Fuel Management

Is your fuel injected Z (1975 and up) consuming a lot of gas, fouling spark plugs, stumbling on acceleration, or hard to start?  The fault may be with your temperature sensor. The coolant temperature sensor (75-79) or cylinder temperature sensor (80 and up) plays an important role in the performance of your Z car. The sensor "tells" the engine management computer the temperature of the coolant or cylinder head so that it, the computer, can adjust the injector pulse width (the length of time the injectors stay open and therefore the amount of gas that can enter the combustion chamber). The sensor talks to the computer by way of varying resistance (ohms). When the temperature is low the resistance is high and vice versa.

How can we accurately diagnose a bad sensor?

First we need a couple of tools. The most important tool is a factory service manual. The factory manual not only shows the location of the sensor but it also contains a graph and chart that clearly indicates the relationship between temperature and resistance. We will also need an ohm meter. With the engine stone cold disconnect the sensor from the harness. Using your ohm meter measure and record the sensor resistance. Start your engine and allow it to reach approximately 120 degrees as indicated by the coolant temperature gauge. Stop the engine, measure and record the resistance. This step is important because the sensor must be accurate not only at the temperature extremes but also throughout it's range.

Restart the engine and allow it to reach normal operating temperature or about 180 degrees. Stop the engine, measure and record the sensor resistance. If any of your findings vary significantly from the factory specifications you have a defective sensor. It's important to note that if your car has a defective thermostat, stuck fan clutch or anything else that prevents the engine from reaching normal operating temperatures. It CAN NOT operate at maximum efficiency.

A word of caution

Some models employ a short wiring harness between the sensor and the main injection harness. If you find that the sensor is OK you may have a bad sensor harness. It too can be checked with your ohm meter. It should read zero ohms. Frequently the connectors at either end can, over time, become corroded effectively blocking the resistance signal from reaching the computer. As a practical matter whenever I find a bad temperature sensor and a sensor harness that's old and therefore suspect, I replace both simultaneously. It makes good sense.

California Looks to Emissions Test Older Cars, Increase Scrappage Opportunities

California regulators are at it again. Scant months since California’s car club community and SEMA helped beat back a legislative effort by the California Air Resources Board (CARB) to eliminate California’s 30-year rolling emissions testing exemption comes news that the exemption is under fire again. Only this time the consequences are potentially much worse.

California’s I/M Review Committee, the group tasked with developing and evaluating the success of the state’s emissions testing program, has issued a report recommending that 1966-1973 model year vehicles be emissions tested and eligible for scrappage. For the first time, California regulators are specifically targeting “muscle-car” era vehicles. From 1966 Chevelles to 1970 Mustangs to 1973 Chargers, some California regulators want your car in their smog check program. This is even more of a head-scratcher when we remember that pre-1974 vehicles were not originally equipped with modern pollution control equipment.

SEMA has learned that there my be plans afoot to use the committee recommendations in the coming legislative session to, at a minimum, again seek a repeal of the current 30-year rolling emissions exemption. At a maximum, California may try to extend testing back to model-year 1966.

SEMA Action Network Director Brian Caudill notes that, “SEMA-member companies, as well as California SEMA Action Network clubs, individual members and publications, have been encouraged to contact their legislators to oppose repealing California’s emissions testing exemption for older vehicles. We anticipate a tough battle this year and we will need everyone’s help.”

To read the SEMA Legislative Alert on this matter, go to . For information on how to turn this alert into a letter you can send to a California legislator, read SEMA’s information on How to Lobby Your Elected Officials available at www.enjoythedrive.com/cgi.asp?id=49&read=821.