After doing alot of engine mods on my 87 Monte SS L69 305 with the 1228079 ECM...I've been experimenting with an adjustable VAC Sensor voltage regulator. I built a regulator to boost the 5v reference to a higher input...Basically it fools the ECM into thinking the engine still has a stock cam pulling a voltage of 4.3v @ 20". Without it, the VAC was 3.2v @ 15" and it cost $10 at Radio Shack.

Anyway....It works great...Timing advance is restored and a TCC issue is corrected!

My question is....If I could build a unit, that would adjust the reference voltage separately on the TPS, Coolant,VAC, and maybe even the ignition module...wouldn't this have the same or similar effect as drilling into the code? I appriciate what you guys are doing and I love this stuff..Electronics and engines go hand in hand and it's a great hobby and my approach is different, but...hey ..it's all about working on cars!!!
what are your comments?

 

I cant say for sure because there are others much smarter on this subject than myself but I would think it would serve a simular purpose. Chip tuning does have the added advantage where as with a "module" it's a "constant change over the entire range, where as with chip tuning you have the ability to change to a different value (up or down) at any given point. I did the exact same thing as you and built a module to manipulte the MAP sensor voltage, but I added a potentiometer to make it adjustable and tunable.

The drawback that I noticed was the farther away from stock the cam profile was, the more the "module" wasn't able to compensate for the change. So in my opinion, if your not straying too far from stock, (like a cat removal, header install, small cam change, cold air kit, ect, ) a module could be an affortable alternative to chip burning as a means to optomize that change.

 

I agree...chip tuning have "load points" I guess..very accurate!
In the automotive electronics world...devices like mine are called "Interceptors". My volt adjuster intercepts the voltage, modifies it, and sends it to the ECM. It's crude and works great for restoring the light throttle cruise timing advance but, at WOT... the voltage is now a little high for WOT causing the timing to bounce off the knock sensor. I built a voltage switch with it so it can switch back to the stock 5v reference input, at what ever voltage I want... which should then restore the WOT volts and timing! Need to install it yet though. I think it will work!

 

I have a 87 el camino. Put mutple ecms in it. Were not getting anything out of the 5v reference pin 21. replacing bero and vac sensor and connectors. Sending ecm back.
all 3 do the same thing . Do you any advice.
Gary

 

Sounds like a bad computer. 5v should be delivered to all the sensors. I built a voltage regulator for $2.00. 12v in from the battery changes it down to 5v, or what ever voltage I need. Check out the LM317 voltage regulator.
(more later)

 

Its much better to actually go in and adjust the parameters, especially the timing. Your probably leaving a lot of performance on the floor by just using whatever was specified for the L69 stock.

Theres also the issue that the sensor may not like being fed more voltage than whats normally specified. Whats the total voltage in?

A better way to do it would be to use an adjustable low gain op-amp to scale the sensor output voltage to the ECM. This way you can have more control over the output and not have to overvolt the sensor.

 

There's also some good info in the Tuning Guidebook in the stickys under "CCC(Computer Controlled Carb)"
Some things can be changed others can not without difficulty.

 

Good point...it's been 3or4years since I installed the voltage device on the vac sensor. I think the volts going in is 5.2, 5.4v...I used a junkyard vac sensor for the first series of tests, so far it's been one of the best modifications that I've done. The 1987 computer q-jets also have an adjustable voltage on the throttle position sensor, that's how I came up with the vac volts idea. I've recently installed a 350 with all the guts from the 305 buildup and with some throttle position, vac volt adjustments,...she's running great!