How to tell if my car is running rich or lean?

Question

hi I have a 1995 240sx stickshift and im catless and proud of it. well my question is if ts running rich how can i fix this or if its running lean how can i fix this thank you =]

Answer 1

Well...since you have obd, you read the computer and it will give you lean or rich codes based on what the 1st o2 sensor is reading. Otherwise you need to actually install a wideband a/f gauge and sensor in your exhaust to read the actual a/f ratio you are getting.



You fix running lean or rich by adjusting the fuel map in your vehicle. Don't just fool with the intake system and add or subtract air because then you'll get MAF codes (or possibly MAP codes if you're turbocharged)...

Answer 2

I'm not familiar with type so this is my opinion only but backed by 20yrs in trade and experience as a Master Tech on Ford and Mazda, You did'nt say if it had always been "Catless" or just had the cat removed but heres a few thoughts,

1/ Get it checked at a garage on a 4 gas analyzer typical correct readings for a non cat would be in the order of O2 1 to 4%, Co 1 to 3%, Co2 12 to 14%, HC 150 to 300ppm, the sooty or dripping tailpipe would tend to show serious departures from norm not the very fine deviation from proper setting.



2/ Didnt mention either if fuelling was done by Injection or Carburettor. for either you will need a manual to locate the Co adjust screw, a Carb it will be near the bottom of the Carb body but you may find there are several, twin barrel units have may have one each or only one if its a progressive type, also may have air bleed screws for fine idle, you realy will need a manual, Most cars from mid eighties now have fuel injection and all cars from 92 in the uk have Cats hence previous observation re Non Cat OEM,



3/ For non cat there will be a trimmer pot either located under the bonnet at some location on inner wing or there abouts, or more awkwardly it will be Built into the Injection control unit which may be difficult to access, another older injection type had a fuel distributor mounted in the air filter box and fed the injectors via reinforced pipes, this version had a 3mm allen screw at the side of the air outlet pipe accessed thro a tube.



4/ If it had a cat on as OEM then there will be NO adjustment for mixture, these systems use and O2 sensor in the exhaust and continually trim the fueling to the correct amount referd to as Lambda 1.0 (This figures on your 4gas sheet also 1.0 perfect < 1 lean >1 Rich ) if this is rich or lean you will need to adress basic engine problem (air leaks missfires etc) or injection problems (High fuel pressure, sensor / wiring faults)



The charm will be knowing which fuelling system you have and what the 4gas results are

Answer 3

On injection car, don't worry about those thing. The computer will control the fuel to inject to mix with air, unless the 240SX use carburator. For visual diagnose, watch the tail pipe. If the color is white, it mean the fuel is too lean. If the color is black or dark, it mean the fuel is too rich. If the right mixture is in the hand, the tail pipe will show grey color. For the correct and detailed value, check the emission.

Answer 4

The best is to use scan tool and monitor short and long term fuel trims, but if you don't have scan tool here is a couple of things: Running rich = decreased fuel economy, engine will have more power, black smoke out of the tail pipe when you step on the gas (bad fuel pressure regulator, leaking injectors, dirty air filter, engine oil contaminated with fuel) Running lean = increased engine temperatures, engine pinging sound, low power on acceleration (vacuum leak, dirty fuel filter, bad fuel pressure regulator, bad fuel pump, dirty injectors, egr stuck open, iac not closing completely)

Answer 5

you are able to in all probability tell if your exhaust smells that like gas or if your vehicle makes use of a great style of gas yet has no potential in case you step on the gas and it has a tendency to stall or backfire or complicated to initiate. Thank God for gas injection!

Answer 6

easiest way is to pull a spark plug from each bank.Real white to lean.Black or wet to rich.That's simple enough.You said your running catless so the guy who says to check your o2 sensor can't read i guess lol

Answer 7

If it is running rich the tail pile might drip unburned fuel and you will smell gasoline. To fix, adjust your timing.