QuestionHi Mike,
I have an 88 grand am LE and I just replaced the fuel pump after getting a lean exhaust code. Now I'm getting a rich exhaust code, and whenever I stop at a light or for a period of time, the check engine light comes on - but goes away once I start driving again. I believe this could be caused by a fuel pressure regulator. The one in the car is the original, as was the fuel pump. What do you think? Any help would be greatly appreciated.
Thank you!
Answer First I would like to know that you have cleaned the injector(s). Dirty injectors can cause all kinds of mixture problems; the fuel comes out in big drops, instead of being properly atomized, and can cause richness at idle and leanness under load. Get a good quality in-the-tank cleaner (I prefer the one made by Redline) and put it in a nearly-empty tank. Run it on that for twenty or thirty miles and then fill the tank with gas. Using it in the nearly empty tank makes it more concentrated and speeds up the process of cleaning. There are far more involved injector cleaning methods using expensive equipment that do a slightly better job, but my experience with the Redline cleaner has been so good that I rarely resort to anything more elaborate.
If this doesn't solve the problem then, yes, I would go after the pressure regulator next. I would also change the oxygen sensor, just for drill, as they are pretty cheap and can also cause mixture problems. The computers in these older cars have no way of knowing if the oxygen sensor is working properly or not, so a new one is not a bad idea, just in case.
But, I would be willing to bet that it's dirty injectors. The gasoline companies would like you to think that they put a cleaner in the fuel, but gunk still builds up. I like to put a bottle of cleaner in about twice a year. If you do that, you'll never have any problems with the injectors, unless one fails altogether.
