aaron7

iTrader: (7)

Ok, first off, this happens when I'm not low on gas as well!

I'm sure at one point you all have gone around a corner, fast, with low fuel. You know that feeling when you push the pedal and the motor acts like it's off? That's what I get all the time around corners!!

It acts like it's out of gas... but I'm not. So, what might it be?

On another note, is there an aftermarket company that makes the baffled 1LE tank?

Stekman

make sure there are no loose wires that are swinging around and grounding out when you round a corner.

Air_Adam

Float level?

Stekman

his info says TPI....

Unless this is some magical new mod....

Crazy canuck

Rustydawg

If you lose oil pressure pulling a fast corner the fuel pump will drop out for a second since it's fed power through an oil pressure switch.

Oil level on the low side? It could be plastered against the side of the pan's sump when you crank the 'high G' corners.

Stekman

Common believe, but not entirely true.

It is nothing more than a back-up to the fuel pump relay. If the relay goes out, the switch will power the pump, assuming 4 psi oil pressure.

Rustydawg

A backup? Why both? I thought the relay engaged the pump to prime the fuel rails, then once the engine is running the oil pressure switch maintains power to the fuel pump.

This way if the engine lost all oil pressure there would be no fuel delivery, safeguarding the engine from catastrophic damage.

Stekman

Yea, it's a common thought, like I said. But, if you look at the wiring, you can see what I mean.

For the sender/switch, there are 3 wires in. A power in, power out, and the wire to the gauge. A switch alone just has the power in/out. If you look at the schematics, you will see that the power out wire is spliced in with the power out from the relay. So, once 4 psi oil has been reached, the switch closes, completing the circuit, allowing power to flow from the in to the out. It is in no way wired with the relay.

aaron7

iTrader: (7)

I thought all FI cars had the tank mounted fuel pumps? There's a secondary one on the motor?

Rustydawg

Okay... So if your TPI engine all of a sudden loses all oil pressure what happens? Are you saying that the ECM is driving the fuel pump relay all this time and the engine continues to get fuel and spins itself dry?

I say the oil pressure switch goes open (due to loss of oil pressure) and the fuel pump stops running.

Similarly, if you go around a high-G corner and starve the oil pump pickup of oil momentarily, the fuel pump will not see power for a moment or two - enough to cause the engine to stumble.

AARON7 - do us a favour and pull the connector off the oil pressure switch while the car is idling and tell us what happens...

aaron7

iTrader: (7)

Oil pressure switch... that's the one on the driver's side of the block above the oil pan right? Or is that the one on the back of the intake manifold? I always get the sending unit and the switch mixed up!

Stekman

For the oil pressure switch, either off the china wall (behind dizzy) of above the oil filter:

1 wire: sender for gauge
2 wire: switch
3 wire: combination sender switch

aaron, only the carbureted engines had a mechanical, cam driven pump located on the block. They (mechanical pumps) are incapable of producing enough PSI to support TPI.

aaron7

iTrader: (7)

Right, so that's why I'm confused as to why oil pressure has anything to do with my fuel delivery!

Thirdgen89GTA

iTrader: (5)

Hmm.... this topic has interested me a bit.

My 89' GTA does NOT have anything near the dizzy back there. I've seen it on other cars, but I only have the Oil pressure sender/switch above the filter. Nothing near the dizzy behind the intake. Should I have one?

Or is it something that was eliminated later on?

aaron7

iTrader: (7)

Not that I know of... it should be down on the block behind the intake right in the middle of the motor. It is a cylinder that stands up...

My friend has a 93 Blazer with a 350, and it has it!

Thirdgen89GTA

iTrader: (5)

Its not there. I've done heads/cam/intake/headers on my car. I had it torn down to the short block and I do NOT have anything on the back of the block. Not a single thing.

If thats the sending unit then no wonder I can't find it.

This is very odd. Not so odd that my car has NEVER read oil pressure correctly. When the car starts the oil pressure gauge in the car just pegs itself.

Stekman

In this case, it doesn't.
In later TPI models, the unit behind the dizzy was eliminated and was changed (location-wise as well as component-wise) to a piece located just above the oil filter. It should be a 3-wire sender plugged in. If so, you are fine.
Once you find this sender, try replacing it. It most likely has an internal grounding problem and isn't operating correctly.

Thirdgen89GTA

iTrader: (5)

Figures thats why I couldn't find the sender. People kept telling me it was near the dizzy on the block, but I kept saying, "There is nothing there!"

Sounds good to me.

DuronClocker

iTrader: (1)

Even when you turn your car off, the pump runs for a few seconds to prime it, so the oil pressure has nothing to do with the fuel pump being on. The pump should stay on the whole time.

I've had this issue when low on gas, but never any other time. Nevertheless, I'm interested in this 1LE baffled tank. What I'd really like to do is put a LS1 plastic tank into my car...are those baffled?

8Mike9

8Mike9

The fuel pump pickup may have fallen out, or the sock is clogged, etc.
Other suggestions to check wiring as well as battery hold down, is important.

Rustydawg

8Mike9, Stekman...

This is my last post on this topic as I don't want to hijack a legitmate thread arguing about the oil pressure switch.

Got a Haynes manual close by? Turn to page 10-22 and you can see that all current to the in-tank electric pump goes through the oil pressure switch! This applies to 1990 and later V8 TPI models. So... no oil pressure, no fuel pump current - simple as that.

If you look at page 10-21 ('89 and earlier models) you will note that any current from the fuel pump relay goes through the oil pressure switch to the electric fuel pump. There is a connection from the ECM to the fuel pump to prime the fuel rails. Apparently in later models they skipped the priming, since cranking speed should muster up the relatively low oil pressure required to close the oil pressure switch and provide fuel.

Don't believe me? Try unplugging the oil pressure switch and drive around the block.

RBob

iTrader: (1)

Please see attached image. This pic is from the '91 GM Helm service manual. The fuel pump relay and the oil pressure switch are in parallel. Either one will enable the fuel pump. Neither one can disable the fuel pump on it's own.

The ECM will enable the fuel pump relay as long as it receives distributor reference pulses. The oil pressure switch will enable the fuel pump as long as the oil pressure is above 4 psi.

RBob.

86IROCTHD

hey why do i have both sensors... one behind the dizzy and one above the filter? its an 88 trans am..... which one does what? and also if it kills the pump is it gonna set a code?

aaron7

iTrader: (7)

I have both as well, and mine is an 88.

Stekman

1 wire: Oil pressure sensor for gauge
2 wire: Oil switch for fuel system
3 wire: Combination sensor/switch