need help on my first LS conversion,04 LQ9 in an 86 K5, no start

My computer has been reflashed and VATS removed. I have good fuel pressure and plugs are wet. I have random and weak fire only on 4 and 6. I have checked pinouts over and over and grounds but do not have 12v supply voltage to the crank sensor if I measure right at the pcm at key on with sensor disconnected. With it connected, I get .5 volts with the key on and off. Fuel pump signal is good to relay and injectors are firing. I can connect a code reader and it communicates and shows all monitors ready to learn. Bad PCM?

thanks

Have you tried replacing both with a known good crank and cam sensor? Are you certain you did not pinch part of the wiring harness between the engine and transmission during the install? Don't ask me how I know to check for this. :whack:

I did check harness routing and I ohmed out all 3 wires from the pcm connector to the crank sensor and they checked good. I have not tried another sensor. Are you saying I might not get the 12v without a good sensor in the circuit?

thanks

pull the connector off the pcm, find the three wires that go to the crank and cam sensors, ohm them out to ground and see if you have a short to ground somewhere.

ok, I'll check them tomorrow

Correct me if im wrong but if you had no crank signal, you would also have no injector pulse. Also you would have no spark at all. If your scan tool displays any data, look at engine rpm during cranking. Kinda sounds more like harness issues than a lack of ckp signal.

Subscribed, im curious.

Did you build or buy your harness? Which pcm?

Thanks for the replys. Just finished checking out crank and cam sensor wiring. No shorts to ground or each other but mysteriously I now have 11.6 or so volts to crank and cam sensors. I'm going to put pcm connector back together and try it again before I buy new sensors. Will be tomorrow before I can get back to it.

I modified an 04 escalade harness per the "pinout" sticky, btw, thanks RedHeartBeat. PCM is 12576106 with Hwd. No. 12570558. I'm using this one because the only trans I had was a 700r4 and wanted to use dbc instead of dbw.

If crank sensor was bad, I wouldn't see rpm on scan tool, right?

Thanks for your help

hey steve iam new to this site: iam not a senior member but i know a bit about automotive u are not to have 12v at any sensor they run on a 5 volt reference voltage to ck for an open ohm out the wire it should read 2 ohms but if on two cylinder u are getting fuel fouled plugs i think ur issue would more likely be stuck open injectors just remove fuel rail make sure injectors are secured on fuel rail with thier locks cycle key dont crank and see which one leaks

Quote:

---

Originally Posted by stevebbc

Thanks for the replys. Just finished checking out crank and cam sensor wiring. No shorts to ground or each other but mysteriously I now have 11.6 or so volts to crank and cam sensors. I'm going to put pcm connector back together and try it again before I buy new sensors. Will be tomorrow before I can get back to it.

I modified an 04 escalade harness per the "pinout" sticky, btw, thanks RedHeartBeat. PCM is 12576106 with Hwd. No. 12570558. I'm using this one because the only trans I had was a 700r4 and wanted to use dbc instead of dbw.

If crank sensor was bad, I wouldn't see rpm on scan tool, right?

Thanks for your help

---

That's correct, if the ckp signal is missing, weather it be due to faulty sensor or wiring, you will see no rpm during cranking while monitoring an engine speed pid. I would certainly check that before buying anything if you're able. Good luck, ill keep checking in.

Tried it again today after putting connector and old sensor back in. Still no start. Ocassional firing with valves still open, back thru throttle body.

So what is sensor supply voltage supposed to be. All the schematics I see of the crank and cam sensor say 12v ref.

Going to try new crank and cam sensor unless somebody's got another idea.

thanks