Okay guys this is my first honda i ever owned and its a 1988 crx dx with automatic transmission, 201k miles and is all stock.

I've been doing a lot of maintenance work on the car to get it to run good but the last thing i did or a shop did was to replace the old worn out and leaking exhaust pipe and catalytic convertor and muffler, a day later i noticed the gas milage is horrible compared to before i took the car to the exhaust shop.

The car runs just a good as before but the problem is fuel consumption , the only thing i can think of is that is running too rich , any other ideas ?

I would hate to go back to the stock cat but i thats gonna fix the problem ill have to do it.

 

Howdy EF'n Guy/Gal and welcome

Whats the size of your piping?

 

My first guess would be something to do with the o2 sensor. I assume the o2 sensor got plugged back in right? Are you getting any CEL codes (check engine light)?

Winter gas blends will tend to reduce your MPG, but only slightly.

Additional background info would help. What MPG did you get before and after? Have you checked more than once? is it running like normal,ect.?

 

Not sure you could get any kind of accurate MPG readings in just 1 day...

You should do at LEAST 5 gallons/150 miles to get a good reading.
Top off the tank
Drive for 150-200 miles
Top tank back off

Record the amount of gas it takes to fill all the way up. Record miles driven since last fill up. Divide miles by gallons.

 

First of all i wanna thank you all for the replies & interest in helping or at least trying to help, second, i didn't get an exact measurement of how many miles per gallon i was getting before this problem for whatever reason, all i know is that i could do a lot of driving with a few bucks in gas. Now the gas needle it's lower almost every time i get in the car and its very frustrating because i bought the car knowing i can get much more mpg's then my toyota but it now is just as bad as the other car lol.

I called the exhaust shop and ask them all kind of questions , he replace the piping with the same as the original one he said 1 3/4" for the piping and 2 1/4" for the cat. The same guy said this is normal when you put a new cat, the exhaust gas flows cleaner and faster making the car less efficient? this sounds wrong, but he said the same thing happen to his car after he installed a new cat, the mpg's drop a little. I don't believe this, to me it should be more efficient not less efficient but i could be wrong.

They also said there was no o2 sensor to mess with so i guess my car only has one o2 sensor and that would be the one on the exhaust manifold?

There are no cel or check engine light , and the rex runs just as good as it did before, like i said the only problem here is that is sucking gas like a v6 or v8 and its got a tinny 1.5L engine, there's gotta be something wrong.

I did use seafoam mixed with gas, i only used half of the can before pumping gas, no seafoam on a vacum line or engine oil just mixed with 87 octane fuel.

 

You should at least get an accurate MPG reading before you make any claims that you are getting bad MPG. It may just SEEM like you are.

Use the above method and let us know what you get.
What engine is it? D15B2?

 

^^ I appreciate your semi- interest , i've been driving this car for a while and know something is not right and i don't have the time nor money to keep dumping it on gas at $3.25/gallon or what you call "accurate MPG reading " but thanks dude.

Any others that might have an idea or can steer me where/what to look for i'll appreciate it.

 

Stop guessing. To drive the car, you need to put gas in it anyway. Zero the tripmeter, fill up the tank, run until near empty, and then refill the tank. Precisely measure the mpg by dividing miles driven by gallons needed to fill tank.

Also:

Does the CEL work?

If you pull the carpet down to expose the ECU, is the LED blinking any codes?

Another cause of poor gas mileage is an exhaust leak near the O2 sensor. Have you checked for that? This seems potentially relevant as you just had some exhaust system work done.

 

It's also possible that the fuel gauge sender unit is bad, sending a false signal. So you may have more fuel in the tank then the gauge actually shows.

 

RonJ@ H-town. Thanks for the ideas, i didn't know the computer was hiding under the carpet, ill look for it and check if it blinks but i believe the light on the dash for "check engine" does work but i can verify following ur suggestion to expose the ecu and check, thanks a bunch.

I did order a new oem ntk O2 sensor so it should arrive tomorrow , something tells me it went bad after the fuel cycle when i added half of can of seafoam cleaner but i could be wrong , ill replace it anyways. But now that you say a leak on the exhaust it remind it me when the exhaust guy was removing the old piping he wiggled the pipe a few times which might of cause something to come a little lose or leak somewhere near the header or down pipe or both.

If you happen to know someone in the Houston area that i can take the ecu to please let me know, maybe the can do some data loggin and figure out what's wrong since these cars don't have obd ports .

yeahd00shaun- im gonna check for that too, but i just pumped a little over 7 gallons of fuel last stop a the gas station so that kind of tells me the gauge was working when it read almost empty.

Alright thanks, for the support.

 

aaaaaand I'm out...

 

Just do everything RonJ tells you to do. He is a wizard with mystical troubleshooting powers lol.

 

^^ Will do! haha.

 

thats cool man keep up the good work

 

Hey ecoweapon, can you please post the outcome if you get it all figured out. I've done a lot so far to my d15b2 but it still smells to be running rich and on my last fillup only got about 22mpg.

 

^ Im still trying to figure out what's happening and you're right Im also getting in the 20~ish mpg which is really bad for a 1.5 litter engine, even worst no warning lights or cel light to al least steer me in the right direction . I will post here once I fix the problem if i can trace it down.

 

How do you know you're only getting "~20 ish MPG" when your self-stated MPG calculator beforehand was that you could "do a lot of driving with a few bucks in gas"?

So the gas needle being "lower almost every time i get in the car" equals ~20 ish MPG according to your butt-o-meter?

Since you refuse to calculate your MPG for diagnostic purposes, how exactly will you know if and when you solve the problem? Just curious