Mazda Repair: Mazda Protege - CEL and, fuel pressure regulator, exhaust gas analyzer

Question
I have a 99 Mazda Protege Lx, with about 60,000 miles. The check engine light came out about 7 months ago for the first time, then turned off 3 months later. One month went by, and then the light came back on again for good. I took it to my mechanic who said that the results were showing the engine was "running lean". After he checked the hoses, etc. he did not find any leaks, and turned the light off. It came back on after only a few hours of driving it around. He then recommended taking it to a Mazda dealership to have them check the sensors. Do you think htis is necessaary? The car is running great, and I have just replaced several of the belts and plugs, putting about $500 into the car, and have limited funds to now get this problem taken care of. What do you recommend doing? The dealerships I have called charge $100 just to take a look at the car, in addition to repairs. Does it sound like a problem that can easliy be taken care of? The car is up for inspection, and I know it will not pass with the CEL on. Please let me know what you would do to solve this problem. Thanks in advance.""

Answer
Have the regular mechanic check the fuel rail pressure during idle and cruse for at least a half an hour. I would suspect that a partially plugged fuel filter, bad fuel pressure regulator, or weak fuel pump could be at the route of this. A defective oxygen sensor could also cause this problem. As for the running great part, it would run great due to the car running in limp home mode all the time and using a very conservative fuel and timing map to keep the engine happy. Find someone with an exhaust gas analyzer to sufficiently determine if the car is actually running lean or just thinks that it is running lean.
You should not need to take it to the dealership for this problem it is well within the scope of a capable mechanic.
Another thing that is common to the protégé model is deterioration of the intake air tube "rubber tube between air filter and the engine" which cracks and leaks unfiltered / unmetered air into the intake tract causing the computer to think it is getting less air and therefore providing less fuel. This can be checked by gently spraying carburetor cleaner on the intake air tube and surrounding connections and seeing if at any point the engine speed goes up when you hit certain spots. If the intake air tube is found to be leaking it can be removed and cleaned with Castrol super clean and some isopropyl alcohol, then use a spray can of tool handle coating "available at most auto parts stores" to coat the exterior of the hose and seal up all the cracks. If large cracks are found you can do the same cleaning steps and then use duct tape on the inside to bridge the missing aria and fill it with a product called Goop. After the Goop sets up you must remove the tape on the inside and then spray it down with the tool handle coating. That would be the cheap fix. You could also find a used one or get a cold air intake kit from K&N or APC that will replace the whole shebang with a new cleanable filter, shiny metal tube, and flexible silicone couplers for around $100 - $150.

Good luck and let me know if you need more help,

Regards,


John