What is the ECM # of the computers in the LG4 cars, 1985 Iroc-z LG4, and I have the equipment to burn chips, is there anything I can do to the chip to get more out of the car or get it to run more efficient? And if so what can I do. Thanks again!

 

The ECM controls primary mixture by looking at MAP/BARO and throttle position and constantly rewriting these blocks by looking at O2 readings. The secondaries are still fully mechanical so the ECM doesn't affect WOT throttle performance except to command full-rich on the primaries at large throttle openings. It does control ignition timing though and some improvement could probably be done here to custom tailor the curve to the engine and mods.

Because the system is so simple it can be mechanically adjusted to work on most streetable systems without PROM tuning. That's probably why there's not a lot out there on these chips.

 

Is there a write up on these boards somewhere on properly tuning these carbs? Also you said that it takes readings from a MAP sensor, I have a TBI car and know that the map sensor is in the cowl lip on my car and there is also one on the LG4 car I am working on, but there isnt any hose hooked up to it, where should that hose run to? Just a vacuum connection on the carb somewhere, I think the car might not be running to its best because this is not connected, thanks!

 

The computer controlled QJet cars actually have 2 sensors. A VAC sensor (measures intake vacuum- exactly the same as a MAP sensor on a fuel injected car, except it reads in reverse) and a second sensor- a BARO sensor which reads ambient barometric pressure (looks just like the VAC sensor but doesn't have a vacuum line hooked up to the hose nipple).

I think one of these sensors is hiding over by the power brake booster, but I honestly can't remember. Trace vacuum lines and you'll find it.

On the primary side there is nothing really to "tune" but there are adjustments that must be set properly. Not for the novice to play around with. If your carb has never been rebuilt or torn into (rare, but possible) then I'd leave it alone unless you're SURE it's an internal carb problem. If it has been monkeyed with before then it's about 99% likely whoever touched it messed it up, in which case it might be worth digging into. Check for factory "anti-tamper plugs" over the idle mixture screws, IAB, rich/lean stop adjustments and TPS adjustment as signs of previous owners monkeying with the carb.

 

Does anyone have a layout of the vacuum routing that is easy to read and deciferable in lamins terms, ive seached and found that one vacuum routing diagram, but heck, i dont know where all of that stuff is or what its called, i need a diagram or pictures or a detailed description of where all the vacuum hoses go, the car i am working on is for a freind and we put a holley rebuilt q-jet on it, but my freind pulled everything out of the car he didnt mark anything or remember where everything went, and im a fuel injection guy so i dont know a whole lot about the q-jets, so any info would be greatly appreciated, thanks!

 

There are a bunch of photos in the Engine Swap forum "Father/Son project" sticky.

There is also a photo thread on this forum.

You should be able to search for any item you don't understand (like what/where EFE is).

 

A shop manual write up on adjusting the q-jet can be found in:

https://www.thirdgen.org/forums/carb...s-problem.html

(Board doesn't like me posting same file twice)

As Damon says: "VAC" sensor at brake booster and "BARO" sensor on opposite side of fire wall. ECM looks at Baro sensor to normalize the vaccuum readings and derive an "absolute pressure" reading rather than a "vaccuum" reading-adjusts for changes in altitude, etc. Vaccuum line to the Baro sensor is a thin, hard plastic line connected to the rear of the carb and coming from the convoluted tubing behind the distributor. Hard plastic and thin to provide more sensitive and quicker readings to sensor than regular rubber line.

 

Ok, read all through that Father son thread, still not giving me the info I need, i dont need the hose routing diagrams, i have those, I need detailed information on the hose routing, and I have a map sensor in the cowl lip without any hose attached to it, i just need some either detailed pics of CC carbs on peoples car or maybe i will post a pic of the carb and number all the connections and someone can fill in the blanks, thanks!

 

The vac sensor and baro sensor are the same part. The only difference is the vac sensor has the vaccuum hose attached and it's mounted near the brake booster. Post your pic, that would probably be easiest.