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Ok so I have searched and read on this and the most common is the missed ground wires, so I double check those and passenger side large ground and small wire, and driver side ground strap and small wire, are all hooked up. Now that is out of the way here is the issue:
Car cranked fine prior to header install. Car cranks over just fine but the fuel pump will not kick on. I have checked the fuse block and it is getting power to the fuse, and the relay is new. I did have to take intake off to remove the air pump hose. Everything appears to be hooked up properly but maybe I missed something here. I do still have the air pump hooked up at the moment, planning on removing after this is worked out. All 4 O2 sensors are hooked up. I have no related codes, but the battery was unhooked the entire time and it took a couple weekends when my son and I had spare time to get it done.
Any idea where to check or probe to see where the power loss is?
No the pump does not run, disconnected the fuel line from the rail to verify no fuel delivery. I have test light and multi meter. I'm pretty knowledgeable on cars/boat mechanics in general, just my first C5 so I'm learning the ins and outs of the car.
No the pump does not run, disconnected the fuel line from the rail to verify no fuel delivery. I have test light and multi meter. I'm pretty knowledgeable on cars/boat mechanics in general, just my first C5 so I'm learning the ins and outs of the car.
Ok, great !!…not to hard to diagnose…being that installed headers it “might” be a ground issue with the relay so we will look at that first…take your test light and connect it to battery POSITIVE…remove the relay and probe all 4 of the relay terminals…the test light should light on 2 of the terminals…if the tip of the test light is fat don’t force it or you may spread the terminals apart…use a safety pin or similar…you can try to jump the load side of the relay…87 and 30.
Ouch !!…85 is control side ground…J11 in wiring diagram…the test light should light on J12 going to the pump because you will find a ground through the fuel pump windings to ground so the test light should light…I think 30 is load side feed so see if you have power there with key ON…if so try jumping 87 and 30…if pump doesn’t run we will have to look at the connectors in the back…C402…since you have an 04 you have the FFS fuel system…fuel pump is on the top of the drivers side fuel tank…earlier C5’s at the bottom which are easier to access…another thing you can do is connect test light to ground and probe terminal 86 while you turn the key on…light will come on for 2 seconds and go out…this is fuel pump relay control…G401 (pictured) is a ground on the left frame rail inside the rear left tire…check that also !!
Every relay will have 2 power sources which would be 87 (or 30..can’t remember) with key on through fuse 30 and 86 will only light the test light for 2 seconds and go out when the key is turned on…if you jump 87 and 30 with key on pump should turn on continuously if power is good to the pump !!
So 85 has constant ground, 87 has constant power, 86 has 2 sec power. 30 has nothing either way, however when I disconnect the neg battery cable, but leave the test light hooked to the neg battery terminal, the test light lights up.
So 85 has constant ground, 87 has constant power, 86 has 2 sec power. 30 has nothing either way, however when I disconnect the neg battery cable, but leave the test light hooked to the neg battery terminal, the test light lights up.
I know you said you checked all the grounds. You also mentioned you removed the AIR system hose. There is a 15mm hex on the drivers cylinder head that holds that bracket down. That bolt also holds down the ignition coil ground. Very/validate that that bolt was retighten to hold down that ground.
I know you said you checked all the grounds. You also mentioned you removed the AIR system hose. There is a 15mm hex on the drivers cylinder head that holds that bracket down. That bolt also holds down the ignition coil ground. Very/validate that that bolt was retighten to hold down that ground.
Are you referring to the bracket on the back of the engine? If so I didn't undo that bolt. I just cut the bracket off with a dremel. I do not recall there being a bracket on the side of the head, did I miss something?
Are you referring to the bracket on the back of the engine? If so I didn't undo that bolt. I just cut the bracket off with a dremel. I do not recall there being a bracket on the side of the head, did I miss something?
The only ground on the left engine block is G105 which is near the left front O2 sensor…that is the control side ground which we checked and was good…85 !!
C5 Diag, where is the plug for the fuel pump on these? I should be able to pull it and check for power and ground there correct? Assuming its just a 2 wire plug, positive and ground.
Yes that is the bracket I'm talking about. Its on the back side of the head. That bolt holds down that bracket and a ground. The bracket is not solid. It is sort of slotted it can be loosened without unbolting the bolt bolt. When that happens the ground may have lost contact. This could have happened from handling or the vibration from dremeling it. If your confident thats not the case then we can rule that out.
edit: apparently its called the G107 ground.
Last edited by chain_5001; Mar 29, 2023 at 11:05 PM.
C5 Diag, where is the plug for the fuel pump on these? I should be able to pull it and check for power and ground there correct? Assuming it’s just a 2 wire plug, positive and ground.
I’m having trouble accessing my Alldata account…I’ll get you the connector views !!
Yes that is the bracket I'm talking about. Its on the back side of the head. That bolt holds down that bracket and a ground. The bracket is not solid. It is sort of slotted it can be loosened without unbolting the bolt bolt. When that happens the ground may have lost contact. This could have happened from handling or the vibration from dremeling it. If your confident thats not the case then we can rule that out.
edit: apparently its called the G107 ground.
G107 is the coil pack grounds (both banks) and not associated with the fuel pump circuit.
C5 Diag, where is the plug for the fuel pump on these? I should be able to pull it and check for power and ground there correct? Assuming its just a 2 wire plug, positive and ground.
C412 is where you can apply power and ground to pins A and D to see if you can power up the pump !!…if good you will have to backtrack to C402 and then to C140 which is near the battery coming from the fuse box.
No start after header install
