Those voltage readings tell us that proper voltage is getting to the pump at no load on the +V wire from the priming tab and maintains adequate voltage under some load but we don’t know yet if you have a proper functioning pump developing full pressure. Also we don’t know the condition of your pump ground because you measured the pump voltage with reference to frame ground. When backprobing, back probe +v and ground right at the pump. That’s the net voltage that the pump sees. If you then see roughly the same voltage when you move the negative meter lead to frame ground then your pump ground wire and connection is ok. If the voltage reading gets significantly better then there is a problem with the ground circuit. All of this needs to be measured under full pump load.

in the fuel pressure sticky I listed the fuel fittings I bought off of Amazon.


George

 

I do have both power and ground back probed at the connector and that's how I got my voltage readings. So 10.something to11v is enough and I shouldn't expect full battery voltage at the pump?

The other thing I was attempting to check was resistance between the ground at fuel pump plug and tail pipe. I read somewhere to check ground that way but not sure where. Seems like it should be close to 0 ohms. My reading 4+. I'm going to clean up that crossmember better where the ground bolts on tonight and test some more. Maybe even run another ground just to see what happens. I'll go look for the sticky on testing pressure at fuel filter. Thanks so far for sticking with me!

 

The pump should run OK at 11V but there may be some loss in the ground side. The way to really check that is to measure with the pump running back probing both power and ground at the pump as you did and then repeat the measurement with the meter ground probe moved over to some shiny clean metal on the frame. There should be almost no difference in the readings. Thats the best real world way to test all of this.

George

 

Updated results, battery at 11.97v. These readings are from the 2 seconds at key on.

Power and ground back probed at pump connector was 10.9-11.3v
Power at connector and ground to shiny clean frame was 11.3-11.5v
Resistance between pump connector ground and shiny clean frame was .8 ohms. Much better reading than using the tailpipe lol.

Checked fuel pressure again just out of curiosity. With ground jumped to shiny clean frame it was 45 and dropped to 40 after 10 min. With the fuel pump connected normally (no jumper to clean ground) the pressure was 48 and dropped to 46 after 10 min.
Seems more likely fuel pump than wiring to me, but what do you say?

 

You don’t have a ground problem and your testing on that was solid. Your positive voltage could be higher but not the cause of those low pressures. You have the hoses, injectors, and regulator in the plenum and pump in the tank, could be any of those.


George

 

Finally got the battery fully charged and I now get 12v to pump but confirmed it still won't start. Of course I already returned the rented pressure tester to the store so am going to go get that again for the weekend. Doubt my pressure will be better but want to make sure.

Meanwhile at some point during all this, the cranking has changed. Excuse my written imitation of the sound...but instead of a steady nu nu nu nu nu, it now goes nu nu nu pause nu nu nu pause. At first thought it was the undercharged battery but that is now ruled out. Starter is almost new. Was going to start a new thread since I haven't been able to find one about this pause during cranking, but figured I'd ask here first. If there is a thread about this symptom, please point me to it. Thanks!

 

The truck will not start at your fuel pressures

You either have:
Tank:
A faulty fuel pump assembly

Intake:
A faulty regulator
Leaking injectors
Leaking hoses in the plenum

The fuel pressure test at the fuel filter cuts this problem in half for you. I do not like the parts cannon in general but especially if that guess is a miserable job like dropping a tank full of gas in the driveway to get to the fuel pump. If you really want to rule out voltage to the pump you can run a wire from the priming tab to the pump positive connector but I don't think that's your problem. Your pump ground is good.

I cannot offer any further help at this point without the complete fuel pressure results. Its the rest of the fuel pressure testing or the parts cannon (fuel pump, regulator, spider). Ill be glad to help if you get more info.

George

 

I do get 60psi now with the full 12v at pump. It will start and run once. But next try it won't start. Pressure drops under 50 and gauge needle twitches like crazy after I let off ignition. I've finally got it up on jack stands so hopefully I can do the testing at the fuel filter. Will try to find your post about the fitting I need there. Thanks.

 

So it looks like I might be wrong about 11v being adequate at the pump. What did you do to improve the pump voltage? When you got 60psi, what was the 10 min leak down pressure?


George

 

I got 12v at pump after I finally got the battery fully charged. (Well it overcharged to 13.1 but settled at 12.9 after I unhooked the charger.) Right now I'm waiting for the magical penetrant to do it's job so I can get fuel filter off.