94 50 Convertable. Horrible Gas Milage 12-13

texmirage · Apr 25, 2013

bought this car about a month ago.
5.0 auto it has
unknown cam
BBK headers
BBK No cat h pipe
Some aftermarket mufflers
filter
pullies
Throttle body spacer plate
rear gear is about 3:27.... or close to that
It had a wet NOS setup but I have disconnected that. That brought it from 10-13.
everything else is Factory. including the injectors

When I get home or go somewhere I will actually smell like exhaust fumes on my clothes.
When I had my other 94 a year ago it didn't do this. It basically had the same exaust set up as this car.

My first guess is the oxygen sensors then i'm not sure what to look for after that. I was thinkin about putting a catted mid pipe on it I'm sure that will help but there has to be something else causing the bad MPG

Any thought would be appreciated.

ratio411 · Apr 25, 2013

Start with the o2 sensors, but since it has a cam, it will probably need professional tuning on the ECM.
The SN95 ECMs are notorious for reacting poorly to cams, compared to the Fox ECMs anyway.

Cats are not going to help. Any obstruction in the exhaust flow, even if cleaning up the fumes, will hurt mileage.

Besides the ECM though, look at 02 sensors as they default rich (more fuel) when they go out, and maybe the MAF.

texmirage · Apr 25, 2013

ratio411 said:
02 sensors as they default rich (more fuel) when they go out, .

That actualy makes alot of since to my problem. it wouldn't hurt to change them anyway

95BlueStallion · Apr 28, 2013

The smell is from a lack of cats, no getting around that. It is only magnified by your rich condition. Have you checked the plugs? They could be fouled and not burning all the fuel in the combustion chambers as well, but will only foul again until you get it tuned properly.

ratio411 · Apr 28, 2013

95BlueStallion said:
The smell is from a lack of cats, no getting around that.

True to a degree, however, there is a difference between the smell of no-cats vs the smell of rich.
Cars were around for 75 years without cats, and as long as the car ran right, people didn't complain of their clothes stinking after they drove a car. The smell created by a lack of cats is just 'different', not overwhelming.

95BlueStallion · Apr 28, 2013

Hence why I said, "It is only magnified by your rich condition."

texmirage · Apr 29, 2013

I replace the o2's and the help out with the gas smell. MPG is up 15 now I have run some more gas and check again.

what other things might I be able to check help MPG.

Chythar · Apr 30, 2013

If I drive in stop-and-go traffic for most of a tank here in LA my Cobra clone can get as low as 15-16 mpg. With some freeway driving (my normal commute) I average 16-18 mpg. Driving mostly freeway I can get 20-21 mpg. Depending on your normal driving habits, you may be at an acceptable gas mileage. I'd also clean the MAF and change the air filter if you haven't done it recently.

ratio411 · May 1, 2013

texmirage said:
I replace the o2's and the help out with the gas smell. MPG is up 15 now I have run some more gas and check again.

what other things might I be able to check help MPG.

Like the last post said, make sure your air filter and MAF are clean and doing their job.
Air up your tires. That makes a bigger difference than you would think.
Alignment...
Run the lowest octane fuel your engine is designed for... Higher octane fuel is less volatile, and won't burn properly if your engine is not built to run it. The fuel companies will never tell anyone that though. They like people thinking that higher octane will give them more power and mpg, but it's not true unless the engine requires it.

joetrainer31 · May 30, 2013

Check your ignition timing. If its not correct (too retarded) you will always have mileage problems. Then check for a clean MAF. Then check for codes. Scanners are $25 on Amazon for OBD1.

94 50 Convertable. Horrible Gas Milage 12-13

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