intermittent fuel pump power

[ryanm1987]

Hey everybody how's it going? I need some help very badly this problem has me and my mechanic stumped.97 Tahoe 4x4 4 door Thought my fuel pump was bad previous owner replaced it with a airtex. So I bought 2 new Delphi whole pump modules new sender unit wire harness and fuel pump relay, intermittent power, got gas to come out of Delphi and airtex before we put gas lines back on so I know the new Delphi pump is good. So I have spark engine fires with starting fluid, so im getting intermittent power to the fuel pump relay, I read on the net to check the rear frame ground by the tank it looks intact but were does that lead to the new harness or the old factory harness the new one connects to? also im going to check the oil pressure sensor, truck ran fine one day it just died in my drive way but since I bought it it usally never primed on the first key turn but always on the second and fired right up and ran good. so im thinking it has to be a bad wire somewhere. please give me some advice or first hand knowledge if you have had this problem in a 350 vortec equipped truck

 

[SunlitComet]

the fuel pump ground wire stands by itself. there are some other grounds on fender wall next to battery as well as some on the thermostat housing that are tied to the pcm. check the bottom of relay box for damage. there are also some on the back of the right cylinder head. but how are the conditions of your relay terminals in the block?

 

[ryanm1987]

thanks for the info truck is at my mechanics shop cant get to it till after work. I haven't checked the connections under the relay panel yet. from up top looks good not burnt or anything or corroded and old relay looked fine just replaced because I was getting intermittent power. the grounds by battery are ok and on thermostat housing haven't checked the one on heads. But I can turn key the relay will click and get power to pump turn key off and back on and then nothing for a couple more tries and then I might get power again. no security lights on. all dash lights and radio and dtr lights work cranks over fine just getting intermittent power to that relay

---------- Post added at 10:53 PM ---------- Previous post was at 10:37 PM ----------

and for the ground on the frame towards the rear by the gas tank, im asking what that wire is supposed to run to I haven't looked where it is running to but im not sure if previous person that did the fuel pump messed with it, is it supposed to run from the frame to the new sending unit harness we put in or does it run to the existing factory harness, or elsewhere. just want to make sure its going where its supposed to be, because my gas gauge was pegged full with old airtex pump in now it works with the new Delphi pump the gauge always works now but just intermittent power to the relay And would the oil pressure switch cause this intermittent power to the relay/pump, or do you suspect a burnt, or bad wire to the fuel pump relay itself, my mechanic really dosent do a lot of electrical wiring trouble shooting so any help I am thankful for, just sucks when its my only transportation

 

[SunlitComet]

after the relay primes the pump it will not let it do it again right away. it has a timer so to speak before it lets it happen again. Of course once the pcm sees the crank moving it is turned on constantly. the left frame rail along side the tank is the sole ground for the pump module. it goes directly to the pump via the existing chassis wiring and then thru the new spliced in connector that comes with the pump. a pegged full indication is the result of an open sender circuit. it is a lot of work but inspect the splices and the connector for contamination or debris of some sort. the oil switch passes power to it or does not. if the oil gauge is acting correctly then then the sender should not bringing on the issue. for the relay power feed you will need to pull up the relay box to see. grab a multimeter and measure battery power at the relay box post with key off and you should find the same voltage at the terminal in the block that feeds terminal 87 of relay at all times. when pcm is activating relay you should see system voltage on the terminal that has a dark green/white wire that feeds terminal 85 on the relay. You will often find those numbers molded into the relay body for identification.

---------- Post added at 09:49 PM ---------- Previous post was at 09:48 PM ----------

oh and check the fuse and terminals for it as well.

 

[ryanm1987]

well I cant get over to my truck until after work on Tuesday im going to call my mechanic and see if he figured anything out, it has to be simple truck ran and drove perfect and just died when I pulled into my drive way 2 new Delphi pump modules wire harness and fuel pump relay, it just doesent make sense to me. And I don't want to take a massive loss on money by selling it because it ran and drove perfect before it just died like it did

 

[ezdaar]

GM Fuel pump hotwire kit and stop the madness.

 

[ryanm1987]

ok guys its been a while with no damn luck, ive looked into the fuel pump hotwire kit but cant find one for my 97 Tahoe, the pump is new and works, new relay, im getting spark, and its not a security issue, I had my mechanic test the fuel pump prime wire with 12 volts and he said he got nothing from it, its like it intermittently primes on first key turn and then nothing if I turn key off and try again it wont prime and don't have power
he said the pressure at the pump is only going no higher than 35 psi, and no gas is getting to the engine. what would cause the pump test wire by the relay box not to work I believe that is my problem and ecm b fuse is also good, the new fuel pump harness Is hooked up correctly because my gas gauge works now lol. and we sanded down and rehooked the frame ground by gas tank. we are going nuts trying to figure this out and ive been stuck without a truck for 2 weeks. these damn trucks have so many problems and so unreliable, but for some odd reason I still love them. seems like someone is always having some kind of problem with obs trucks in general. And I have over $1500 in suspension, exhaust, tuneup ect. on top of what I paid for it and don't want to take a huge loss selling it for someone to do a simple fix and have a great truck with hella new parts. Also if anyone with experience with the fuel issues on these trucks lives close to me in Illinois or iowa please let me know I will gladly pay you to help me out, my zip code is 61201, rock island Illinois, my truck is in Bettendorf Iowa not far from where I live maybe 10 min away

 

[ezdaar]

Build one, its nothing more than a relay, wire, fuse, butt connectors and a couple female spade connectors.
No different than a fog light or electric fan relay kit.

 

[ryanm1987]

well a little more info I went to my car today and put direct battery power to the fuel pump wire the pump runs but still wont start unless I spray starting fluid in the intake which I heard is not good to do me and my mechanic are super stumped, so In I don't think a fuel pump hotwire kit will fix my problem because I hotwired it and pump runs but still no start and I do have good spark. could my fuel pressure regulator or spider injectors play a role in this I don't want to buy new regulator and updated spider and get the same issue I just don't have that kind of money to throw into problems that arnt going to fix it any help will be appreciated and if anyone again is local to me and can help me out I will gladly pay you for your time and help, I just keep getting half ass answers to bypass it all but I did I ran straight battery power to the pump it runs but wont start and I don't have the money to convert to carb and different tranny which I see as my only option now but its ****** up because the motor and tranny work great it just died one day and now thish

 

[ryanm1987]

anybody else have any other opinions on what my problem could be or had the same issue, and like I said if anyone is very knowledgeable in obs trucks and is local to me rock island Illinois 61201, very close to davenport iowa also I would gladly pay you to help me fix my truck ive been without it for weeks and its my only transportation