The mechanic told me I only had 51 PSI after a trouble code kicked on the check engine light. The truck still started and drove normal around town mostly 25 35 mph. On the highway at 55mph my wife expierenced complete engine stall for a few seconds and a decrease in speed then back to normal. I am 90% sure that the fuel pump is the problem the mechanic agrees like I said above. I have changed the fuel pump I bought a US pump for $100 I know not smart , I did not read the info about ac delco and delphi untill later geees. The shop wnated 850 for the job , they have already charged me $90 diagnostic. I changed the pump and its all wired up however the OEM 4 pin adapter for power ground etc is a square block and the new pump requires a flat rectangle. However they supply a pre spliced adapter that plugs into the flat rectangle on thier pump and you just cut off your OEM square four pin adapter and splice to wire in thier new pump. Fine not happy but I did it, the colrs were correct purple 2 purple, grey to grey, larger black 2 larger black, and smaller black w/ white stripe, to the new pump smaller black no stripe Fine all wired everything looks and seems correct. I plugged everything back in and left the pump on a bucket in the upright posisition. I turned on the key just wanted to hear the pump run, and nothing? no priming? SO ichecked the ground back by the rear part of the frame near the bumper.Cleaned that up well and bolted it down, still nothing? ARRRR so I want to hear something before I bolt all of this back up what should I do? Does the other ground wire that is attached to the smaller side next to the filler tube need to be attached as well? Originaly both of those ground were together when I removed it.... The smaller hose is a relief return correct? the bigger side is the filler, so does that smaller side need to be attached just to hear the pump run? I understand the ground that is wired in does but I dont think the other makes any kind of circuit? Oh geeees , thanks for any hlep fellas......

 

Repeat repeats... Simple things first. Test for +12V at the pump and for no more than 5 ohms from a good ground to the ground at the pump. Both +12V and a good ground MUST be present for the pump to run.

And no, the return does not have to be plumbed.

 

alright I will try to go find a volt meter , so 12v on purple wire or grey wire at the pump? and 5 ohms on the smaller black wire at the pump or the larger black wire at the pump? or do I use the wire thats bolted at the rear of the frame? If the other pump was working and the truck was driveable why am I now testing for voltage? just a question sorry I am total novice today not sure why... thanks .>>S

 

The ground that runs up to the fill pipe is for static discharge only and doesn't have a thing to do with the pump. Testing for +12V & ground is your quickest way to determining the source of the problem. I wouldn't go undoing any butt connections, etc until you have put a multimeter to the connector pins & determined exactly what is missing, if anything.

If you have +12V on the grey wire and <5ohms to a known good ground (that bolt in the back, provided it is clean, will work good) on the large black wire, then that only leaves the pump as the problem. If you want to verify your choice of the ground reference beforehand, put one lead on the negative battery terminal and the other on the location you want to use as your reference ground. It should show less than 5 ohms resistance as well especially between the battery & the frame.

As far as why the original pump worked and the new one doesn't... Could be a popped fuse if wires touched at some point during the project. Could be a marginally healthy wire near the pump that broke inside the insulation once it was moved around during the dis-assembly & rewiring tasks. Could just be a bad pump. But before doing taking anything apart, aside from the connector, a quick test with a multimeter would confirm that the prerequisites are there, namely power & ground.

 

alright so with the key on the grey wire should have 12 volts positive side of volt meter and the ground, clean bolt on the rear frame should have 5 ohms negative side of volt meter just switching the position on the meter correct? Would it have made a difference that I did not disconnect the battery thru any of this process? thanks again for the great replies sorry I am bombing on this one....

is it hard to find a multimeter that will test the 5 ohms resistance? the two I found here locally say they only test up to 2 ohm? both sperry and GB? they are in the thirty dollar range.... any ideas on a decent get the job done $30 range multimeter tester? thanks again very much...

alright volt meter in hand , just gotta make sure I have the leads and switches dialed in correctly, thanks .>S

alright thanks for standing by I have verified that volt meter is correct using some 9 volt battery both new and used to check readings.

when the key is on I get no volts on the grey wire using positive probe to grey and negative probe to larger black

when the key is on I get 5 volts to purple with posi probe on purple and neg probe on larger black

so just keep in mind I had to cut off the OEM square 4 pin 4 wire adapter because the US pump I bought had a flat rectanlge 4 pin 4 wire adapter

all the colors and sizes matched up but maybe one of the butt splicers I used is not on properly? I guess I will remove the splices and just test the leads from the harness of the vehicle Grey, Purple, small black w/ white stripe and larger black

grey is the 12 volts right? larger black the ground right?

so the bolt that mounts to the rear of the frame for ground should be 5 ohms resistance when key is off right?

thanks again for all your help and paitence , trust me your on the christmas list LOL gotta get this thing rolling!!! I feel like a complete *** having my mother in law show up everyday to take the two kids to school while my wife is at work. I look like a loser with no wheels working at night just using my wifes truck and I am not able to drop off or pick up the kids while she is gone YIKES!!!!! thanks again in advance I dont mean to be a pain in the *** just getting desperate on day three of what should have been a fairly straight forward swapp???

update so it seems other chevy owners have this wierd dreaded 5 volt anomaly back at the wiring also???

I did try swapping the horn relay with the fuel pump relay they show the exact same part number and both relays let you use the horn.... seems like I could rule out the relay

I wonder if I will have to run my own wire from the fuse box to fuel pump? I was told to check the sending unit also? It has heat damge issues? Have not looked yet ran out of time and energy..... Thanks to everybody who helped out !!!!

this was the reply.... any thoughts????


Had to replace the sending unit. The connection on the bottom side of the mounting plate (black wire to pump), was weak and caused loss of power, ( it had even gotten hot enough to start to melt the pigtail on the underside of the plate). Hope this helps alot of you out there!

 

Did you end up checking if any fuses were blown?

Edit: Oh, nevermind then. I'm glad you got it figured out.

 

yes I checked anything labeled ignition or engine, but I have not checked them all, yet anyways

 

The fuel level sending unit is powered by a 5V reference from the PCM... No anomaly there.

Purple wire = fuel level sending unit +5V feed from PCM
Small Black wire = fuel level sending unit ground back to PCM
Larger Grey wire = Pump +12V feed from fuel pump relay
Larger Black wire = Pump ground to chassis ground

So did you get it figured out? Your 6 consecutive replies (please read the rules) are ALL over the place... Are you quoting something else? If so, please use the quote tags to keep things separated...

 

oh alright thank you for the description that clears things up a bit for me!

So I have everything testing well accept the 12 volts on the grey wire?

I still have the factory OEM plug for the small black adapter that plugs into the top of the pump. I did not realize that was the sending unit. I have not tested this but since I did not cut or splice, that was plug in play from the harness to the new pump so I should be all good on that.

I am hoping the butt splice on the grey wire between the OEM harness and the new pump is why I am not getting 12 volts on the grey wire at that pin that plugs into the new pump. I wish it had been a direct fit, I feel like the splice must be the problem.

Sorry for the confusing thread I was trying to update that I found a multimeter, tested it to be working, swapped the relays to test that between horn and fuel pump, and then again the readings on the four pins back at the new adapter for the new pump, thanks .>>S

 

I think some things need clarified:

First.. you replaced the 2x2 Fp connector with the new 1x4. Good thing.. the old style failed a lot, particularly on pump pwr.

Second: As Kyle said..fuel gauges {nearly universally} start with 5 v ref to one side of gauge, other side gauge goes to one side of sender in tank, other side of sender connected to frame ground. So with key on you should read 5 volts at end of connector at tank.. OR if circuit is completed and working right, then your volt reading will be less than 5v, depending on fuel level.

Third OHM is measure of resistance. In power circuit any ohm reading of more than 1 ohm on the black, black/white stripe is bad ground. Note that is one ohm.. look for decimal on DVM, .1 {point one} is in range of error. There is no negative resistance reading. Zero is low as it goes.
Check your meter and leads by touching lead probes together. Then put each anywhere on the frame and scratch till meter shows less than an ohm.

Black and black/wh should read same resistance to frame, and less than 1. Actually should be under point 1.

The Ground point is on top the crossmember, rear of tank. There is a splice pack between the FP connector and the grd point. If the grd point is good and / or the two wires read different open the harness till you find the splice and fix it.
ALWAYS disconnect battery before doing resistance checks just to make sure you dont get crossed up with live power.

OTHERWISE read voltage on black and black/wh - with connections made and fp running - any voltage reading more than one volt to frame shows resistance in ground circuit. Again check ground point and splice pack.

For future readers, if you arent going to solder those connections on the new pigtail, rather than use the supplied crimp type, use house wiring type twist connectors filled with silicone grease. FAR more reliable.