Turbo using up 1/4 tank of gas in 10 miles!

[cine135]

Hello to everyone, I'm a bit of a lurker here, I've been reading up and following the various dimensions of DSM tuning and have learned much, I currently own a Silver 1997 GS, the motor has about 120K on it, I bought the car from a dealer when it had 72K I've been gentle on it so far though I have installed:

1.) Cone air filter
2.) Stainless straight exhaust

3.)A Turbopac 1500, this unit is NOT production it was obtained from Turbodyne, in carpinteria CA

The intake and exhuast produced the predicted 10 hp gain from stock, The turbo however is another story altogether.

The turbopac is designed for engines up to 2 liters, it produces 5psi of boost @ 45,000 rpm
The turbopac 1500 has no oil lines as it utilizes bearings.
The instant on effect is great since I can control when the turbo works eliminating turbo lag.

I installed the the comressor unit and all switches correctly, I did NOT modify the ECU or fuel pump, fuel injectors or any other components in the car.

When installing a 5 psi turbo, is there any fuel system modification or other (excluding the turbo tubing and manifolds) modification required?

Sometimes when I actuate the unit @ 1500 rpm the engine sounds like it is struggling to rev, this never happens @ 2500 rpm and above, can too much air @ a low rpm impede essential engine functions?

After a spirited run of say 10 miles, the fuel guage shows 1/4 tank less fuel!!!

All other problems aside, when taking a 420a from non turbo to turbo, a 5 psi setup at that,
The fuel economy doesn't go from 22mpg to 3mpg!!!

What is going on here? I don't belive that my stock fuel pump is emptying out 1/4 tank of gas in 10 minutes.

10miles/3.25 gallons= 3.07mpg

Does anybody have a clue, is the fuel guage giving faulty readings?


The turbo system draws on the order of 80 amps for a 10 second duty cycle, of course the duty cycle resets everytime I press in the accelerator pedal effectively making the duty cycle as long as I want providing I either shift or pump the gas pedal.

I can see the gauges and headlights get slightly dim when the system comes on, can this cause the fuel gauge the give a faulty reading?

[I-luv-em-all]

Do a compression test and see if you get normal readings. If not then that could be a partial problem.

[GSGoinFast]

Originally Posted by cine135

Hello to everyone, I'm a bit of a lurker here, I've been reading up and following the various dimensions of DSM tuning and have learned much, I currently own a Silver 1997 GS, the motor has about 120K on it, I bought the car from a dealer when it had 72K I've been gentle on it so far though I have installed:

1.) Cone air filter
2.) Stainless straight exhaust

3.)A Turbopac 1500, this unit is NOT production it was obtained from Turbodyne, in carpinteria CA

The intake and exhuast produced the predicted 10 hp gain from stock, The turbo however is another story altogether.

The turbopac is designed for engines up to 2 liters, it produces 5psi of boost @ 45,000 rpm
The turbopac 1500 has no oil lines as it utilizes bearings.
The instant on effect is great since I can control when the turbo works eliminating turbo lag.

I installed the the comressor unit and all switches correctly, I did NOT modify the ECU or fuel pump, fuel injectors or any other components in the car.

When installing a 5 psi turbo, is there any fuel system modification or other (excluding the turbo tubing and manifolds) modification required?

Sometimes when I actuate the unit @ 1500 rpm the engine sounds like it is struggling to rev, this never happens @ 2500 rpm and above, can too much air @ a low rpm impede essential engine functions?

After a spirited run of say 10 miles, the fuel guage shows 1/4 tank less fuel!!!

All other problems aside, when taking a 420a from non turbo to turbo, a 5 psi setup at that,
The fuel economy doesn't go from 22mpg to 3mpg!!!

What is going on here? I don't belive that my stock fuel pump is emptying out 1/4 tank of gas in 10 minutes.

10miles/3.25 gallons= 3.07mpg

Does anybody have a clue, is the fuel guage giving faulty readings?


The turbo system draws on the order of 80 amps for a 10 second duty cycle, of course the duty cycle resets everytime I press in the accelerator pedal effectively making the duty cycle as long as I want providing I either shift or pump the gas pedal.

I can see the gauges and headlights get slightly dim when the system comes on, can this cause the fuel gauge the give a faulty reading?

your running 5psi without any fuel enrichment? you need an fpr, to raise the fuel pressure with boost. one way to check if the gauge is messed up is to fill up your tank, go on one of these "spirited runs", then go back and fill it up. if it fills up lest say 2.5 gallons, you might have a problem, but if it fills up less then a gallon, then i would say your gauge is not working.

[cine135]

Ok, I visited the local speed shop and they recommended either a new rising rate FPR or A piggyback FMU.

I know about the vortech FPR and the Apexi safc.


With the FPR I know I'll be getting fuel pressure levels not limited by factory componentry (other than the injectors, which can stand to blast a little bit more fuel) Though I have a feeling that with the Apexi safc, the signals sents to the ecu will simply cause the ecu to deliver a factory set "rich" condition at the rpms I specify. Is the Apexi unit really effective for a turbo setup?

I'm trying to decide which to go with, this car is not going to be setup for high HP so the boost is staying @ 5psi for the forseeable future.

Which would you recommend?

P.S. If I do go the FPR route what boost to fuel ratio is the 420a fuel system suited for? The speed shop suggested a 12:1, how does that sound?

[GSGoinFast]

Originally Posted by cine135

Ok, I visited the local speed shop and they recommended either a new rising rate FPR or A piggyback FMU.

I know about the vortech FPR and the Apexi safc.


With the FPR I know I'll be getting fuel pressure levels not limited by factory componentry (other than the injectors, which can stand to blast a little bit more fuel) Though I have a feeling that with the Apexi safc, the signals sents to the ecu will simply cause the ecu to deliver a factory set "rich" condition at the rpms I specify. Is the Apexi unit really effective for a turbo setup?

I'm trying to decide which to go with, this car is not going to be setup for high HP so the boost is staying @ 5psi for the forseeable future.

Which would you recommend?

P.S. If I do go the FPR route what boost to fuel ratio is the 420a fuel system suited for? The speed shop suggested a 12:1, how does that sound?

you need a rising rate fpr. go with the vortech fmu. a s-afc is for fine tuning, not for increasing fuel for boost. your injectors can only open for so long at high rpms. get the 12:1 vortech fmu. you will also need a new fuel pump, get a walbro 255

[cine135]

Thanks, that settles it

[Dave Chan]

i hope you solve your problem

gas is just too expensive!

[GSGoinFast]

Originally Posted by cine135

Thanks, that settles it

oh yeah, get the 12:1 if your still using stock injectors

[siueclipse]

Im going to throw one piece of advise out. Get the Vortech SFMU, not the Vortech FMU. The SFMU will allow for greater tunability with all sizes of injectors.

[cine135]

GSGoinFast:

Used up .58 or so gallons in 11 miles with the turbo.
So I guess I'm getting about 20-22 mpg, no fuel enrichment proabably explains that.

I do feel quite a bit of power, is this stock fuel ratio dangerous under 5psi boost and why?

Why would the fuel gauge do something THAT wierd?
Would a massive electrical draw if only for a few seconds cause that?
I'm probably pulling about 1kw through the turbo system from the battery for 10 seconds.
Mind you the electrical wiring is all 4 awg with an isolated relay etc...
Wierd, is there an aftermarket fuel gauge or just one that doesn't take forever to update, I really liked the older gauges that responded instantly to the fuel level. They weren't in any dsm's though...