LS computer gurus. no power at fuel pump

[chevydog66]

Ok, so my truck was running fine for over a week. It has had reoccuring codes 0134 and 0154 o2 sensors no activity. I have cleared them and they keep coming back. I installed 2 new Bosch o2 sensors when I installed the motor. I am running DT 324 headers. I hooked up efi live and it shows the o2 sensors are heating up but also shows a flat line which should be an up and down line. I checked voltages at the harness that plugs into o2 sensors and get 11.3 to 11.8v. So today I get in it to go to work it starts and runs for about 3 seconds and then dies. Wont start back up. I checked fuses, good. I check for power at fuel pump, no power. I check for power at fuel pump relay, no power. Any ideas? Is there a failsafe built into the computer that would shut down pump? I also checked red and blue connections at the computer. Removed + and - battery cable for a minute or 2. What the?

[Shon]

will the PCM still read?

Check the Park/N safety switch. Sometimes if I dont get my shifter (stock) all the way back or too far back in the P position it will not start. first time I freaked out.

Put it in Open Loop till you can figure out the O2 issue.

Be 100% sure you are connecting to the front O2s.

[Super73]

When you key on, the pump only sees power for aprox 2 seconds before it turns off. It does this to pressurize the system but not keep the pump running if the motor is not running. You are really going to need to people to test this one if the first suggestion does not work.

The PCM sends a ground to the fuel pump relay. When that ground goes through the PCM, walla, your relay fires and your pump should come on. So the relay wiring should look like this (see attached):

30 - 12v constant
87 - 12v out to pump
86 - ignition
85 - PCM
87a - not used

First step would be to take the ground away from the PCM, key on and ground the relay manually. Your pump should run. If it doesn't you have either a relay issue or relay wiring issue.

If the pump turns on, if it doesn't, you need to check the ground wire to the PCM (out put of the coil in the relay). If it looks good with your meter (checking resistance from the relay to the pcm) You could pull that pin out of the PCM, make a jumper wire to go in it's place, put one end of your meter on that, the other to ground, have someone hit the key and watch for continuity with your meter. You should see it for 1-2 seconds max.

If all that checks out, then you probably have a problem at the pump..

And if all of that checks out, IE it will fire for a second then go dead, check your crank and cam sensors. If the PCM is not seeing RPM, it could be turning the pump off after 1-2 seconds.

[chevydog66]

Figured it out. It was a loose Pink wire. After checking lots of fuses and connections with the test light, I was wiggeling everything to find a loose connection, and finally found it. I drove my truck down to John at Speartech, and we figured out that the Bosch o2 sensors were not compatible with the computer. They were coming on and heating but not trimming and fluctuating like they should. John is a great guy and very knowledgeable, he spent at least an hour and a 1/2 figuring out the problem. He said that the o2 sensors actually have something to do with the transmission parameters and since I am running a 4L65 and not the 4L80 that the computer was originally set up for, he had to change some things. He had some used original GM o2's laying around so we put them in and it works great, no codes. I drove it home over an hour on I-69 doing 80mph, after stopping at the local White Castle in Anderson, In. for lunch and a 30 pack of White Castles. Thanks John!!

[67C10BUB]

Originally Posted by chevydog66

Figured it out. It was a loose Pink wire. After checking lots of fuses and connections with the test light, I was wiggeling everything to find a loose connection, and finally found it. I drove my truck down to John at Speartech, and we figured out that the Bosch o2 sensors were not compatible with the computer. They were coming on and heating but not trimming and fluctuating like they should. John is a great guy and very knowledgeable, he spent at least an hour and a 1/2 figuring out the problem. He said that the o2 sensors actually have something to do with the transmission parameters and since I am running a 4L65 and not the 4L80 that the computer was originally set up for, he had to change some things. He had some used original GM o2's laying around so we put them in and it works great, no codes. I drove it home over an hour on I-69 doing 80mph, after stopping at the local White Castle in Anderson, In. for lunch and a 30 pack of White Castles. Thanks John!!

Good to hear about Speartech. I just ordered a harness from him, so it's nice to know that he stands behind his work.