I have no idea where else to ask. I have a 95’ Z34 3.4L car that I’ve had for almost three years now. I drive it daily, and used to average 16-20 mpg. Now all of the sudden I'm averaging 9-11 MPG. No engine trouble whatsoever. No knocking, vibrating, stuttering, etc. the vehicle performs as it always has. No hesitation or anything like that. The only thing I have done recently is changed the timing belt, but all of the timing was still in check, and this is my second time replacing that (which is a whole other issue). The first time changing it I had no MPG loss at all. I have no idea whats going on. No codes or check engine lights either. Any ideas?

 

The few things that come to mind would be:
1. Fuel filter, Air Filter
2. PVC valve is going bad
3. Fuel injectors need to be cleaned
4. Mas Airflow Sensor is dirty
5. Exhaust system is choked off might be a bad Cat Converter
6. The fuel pump might be going bad
7. down stream oxygen sensor
8. Spark Plugs
This is all usual maintenance things you should be doing in a 25-30K window if you haven't it could be something in this list
Check the fuel lines to see if there are any leaks in the system from the fuel tank to the engine.

 

Thanks for this, I have to replace the power steering pump tomorrow, so i'm going to go over all of these things tomorrow. Bad thing is I have a lot of driving to do in the coming weeks, trips 2+ hours or more in one direction multiple weekends. Hoping to get it sorted before then. I think I will go ahead and replace the the mass airflow sensor just to do it no matter what.

 

Did yoy ever figure out the issue? I have a 96 and am at 8 mpg