why is my 96 neon getting bad gas mileage (120-150 miles on full tank) and driving at higher than normal rpm?

Asked by Nov 19, 2015 at 10:38 PM about the 1996 Plymouth Neon 4 Dr Highline Sedan

Question type: Maintenance & Repair

The catalytic converter was completely
plugged, so i removed it and ran a straight
pipe. I put new plugs and wires. Installed
new fuel pump and filter. Ran sea foam
through it with premium gas. Replaced oil
pressure sending unit (it was leaking). New
oil and filter. Sprayed some carb cleaner
through the throttle body while it was
running and had someone give it a little gas
so it wouldn't stall out.

I believe the car to have 70k or less miles.
The speedometer/odometer works off and
on and is only at 57k. But the car is pretty
clean under the hood for a 96.

I have to almost stomp the gas to get it
moving sometimes. It accelerates okay
through 1st and 2nd but from 2nd to 3rd the
rpms drop and i have to press the gas pedal
more to speed up. When i do that it jumps
to 3500-4k rpms until it hits the next gear. It
drives at about 2000-2500 rpms when
driving down the road at 35-45. On the
highway it drives from 3k-3500 to maintain
speed.

I know the rpms are higher than normal and
the car seems to be working too hard.

When the rpms jump up high while
accelerating, i can see a cloud of smoke in
my rear view mirror (granted the converter
is removed).

I think its gotta be the map sensor, throttle
body, or injectors. Or possibly the O2
sensors. I just don't know how to pinpoint
the problem. Id replace everything, but ive
already put a lot of money into it, and new
injectors are expensive.

Im going to hook it up to a code scanner in
the morning to check trouble codes. But
prior to all the repairs i did, it was getting a
misfire code and a code saying fuel system
too lean bank 2.

6 Answers

82,835

What color is the exhaust smoke? Black is running rich and blue is burning oil.

Its definitely black

10

My 99 Neon at 75 mph is 3000 Rpm Your clutch might be slipping 2000-2500 Rpm range should get You Interstate speeds 55-65Mph

10

Also may answer bad acceleration problem A way to see if its your clutch, Driving in say 4th gear mash the gas see if Your RPM's jump up without speeding up the car. I am guessing you have a manual transmission.

10

Black smoke =carbon Blue smoke =Oil White Smoke =Water Black smoke most times clear up after a few hard driving sessions/High RPM driving expelling carbon buildup. Blue smoke can be bad valve seals,worn piston rings,Bad PVC system allowing Oil to get into combustion chamber and burning. White smoke after engine warm up means water/coolant is getting into combustion chamber.

10

As for running without a catalytic converter Your on board computer/PCM will generate engine codes like PO420 or code 72 for on board Diagnostics and make the computer run Your gas mixture too rich or lean. Rich sounds like your gas use. Remedy for No CAT Converter is get your PCM special programming, Aftermarket TUNER products can change Your engine timing spark advance gas to air mixture. Not sure if the cost out ways A new CAT and new o2 sensor. Just so happens I am getting a new CAT installed now the cost for My 99 Plymouth Neon is $562.00 with down stream o2 sensor included. 99 Plymouth Neon 2.0 DOHC 5 Speed Manual Coupe 28-42 MPG

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