguardless, the CPS is about $25. and it does not look that hard to change and I know that it is old so I'm going to just change it out.

Thanks again
Jim

special55 · 3 Weeks Ago

Hey Jim,

Chances are if you have spark your crank sensor is good.

Look at the RPMs while cranking on your scan tool. The PCM receives it's signal from the crank sensor so if you are showing RPMs while cranking the sensor and wiring are good.

I would more suspect a bad ground on the injector driver circiut, bad cam sensor(this is what sets your injector timing) or a faulty PCM itself. The injector driver can go bad inside the PCM and all else can look fine.

You may even try giving the PCM a couple of taps on the case while powered up. If the car fires the PCM has a cracked circuit board and needs replaced.

Good luck,

Rich

badwench · 2 Weeks Ago

Well $30.00 + for a cam sensor and still no pulse for injectors--ready to put a match to it! NOT

Just so frustrading!
Thanks anyway

special55 · 2 Weeks Ago

Do you have a service manual for the car?

I'm going off memory here but it has been a while since I've put a wrench to one of these.

If you have 12v at the injector harness then the signal side is the issue. The PCM is what gives it it's signal via completing the circuit with a ground. That's why I mentioned checking the PCM grounds because if they are bad it cannot complete the circuit.

The other thing I just thought of was once in a while one of the injectors would short out or have very low resistance. This would draw the ground circuit down and prevent the injectors from firing.

Did you have all injectors disconnected when you checked for signal? If not you may want to give that a go. No cost involved with that other than your time.

I can't remember the exact resistance of the injectors but they should all be within a couple ohms of one another.

Let us know what you find,

Rich

Larry Schramm · 2 Weeks Ago

What kind of mass air flow sensor does it have? Is it attached to the intake, or is it black and round and in line with air cleaner to the intake?

Also, a tech 1 or 2 is that scanner that GM has for vehicle diagnosis that will tell more than the codes in the car. It would tell the opeating data of the vehicle while it was running. The Tech 1 was for 1980 to about 1995 and the Tech 2 from about 1992 to 2009/10

It has been a long time, but I think that if you press off and warm at the same time that vehicle might have onboard diagnositics. You can scroll up and down the data list by pressing the temp up button.....I think