Hey guys,

As of late, its been bothering me how my truck cranks for a long time before the fuel kicks in ... I know my fuel system isn't to blame for this. I suspect my oil pressure switch is to blame for this slow start condition ..

Is this oil pressure switch the one on the very back of the intake manifold behind/underneath the distributor with what looks like a two wire connector going to it? There is a new oil pressure sender, which is located directly above the oil filter. That one only feeds my gauge, but I was curious if the oil pressure switch is the one by the distributor ... I'm thinking i'll replace it, but is this the right sensor?

Duralast/Oil Pressure Switch (PS215) | 1989 Chevrolet C1500 1/2ton P/U 2WD 8 Cylinders H 5.0L TBI | AutoZone.com

That link is what Autozone says goes to my '89 C1500 with a 5.0L TBI engine.

Any input is welcome

 

Right after making this post I went outside to investigate this a little bit more. What I did was disconnect the oil pressure sensor in question, and she fired right up like normal (long crank before fire). Next I unplugged the relay and plugged back in the sensor - same deal. Third I took the relay out and checked the pins with my ohm meter, relay checks out fine.
Next I took my fuse out and jumped 12+V to it and the fuel pump spun up like it should.

So ... I'm left with a seemingly working fuel pump relay, a questionable oil pressure switch that doesn't seem to make a difference when starting, and a pretty lame fuel system "prime" when you key on before cranking. My gauge reads a solid 13PSI, and it only once in a while primes up to 8PSI if you're lucky ..

Things to know: My key cylinder is all worn out and I can remove the key while it's supposed to be "locked" in there, it could quite possibly be a bad ignition switch giving me this starting issue, or my relay could be worn out. So far, the relay looks okay, the oil pressure switch in question seems to have no impact on the circuit, my fuel pump works great and the truck does start and run. It just doesn't start up quick like other trucks do ..

 

This was a pretty common problem with these trucks. It is likely a drop in fuel pressure. The pump should run for a few seconds after the engine is shut down. This builds pressure for the next startup.
I am assuming you already checked for leaks from a rotted fuel line or a clogged fuel filter.
Pull the fuel pump fuse while the truck is running. After it stalls, turn the key off and reinstall the fuse. Turn the key to run but don't start...did the pump cycle? Try starting....it should start easily.
If it didn't cycle, it could be the fuel pump itself or the fuel pump relay. Try swapping with the other relay right next to it...they should be identical except for the bracket. If that doesn't help, that narrows it down to either a fuel pump leaking down or the fuel pressure regulator leaking down.
I would try the pressure regulator just because it's an easier repair.

You can find it for under 40 bucks at TheAutoPatsShop.com

 

Thanks for the response, johntaps.

I have all new fuel lines, filter and pump already. If I recall, pulling the fuel pump fuse does not cause the truck to stall, but I could be wrong. Also, these particular pickups have a "self bleed" "feature" that removes pressure from the system while the truck is off. My truck isn't equipped with factory air conditioning, so I only have one relay there on the bulkhead by the "buss bar" (the studs that have constant 12V). I'll pickup another relay and see how it does. I believe Autozone/Advanced/O'reilly's/Napa/Carquest all sell one.

I don't believe that the new pump I put in had a check valve on it like a modern pump would have, so that explains the self bleed down. I've heard of compression fittings that have check valves in them. I could install one of those for even better fuel pressure retention. I also think my throttlebody needs rebuilding, because I have a gasoline vapor scent when I pull my air cleaner, and I have wet bolts that hold the throttlebody down. Plus I know who rebuild the throttlebody before and it's possible that not all of the gaskets were properly replaced.

So many thoughts. This is more often how I fix a car, just eliminating ideas from my head until I conclude something. Thanks for any other responses - all are welcome.