Relay not showing power 94 Sonoma only for 87

Edited the question for clarity and the correct name of the model!

It is worth a try. Back of the engine to the transmission should be the same. Others have done engine swaps in the link.

https://www.google.com/search?q=will+a+engine+from+a+94+sonoma+rwd+swap+with+a+94+sonoma+4wd

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Pull the fuel pump relay. Jump pins 30 and 87. 30 has power all the time, 87 is the fuel pump. The bottom of the relay will show you which ones to jump.

Check in main fuse block with other relays. Should be labeled. Relay kicking out may be caused by overheating = bad fuel pump or dirty filter. Test fuel pressure too.

Easiest way is to swap in another relay. Many others on the car will be the same relay, same part number.

To test a relay, put voltage across the coil side of relay with jumper wires, and check that the power side of relay then shows continuity. If it does, relay is good.

Maybe the oil pressure sensor or switch that keeps the pump running after engine started.

If you jumped 87 and 30, it should have turned the pump on. If those are the right terminals at the fuel pump relay, and I think they are. Those are usually the right ones.
Try this: one of those terminals should be hot at all times, the feed for the fuel pump. Check for a hot terminal there. If the feed for the pump is lost, it will probably be a blown maxi fuse or fusible link supplying that relay's power feed.
If it still starts and dies, check the fuel pressure. If pressure is at specification, both key on, engine off and with engine running, it could be an ignition problem (crank sensor?), not a fuel problem. But you may be right to pursue the oil pressure switch or the pcm, if the pump was still running as you say at the fuel filter .

At terminals 85 and 86 of the pump relay, you could check for the computer signal on one of those with the engine cranking. With engine cranking, the computer sends a signal to the coil side of the relay, either the 85 or 86 terminal, and the other terminal will go to ground. Do you have a test light or voltmeter?

on a replay there are 2 particular connections that cause that. When you look for numbers on that relay you will find the numbers 30, 85, 86, 87 and 87a. The problem is their is power going to 85 or 86 (they are the 2 control terminals that control the relay). that should not be. basically 87a allows power to go through the relay when the system is shut OFF, Terminal 87 is the path of power that turns on whatever is connected to it. Now... 85 and 86... one of them is ground... the other power. Typically 85 is ground and 86 power. Now to better explain what is going wrong. you have a connection that feeds power to 87a. that power is powering 87 which powers 86. when power is turned on at 87... it turns on 86... that causes the relay to pick up an break the connection of power to 87a while at a fraction of a second later making the contact to 87. So... the path of power is turning the relay on and off all by itself, LOL. I know this is confusing, sorry. But I hope it helps

If you turn the key on and do not hear the fuel pump run at all after you have replaced the computer then i would look at the (ASD) relay (auto shutdown relay) for the problem. Remove the relay from the power panel. To test the relay,use a ohm meter and connect one end to the #85 and the other end to #86, the resistance should be between 70/80 ohms. Then check continuity between terminals #30 and #87a. The meter should indicate continuity. Then check for continuity between #30 and #87, the meter should not show any continuity. Then connect a jumper wire to terminal #85 and negative post on battery and connect the other jumper to terminal #86 to the positive post of battery. By doing this it will energize the relay and during this time connect the ohm meter between #30 and #87. This should show continuity. If not replace the relay. Hope this will help you.

see if you have power at the relay housing in relay fuse box for pins 87(look on relay shows #next to pins)with key on check for power at pin hole 85 or 86.You can also put jumper wire from pin hole 30 to 87 without key on fans or fan should start(keep fingers out of fan area)

When was the last time the fuel filter was chg.? If thats not an issue best to get a fuel pressure test.

I have the same problem with my 95 blazer I have heard that it is the fuel pressure regulator. That is the next part I will be replaceing.

Good luck to all.

If any one finds any thing out please let me know!