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Old 12-28-2010, 04:10 PM
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How to keep stock Fuel pump?

Hi everyone, I have a 1989 chevy c-1500, I recently did an engine swap and the trouble that I have now is keeping the stock fuel pump on. Is there any way in which I can bypass the relay so the pump does not shut off? The main problem is that the computer does not know that the engine is on and it shuts the fuel pump off. Is there a way in which I can bypass the relay or something, in order to keep the pump on as long as the ignition is on or the engine is one? If so how can I do this?

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Old 12-29-2010, 01:35 PM
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The fuel pump system for that truck uses the oil pressure switch keep the pump running. Make sure that this is installed and operating.
Also it has a fuel pump prime terminal under the hood to enable fuel priming after the fuel system has been serviced. Apply 12 volts to the prime terminal. This will activate the relay and run the pump. This terminal is not to be used for anything other than temporary needs.

vicrod
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Old 12-29-2010, 02:32 PM
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Quote:
Originally Posted by inrc
Hi everyone, I have a 1989 chevy c-1500, I recently did an engine swap...
And apparently didn't correctly connect the oil pressure switch.

Just to expand on the post above, the fuel pump is controlled two ways. The relay is only used to run the pump for two seconds when you first turn the key to START. The relay allows the low-current computer output to switch power to the pump. As noted above, once the engine is running and there is oil pressure, the oil pressure switch bypasses the relay and allows the pump to operate so long as the engine is running.
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Old 12-29-2010, 04:15 PM
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I checked to see if there is any spot on the manifold to place that oil pressure switch and there is no other place, the only other place is where the oil pressure sending unit is located at, on the driver side back below the manifold, and there is only one wire going to it. Do you think this might be it?
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Old 12-30-2010, 10:43 AM
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Quote:
Originally Posted by inrc
I checked to see if there is any spot on the manifold to place that oil pressure switch and there is no other place, the only other place is where the oil pressure sending unit is located at, on the driver side back below the manifold, and there is only one wire going to it. Do you think this might be it?
The original engine should have an oil pressure sender with three wires. One is for the idiot light and the other two are for the fuel pump. Either get the original sender from the original engine or get a new one for that year and model.
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Old 12-30-2010, 02:09 PM
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Ok I have another question, The engine is a 1979 and i put it in a 1989 chevy, would it be the same? I have an oil pressure sending unit but there is only one wire, should I get the one that has three and wire all four of them together or would this cause a short?
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Old 12-30-2010, 02:22 PM
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Quote:
Originally Posted by inrc
Ok I have another question, The engine is a 1979 and i put it in a 1989 chevy, would it be the same? I have an oil pressure sending unit but there is only one wire, should I get the one that has three and wire all four of them together or would this cause a short?
You need the sender for the 89 engine if you are keeping the electric pump.
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Old 12-30-2010, 02:39 PM
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The 1979 engine had a carb. Did you use the 1989 fuel injection system?
If not the fuel pump pressure will be to high for the carb. A proper pressure regulator will be required to drop to about 7 psi.

vicrod
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Old 12-30-2010, 02:41 PM
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Quote:
Originally Posted by vicrod
The 1979 engine had a carb. Did you use the 1989 fuel injection system?
If not the fuel pump pressure will be to high for the carb. A proper pressure regulator will be required to drop to about 7 psi.

vicrod
The good news is that the TBI pump only puts out about 15 PSI, so that's an easily obtained regulator.
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Old 12-30-2010, 04:08 PM
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No I replaced the TBI with an 850cfm carburator and I have a regulator installed, the only problem is that there might not be any place for me to install the other oil pressure unit that tells the computer the engine is on. I just need to know how to bypass the relay or computer so the fuel pump stays when the ignition is on.
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Old 12-30-2010, 04:22 PM
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Install a tee fitting and run the 89 sender for the electric pump if you have a aftermarket mech. or electric gauge. If you are using the dash gauge eliminate the one wire sender and use the oe 3 wire.
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Old 12-30-2010, 06:58 PM
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Ok what does the three wire one look like becasue all i have is a two wire one that is the closest to what we are talking about
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Old 12-31-2010, 12:19 AM
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This is the 3-wire for Oil Light, Part #8140 @RockAuto >> http://www.rockauto.com/catalog/moreinfo.php?pk=2401514
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Old 12-31-2010, 12:07 PM
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An optional method to changing the oil pressure sender is to add a relay that is controlled by the existing sender.
See attached diagram.
The relay will de-energize when the sender switch opens thus closing the contacts and completing the circuit to run the pump.

vicrod
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Old 12-31-2010, 01:30 PM
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Quote:
Originally Posted by vicrod
An optional method to changing the oil pressure sender is to add a relay that is controlled by the existing sender.
See attached diagram.
The relay will de-energize when the sender switch opens thus closing the contacts and completing the circuit to run the pump.

vicrod
Unfortunately most idiot light oil senders are CLOSED with no oil pressure and OPEN above 4 PSI.

Let's get back to the original question. Is the truck now carb or TBI? Was it carb with the old motor? How did you run the pump then?
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