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Oil pressure switch or not? HELP! 1996 v6 s10


kevnchelle
08-12-2007, 04:40 PM
Hi this is my first s 10 its a 1996 v6 i got it from a friend, it was not running when i purchased it. Friend said that it was the fuel pump and had already purchased one. i put the fuel pump in and ended up having to run new wires to that also. now to get it to start i have to let it crank until the oil pressure gauge gets to 30 somtimes it takes about 3 or 4 minutes and the whole while the gauge jumps around erratically when it finally starts it runs great. i had a similar problem with my mustang and it was the oil pressure switch but looking in the haynes manual i cant seem to locate it. im sure it has one could someone please give me some advice..:banghead: otherwise it may just be the scrap yard for this thing!

16th hippy
08-13-2007, 02:56 PM
1996 v6, must be the 4.3. i think(could be wrong) the oil pressure switch is on the back of the block next to the distributor sticking straight up.

old_master
08-13-2007, 05:46 PM
Fuel pump operation:
The fuel pump circuits are designed to energize the fuel pump through a relay continuously any time the key is in the START position. When the key is in the RUN position the fuel pump will operate provided the engine is running. If the engine stalls, or is not running for any reason, the PCM/VCM will shut off the fuel pump after approximately 2 to 3 seconds.

The oil pressure switch will not cause the problem you are experiencing. There is a redundant circuit that runs through the oil pressure switch that supplies current to the fuel pump when oil pressure is above approximately 7psi. The way you are describing the problem, the switch is doing it's job. Check the fuses and the relay, that's where you'll find the problem.

kevnchelle
08-13-2007, 08:28 PM
Checked relay and fuse, both seem to be functioning properly. and if they were not, would the truck run great once started ? thanks for replying

old_master
08-13-2007, 08:42 PM
When oil pressure rises above 7psi and the oil pressure switch closes, it will supply the pump with the necessary current and the pump will operate. Here is a simple test to try: With the engine at idle, disconnect the oil pressure switch. If the engine stalls after a few seconds, the circuit for the fuel pump relay to the fuel pump is not supplying current to the fuel pump. Try it and post back your results.

kevnchelle
08-14-2007, 05:30 PM
thanks alot i will give it a try! and let you know

kevnchelle
08-15-2007, 06:10 PM
okay i unplugged the oil pressure switch and the truck did not stall..i just lost the gauge on the dash but i did find a loose screw on the distributor cap along with some walnuts..and it wont screw in huh maybe thats the problem? darn squirrels.

old_master
08-15-2007, 07:00 PM
The PCM is able to power up and control the fuel pump. The next step is to check fuel pressure. Here is the complete procedure:

Fuel pressure is not monitored by the On Board Diagnostic (OBD) system and therefore cannot set a Diagnostic Trouble Code (DTC), or illuminate the Service Engine Soon (SES) light.

Fuel pump operation:
The fuel pump circuits are designed to energize the fuel pump through a relay continuously any time the key is in the START position. When the key is in the RUN position the fuel pump will operate provided the engine is running. If the engine stalls, or is not running for any reason, the PCM/VCM will shut off the fuel pump after approximately 2 to 3 seconds.

Fuel pressure test:
Install the fuel pressure gauge to the test port near the distributor. Turn the key to the RUN position but do not start the engine. While the fuel pump is running, fuel pressure must be 60-66psi. After approximately 2 to 3 seconds, the fuel pump will shut off. Fuel pressure must remain between 55-60psi for several minutes. A drop in pressure below 55psi indicates excessive leak down. Likely places to leak are the fuel pressure regulator, the fuel lines under the upper intake manifold, a fuel injector that is stuck open, a leaking fuel line or connector, or the check valve in the fuel pump assembly.

Here is a link to an inexpensive yet ample fuel pressure tester: http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=92699 Accurate diagnose of an internal fuel leak requires additional test equipment. In some cases it requires the removal of the upper intake manifold.

Edit: The loose distributor cap screw is a problem, but probably not what's causing the hard starting. Use a machine screw and nut with a washer on top and bottom to secure the cap in place. Do not install an oversize screw! If the aluminum distributor housing is cracked, you'll need a new distributor.

kevnchelle
08-16-2007, 03:10 PM
where is the fuel pump relay located?

old_master
08-16-2007, 03:49 PM
On 1996 I believe it is located on the bulkhead, (firewall) just to the passenger side of center, under the hood. On later models they are located in the underhood fuse panel. Should be 4 wires going to it and one of them is grey. It goes to the fuel pump, and should have battery voltage when the relay is energized.

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