Manipulate FSD signal for increased fuel?

[AndyL]

I am guessing the PCM to FSD signal is a PWM type. Any particular reason I couldn't read and change that for increased fuel? A Basic Stamp, ADC and a POT on the dash would make for a pretty trick setup.

[ucdavis]

might work, but the PCM receives feedback to determine pulse width & store pulse width long or short trouble codes (36/1216 or 36/1217. In the early years these were called "pulse width long" or short, but later (by '98) they were changed to "fuel solenoid response time long" or short. If your gizmo left the return signal pulse width feedbacks reading correctly according to the PCM, you could do your thing. If not, the PCM will put you in "back up fuel mode" (which isn't to say it would actually make you back up) aka limp mode.

[S\W Off Road]

You will never know unless you try it. You are more then likely to have someone here tell you it wont work.

[AndyL]

There must be a slightly different behavior between the PCM and the IP pulse timing. If it was a direct relationship then all FSD failures would trip the Long or short SES. Most of the FSD failures I hear about (including my own) there was no SES. I guess I will have to just try it!

[lupey6.5]

can't you switch out the resistor in the fsd plug for one with a higher value 9 is the highest available. i have heard of this but i don't know how to get your ecm to accept the new value. i am sure that someone here knows, and i would too.

[tom.mcinerney]

Andy--Such an arrangement would be trick. I assume you are aware of existing 'power chips' by Kennedy Diesel, et al. Notwithstanding my "FSD FAILURE FEAR", I'd like to see a means to vary output from 'fuel-miser' to 'power-chip'!

[JohnC]

The FSD is not pulse width modulated, per say. There is one pulse for each injection event. The duration of that pulse determines the amount of fuel injected. Any variation between the commanded pulse and the measued pulse will cause the PCM to shut the engine down. If it can't control the pulse width to its liking it shuts down to avoid a potential runaway engine. All performance tricks involve tricking the PCM into setting a longer pulse width.

[AndyL]

Originally posted by JohnC:
The FSD is not pulse width modulated, per say. There is one pulse for each injection event. The duration of that pulse determines the amount of fuel injected. Any variation between the commanded pulse and the measued pulse will cause the PCM to shut the engine down. If it can't control the pulse width to its liking it shuts down to avoid a potential runaway engine. All performance tricks involve tricking the PCM into setting a longer pulse width. If this is the case why doesn't the PCM set a code when the FSD fails? In most FSD failures the PCM says pulse, the FSD says no way I am dead, and no code.

[JohnC]

I'm not sure why it doesn't set a code. There are reports that if you have an analyzer attached to the data port when the FSD is acting up you can read variations in the solenoid closure time. My bet is that the problem doesn't persist long enough for the PCM to set a code as it shuts down almost immediately. Most conditions that set codes have to persist for a reasonable ampount of time before the PCM sets the code.

[AndyL]

If that is true I guess I would have to subtract the longer duration from the IP feedback to satisfy the PCM. Maybe this idea is losing feasability.

No other sensor offset would increase fuel above the normal max would it?

Ideally I would reprogram the GM maps but I have been unable to find any usuable information on PCM data locations or protocols.

[lupey6.5]

what about the resistor i posted about? in the fsd plug

[Turbine Doc]

Not sure how it works exactly but the FSD resistor value isn't reset until offset learn is enabled. The manual says it is read at every start, which can't be, because as you have already learned remove one or fail one a SES isn't set. Try to learn a offset without the resistor installed in a PMD you will set a SES fault code.

How that happens is PFM Pure Freakin Magic nobody has been able to tell/teach me why.

There is a vendor that swears by a device they offer that says it's possiblke to tune on the fly but gets very defensive about the how it works part.

I'm thinking if it were possible one of the enterprising gear heads on the forum here would have "hotwired" a variable resistor across the same 2 pins/terminals the Stanadyne resistor contacts and made a go of it.

Looking at that side of of the fuel delivery loop isn't rocket science, the transistor outputs biased by a fixed resistance modifies for X delivery at IP, now the pulse to/from the IP and why a bad FSD or resistor does not set a code is the PFM part for me. There was a good thread that described the IP should still be here somewhere Britanic Post IIRC.