New Transmission & Fuel pump failure

[K5pilot97]

Picked my 89 Jimmy up yesterday after transmission rebuild. Made it about two miles and it quit on me. I had it towed home and started troubleshooting. Fuel pump isn’t turning on (pumps about 1.5 years old) so I did the following.
-Replaced pump
-Replaced fuel pump relay
-Checked all fuses

neither one worked. Is it possible the transmission shop broke something when installing the new trans? Am I missing something?
My plan is to trace the wiring harness back from the tank. If it is intact I’m thinking the next step is replacing the ECM.
Any suggestions are welcome.

-Gerard

 

[Wes Harden]

There is a test wire near relay, provide battery power if wiring from relay and pump are good fuel pump will run.
Look down by the oil filter. You should find an oil pressure sensor there make sure it is connected.
Trans shop might have bumped that.
This sensor is part of the fuel pump circuit, and will open the circuit if engine has no oil pressure.

 

[swettysblazer]

Wes is correct, there is a fuel pump relay on the firewall right to the right of the heater box. There is a red wire coming off it with a spade connector on it. Jump power to it and you should hear the pump kick. Times 2 on the oil pressure sensor as well. There is a cutoff built in if the sensor sees 0 oil pressure the fuel pump shuts off. Also double check your ECM B fuse.

 

[1-ton]

Like said...check the oil pressure/fuel pump sender. If the transmission shop removed your transmission, and the engine leaned back far enough to lay the oil pressure/fuel pump sender against the firewall then there could be some damage back there.

 

[6.2Blazer]

As said above, there is a chance some wiring could have been damaged during the transmission R&R. I would do a visual inspection of the wiring harness and sensor locations to look for any obvious issues. The other quick check is simply put a test light or multimeter at the power wire at the fuel pump and then turn on the key and see if you have power there. If you are getting power to it then obviously there is no breaks in the wire.....and if no power then a strong indicator there is a break in the wire or some other issue upstream of the fuel pump.

 

[K5pilot97]

I cannot thank y’all enough for the help. I looked for the oil pressure sensor but couldn’t find it. Is it possible that the sensor in the picture is the oil pressure sensor? Located on the passenger side of the block by the starter.

 

[Wes Harden]

That is the knock sensor. Should set a code if it is not connected

 

[swettysblazer]

I cannot thank y’all enough for the help. I looked for the oil pressure sensor but couldn’t find it. Is it possible that the sensor in the picture is the oil pressure sensor? Located on the passenger side of the block by the starter.View attachment 394288

Look right behind the distributor towards the driver side of the truck.

 

[dyeager535]

There is a cutoff built in if the sensor sees 0 oil pressure the fuel pump shuts off. Also double check your ECM B fuse.

That is not how it's wired. The pressure switch is redundancy for the relay. The truck will start and run with either the relay or pressure switch bad. But a bad relay will result in delayed start times as the oil pump has to build enough pressure cranking to close the switch.

You cannot easily test voltage at the pump without bypassing the relay as already mentioned with the red wire off the relay. The ECM only runs the pump for a few seconds key on/engine off, at which point there would be no voltage showing, even if working properly. Run 12V from the battery directly to the fuel pump relay red bypass wire as mentioned previously. If the pump doesn't run, there is something wrong with the wiring between that point and the tank. Or the pump is bad.

The circuit is very, very simple. Understand how it works, and diagnosis will be much easier.

If you like, you can read GMs statement in this post. Picture of the manual explaining what I said regarding the switch at the bottom: https://ck5.com/forums/threads/fuel-pressure-relay-question.324927/page-2#post-3625396

 

[K5pilot97]

Thanks for everyone’s help. The fuel pump was shot. Swore I would never cut an access panel for the pump but that’s the second one in two years so panel it is.

 

[Wes Harden]

wow 2 in 2 years what brand if you recall ?

 

[cheavyk10]

When I swapped the dead pump out for a new one in my blazer, it was recommended that I change out the pump wiring harness ( the short pigtail in the sending unit) as well.
Well I'm cheap and the harness looked good so I didn't.
About a month later the pump quit again, and guess what the culprit was. Nothing like dropping the tank twice.

 

[K5pilot97]

wow 2 in 2 years what brand if you recall ?

The first was some cheap pump from a Amazon. The second that I just installed is an AC Delco that was just north of $200.00. The reason the new pump wasn’t working after I replaced it was the fuel pump relay they sold me as the wrong one for my truck.