In tank fuel pump

[my79monza]

I have a 79 Hatchback base model with the I think its the 2.5 crossflow 4 cyl and it has an engine mounted fuel pump.
I was thinking about converting it to the tank mounted pump so when I put the V/8 in it I don't have to notch the motor mount bracket.
Today I was looking under it and I noticed the wiring to the tank and there was three wires going to it.
I looked in my 79 monza GM wiring diagram book and all it shows is tank mounted fuel pumps on all schematics, now I am really confused how/why would it have a tank pump when it has an engine mounted pump.This does not make sense to me.
I checked the fuse panel and it has a fuse in the spot marked electric fuel pump.
Whats up Doc?
Merle

[monzajer]

Merle, someone will probably put this better than I, but here goes. The fuel level sender has to have wires-could those be what you are seeing going to the tank?

I run an after market electric fuel pump on my 355 and have never had a problem with fuel delivery. Albeit I don't race it either, but I have got kinda "loud" with it. You can tap into a "key on" circuit or flip a switch type circuit to power the pump. There is no need to engine mount the pump. There are easier ways to do this.

Good luck and have fun.

cheers jer

[my79monza]

Usually only two wires are required one for the sender and one for ground.
My notchback has the tank mounted pump and has three wires, as does this one.
The kicker is the fuse in the elect pump slot.
Merle

[starfire383]

Your car originally had an electric pump and somebody converted it to mechanical. There's a good chance the original pump is still in the tank and the mechanical pump is pulling thru it, works fine for most low-demand fuel systems.

Even if the new motor has a mechanical pump, you'll need to know if the original pump is there or not because it's too much of a restriction for a healthy V8.

good luck

[my79monza]

The car was one owner,female, car only has 25k on it so it is original.
Don't make sense to me, I suppose I will have to pull the tank and find out for sure whats up.
Merle

[starfire383]

I thought monzas were all electric pump? Granted, most of the ones I've messed with were factory V8 cars but my impression was even the 4/6 cyl cars got electric pumps for manufacturing efficiency reasons. Somebody who knows more will hopefully chime in.

Nice looking car by the way

[my79monza]

OK, all indicators point to the car having both mechanical and electric pumps for whatever reason is beyond me.
Now the question is will the stock Monza tank electric pump supply enough fuel for a 355HP V/8? or do I need to mount an aftermarket pump back by the tank and remove the factory pump from in the tank?

Merle

[kam]

Merle,

The stock electric pump will work for slow starts (from stops) and level roads however the engine will be starved for fuel if you get on it or pull a hill.

I have a '76 Vega with the stock tank pump and put a red holley pump outside the tank.

I have a switch installed in the glove box to turn on/off the holley as it is noisy but like I said only need to use it to pull a grade or mash the pedal.

Kerry

[res0o7eb]

According to my 1977 Pontiac Service Manual, the diagram of the Fuse Block shows the Electric Fuel Pump fuse is in the upper left and it takes a "(10 AMP. EXC. 151)" fuse. In the Engine Oil pressure Indicator Lamp section, I found this: "H and HM Series use an electric fuel pump with 140 L-4 and 231 V-6 engines." There is a diagram showing 3 wires coming from the "FUEL PUMP AND SENDER" - Tan to the fuel level gauge, Dark Blue to a pin on the oil pressure switch through the "DZ" pin on the bulkhead connector. The wiring diagrams do indeed show an electric fuel pump and there is no disclaimer for the 151 engine.

It appears that Merle may have stumbled on to something unknown previously.
I will check my 77 Sunbird 151 for an electric fuel pump when I get some time.

It sort of makes sense in that it could have been a cost savings for GM to just include a fuel pump and wiring with ALL H-bodies on the line at the factory. If the H-body was to have a 151 engine in it, then the pump was just disabled by not putting in a 10 amp fuse.

[starfire383]

When the 383 hit my starfire it had the stock pump for a month. Engine leaned out and nosed over at 5500 in first and 4500 in second. I don't mean nosed over a little, the frickin thing ran out of gas and started to shut off. So if your car does have a pump back there, you'll need to remove it and install a normal pickup. Not a big deal, just get a normal 3/8 fuel sock, cut a piece of 3/8 line to replace the pump, braze the new line in place of the pump.

If you have a normal pickup without a pump, you started with the right car!

Then mount an aftermarket fuel pump over the axle, personally had decades of good luck with 6psi carter street pumps. Durable and quiet and usually under-rated by 1-2 psi. Napa sells them as a federal-mogul universal, but getting the counter guy to believe you is like pulling teeth. But open the box, and there it is, carter street pump, label and all.

[my79monza]

OK, The mystery has been solved.
Today I pulled the tank and sure enough there was the three wires to the sender the same as my V/6 car with the electric pump.
After removing the tank and taking a good look at the sender it became apparent what GM did, they wired it for the electric pump but it only had the 2 wire sender, no electric pump.
My engine will be a 350 ZZ4 will it require the aftermarket fuel pump? or will the stocker feed the 350?
At least the wire is there if I do need to go aftermarket.

Suggestions appreciated.

Merle

[cjbiagi]

I have been running the stock V8 electric pump with my 355 4 speed forever. Never noticed any fuel delivery problems. I can wind it up to 5500 rpm in first and second gear without any stumble. It's interesting that in my 75 GM service supplement it shows specs for a L4 electric fuel pump with 3 - 4 1/2 lbs of pressure @ 12.6 volts and also a V8 of 7 - 8 1/2lbs @ 12.6 volts. So, must have been 2 different pumps.

[my79monza]

Starfire, how does your 383 compare to my ZZ4 performance wise?
I would guess that it would require more fuel than mine.
I have already bought a stock fuel pump but it can be shelved as a spare for my V/6 if need be.
I looked at Summit and they have a butt load of carter pumps, went to the NAPA web site and came up with zip on the Federal Mogul universal pump.
Merle

[starfire383]

My 383 is moderate and high torque, likely very similar fuel demand to a ZZ4. No way I'd ever run a stock pump with any kind of performance V8. These are cheesy little pumps and completely unlike modern F.I. in-tank pumps that can easily support a 400hp V8.

Napa part number NFP P4070. $85

Summit sells the carter P4070 for $75 plus $10 shipping.

However now I'm curious.....electric pump technology has come a long ways in 30 years. Makes me wonder if modern replacement pumps would outflow an original pump. Still don't think I'd take the risk, as those carters have been very good to me over the years.

[my79monza]

Thank You,
Merle