Chevy Silverado
Check Engine Light
Chevy Cheyenne

Why would a 1998 Chevy Cheyenne with a 305 v8 have the service engine soon light come on occasionally and the codes say the right and left bank are running rich what could it be?



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I recently ran into the same codes on my volkswagon, and, through a system of elimination, I was able to find the culprit. Here's my suggestion: Since you've ran a computer diagnostic on it, and the banks are running rich, go through the components and subsystems. 1. When was the last time you had the fuel injection cleaned professionally? A clogged head can cause the fuel injection system to use additional pressure to force fuel past the clog, there by adding too much fuel. A good, professional fuel system cleaning costs about 80 bucks. If you haven't done it in, let's say 60,000 miles, It's worth it to get it done anyway. 2. Is the air filter clean? If it isn't, or if it hasn't been replace in 15,000 miles or so, Go get a new one. They generally run about 10 bucks, but it is vital to the fuel injection system to maintain these minor components. Lack of air, or dirty air often causes the same issue's your seeing. 3. Fuel evaporator valve. Sometimes, they clog, and don't return unused fuel back to the tank. This causes the vehicle to run rich in the air/fuel mixture. They again, are generally cheap, (mine cost 10 bucks) and takes a minute to install. It's a simple plug/ unplug proceedure. 4. Mass Air Meter/ Airflow Meter/ etc... Different vehicles have different names for it. It is the large box that is connected to the intake, it's job is to regulate the amount of air entering the vehicle, and regulate it to make the proper air/fuel mixture. This is mainly a computer issue. Generally speaking, the physical component stays intact, but the sensor/ computer component associated with it goes bad. These items can vary in price tremendously. My first car, a Mazda MX3, had one that went bad, cost 900 bucks. My VW cost on 173 dollars. Do your research on these, try a junk yard, you might be able to get one dirt cheap, and then if that solves the problem, buy a new one down the line. They are generally easy to install, so a home mechanic can replace one in a hour, tops. Hope this helps. My VW was in and out of the shop for two months before we figured it out. I went through all the steps listed about, as well as a few others, and mine turned out to be the meter. IT could be a dirty air filter or a sticking injector.