v10viper04

I am trying to get the car running after she sat all winter. It was originally a 305 TBI car, now it has a 357 and 600 CFM holley on top instead. The problem I have is that when I turn the key forward the fuel pump will prime but when I start the car the pump doesn't run. (I know that because i have a fuel press. gauge after the FPR. She runs a TPI pump to a regulator that lowers the pressure to around 6 PSI i believe. It has never had this issue before, oil pressure reads normal on the dash. Could the sender be faulty to only the fuel "pump on" circuit? The prime fills the bowls in the carb b/c the car will run for around 20 seconds then just dies off when the fuel in the carb is used up. The ECM is still hooked up and has been for a long time since the swap to carb. Never had an issue with the system I have until now. What do you suggest I do? Replace the oil pressure sender?

vetteoz

iTrader: (13)

Pull the connecter off the switch , jumper the terminals in the plug and see if the pump runs
If it does , you have found your problem
If it doesn't you have other problems , start by checking for 12V at the plug

v10viper04

Will try this when I get up today. Thanks a lot.

v10viper04

Problem has been solved. It was in fact the oil pressure switch. I pulled the connector and jumped 2 of the 3 leads and it primed up. So I changed the oil pressure sender and it is all good now! Thanks for the tip!

Wickydooda

iTrader: (1)

If you want to run an oil pressure sender from the port next to the distributor, and cap the 3 prong oil pressure sender port, can you just splice a couple wires from the factory oil pressure sender 3 prong plug into the distributor-located oil pressure sender and still have it work like factory?

Abubaca

iTrader: (3)

So I know this is an old thread, and I'm not an electrical genius by any means. Also, I'm not trying to dispute what the OP said fixed his problem.

...however...to my knowledge, you don't NEED oil pressure for the pump to run. When you have oil pressure, it acts as a secondary source of power for the fuel pump. I think if you look at the schematic, you'll see that. (don't have it in front of me). Point being you can remove the oil pressure sender and you should still have primary power to the pump, just no secondary power.

Abubaca

iTrader: (3)

...but to answer your actual question....I don't see why your idea wouldn't work. Oil pressure throws the switch and send power to the pump. Don't think it cares where the sending unit is actually mounted. Just want to make sure it's the same signal voltage as the GM sender.

Wickydooda

iTrader: (1)

Abubaca, I went to the hardware store and made a Tee adapter so I am using an aftermarket fuel pressure sending unit with gauge and the stock 3 prong oil pressure sending unit, both of which are connected to the same port next to the distributor.

So far so good and the car seems to be delivering fuel better now. Since this is a brand new engine I still have a few things to do until I can give an accurate report on my tee adapter, but at least the inline fuel filter next to the carburetor is now filling up.

And to my knowledge and experience with my 1989 Firebird Formula 350 TPI, you need at least 4lbs of oil pressure or else the ECU will disable fuel flow from the fuel pump. This is also according to my extremely detailed field service manual from 1989.

Wickydooda

iTrader: (1)

I made an adapter Tee to run both an aftermarket oil pressure sender (because the new oil pump will run at a higher pressure than the stock gauge will read) and the stock oil pressure sender (in order to keep the ECU from shutting off the fuel pump due to no reading of oil pressure), and they are both plugged into the oil pressure sender port next to the distributor. The other oil pressure sender port on the driverside of the engine block has a plug in it still from when my machinist put it there. Easier to make a $20 adapter to run both senders than it was to fit a wrench down there to remove the plug. Now that the ECU is reading the oil pressure it does not shut up the fuel pump in "run" mode. Car runs fine now.

Abubaca

iTrader: (3)

I would bet lunch that you don't need oil pressure. The diagram I have shows it not being necessary. I wouldn't be a weeks pay....but I'd bet lunch!

Wickydooda

iTrader: (1)

I'm thinking Arbys. As soon as I hooked up the stock oil pressure sender, the fuel pump started pushing fuel to the engine when the engine was on. That was literally the only change i made between it not starting and it starting on the first crank. #5 with a side of fries. Jk
A simple test you could do to see if I'm correct is just unplug the pigtail on your 3 prong oil pressure sender and try to start the car.

Abubaca

iTrader: (3)

I'm staring at the schematic and I can't see how it's necessary. ....I'm running a Holley ECU, so I can't try that.

Abubaca

iTrader: (3)

For the record, Arby's fries are delicious, but the large fries have like 1500 calories!