FAST frustration

[Rickerbucks]

Well I'm not making much in the way of progress with my FAST. Anyone have answers to these questions?

I have an LT1 with the FAST spliced into the factory PCM. When I change the pump prime second variable in the FAST it makes no differance at all. Does the factory PCM still control the fuel pump prime?

Also the AFR moves really really fast and volatile even when I keep the car idleing in one cell. That does not seem right.

In summary, my primary problem seems to be the AFR from the sensor is sovolatile as to be almost useless AND it bounces about erractically even when the car is held in one cell.

Finally, any idea what symptoms an exhuast leak would have? I cannot see or hear any leak but *shrug*

Craig: You told me to send it to Kevin but I have already done that. He checked it out and said it was OK.

 

[bobc455]

>I have an LT1 with the FAST spliced into the factory PCM. When I change the pump prime second variable in the FAST it makes no differance at all. Does the factory PCM still control the fuel pump prime?

Depends how it is wired. Does the FAST control the fuel pump relay? How did you wire it? Is there any prime at all? If someone else installed it or designed a special wiring harness, they would be the ones that can tell you how it is wired.

>Also the AFR moves really really fast and volatile even when I keep the car idleing in one cell. That does not seem right.

How far does it move? It will never be rock-steady, but if you are going from 10:1 to 15:1, that would not be normal. I assume the values in your VE table are fairly smoothed?

>Finally, any idea what symptoms an exhuast leak would have? I cannot see or hear any leak but *shrug*

A vacuum leak can cause air to be sucked back into the exhaust pipe, so the O2 sensor will see more Oxygen than what is actually coming out of the engine. This will have the greatest effect at idle, but vary widely depending on load, etc. Also, the amount of leakage / suckage can vary according to temperature, etc. (as the surfaces/gaskets heat up/cool down, the gasket leak could increase/decrease). If you have an exhaust leak, it could definately be contributing to a wandering A/F ratio.

To detect an exhaust leak, usually you would hear a ticking and/or smell a bit of exhaust, especially at higher loads/airflows.

 

[Rickerbucks]

Thanks Bob.

I'm pretty sure after some testing the the PCM is still controlling the fuel pump, which is not a problem.

I seem to have found out a little more about my widely volatile O2 reading.

If I open the VE map ONLY, the AFR ratio seems to change up and down, literally 100 of times per second.

However, If I open the DASHBOARD first and THEN open the VE table, then the VE map takes the reading from the dashboard which SEEMS to only change maybe 10 times a second, making it a lot easier to see a trend.

I'm 90% sure I do not have an exhaust leak. There is no audible or visible clues BUT I do have an air pump 'hole' that is capped with a welded screw on bung. I may take that off and see if it is 'leaking' some how.

If I try to hold the throttle in a given location and a given cell, the AFR seems to move maybe 2 points - say 13:1 - 15:1

So far spent almost $20 CDN in gas just ideling. LOL

Wish me luck

 

[RickWI]

There is a gain adjustment in the A/E setup menu that you may want to try adjusting down a bit.

 

[TURBOZ]

Your most likely grabbing fuel from another cell allowing a/r to jump that much.