Stormshadow GTA

I was stopped at a light and i noticed with horror my Oil pressure guage was at 0 .so i freaked out gave it some gas and it went back up.Does the computer shut off the fuel when oil pressure is 0.Can the computer not notice it and keep it running on 0 pressure until it blows obviously.I heard the ECM cut fule off if oil pressure dropped to 7 psi or less

------------------
1987 Trans AM GTA
305 5SPD
Hypertech airfoil
gutted maf
kn filter
High Flow Cat,
3"Walker pipe
Dynomax Super turbo Muffler
TB Coolant bypass

"Three of the scariest letters you will ever see GTA"

[This message has been edited by Stormshadow GTA (edited June 18, 2001).]

[This message has been edited by Stormshadow GTA (edited June 18, 2001).]

rezinn

I think it may just be that your guages are getting old. All of mine go down when I stop, but they all go up when I rev the engine.

8Mike9

The ECM will continue to keep the FP relay energized as long at it(ECM) continues to see ignigition pulses and RPMs greater than 400? I believe.

So, the answer is no, there is no fuel cutoff safety device for low oil pressure.

Corry

Before you worry about that pressure buy a good mechanical Oil pressure guage and test it....the cars easily outlast the sensors I had gone motor shopping...and bought tools to remove a moter (cherry picker/stand/etc...thought my main bearings went...turns out it was the oil pressure sending unit located on the back of the motor near the distributer

------------------
Corry Lazarowitz
clazarow@voicenet.com
clazarowitz@hotmail.com
1987 Pontiac Trans AM (GTA?) 350 or is it a 305?! TPI
SLP 1 3/4" headers, 3" cat back (stock cat
MSD ignition.
MSD Blaster SS coil.
3.73 Rear end gears
Accell 8.8 Wires
Bosh +4 Spark Plugs (Don't know if they really help but hell!)
Holley AFPR
Race Built Automatic trans ('vette servo, shift kit, tightly packed clutches)--just needs titanium gears now!
Newly gutted cat (the car gutted it's own cat!)
Hypertech Chip (Just found out I had it! :eek
More soon when funds are avail...

Glen

There is a fuel pump cutoff switch by the oil filter that shuts the fuel pump off if the oil pressure goes below 4 psi. The ECM has nothing to do with this function. I just had to replace the oil pressure sending unit in my camaro for the same problem that you are having now. It scared the hell out of me when it happened too, before I remembered about the fuel pump switch. The gauge was reading 0 at idle but the engine was still running so I figured it must be at least above the 4 psi point. After replacing the sending unit (by the distributer on drivers side) all was well.

------------------
Red '85 MPFI V-6 T-5 Sport Coupe (bought new),now an IROC in sheeps clothing.
Rebuilt and installed '88 IROC L-98 TPI,700-R4,3.27 posi/disk rear,instrumentation, steering gear, and all suspension parts (even the wonder bar)
Mods:
IROC wheels, Hi-perf. rebuild on 700-R4,TCI sizzler torque conv.,B&M megashifter, L-98 .030 over,balanced,decked,blueprinted, SR Torquers, KB pistons,9.1:1 CR, port matched stock TPI, comp cams .450/480 206/210 cam, all free mods, subframe connectors, Edelbrock TES/jet hot coated, CATCO cat, Hooker catback, MSD 6A, airfoil, AFPR, K&Ns, polygraphite bushings all around, 1989 IROC memcal in summer, ARAP memcal in winter.

Stormshadow GTA

thanks for the info.i can relaz a bit now

------------------
1987 Trans AM GTA
305 5SPD
Hypertech airfoil
gutted maf
kn filter
High Flow Cat,
3"Walker pipe
Dynomax Super turbo Muffler
TB Coolant bypass

"Three of the scariest letters you will ever see GTA"

Kevin Irving

Don't get me wrong, Mike, I've read your posts on here for years and value your opinion but I don't think that's right. There IS a safety with the oil pressure switch providing a holding circuit for the fuel pump relay. That's the reason why many times the fuel pump continues to run for a second or two after the car is turned off.... the oil pressure switch is keeping the fuel pump relay energized. Obviously the ECM is not getting pulses. If there is no oil pressure within 4 seconds I believe after the car is started then the holding circuit to the fuel pump relay is opened, and the pump loses it's power. I MAY be wrong about this, but I don't think so.



------------------
Kevin Irving
85 Trans Am WS-6, 305 TPI, custom burned '86 PROM with '87 "165"ECM, Accel Supercoil & 8.8 Wires, Rapidfire #2 @ .055", MSD 6AL, 1.6:1 Roller tipped rockers, Homemade AFPR, K&N cone, no airbox, Aluminum Driveshaft, Wonderbar, TB Coolant Bypass, Ported Plenum, Descreened MAF, Syclone Fuel Pump, JET Airfoil, Mobil 1 synth in all but transmission.

http://www.geocities.com/transam85tpi/

8Mike9

Kevin,

I *knew* someone would read this

The oil pressure switch is in parallel to the FP relay, which gives an alternate path to supply voltage to the fuel pump in case of FP relay failure or in case of ECM failure...this way the FP will continue to supply power to the pump.

I had always thought that the oil pressure switch was a safety device, until I read in my Helms what I wrote above...As long as the ECM see's ignition pulses, the FP relay is energized".

I think with the correct PROM burning you could make it a safety device...i/e have the ECM only energize the FP relay for "x" amount of time after start up...or maybe until the ECM first see's closed loop, then drop the FP relay enable signal and have the oil pressure switch take over control...now IF it does this somehow, it's not documented anywhere that I can find, and since the voltage through the FP relay and the voltage suppplied to the oil pressure switch both come from the same line, testing it to be sure would involved cutting wires or pulling wires from connectors to verify.

But to be 100% sure in either case, maybe we can head over to the PROM board and have someone look in the PROM and see if the FP enable signal is always present when the engine is running?

RB83L69

Mike, I believe if you look at the schematic for that circuit, you will find that the relay supplies hard battery to the FP when it's in its "start" position, and battery through the OP switch when in its "run" position.

On your own car you can test it easily enough... just unplug the OP switch (not the gauge sending unit, the other one) while the car is running, and see if it kills the motor. It should.

------------------
"So many Mustangs, so little time..."
ICON Motorsports

8Mike9

According to the schematic for code 54 in my Helms, battery voltage runs through a fuse, then to "D" on the oil pressure switch and to "E" on the FP relay socket.

Pin "C" (output of the OP switch) and Pin "A" (output of the FP relay) both come together then through a bulkhead connector, then to the Fuel Pump.

IN the diag description for code 54 it says:

"There should be 12volts on CKT 120 for 2 seconds after ignition is turned on, or anytime refernce pulses are being received by the ECM".

This statement leads me to beleive that as long as the engine is running, the ECM will keep the FP relay on...I wonder if the reference pulses they are referring to are cranking (under a certain RPM) and not running (over a certain RPM)?

Pulling the connector on the OP switch would/should verify this...I can't do it though, I have my topend apart right now.

When I get it running I guess the easiest way would be to backprobe the fuelpump drive signal on A1 of the ECM and see if it stays high when the engine is running.

Just another "things to do" I'll add to my list

Corry

I just looked in my helm too, code 54 for Injection (port). I too see the wire running parallel to the FP relay...
I assume that current all runs one direction, and that isn't a countering force...however, if it were -12 v going through, and the switch *closed* when the FP dropped, it could shut off the fuel pump...Wish I had my scanner here, would scan the page and see what everyone thought...

Vader

You mean like this?:



Incidentally, Mike is correct.

------------------
Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader