I have a 1991 Z28 with a 305 V8 and an automatic transmission. It gets about 11-12 mpg around town. I drive to school and little around not, but that's about it. How come I look on other mpg threads and people are getting 16+?

If I drive my car around for about 15 minutes or so service engine soon comes on. If you check the code it gives a 32 - EGR failure code. If you shut the car off and turn it back on it goes away. We are planning to fix the EGR problem soon. Could the EGR be causing such low gas mileage?

 

Anyone at all?

 

I'm not totally sure, since I still need to replace my egr valve. but I get pretty bad gas mileage myself...(although I hot rod it pretty bad, do you also? that will also make a difference) but have you tried a regular tune up? oil change, spark plugs etc. depending on how bad they are it can make quite a notible difference. also, the guys at autozone might be able to tell you about your egr valve.

 

You haven't provided a lot of information, such as how many miles are on the motor, if it has been rebuilt, and recent maintenance done that may have contributed to this situation. Poor mileage can be caused by many things, i.e. O2 sensor gone bad, disconnected or broken vacuum hoses, and a number of other things which escape me right now. The fuel injected engines need input from the coolant temp sensor and the oxygen sensor, so if there is a problem with those, then the computer goes into open loop mode which is full rich. That can cause bad mileage. Are all your sensors connected?

 

The motor has 154,000 miles on, I don't think it has ever been rebuilt, we added transmission fluid to it and some anti freeze in the reserve tank. We have not done spark plugs because they are hard to get to and oil doesn't need to be changed till 156,000. The main vacuum hose had a crack in it for about the first 3 weeks I had it, and we have since fixed that, which makes it idle much smoother.

As far as I know all sensors should be hooked up. I don't know where they specifically are though to check.

As for hot rodding around, I really don't do that much. I coast up to lights if they are red, and don't get off lights fast, and don't drive over the speed limit, so I don't think I should be getting such poor results.

 

If you answer yes to the following question, then there's your answer..

1) Do you have a Quadra-junk equipped F-Body?

 

With that amount of miles on the motor, and no history of maintenance performed, it is possible that the oxygen sensor has died. These sensors can last almost 100k miles, but beyond that it's a crap shoot. This is the exhaust gas sniffer that's located usually under the car below the exhaust manifolds. If it is bad and causing the computer to go full rich, then it won't be long before your catalytic converter dies as well. Here in California we have to pay attention to this because of our smog checks. If it is a simple one wire sensor, it is fairly inexspensive. The hard part is getting the old one out. I recently went through this and took my car to a muffler shop. It cost me $80 bucks and was worth every penny as the mechanic had to struggle with it even with the car in the air.

Other items to check for excessive fuel consumption per most Haynes manuals is: dirty air filter, incorrect timing, incorrect idle speed (should be about 750 rpm), fuel leaks, and dirty or clogged fuel filter and or fuel injectors.

Is your engine the TBI model or the TPI model? The TBI has a typical air cleaner on top of what looks like a carb and only has a couple of injectors. The TPI has the metal plenum with a snorkle coming off the front and has an injecor for each cylinder. I don't mean to be condescending but I don't know your knowledge level. Do the easy things first to eliminate those possibilities. This will help you isolate the problem. Good luck and keep us posted.

 

lol.. did you root him on... you should have suggested a breaker...

 

My car is a TPI. It barely passed emissions here so that might be the problem. When we go to look at the EGR problem I'll suggest looking at the oxygen sensor, because I just filled up on sunday and have only driven 43 miles and I'm already at 3/4 tank.

 

Check idle, it runs at about 760 RPM. Also, it needs the heads to be redone because it blows out a big puff of blue smoke upon startup if that matters at all.

As for timing, I don't know anything about that.

 

Your idle seems to be fine; right in the ball park. The blue smoke is oil from worn valve stem seals and has nothing to do with poor gas mileage. But it is an indicator of engine wear. Having the heads reconditioned is a good idea. This would be a good opportunity to replace that EGR valve, which is probably an original part.

Is your acceleration good with no pinging, and is your idle smooth and steady? If so, then your timing and injectors are probably fine. It would lead you back to a sensor causing the ECM to go into open loop mode. I have no idea how long the car has been operating like this, so its possible that your cat is on its way out also. Do a search on the board for TPI systems and you'll find plenty of information.

Keep us posted.

 

That's pretty sad. Cars are engineered to get approximately 300 miles to a tank. At the rate your going, you'll barely get 200. I have a '96 GMC truck with a 350 and I can get between 300 to 350 miles out of a tank. Check Amazon or go to your local book store and see if you can pick up a book on GM fuel injection systems. Heck, go to your local Kragen/O'Reilly or Autozone and pick up a Haynes for 82-92 F-Body cars.

 

This is a bit extreme as far as some of the maintenance practices, but much of it is good advice.

https://www.thirdgen.org/forums/tech...ce-fellow.html

 

Ok I'll be sure to check all of those things. There is no pinging while driving or accelerating, so I'll just have to check it out. Thanks for all your help