Toby Van Horn

I have no fuel pressure, there is no power to the wire that gives power to the pump. Is there a fuse? I saw a relay under the hood.

Also if there was an ignition switch / lockout issue is it possible that it would give no power to the fuel pump?

Any help would be great.

Thanks

lucky131969

The fuel pump will only have 12 volts at the connector for 2 seconds when the key is turned to on. If the motor does not crank, or start, there is no output from the crankshaft sensor to the PCM, and it will not allow the fuel pump relay to stay engaged....so the voltage at the pump drops out.

You can check the fuse and relay with the schematic below. You need to make sure the fuel pump relay is engaging. To test the circuit from the relay socket to the pump connector, you can install a jumper wire in the relay socket. The jumper should be installed from 30 to 87 as labeled in the pic below. There should be a good ground on 85, and 12 volts is supplied by the PCM at 86 when the ignition is turned on.

Toby Van Horn

thanks

Toby Van Horn

so I do not know where to go from here, 30 has power, 85 does not have a good ground 86 does not have power when ign is on.

The car ran fine, then died, no fuel pressure. Any help would be great. Where does this relay get its ground? If no power from the PCM is it a bad PCM?

Toby Van Horn

sorry looked at it wrong, the only one with power is 87 when the ign is on. All others have no power, tried to jump and nothing coming out of the pump. No ground on # 85

Toby Van Horn

looked at codes and saw bcm codes
B2721 PASS-Key Detection Circuit
B2723
do not know if they are related, in the past the security light would periodically come on

lucky131969

Any other important info you'd like to share?

If you are checking at the relay socket(i.e relay removed), you should have the following(as label in the pic):

Measurements taken key to on position:

30 = O volts
86 = 12 volts ( for two seconds)
87 = 12 volts ( constant)

Measurement taken key to off position:

85 = Ground (should be low resistance i.e. .3 ohm or below)


No offense, but I'm questioning how you are taking the measurements, since all these things failing at the same time are unlikely....unless the car has been in an accident.

When you jump 30 to 87(of the relay socket), you should have 12 volts at the fuel pump connector.....unless there is a wiring problem.

There should be a ground at 85.....unless the ground is corroded at SP122 (located under the battery tray), or G105 (left lower side of block) is damaged.

There should be 12 volts at 86 when the key is first turned on, unless the PCM is not providing it.


http://forums.corvetteforum.com/c5-t...e-grounds.html

Toby Van Horn

I will check again.

The only thing that happened is that I was driving it and it died. When I looked at the fuel pump connecter on the fuel pump side the terminal that gets power for the fuel pump was pushed in. I replaced the end as I thought it was the issue.

I then checked the relays last night. I did not have someone help me so I may have missed the one that gets power for 2 seconds. I tried and tried and did not get a ground to register on the other one.

I will take the battery and tray out to look at all ground connections as I guesse that may cause an issue.

I need to spend more time on it and I appretiate the diagram as it shows me what should be there.

Toby Van Horn

codes were "H" and I think un related

lucky131969

While they are unrelated to this specific issue....those codes will leave you stranded for sure. One thing at a time........

Toby Van Horn

did further testing, I must not have had the pin connected right in the junction box. I need to check the wiring back and grounds at the pump.

Toby Van Horn

all the junction box power / ground ect work fine. Will keep you posted.

lucky131969

Ok, that's good. That means, if you jumper 30 to 87 of the relay socket(with the key on), you should have 12 volts at the pump connector continuously.

Toby Van Horn

OK, and according to my manual A and C at the pump should have power and B and D should be ground.

Toby Van Horn

have power and ground at pump, I guesse the pump is no good

ramcharger

Are you sure about this? What was the final solution to the bad ground? (sorry if I didn't read it properly in the thread)

I went through this and found out the pump was not bad, after buying a new one. If you want a C5 application walbro 255 let me know.

Toby Van Horn

good point, were are the best places to check grounds.

FordDefector

I know this is an old thread, but maybe someone can help me.
I have an '01 C5 and only have 5 psi fuel pressure with the key on. It has a Racetronix fuel system with the harness that runs power direct to the pump. It was installed by the previous owner and I tried contacting Racetronix to get instructions or a wiring diagram and never heard back from them.
The car ran fine for a long time after I bought it. It just quit on me one day and now no fuel pressure.
Fuse and relay both tested good.
On the factory fuse block I measured voltages and I have no voltage on 87 where I should have constant 12V.
I do get 12V on 86 when I turn the key on.
Does anyone have info on how the Racetronix stuff is wired in?
Any ideas would be appreciated.

lucky131969

If you are doing the voltage checks per the pic I posted, and there is not 12 volts at 87, that suggests that the fuse is not getting 12 volts either. Do you have 12 volts to fuse 13, with the key in the on position?

FordDefector

I was able to find the direct power harness that goes from the alternator to the fuel pump. The 20A fuse there was melted. It apparently had gotten very hot before it blew, almost like when you have a big amp with a power wire that is too small, but it's 10 gauge wire.
I replaced it and ran the car for a while and the fuse didn't get hot and had good stable fuel pressure.