Does the computer reference the VSS for fuel requirements? Do the inputs from the VSS contribute to alterations in the BLM? What effect will disconnecting or deleting the VSS, or simply grounding the park/neutral switch have on WOT performance? The concept that brings this topic about is the fact that fuel requirements in third gear at WOT are different from those in first gear.


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355 c.i.
Dart 180 Heads
Lunati 224/224 cam
Harland Sharp 1.5 rockers
Performer RPM Manifold
Holley 600 cfm double pumper
Hooker Super Competition Headers
Flowmaster Exhaust
Competition Engineering Sub-frame connectors
Super T-10
GM posi 3.42 rear
Hurst Roll Control
13.9@102

 

The $8D references the VSS in a number of spots, the least of which is the Max MPH Fuel Cutoff. Get a copy of $8D hac and do a "find" on "VSS", you'll be surprised how often it comes up.

A non-functioning VSS will throw an SES code and make the ECM go into "safe mode". Unless you want to start altering the Source Code (and few do that) the VSS is an integral part of the $8D code.

Why do you want to disable the VSS?

 

Does the computer reference the VSS for fuel requirements?

Yes for the fuel cut off and decel enleanment

Do the inputs from the VSS contribute to alterations in the BLM?

No

What effect will disconnecting or deleting the VSS, or simply grounding the park/neutral switch have on WOT performance?

The stock chip has a byte for min MPH to enable knock retard.

The concept that brings this topic about is the fact that fuel requirements in third gear at WOT are different from those in first gear.

Do you believe that the amount of air taken in(per cycle) at WOT is different from one gear to the next? What about the horsepower at the crankshaft? I think you will find that the WOT requirements are similar enough.

But……..

I think it is foolish to consider WOT performance in a vacuum when it comes to fuel injection. You should also be concerned with light throttle. Why would you have FI if all you do is race and never drive. The beauty of FI is the monster motor with better manners than a carb. This is important if you drive the car very much. VSS is coupled to a lot of things that affect the way the engine performs off of WOT. I do not in anyway recommend deleting it.

John

Heart of Texas Power and Performance

 

I believe that the increased load on the car due to wind resistance and aerodynamic drag will alter the fuel requirements of the engine. I'd like to believe that the engine performs exactly the same at all point points in the hp v rpm graph, but I dont think it is as simple as that. I think the fuel requirements when you throw your car into 4th at 25 mph and 1200 rpm to simulate load at full throttle and those of a car coming off idle and 1200 rpm in first are different. I don't know.

I don't really want to disable the VSS, but I am doing a tpi retrofit and want to know whether deletion of the vss is going to hurt performance.

 

I believe that the increased load on the car due to wind resistance and aerodynamic drag will alter the fuel
requirements of the engine.

How ? Your engine will produce the same power for any point where RPM, and MAP (this is not completely true but this generalization can be made) For example if your engine produces 200 ftlb of torque at 2000 rpm at WOT then that is all it will ever produce. It sounds like you are asking if adding drag to the car by going faster adds to the ability of your engine to produce power. The power available for acceleration is the power produced minus the power consumed by steady state cruising. As speed increases the amount of power available for acceleration decreases as drag increases but the total power produced at any discrete point is unchanged by the drag loads imposed upon it. This is for WOT.

At light throttle cruise the amount of power produced is equal to the drag loads. Therefore there is no acceleration. An increase in drag loads requires more power output. More power requires more air. This is reflected in a greater MAP or MAF reading. The greater MAP or MAF reading causes the ECM to add fuel to maintain a given Air Fuel Ratio. Since it takes more power to cruise in 3rd than in 1st the ECM does give more fuel but only in response to an increase in airflow not because the VSS is telling the ECM that the car is traveling faster.

I'd like to believe that the engine performs exactly the same at all point points in the hp v rpm graph, but I dont think it is as simple as that.

For any engine at any RPM the WOT fueling requirements do not change as a function of applied load. As far as engine performance goes the act of accelerating the reciprocating masses is a leach on power. The will reduce the crankshaft horsepower by a drag amount that increases as the acceleration rate increases. This does not change fueling requirements since fueling requirements are based upon airflow and AFR.

I think the fuel requirements when you throw your car into 4th at 25 mph and 1200 rpm to simulate load at full throttle and those of a car coming off idle and 1200 rpm in first are different. I don't know.

I don't really want to disable the VSS, but I am doing a tpi retrofit and want to know whether deletion of the vss is going to hurt performance.

For this you will have to define performance(as there are many scales by which it can be measured.) My thoughts on leaving out the VSS are simple. DON'T! If you are bothering to install this as a retrofit why would you choose to cripple your system. I know it seems like I am arguing both sides of this point but my opinion is that VSS is very important just not for the reasons you asked about.

John

Heart of Texas Power and Performance

 

I have no active VSS. My car runs wonderfully and even gets decent gas mileage. This may be attributed to the fact that I have a manual tranny though. I really couldn't see spending a bunch of money to retrofit a vss. As for crippling the system; I have yet to witness any indications and wonder how my car could run better at part throttle.

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1991 Firebird
350 L98 (was a 305 TBI),T-5,Edelbrock TES and cat back,Accel manifold
NOS,subframes,jegster torque arm,MSD Digital 6
AFPR,Lakewood lcas
Hurst linelock,SLP cam (206 212 .480 .486),relocated battery,cold air,Hypertech chip,centerforce df,clutch
poly bushings and mounts
AFR 190s
Harland sharp 1.5 rockers
autopower rollbar

12.33 @ 114.83 juiced uncorrected

13.510 @ 102 non juiced uncorrected

 

So Glen91, my car is in safe mode? I have an off the shelf hypertech chip.

 

I hope I don't have to fiddle with the VSS.
My setup is like this, sensor in T5 tranny goes to the little yellow VSS Buffer box and then to the speedo cluster.
My car was an LG4, but now I have an 87 TPI with a 91 ECM+prom and I am almost finished with the swap.
Do I need to hook up my tranny to the ECM?
If I do that, then how do I hook up my speedo?



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WS6 Trans Am.

View My Ride @ thirdgen.org