MX-3.com

Hello all, I bought a '94 MX-3 with a 1.6dohc about 3 months ago and I am getting very poor gas milage. Last tank I got 14mpg and the tank before that was about 16mpg. I only drive about 8 miles per day. I have done the following maintance fixes with no change in the cars mpg.

New Plugs
New Wires
New Dist Cap & Rotor
New Fuel Filter
New CAI Filter
Checked for any intake leaks
New Valve Cover Gasket
New Ball joints % Tie rod Ends
Complete breakdown of intake throttle body, IAS including
a scrubdown, New gaskets, and adjusted and cleaned everything as in Tunes writeup
Checked air in tires and all are @ 44psi
Replaced O2 Sensor
I also tested and Cleaned all the EGR selenoids
Did Seafoam cleaner in brake vacuum 2 tanks ago
Ran Fuel injector cleaner 3 tanks ago

The car only has a few mods including a CAI, Aftermarket exhaust, and 17" low profiles tires/wheels. I dont run the A/C nor drive the car very hard. I am stumped and have no clue what to do next. Could this be a stuck injector or a problem with the fuel pressure regulator? Or possibly a bad Cat?


Any help is greatly appreciated.

Thanks Tony.

First thing I would do would be to do a compression test on your engine. Simple test to do, you can get a compression tester at any autoparts store and they are relatively cheap ($20 on up). You will find procedures in the online shop manual on how to do the compression test. When I bought my car at the end of January.. It too showed low mileage.. oddly enough.. same year and engine as yours. My problem turned out to be a burned valve. My #3 cylinder had almost no compression. (If you do a search you can find my original posts where I stumbled along before finding the problem LOL) Now my mileage wasnt quite as bad as yours.. I was averaging around 20 mpg. So you might have more than 1 burned valve. Another symptom of burned valves would be an relatively harsh idle. Just for reference.. My engine now shows 185 PSI in all 4 cylinders (after my machinist and I rebuilt the head and replaced all the exaust valves)

Another thing to check would be your initial timing. It should be around 10 degrees BTC. Again you will find procedures in the online shop manual on how to check it.

Is your car an ATX car or MTX? If ATX.. like me.. you got hosed LOL The ATX trans in these cars suck big time.. One of the more inefficient ATX's I have come across.. They sap horse power and as a result.. gas mileage. On top of that.. you have aftermarket rims as well. If those rims and tires weigh significantly more than the factory ones.. that will also affect your mileage adversely. Also.. the wider the rubber the more friction your power train has to over come to get your car rolling. Pizza cutter tires & wheels get better mileage than wide performance tires. Hope this helps out man. Post back with your findings.

Tunes67

Thanks for the speedy feedback Tunes. I'm picking up a Compression tester in a bit and will run the test tonight. I'll post results soon as I have them. My car is a Manual so that should help milage a bit. My car idles awesome the only problem with any idle issue is sometimes it will idle at 1k then like 1-3 seconds later drop down to 800rpms other times it idles down too 800rpms smoothly. My tires dont seem too much heavier then my freinds civics stock steelys but I havent put them on a scale to get actual weights.

I'll post some results after I leave my store.


Thanks again.

Tony.

Think maybe its running in safe mode?
Try resetting your ecu.
Remove - battery cable and push on the brake pedal for like 30 seconds . Reconect and drive around.

Ok just did a compression test with the engine both hot and cold. Here are the results.

Cold:
Cyl 1 - 183, Cyl 2 - 181, Cyl 3 - 183, Cyl 4 - 179

Hot:
Cyl 1 - 182, Cyl 2 - 182, Cyl 3 - 182, Cyl 4 - 178

Are these ok???


I have reset and cleared out the ECU, also set it back up when I cleaned out the whole intake system with the 10 and ground jumper. I'm stumped other then a stuck injector. Every once in a while I do get a check engine light that comes on. If I down the key off then on it goes away. I'm not sure how to read codes and cant seem to find a walkthru on how to do it.

Tony.

Forgot to mention on my last inspection a couple weeks ago I failed NOX. The mechanic said my car could be running to rich and thats what causes high Nox readings.



Thanks again guys.
Tony.

Your compression is fine. A few PSI variance isn't going to matter.

how do you fix NOX readings, lean out car

Yeah those compression numbers are great man.. no issue there.. try pulling CEL Codes and see what pops up from that. And check that initial timing

Tunes67

chec your coolent temp sensor,your ecu mite be getting wrong temp signals and running rich.

Pulling codes is easy..

Jumper TEN and GND
Turn your key to the run position (do not start)
count the flashes from your CEL

There are a few posts around about it.. and once you have the codes there is a list of what the codes are. Cheers

Tunes67

Ok I know about the 10 and ground jumper but what the heck is a CEL?

Lol, sorry for being stupid.
Tony.

CEL = Check Engine Light

And dont worry about appearing smart or whatever.. Intelligence isnt measured by knowledge.. its measured by what you do with your knowledge

Tunes67

Ok here is the Code, I realized CEL meant check engine light but it was after I posted, lol

Its one long, then six shorts. Like this

---------______--_--_--_--_--_--_

_ is the Pauses, - is the CEL



Tony.

That would be code 16 then.. Grants has a list of all the codes on his website under "Info" hang on a sec and I will look it up.

Tunes67