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Fuel Pump works only when Using OBDII tool?

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Old 04-16-2016, 08:15 PM
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Default Fuel Pump works only when Using OBDII tool?

Hi Guys,

My car did not start today (I recently rebuilt it, and it has been running, and never had any start up issues) but today was unique. I went to go start the car and the fuel pump didn't prime. I tried again, and nothing happened. (everything else was working as usual). So I began troubleshooting, I checked the fuel pump fuse underneath the hood and it was good, I swapped the relay with the A/C one right next to it and nothing happen still. So I went to autozone and got a diagnostic tool to see if it would give me any errors. but when I turned the key to the "acc on" position, I heard the fuel pump prime! I disconnected the diagnostic tool and turned the key again, and nothing. I plugged the tool back in, and it works. How can this be? what can I do to relieve this problem??

Thank you in advance,

2000 Manual Trans Am
Old 04-16-2016, 10:04 PM
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Anyone?
Old 04-17-2016, 12:22 PM
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What did you rebuild? Maybe a bad ground that is getting grounded through the obd2 port when connected
Old 04-17-2016, 12:57 PM
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What he said^^^^^^
Old 04-17-2016, 06:39 PM
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Thanks for the conformation guys! Last night my friend brought that up as well and I thought he had a good point. Now that you, both, said that as well also makes me feel more confident. Does anyone know where the ground should be? I can look in my Haynes manual, but if someone knows off the top of their head then that would save me some time!

Thank you!
Old 04-18-2016, 10:51 PM
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Default Fuel Pump works only when Using OBDII tool?

Rear of driver side (LHS) head.
Old 04-19-2016, 10:14 AM
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Originally Posted by Firebirdfan04
Thanks for the conformation guys! Last night my friend brought that up as well and I thought he had a good point. Now that you, both, said that as well also makes me feel more confident. Does anyone know where the ground should be? I can look in my Haynes manual, but if someone knows off the top of their head then that would save me some time!

Thank you!
Thats why I asked about what you rebuilt. Could be the grounds on the back of the DS head, should be 3 different ones if I remember correct.
Old 09-01-2016, 08:27 PM
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Thank you guys so much for the info. jrpimp00 I rebuilt the entire engine, so everything was disconnected. My freeze plug was leaking on the rear Driver side cylinder head (where those grounds are) and I must of loosened the ground or something when I was trying to pop out the freeze plug. I will check this weekend, and update you guys on the results. It may solve the issue!
Old 09-02-2016, 10:47 AM
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While you are in there check for corrosion.
Old 10-11-2016, 11:00 AM
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In for an update, my car has a similar issue but not quite the same. Fuel pumps prime but won't attempt to start unless OBD scanner is plugged in.

Not a high priority deal because I use a scanner for certain gauges like fuel level, fuel trim, timing and temp readings.
Old 10-11-2016, 04:08 PM
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Originally Posted by imma_stocker
...

Not a high priority deal because I use a scanner for certain gauges like fuel level, fuel trim, timing and temp readings.
Not so...

you don't want the sum of all currents passing thru this tiny little ground.
Old 10-13-2016, 08:36 AM
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Poked around and found a misplaced chassis ground while I was doing the ABS delete, line lock install, and manual brake conversion. Then found a DS head ground on the block and extra ground on the head.

Fixed those and relocated the extra ground circuit to connect: front block, rear block, PS head, shock tower, and battery ground in trunk.

Removed scan tool and she fired up. Didn't realize how picky these cars are about ground locations.



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