On my '91 305 TBI, the engine cranks but won't run. I have spark and noid light shows ecm signal. I haven't had anyone around to see if there is actually any gas coming from injectors when I try to start. I do NOT hear the fuel pump prime.

I did run a jumper from the battery to the fuel pump test connector and still don't hear the pump. Barring a bad pump ground, doesn't this mean the pump is definitly bad?

 

I also changed the fuel pump relay.

 

What about the fuel pump relay fuse?

 

1) get some help - check fuses - if nothing, then
2) crawl under car, put ear to tank, have helper turn key to on, listen for pump (they are quiet - can't always hear from up top)
3) if nothing, then pull wire pack from relay, and connect the orange wire to the grey wire (jump it in the pack), crawl under car, have helper turn key to on, see if pump runs
4) if pump runs, then it's oil pressure sending unit - replace.
5) if pump not running, then it's bad pump

 

Thanks guys. All fuses are OK. The pump test connector shows test light continuity from bat pos to ground (thru pump or to short). So, unless it's shorted to ground somewhere under the car, I suspect the pump. I swear I used to be able to hear the pump run but tomorrow I'll follow your suggestions with a helper and post back.

 

Well, good news for me. Today I hear the pump run when orange to gray jumper is at relay pack, when I give 12V to pump test connector, and for 2 sec. when the ignition is switched on. No one was mowing their yard today so I could hear it. There is gas from injectors when cranking and I replaced the fuel filter. One thing I was unable to do on the shop manual diagnostic chart was to check voltage at the TPS because I'm not sure how to do it (which wire, connected or disconnected, etc.). I'd like to check that before I crawl underneath for the oil pressure switch but if I don't find out then oil switch it is.

 

The oil pressure sending unit should be just above oil filter - don't waste you time with advance or autozone parts on this - get Napa, carquest, something decent - my autozone unit crapped out in less than 500 miles!

 

Check all constant 12v wires coming off the battery that feed the ECM and fuel pump relay for breaks or repairs.

One of these wires was hacked by the previous owner of my 87 GTA and it only cost me being stranded twice, two tow bills and a replaced fuel pump ($570.00+) to find it!

 

And the winner is...oil pressure switch. Thanks to all.

 

As someone that's done 2 fuel pumps in the last 6 months - trust me - that was much easier! Glad it worked out.

 

Amen brother, leave it to another Carolina boy to come up with the answer!

 

I don't know about all that LOL.

I like guessing at solutions to problems here - It's like sex - I think about it all the time, and just sometimes I get lucky!

However, what little bit of info I do know about F-bods, I learned from everyone else here! And I greatly thank everyone on TGO for that!

 

Don't get too happy just yet. The oil pressure switch by itself will not kill your pump. You can disconnect it and if the f/p relay is in working order, your pump should still run.

 

And before anyone starts saying that the above is wrong...

https://www.thirdgen.org/forums/elec...itch-only.html

https://www.thirdgen.org/forums/tech...fuel-pump.html

Tis a fallacy that has been disproven a zillion times. If you want further info, bug Trickster or Vader.

 

Red Devil,

I too didn't see from the wiring diagram how the o/p switch could be the solution. The Chevy service manual states that the switch merely keeps the pump working in case of relay failure. But when I had looked at everything else, heck I'd try anything. We'll it worked for a few days and then had the same problem again. I siphoned out almost all of the gas and refueled at a known good station...problem solved, bad gas. It hasn't hicupped since. I can't help but fell a little fuelish about not coming to that conclusion earlier although I learned alot during the process. Oh well, at least now I have a new fuel filter, o/p switch, spare pump/fan relay, injector noid light, and efi fuel gauge. While I was at it, I did a new intake gasket job to stop that pesky little oil leak at the back of the intake!

Thanks to all who gave advice to this and other "won't start" posts. I can always count on TGO members for help.

 

As a side note, I can't say how handy it was to add WinALDL to my "toolbox". It's a cheap and easy way to, at the very least, check some of those sensor voltages (and a whole lot more!). I would say everyone ought to have some type of diagnostic scanner/program at a minimum. I would have saved me a lot of time and head scratching.

 

Maybe someone has an Idea for me at the connector by the tank.....Key on 11.2 Volts constant....Cranking it drops to 1.52 Volts.... Has me baffled Is that correct Cranking voltage?

 

During cranking, the starter has a rather large draw. It wouldn't suprise me to be correct, though I've never actually measured the volts during cranking.