Could the PCM cause the fuse relay to have low or no voltage. If so how do I check this? Replaced transmission, when I went to start truck it would not start. Check fuel pump it is good. Replaced relays and fuses. Started tracing wires for breaks and found none. The relay seems to transfer only 4.5 volts to the fuel pump. I will get some fuel build up on the pressure check on the fuel rail but not much pressure. At my wits end as to why the pump will not run.

 

I take it the engine cranks, but, won't fire?

What's battery voltage look like?

Didn't pinch any wires installing the trans did ya?

Fuel pump should see battery voltage for about three seconds when you turn the key on, and while the engine is rolling over. Fuel pump relay is in the PDC behind the battery. You can try swapping the FP relay with another one..... I do believe they are all pretty much the same.

 

Crank and fire. Battery volts 12 plus. Forget to mention. There is 12 volts coming into the relay. But not transferring to the fuel pump. No wires pinched check with ohms meter and and visual trace. Already did the relay swap. And used one out of wife's jeep also. I did mess up the wiring on the 02 sensor though.

 

Erm, you lost me. Does it fire? Does it crank? Will it just not stay running??

 

Sorry, it does crank and there is fire but no fuel for it the start.

 

So you are getting spark?

Wonder if the crank position sensor didn't get tweaked when you installed the trans, and is now giving you trouble.....

 

unless the camshaft position sensor will stop the fuel pump from running that is not the problem. The problem is that the fuel pump relay is is not getting enough volts to run the pump at capacity or not at all.

 

Need to find out where the voltage drop is happening then. If you have a good 12 volt supply TO the relay, then somewhere after that you have something odd going on. Trace the wire from the PDC, back to the pump..... and also check the ground wire. Might be just a bad ground.....

 

Already traced wire, no breaks. Check with ohms meter. No resistance. Already tried the ground thing by running a new ground straight from the battery. This is a complex problem. I was originally asking if the PCM would cause this problem. If so how do I check.

 

PCM only trips the relay, or not..... that's the only control it has.

Swap your ground wire over to power, and run the fuel pump that way, see if the pump is a little more enthusiastic.

0 resistance at the low (milliamp) load the meter tests at, and putting it under the load of the pump itself, can be two entirely different things....