Anyone burned a custom PROM for their Q/Jet LG4? Is it worth worrying about? I want to up the anti on timing curves.

Cheers.

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Neither my L69 nor my LG4 computers had reburnable proms. You could probably buy a blank prom for $10 or so and burn it yourself if you really want to do it. The early LG4 computers did not have knock sensors which limits the safety of such an expierement.

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 Trans Am T-tops
4-bolt main 350, performer intake, headers, Holley 650, T-5, hayes clutch, dual elec. fans and 3.23's.
Daily driver and restoration
13.98 @ 101

 

The problem with burning an eprom for the "compu carb" is that there is very little information available for it. Getting the "bin" is easy enough, you just read your existing eprom. But then you need an Editor to "change/edit" the bin and there really isn't any out there. I am able to write a "TDF" for TunerCat which could edit it; but there is no "hack" available.

The reason is that by the time everyone got into "eprom burning" and "hacking the system", we were well into EFI and you had no other choice. With "compu carbs" the choice everyone made was simple; dump the ecm and put on a good old fashion non-computerized carb and distributor. Thus, there is no "development" of the knowledge for these systems.

Faced with the task of either "reverse engineering" the ecm/eprom or swapping the carb and distributor, which would you do?

But yes, you COULD burn your own eprom, but you are really on your own unfortunately.

 

Thanks for the info. I guess going backward is the path of least resistance either that or nowhere.

Cheers.

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83 Berlinetta - LG4, Mr Gasket Shorty Headers, Custom Y pipe, 3" pipework, 3" Vortech Muffler, Performer Intake, Open Element, QJet mods. Best 1/4 Et 15.11 @ 90.4 mph, 2.097 60ft.

 

Personally glenn, if i still had my 85 i would be reverse engineering the PROM.Why not...it could idle cleanly and get great gas mileage as it was. All i needed was the ability to tailor the spark curve and it could have been perfect. I was planning on either hcaking the ECM or just building a stand alone timing computer from discrete components, depending on how insane i was feeling at kick-off.

Aha, i think i have found the compromise solution....there is an IF but i'll get to that in a minute. Rather than building a stand alone timing conputer myself, just use an inexpensive TBI ECM as my timing computer, burning spark curves based on as few (rpm alone) to as many (VAC/TPS/CTS/rpm) as desired. Piggyback the TBI ecm into the actual 'fire' signal to the distributor, cutting that line to the old carb ecm.
The IF is this, i don't know IF the carb ecm would get pissy if it didn't see it's idea of timing coming back on the reference signal.
Hell, even IF it did **** off the ecm, you could always switch which ECM controls the distributor based on a full throttle microswitch. So when you go full throttle you start using the TBI imagined spark curve, throwing a code but since PE mode in a carb is the same as limp home mode as far as fueling is concerned, and the spark curve was being sent by a happy ecm, you'd have the best of all worlds, and for no real invetment of time other than splicing in teh sensors and hooking up a double throw relay to the microswicth to decide which timing to use.

It would work....hell, it will work...when i add a musclecar to my stable, i am going to swap CCCS in, on purpose, just to use this idea. People will call me mad, but i'll laugh as i get TPI like gas mileage and still be using inexpensive carb parts.
....ed

 

I wrote a bunch of crap about modding the computer quad,, just to go back and see you were asking specifically about the ignition curves,, and you already ahd "mods" on the Q-Jet.

I don't know how much benefit you'd gain over the existing system's program,, but you can't compare a mechanical advance system to the computer controlled system - nothing new huh?

I've got an old stand alone computer controlled distributor system made by Edelbrock. Can't figure out why they discontinued it,,, probably cause they marketed it mainly for "towing" - I know no one else that has one,,, and only the people that know I have one around here,,,, have ever heard about it. What a shame!!! It's got a number of predetermined curves you can select. I'm pretty good with tuning in a mechanical advanced distributor,,, but the computer control advancement (Edelbrock system) is usually good for at least .10 better ETs,,, and just a HUGE HUGE difference in part throttle response!!!!

Best of luck in the programming quest.

[This message has been edited by BadSS (edited February 21, 2001).]

 

Hey badSS i know what you're talking about...called something like the micro-plus timing computer. An OLD regular (Paul Huryk) had at least one or two of 'em in his cars.

Besides this outburst of using an easy to program TBI computer to piggyback the timing, i had played with the idea of making a stand along timing computer of my own with discrete components. That idea fell apart when the information i needed never fell on my lap, and i never had the time, or was too lazy to find it. I also realized the easiest way would be to use a homemade stand alone processor driven piggyback rather than building a super complex state machine, as code is a lot easier to rewrite than tweaking hardware. But of course, even easier still is my current rant on using GMs stand alone timing computer, also known as the well hacked 747
...ed