454 long block replacement and associated sensor issues

[91 Jimmy]

You don't need #3 if your vehicle is now carbureted and running a mechanical fuel pump. That oil pressure/fuel pump switch is required with an electric fuel pump in the event of a crash and subsequent loss of oil pressure when the engine dies, it opens the circuit to the fuel pump so it shuts off and doesn't keep pumping fuel up to the engine and start/feed a potential fire. When you turn the key on with the original system, or any modern vehicle for that matter, you hear the fuel pump kick on for a few seconds and shut off, and then when you crank the engine and it fires up and the system/sensor/switch sees oil pressure it closes the circuit so the fuel pump will run while the engine is running. No oil pressure at that location= no electric fuel pump.

OK, that's what I thought. Now for the next question; here is a side by side of the oil pressure sensor (or switch, I'm not sure what the difference is?) I bought from Rockauto vs. the one that was on the old engine:

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The new one is a little longer, but they both have the same thread which brings me to the following question: The thread on the Tee is larger than the thread on either the new or old oil pressure sensor so I can't thread it directly into the block. So, do I use the tee but plug the other end if I don't need number 3 in the schematic above as QBuff02 mentions?

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[AuroraGirl]

OK, that's what I thought. Now for the next question; here is a side by side of the oil pressure sensor (or switch, I'm not sure what the difference is?) I bought from Rockauto vs. the one that was on the old engine:

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The new one is a little longer, but they both have the same thread which brings me to the following question: The thread on the Tee is larger than the thread on either the new or old oil pressure sensor so I can't thread it directly into the block. So, do I use the tee but plug the other end if I don't need number 3 in the schematic above as QBuff02 mentions?

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with the one tab on the thing, I would be tempted to tell you the thing relies on the threads to ground properly. You may want to undo some of your PTFE there so the threads can contact metal. If that was an issue you found
Also, because your engine was designed to have both the Sensors on that distribution block, I would say you are correct in that you should clean it up, plug the unused one(carb from efi, right?) and thread back in and go that way. Otherwise, I would think a non EFI sending unit would be the right thread size unless it was made bigger for the t for the 2 sensors. (factory wise\)

 

[Turbo4whl]

OK, that's what I thought. Now for the next question; here is a side by side of the oil pressure sensor (or switch, I'm not sure what the difference is?) I bought from Rockauto vs. the one that was on the old engine:

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The new one is a little longer, but they both have the same thread which brings me to the following question: The thread on the Tee is larger than the thread on either the new or old oil pressure sensor so I can't thread it directly into the block. So, do I use the tee but plug the other end if I don't need number 3 in the schematic above as QBuff02 mentions?

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You could just use a pipe bushing, 1/8 pipe to 1/4 pipe.

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Any local hardware/ home store will have this.

 

[jethrogasser]

You don't need #3 if your vehicle is now carbureted and running a mechanical fuel pump. That oil pressure/fuel pump switch is required with an electric fuel pump in the event of a crash and subsequent loss of oil pressure when the engine dies, it opens the circuit to the fuel pump so it shuts off and doesn't keep pumping fuel up to the engine and start/feed a potential fire. When you turn the key on with the original system, or any modern vehicle for that matter, you hear the fuel pump kick on for a few seconds and shut off, and then when you crank the engine and it fires up and the system/sensor/switch sees oil pressure it closes the circuit so the fuel pump will run while the engine is running. No oil pressure at that location= no electric fuel pump.

You wouldn't happen to know where I could get the correct wiring for this system? I have a couple trucks with deleted mechanical fuel pumps and would like this safety feature on the electric Fuel pump that was installed.

 

[AuroraGirl]

You wouldn't happen to know where I could get the correct wiring for this system? I have a couple trucks with deleted mechanical fuel pumps and would like this safety feature on the electric Fuel pump that was installed.

a gmt400 setup would work, you can use a oil prressure can like above for your gauge, and use the standoff and switch on the lower block on the driver side

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heres some pictures of places/options to put things

Everything related will be NPT national pipe thread, seals with tapered threads, but using sealant is a good idea to prevent galling/corrosion and removal in the future

 

[Bextreme04]

You wouldn't happen to know where I could get the correct wiring for this system? I have a couple trucks with deleted mechanical fuel pumps and would like this safety feature on the electric Fuel pump that was installed.

He is wrong about this. That is not a safety feature in the way described and it doesn't work that way to begin with.

The electric fuel pump on TBI and MPFI GM engines is primarily powered by a relay. On truck systems from 87-97 they also had a separate power feed that spliced off from battery power and went through an oil pressure switch then spliced back into the fuel pump power wire. This allowed the fuel pump to keep running as long as the engine keeps running, even if the fuel pump relay failed.

After 98 they completely removed that bypass. If the fuel pump relay fails the engine will immediately shut off.

 

[edgephoto]

The coolant temp sensor you showed with the button type fitting takes a spade connector. It slides on sideways so on with a standard type will also work.

The 8th digit of your VIN will tell you what the original engine was supposed to be. "N" is a throttle body injected 7.4L and a "W" is for the Carb 7.4L engine. I posted the chart from the parts manual.

The fact that your engine has both an oil pressure sender and an oil pressure switch means it probably was injected. The sender is the bell shaped single spade terminal and that is for the gauge. The 2 pin switch shuts off the electric fuel pump if there is no oil pressure.

 

[AuroraGirl]

The coolant temp sensor you showed with the button type fitting takes a spade connector. It slides on sideways so on with a standard type will also work.

The 8th digit of your VIN will tell you what the original engine was supposed to be.

The fact that your engine has both an oil pressure sender and an oil pressure switch means it probably was injected. The sender is the bell shaped single spade terminal and that is for the gauge. The 2 pin switch shuts off the electric fuel pump if there is no oil pressure.

no, it turns on the fuel pump by grounding the fuel pump relay in the event that the fuel pump relays normal grounding method is not working , so you wouldnt have a key on buzz, but after cranking for a bit youd have fuel start pumping. As bex said, they got rid of it in 98