Engine swap woes.
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Intermediate
Joined: Jan 2024
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Engine swap woes.
I have a 1988 with the 700R4. It was a bit of a basket case electrically so I've done away with the TPI and the L98 altogether and am installing a Smeding Performance power adder 383. The aftermarket block has the oil pressure port near the bell housing flange instead of at the rear of the intake manifold, so installing the oil pressure switch and sensor are out of the question. There just isn't enough room to install them in that place.
Mind you, this car is now carbureted and most all of the unneeded wiring has been removed. I know the ECU needs the oil pressure switch to run the fuel pump. Can I just jump that connector and delete the oil pressure switch to force the ECU to run the pump all the time? Will it turn off with the key?
I have enough room at the front of the engine for the oil pressure transmitter to monitor oil pressure via the gauge, but not both transmitter and pressure switch.
Mind you, this car is now carbureted and most all of the unneeded wiring has been removed. I know the ECU needs the oil pressure switch to run the fuel pump. Can I just jump that connector and delete the oil pressure switch to force the ECU to run the pump all the time? Will it turn off with the key?
I have enough room at the front of the engine for the oil pressure transmitter to monitor oil pressure via the gauge, but not both transmitter and pressure switch.
Last edited by Eightrac; Apr 13, 2025 at 06:46 PM.
Melting Slicks
Joined: Nov 2016
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From: So Cal
2023 C4 of the Year Finalist - Unmodified
If it is now carbrueted, why will you retain the "ECU"?
For safety, you don't want the pump to run if the engine is not running. So you will still need a dedicated oil pressure switch for the fuel pump. I suggest a 3-terminal, single pole, double throw switch. (Use "1971 Chevrolet Vega" for your search. The Vega had an electric in-tank pump but was carb'd.) The Common terminal is to the pump. The Normally Open terminal is to a fused Hot in RUN (IGN) source. (In GM wiring, this is usually Pink at the ignition switch.) The Normally Closed terminal is to a fused Hot in CRANK source. (In a C4 this is Yellow at the Ignition switch. There may also be a CRANK fuse in the fuse box, or the CSINJ fuse behind the radio. These wires will be purple or pur/wht).
When starting, with no oil pressure, the pump will run in the START position through the NC contacts. When oil pressure rises, the pump is now powered by the IGN through the NO contacts. If you take the power for the crank terminal prior to the neutral safety switch (yellow wire), you can "prime" the pump and carb by placing the shifter in drive or reverse so it won't crank, but the pump will run in START.
For safety, you don't want the pump to run if the engine is not running. So you will still need a dedicated oil pressure switch for the fuel pump. I suggest a 3-terminal, single pole, double throw switch. (Use "1971 Chevrolet Vega" for your search. The Vega had an electric in-tank pump but was carb'd.) The Common terminal is to the pump. The Normally Open terminal is to a fused Hot in RUN (IGN) source. (In GM wiring, this is usually Pink at the ignition switch.) The Normally Closed terminal is to a fused Hot in CRANK source. (In a C4 this is Yellow at the Ignition switch. There may also be a CRANK fuse in the fuse box, or the CSINJ fuse behind the radio. These wires will be purple or pur/wht).
When starting, with no oil pressure, the pump will run in the START position through the NC contacts. When oil pressure rises, the pump is now powered by the IGN through the NO contacts. If you take the power for the crank terminal prior to the neutral safety switch (yellow wire), you can "prime" the pump and carb by placing the shifter in drive or reverse so it won't crank, but the pump will run in START.
Last edited by IHBD; Apr 13, 2025 at 09:53 PM.
Safety Car
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From: Saratoga Springs NY
2024 C4 of the Year Finalist - Modified
2022 C4 of the Year Finalist - Modified
Also, on my engine, my oil pressure switch is installed in the port above the oil filter. Plenty of room there. Mine is on a T fitting along with fuel pump switch. You can also install one near distributor on top of block, but its tight there.
Melting Slicks
Joined: Nov 2016
Posts: 2,256
Likes: 3,082
From: So Cal
2023 C4 of the Year Finalist - Unmodified
I have enough room at the front of the engine for the oil pressure transmitter to monitor oil pressure via the gauge, but not both transmitter and pressure switch.
There should be room off of the block port above the oil filter. Be creative with fittings. If there isn't room because of headers, use a braided hose extension to a remote location for the sender and switch.
