Hypothetical basis is this: Using the PCM in conjunction with alternate fueling capable of delivering a static A/F ratio.

If you could run a static A/F ratio, along with an HP Tuner giving the same command A/F ratio, is there a way I could run dummy drives so the PCM "thinks" it is driving the injectors, so it would deliver commanded timing tables. It would also continue to monitor important engine data.

Is this possible?

 

Can I ask why?

 

No, the pcm makes decisions on multiple inputs. The process is to linear for a second processor to predict output signals capable of producing positive results. How about you sticking your hand in a fire and pulling it out when I tell you to?

 

I get what you are saying.

I get your analogy. Here's mine, how about you tell me how close to put my hand using only two of my 3 senses.

 

I'm wiling to bet the "why" is to get around a smog (or similar technical) check with a vehicle combination that otherwise wouldn't (assuming it passes the visual). Outside of this, I see no logic to even ask this question on a forum.

In the smog case, the stock PCM appears to be in control. This allows the VIN and all emissions checks to pass. For a racing situation, there could be a locked PCM to disallow tuning. In this case the secondary PCM is installed in a hidden location and configured to run the engine at maximum power or an elevated redline while the first PCM is only in place to pass tech. A few extra horsepower or a higher redline could give a strong advantage to someone in a spec class.

 

Those sound like valid possibilities. They are not, however, the reason.

Vapor fuels, such as propane, run static stoichs. While there are injection controls with LPI systems, I want to experiment with a basic fuel delivery system & being able to utilize the factory PCM with a stoich burning fuel would allow retention of a programmable spark table while keeping the functionality of factory gauge cluster & other factory peripherals the PCM is tied to.

 

I have an uncontrolable urge to do stuff considered different & impossible by most people, to prove it can be done & is the better way of doing it.

Nothing ventured, nothing gained.

That being said, is there a way to keep all the gauge cluster, VATS, etc, operations in a late model vehicle aside from the factory PCM?

 

Well, well, well... that would be the OTHER reason. Hahaha. I wish you well. I think you need a build topic in the conversions and hybrids section.

I like different and "impossible."

Interesting concept. I think that would depend on the vehicle. If the instruments run on the CAN bus, are they part of the OBD2 datastream or do they have separate sources? I.E. a 2002 Silverado has independent speedometer and tach output signal wires going to the dash and the oil pressure is direct from the sensor. I believe the driver information messages come from the dash cluster itself and / or the BCM depending on the message. This would be easy to duplicate compared to CAN bus which uses data packets and each device has a bus ID, etc.

 

Thanks for coming back to the topic. I wasnt trying to be an *** or anything, so I hope no one takes it that way.

This would be in my 04 GTO. I havent dug into what comes from the PCM as of yet, but if you know I am all ears.

Once i get a few things ironed out & proceeding I will be posting it up, but the whole project is going to take time to get right.

One thing that I will probably take up on the HP tuners forum is the progressive fueling. This is the main issue I see as that is what determines how much the PCM sweeps the pulse width to get the O2 response. What I dont know is where in the programming I can get rid of that command fuction or if there is a simple way to turn it off. I dont know if in OL I can just turn the value to "zero" & it wont try to bounce the pulse width & thusly look for the changes in O2 output. Or if in OL it will look at them at all.

If I can I should, hypotheticaly, be able to set the A/F for the delivery method & then copy all tables and command A/F's to mimick that. My plan is to run this in SD & in open loop. That way it is only going to dynamically tune for engine speed, TPS, MAP, accel & decel rates, AIT, ECT, etc.

Add: If everything but the tach will function on its own, like the trip timer & fuel consumption display when in trip mode, works through the gauge cluster then I have more options. I am trying to plan for worst case scenario of having to use the PCM. I mentioned in another thread I have a nice logger that would monitor everything the PCM monitors that would be important to me but I would have to invest in a programable ignition controller. Otherwise I have the box in mind I need to run in conjunction with the PCM.

 

So many words that mean nothing.

 

I did make a mistake & say progressive fueling & I meant proportional fueling.

Other than that what did I mis-speak about.

 

You do realize that you can disable closed loop trimming and program fueling to be flat constant... is this what you're after...?

 

That's exactly what I'm asking, so Yeah, pretty much. While at the same time the PCM will think it is driving injectors but wouldn't. To my knowledge the drivers need something to drive, otherwise it can damage the driver is what I have been taught. I've also been taught that a dry running injector will lock up eventually, so just running injectors not getting fuel isn't an option. But, please, correct me if I am wrong.

 

The problem is more so with ignition coils, if the coil is not allowed to discharge (i.e. no where for spark to go) then it can back feed into itself and into the driver in the PCM (driver blows out).

The drivers (for injectors and ignition coils) in the PCM don't really have this problem, they are basically a transistor/FET switch, and even though they are able to sink several A and freewheel the 100-200V kickback spike (from injectors and ignition coils), their input is low current (only 10's of mA), so if their output is open circuit it is harmless; of course several DTC's will trigger, some of these may push the PCM into some sort of limp mode.

My understanding is that the fuel running thru an injector cools it.

 

Ok, so the PCM must monitor resistance across the driver to know if an injector is firing or not or is it that it has a way of sensing the feedback or lack of voltage across the circuit? Couldn't I make a box housing low amperage relays mounted on a green-board that would be circuited with the proper resistance?

 

The PCM looks at the voltage across the driver before/during firing an injector or coil, and if it sees the wrong voltage then it goes thru it's diagnostic chart to turn on a DTC and/or MIL.

Sure, GM injectors are high impedance, 12-14 ohms resistance.

 

So is that it?

Disable trimming, & make the box to simulate injectors being fired by the drivers?