89 S 10 fuel pump?

[jacespeed]

Hey all, My 1989 s10 2.5 L idles a little rough and the fuel pump runs for up to 15 seconds after the ignition is shut off. I have not checked the fuel pressure (since this is the first TBI I have owned) because I am unsure where the shrader valve is. Any way any ideas on what this could be besides a weak fuel pump? or should I just replace the pump and see? I guess I should add that the MPG has dropped lately.

[Oldsmobile Doctor]

Check the fuel pressure, my guess is that the pump is OK. Bad pump will cause truck not to run, run out of power at higher speed (fuel filter will also cause) and extended cranking. The pump is run by a switch on the oil pressure and will run until the pressure go's down. Mine has 15w 40 and will run for a long time if the oil is cold. There isn’t a shrader valve on the TB GM engines you have to unhook the line and put a T in it. If there is enough room I do it at the filter.

[jacespeed]

hey oldsmobile doctor thanks for your help.
I have noticed that the pump runs much longer when it is cold. so do you think that I need a new oil pressure switch? I should probably mention that it sputters 2 or 3 seconds when it first starts up. but if I turn the ignition to on for a few seconds then crank it then it wont hesitate to start.

[Oldsmobile Doctor]

When you first turn the ignition switch on the engine computer will run the pump for a few seconds. That pressurizes the fuel rail which allows the truck to start. When it starts running the oil pressure switch takes over. Cold oil will hold pressure longer, as long as the fuel pump doesn't run excessive I would not worry about it. As for your original issue I would check the plugs & wires. You may even run a compression check. That said the question is how bad is the idle a domestic push-rod 4 cylinder won't run as smooth as an overhead cam engine.

[jacespeed]

OK I am learning a lot here. I always thought that the fuel pump should hold pressure after the ignition is shut off so that the pump would not have to repressurize the system when the ignition is turned back on. Is this not the case?

[rhandwor]

Originally Posted by jacespeed

OK I am learning a lot here. I always thought that the fuel pump should hold pressure after the ignition is shut off so that the pump would not have to repressurize the system when the ignition is turned back on. Is this not the case?

The fuel pump has an internal check valve. You can purchase an in line check valve.
http://www.ebay.com/ search inline fuel check valve. After you look at search amazon or http://www.tooltopia.com/ for a better price.

[Oldsmobile Doctor]

The pressure will bleed off while it sits that is why the ECM runs the pump when you first turn the key on. If the fuel system hasn't been opened like to change the filter it will come up to pressure almost immediately.

[jacespeed]

ok got ya, Thanks guys!