Injectors won't pulse
 

Hello, I'm looking for help. I have a 68 impala wagon that I have converted to a 5.3 ls with a blue / Greek pcm, and dbw throttle. Computer has been flashed. It won't run unless I prime the manifold, and quits when it has burned up the fuel. When I put a " Large" prime in it I can rev it very high, and it is definitely hitting on all 8 cylinders. It sounds great. But no injector pulse. I have 58 psi on the gauge. You can hear the fuel pump running for a few seconds after the engine quits. I have verified 12 volts to all 8 injectors, and at the blue pcm connector. I have tested the injectors on my " test rig", and the open and close, and flow carb cleaner very well.

So, since the engine runs correctly under a prime condition doesn't that mean that the crank, and cam sensors are synced? I am under the thinking that it's an electrical gremlin. My harness is a CBM. I have been communicating with them for the last month. I think we are about one email away from me pulling the harness out of my car and sending it back to them for testing. I'm sure it's one simple thing, but what?

Check all connections to the ECM. There will ALWAYS be 12V at the injectors as they are activated by grounding them thru the ECM

Yes thank you. I am aware of that, and have tested 8 leads at the ECM. Anything specific that would cause all the injectors not to fire? I have also done the noid light test, and it doesn’t light.

Cam sensor, grounds at back of intake, and complete vats removal.

If vats are still active it will fire and shut off.

Cam sensor fires the injectors. Make sure its plugged in correctly.

And grounds.

Another thing is to make sure u have complete key ign hot to your pink wire with key turned to start/starter spinning. Usually easier to just jump this wire to straight battery to test a harness.

Ok this is beginning to get a little clearer. On Sunday I unplugged the cam sensor and expected the engine not to run when primed, but It ran exactly as it had before. So I replace the cam sensor with the original old one, and got the same result. So if you know, how do I test that the computer is getting information from the cam sensor? It’s plugged in, and the harness is grounded at the block next to the cam sensor.

Help me out here, please. I thought the crank sensor both fired the injectors and ignition, and the cam sensor ONLY told the ECM which part of the cycle the engine was on.
Which is why Gen III uses 2 "lobes" either on the cam or in front on the sprocket, and Gen IV uses 4 on the sprocket.
I've seen many instances here where if the cam sensor was DOA, it would start, but after a lot of cranking while the ECM "figures out" where in the cycle the engine is. The cam sensor mainly helps the ECM see where the engine is during the cycle.

My engine has only run when primed, and quits when the fuel is burned up. The injectors have never fired

Ive personally seen an engine with no cam sensor not crank. No injector pulse with noid light. Fixed sensor fired right up.

Ive seen the same thing with a bad ground.

I agree the crank sensor is the main one for pretty much everything but the cam sensor does play a part as well.

All my grounds are in one terminal from the harness manufacturer, and bolted to the back of the block next to the cam sensor. I've had 2 cam sensors in, and no change. I would certainly appreciate any suggestions on what to do/ check next.

thanks

It will run without a cam sensor...it will just have spin over longer to start....are you sure VATS was deleted?

Yes it was flashed in Kentucky by a reputable shop, and then to California where it was verified that VATS was removed

I'm glad you said this! Others have said a bad cam sensor shuts it down, even say the cam sensor fires the injectors. Thank you!

Like i said im goin by what ive seen personally. Just my .02

I will say the car tht i worked on didnt have a cam sensor signal at all. Maybe tht could have been the issue.

We had a LS2 with the wrong cam sprocket on it and also a LS1 with a cam with no cam sensor ring on it, both ran. We also used to see alot of LS2 swaps with the outside cam sensor wires swapped, they all ran just took longer to spin over. That was on a P01 and E38 if that matters.