How do I bypass the oil pressure switch?

[ArmyVet]

Hello again folks. I've been overhaulin my '87 S10 Blazer for the past few weeks. Everything was going smoothly until it left me stranded in the middle of the road. Luckily, I was not far from home. The engine cranks just fine, but it will not start. I replaced the fuel pump, spark plugs, ICM, cap, rotor, fuel filter and coil a few weeks ago. The coil is sending a strong spark to all plugs. Fuel is NOT making its way to the injectors. Upon further inspection I discovered that my oil pressure switch is busted. It litteraly came apart in two pieces as I tried to unplug the electrical connector from it. I was wondering if the oil press. switch can be bypassed or jumped with a wire. If so, can someone kindly instruct me how to jump the switch? My truck is stuck on a block thats not too great and I wont get any sleep tonight knowing that my baby is sick. TIA folks

[ArmyVet]

Anyone??

[ArmyVet]

Hello again. I was hoping to read a response from anyone out there that may be familiar with jumping/bypassing the oil pressure switch. I'm still not able to get my truck started. I've tried everything I can think of to trouble shoot this problem. Im getting very strong spark to all spark plugs, checked for power at the fuel pump connector at the fuel tank (no power there at all with ignition switch open), checked and replaced both ECM fuses, checked if the fuel pump relay was working (it is) and attempted to send power directly to the fuel pump via fuel pump prime plug that hangs on the firewall. still no luck. Im running low on funds so cant buy the OPS until monday afternoon. If anyone can please help me resolve this problem I would be extremely grateful. I need my truck Thanks in advance!

[jwvess00]

Hi there!

The oil pressure switch isn't strictly necessary to run the truck. The fuel pump relay is in parallel with the switch, so if the switch fails, the relay will still run the fuel pump.

That said, I don't remember off the top of my head *where* the fuel pump relay wiring and the oil pressure switch wiring come together. If it comes together at the oil pressure switch, then you may be in for some harness repair at the switch connector. If the switch fell apart, it makes me wonder about the condition of the connector, too.

Is the oil pressure switch two pins, or three? If it's two, just jump across them. I think the three-pin switch is for the oil pressure light as well as the fuel pump, right? If so, you should be able to find 12V on one of the wires. One of the others will be for the light/gauge. Ground one of the pins (that's not 12V! ) and see if it affects the light/gauge. One of them, when grounded vs. being open, will cause the gauge to move or the light to turn on/off. The other is fuel pump power.

[ArmyVet]

Thanks for getting back to me jwvess00. To answer some of your questions, my oil pressure switch is a 3 prong. It operates a gauge in the dashboard. I managed to replace the oil press. switch with a new one. As a test, I tried to start the truck; but it would not start. I replaced the fuel pump relay with a new one, once again, truck no worky! At this point Im ready to bang my head against the wall. Alas! After some brain storming, I went to the fuel pump connector to test for 12v power with a multimeter. My multimeter showed I was getting 4.89v at the pigtail connector at the pump...Huh!? Shouldn't the connector have at least 12v? Anyhow, After fiddlin' around with the connector, I had my trusty assistant (girlfriend) open the ignition switch so i can listen for the fuel pump to prime. It did. Great! The truck started right up. But, the voltage at the conector is still low. (4.89v +/-) Regardless, I was able to take the truck for a test drive around the block. I noticed that it wanted to stall out as if the fuel pump was ready to cut out. I gave it some gas and it stayed running. Hmmmm?? Do you think my ECM is the culprit? I'm about to head outside to continue troubleshooting the low voltage problem. At least I got the truck running again, Yay! I will recieve your replies to my Blackberry as you post. Gotta love a Blackberry! Thank you for your time and expertise.

[jwvess00]

Hi there!

The connector should have full battery power. I'm guessing you have a wiring fault (high resistance connection). Suspicious areas include the oil pressure switch connector and the relay socket.

When you measured the 4.89V, what did you use as a ground for the meter? I'd measure across the pump power and pump ground wires. If that's what you did, I'd give the pump ground wire a good look, too, in case it was damaged when the pump was replaced.

You can jump across the fuel pump relay to make measuring this easier since it will always be powered.

The ECM doesn't directly power the pump, so I doubt it's the ECM. All it does is energize the pump relay.

[ArmyVet]

Hey there JWV. Thanks for your quick reply. I'm in the process of jacking the rear of the truck up to thoroughly inspect the connections to the fuel pump. I will keep ya posted

Reply from my Blackberry Bold

[ArmyVet]

Hola again! Got it all sorted out JW. I hated doing it, but I dropped the fuel tank to inspect my connections and grounds. All checked out to be okay there. When I checked the wires with my meter I used the pump ground wires and the earth ground wire from the chassis. All checked out okay too. I reinstalled the fuel tank double checked the connections, disassembled and reassembled the main harness to fuel pump connector and made sure everything was squared away. I disconnected the ECMB and ECM fuses and unplugged the battery (before I dropped the fuel tank) in order to allow the ECM to reset. While I was so motivated to wrench on my truck like a runaway grease monkey, I went ahead and replaced the valve cover gaskets. one of them was leaking bad. FYI, the passenger side valve cover gasket is a B*%@h to do! . Anyhow, everything seems to be working as it should now. The truck is purring like a tiger. I'm happy and can move on with my life now. You have my sincere gratitude for your time and help. You've been an asset to me! Gracias amigo!! TTYS

PS: I will post pics of the truck this week. I've owned it for 12 years without a hitch. Until now. Guess it was time Cya