2 questions

[opto]

What is the device back in the valley where the old vacuum pump used to be?

Actuating the lift pump doesn't get the fuel pumping through the IP, either with ignition off or on with engine off.
Is it supposed to be like this?

[More Power]

The 1980's vacuum pump was driven by (sat atop) the oil pump drive assy. Later 6.2 & 6.5 engines (that used a vacuum pump) saw the vac pump moved to the front of the engine where it was belt driven. 1991 was the first year for the 4L80-E, and the oil pump drive assy was equipped with an engine speed sensor to provide input to the trans TCM.

The 6.2/6.5 electric fuel lift pump, 1988 through 1995, was powered via relay when the ignition key is rotated to the crank position and by the oil pressure switch with the engine running.

Jim

[AKMark]

My 91 K1500 Suburban had no electric lift pump, and the vacuum pump was on the back of the motor connected to the oil pump shaft, just like my 85.

[DmaxMaverick]

The Burb's lagged a couple years in the body tooling. The engine spec's usually follow the sheet metal tooling. IIRC, 91 was the changeover year for the Burb's, so it could have been before or after the initial model year introduction. Many times, they will make these changes about January of a year, especially if emissions issues are involved.

[AKMark]

The Burb's lagged a couple years in the body tooling. The engine spec's usually follow the sheet metal tooling. IIRC, 91 was the changeover year for the Burb's, so it could have been before or after the initial model year introduction. Many times, they will make these changes about January of a year, especially if emissions issues are involved.

I figured as much. 92 was the first year using the body the 88 trucks got.

[opto]

So, it's a engine speed sensor
I have the vacuum ehhh had the vacuumpump in the front , belt driven.
This is a 91 with a T700R4, doesn't that make it a bit strange to have the ECM read the rpm and TPS, as it really can't do anything with the information??
What is the output of the engine speed sensor? Pulswave??

Yepp I know about the OPS and relay and also the direct cable in the diagnostic connector.
I used this one to connect to a switch to be able to manually engage it.
But when I do engage it, it pumps fuel and builds pressure (6 psi) but the fuel is not flowing througt the pump as I thought it would. It acts as if a valve would be shut in the pump.