Date: Thu Nov 28 08:34:28 1991 Subject: Need More Fuel >A friend of mine has a 77 Z with a larger throttle body, mild cam >and somewhat opened up exhaust (no headers though). When I drive >it and compare it to mine, there seems to be little difference and >considering that my car is stock (I had headers for a while, but >got tired of the noise) it would seem that there should be more >power from his setup. > >I also seems that perhaps he needs more fuel in the engine. There >is a larger fuel injector available, I have been told, but I was >wondering if it would be possible to add some resistance to the >water temperature sensor loop to make the fuel system think that >it is colder, and dump in more fuel. > >Has anyone tried this. Any thoughts on whether it might work? The water sensor is not the place to do it. The optimal way is to recalibrate the air flow meter. Once the cover is removed by breaking the silicone seal, there are several adjustments available. Among them: spring bias - serves as a span adjustment wiper offset - serves as a baseline adjustment segment resistors - calibrates the mixture at a particular throttle opening. The wiper offset adjustment, accomplished by loosening the screw that locates the potentionmeter wiper on the flapper shaft, has the most marked effect on the low end of the range. This is because the resistance vs flow is very non-linear and the most rapid change is off-idle. Small changes make BIG mixture changes. Changing the segment resistors, while a lot of work, is well worth it. One can then change the mixture at a particular flow that might be problematic. the segment resistors are those laser trimmed silk screened resistors that shunt various parts of the main pot. resistance. The procedure is as follows: Cut one trace to each resistor as near to the resistor as possible. Measure the resistance and record it. Select a 10 turn trim-pot equal to twice the value for each resistance. This means that the pot will be set at approximately the midpoint for stock conditions. Mount the pots appropriately. Very small pots can be fit under the cover. Larger ones can be mounted in a small box with wires run to the flowmeter. Attach the wires to the main resistance by carefully scraping the traces to the old resistors clean, superglueing a wire down to each trace for mechanical strength and then making the electrical connection with silver-bearing electrically conductive paint (or epoxee if you have it.) The paint for repairing rear window defrosters works fine. The wires should connect such that they connect to the traces upstream of where you cut the original resistor out of the circuit. It should duplicate the electrical circuit of original setup. Calibration is most easily accomplished by setting each pot to the midpoint by measuring the ohms before glueing them down. After the pots are bonded in place, connect a voltmeter between the low end of the pot (where the wiper rests when the engine is off) and the wiper. Run the leads so that the voltmeter is in the cockpit. Drive the car and note the voltage at which some problem is observed. Stop and manually position the air flapper until you get the same voltage reading. Then observe the arm position and notice which pot spans that location. That pot can then be adjusted. As you might expect, the adjustments interact so make small ones and keep careful notes so you can duplicate where you were last when you screw something up. An exhaust analyzer makes the task much easier. Inexpensive lambda sensor-based units are available from MSD and Summit Racing. tuning the air flow meter combined with adjusting where the WOT contacts make up on the throttle body (essentially a step change enrichment.) will yield a very responsive engine that can easily pass an idle emissions sniff test. John |