I just pulled my 88 GTA w/ L98 TPI 350 out of storage a few weeks ago. When I parked it in early December, I was getting between 18-21 MPG, and now for some reason I get 10-12 .

The car runs great, I don't see any fuel leaks/puddles, or smell raw fuel. No check engine light either. It seems to run exactly the same as it did when I put it away in December, only it consumes twice the fuel it used to. Does anyone know what the problem might be? How to fix it? Getting 130 miles to a tank before having to fill it up again sucks!

 

check for a stuck injecter, make sure regulater is ok. seems if you've lost 50% of the milage you'd notice a change in preformance. guess checking all the tune up parts would be good idea too.

 

I replaced the cap, rotor, and plugs about a year ago. The wires are less than 2 years old, and the coil was replaced about 3 years ago. I have a Holley AFPR on it, which is set a bit rich...but I haven't touched it in a long time. I'm thinking it's probably a stuck injector like you said. Is there any way I can do a shop-quality injector flush myself?

 

You're in E. Lansing, and not very far from Cruzin' Performance at all.

You might also consider a lazy O² sensor as a prime cause. Is it more than 30K miles old? Is the EST functioning?

 

The O2 sensor is only about 20k miles old. How do I tell if the EST is working properly? I'm not getting any pinging or anything...

Thanks for that cruzin performance link, I may end up sending my injectors over there. Only problem with that, is my car will be down until those come back .

 

Connect your timing light, start and warm the engine, then check timing. Remove the EST bypass connector and observe the timing for any change (might as well check the base timign while you're at it). You should see some significant advance when the EST is active.

 

Well, thanks for the help guys....but I think I've found the problem (or lack thereof). It's called "some asswipe has been siphoning my gas in the parking lot."

I got 130 miles out of my last full tank. Fast forward to yesterday, I fill the tank and put 150 highway miles on my car, and it's sitting at half full right now.

Locking gas cap goes on today.

 

that happend to me before... my neighbor used to steal my gas to put in his 5.0 lx m*****g... my cell phone rang at like 2 am and i went outside to answer it because i have no reception in my house, and i see the assfuk there at my gas tank with about 4 gallons filled in his 5 gallon tank... taking my gas cost him a tooth and 2 broken ribs. i never would have thought that was happening in a million years, lmao.

how'd you find out someone was siphoning your gas?

 

I set the trip odometer last time I filled up, and I was on fumes after only 130 miles. Then, I filled it up again and reset the trip odometer and got well over 200 miles out of that tank, without changing anything except I was at a buddy's place and not parked at my apartment overnight.

Basically I eliminated everything else, and figured out that somebody must be stealing my gas. And what do you know, I haven't noticed any abnormal gas mileage since that locking cap went on there.

I still wish I could have caught him in the act though.

 

At $2 /gallon, that's going to become more of an issue in the U.S.