I have an '88 FC GXL. It's 5th and 6th are seized shut and I recently had my rusted out exhaust and catt replaced with a nice long piece of alluminum tubing for $40.

I'm getting horrible gas mileage these days. I drive mainly in the city and normally shift at or before 3,000rmps.. I'm getting about 16.5-17.5mpg (200miles per tank).

Is this normally fo an N/A or is this because of the exhaust (o2 sensor issues) or 5th and 6th port? What else can I look into and replace to help my engine run better? Is uncloging my ports something I can do with ease and in a few hours or should I take it to a Rotary shop and shell out the cash. Will deleting my air-pump improve fuel economy and power?

Thanks.

 

it is normal for a n/a to run rich because the factory program the ecu that way. but if your aux. ports are seized then you should consider cleaning them out. if you get it done, try driving a lil above 4k to open them up. and also check your actuators to see if they're working properly

 

btw, your mileage is pretty normal.

 

I dunno about that. I get around 300 miles to the tank in my 86 N/A. The only thing I have done to it is intake filter and catback exhaust really. It really depends on how heavy your foot is.

 

Never above 3k, thats the thing, I would expect this kind of mileage if I was flooring it and shifting at 5,500 RPMs all the time, however I'm not. 16-17mpg is TII territory to my understanding. I'm only making 100hp at this rate.

 

flooring and shifting at red gets me like 10mpg, stock 86 n/a was rated at 17 mpg city and 24 highway.

 

I got 18 or so with a pretty heavy foot, but that was with a fresh rebuild. For an older engine with lower compression 16-17 isn't that abnormal. Its also possible the injectors need to be cleaned which can hurt milage.
If the aux ports are siezed shut then I can say without any doubt that they have no effect whatsoever on the gas milage, except possibly helping it in high-rpm driving.
Also, hes only getting 200 miles per tank because hes not running near empty. Assuming 17 mpg and using 16 gallons (almost a full tank) he could go 270+ miles. Quoting milage per tank is very misleading because you don't know how empty it got.

 

17mpg is on the low side of normal. You could improve it with basic tuneup stuff maybe.

And believe it or not people, N/A's don't run that rich in around town driving. I'm probably one of the only people here who actually has a wideband on his N/A, and I can tell you that it will stay around stoich (between 14 and 15:1) just like any other car. Under light acceleration it will drop into the 13's. It's only under WOT that it will drop into the 11's once you hit around 5 grand or so, at least on my car (which is heavily modded for a street car).

 

i i have a 88gxl. a new fuel pump filter n o2 sensor will unbeleivably bring your gas mileage up. i had close to 180 hp and i was getting around 23 mpg. its all in the tunning.

light rims help a lot too lol. i had convertible rims so it helped a lot.

 

It is normal for any stock engine to run rich under load, but it is not normal to run rich at other times.

 

including idle?

 

i get almost 300 from a tank on both my 85 gsl se and my 88 gsl both na. between 17 and 20 mpg pretty much however I drive it.

 

If the cats are gone with a straight pipe then the auxiliary ports won't open even if they are unstuck. If the problem with the ports didnt develop until after that exhaust work then they are not stuck, they just wont open without the split air pipe from your old main cat hooked up somehow. You'll have to rig up some other way of activating those. As far as the mileage i agree that is on the low side of normal a tuneup might help a little. I get ~20mpg and usually shift around 4 with mostly light throttle.

 

Rotaries like to idle a little bit on the rich side, but nowhere near as rich as full load.

 

the 5th&6th where clogged before the exhuast.