the gas mileage blues!!!!

[specialK]

this is on my 88 GTC vert TI. It has very little power off the line and feels
like an N/A except on the highway. My gas mileage around town averages about 14MPG. I checked the codes and got a 13(map) and 53(oxygen sensor). Is it possible for the map to be throwing the engine off enough to be causing this?? I have checked the cam and ignition timing and both are spot on, and I did away with all the factory vacuum lines and there are no leaks. When I got the car about a month ago it wasnt boosting right, so I have the WG hooked up to manifold vacuum for now yeilding only 5lbs of boost.

any suggestions guys???

[NAJ]

Map is dominant fuel control so if there is a problem with the Map circuit fuel control, ignition timing and boost limits will be compromised.
Be sure engine vacuum is correct(15-20"HG), that you are reading engine vacuum at the Baro Solenoid and from the Baro to Map.

[GLHNSLHT2]

13 is vacuum/boost line to baro/map. You've got a leak or something wrong with the vacuum line to it.

Are you sure it's a code 53? Fault Code 53

[specialK]

Ok ill check the vacuum and then if its ok replace the map? It was code 51 sorry.

[GLHNSLHT2]

check the wiring of the O2. that obviously makes the car add more fuel. That site above has a description for all the codes.

[specialK]

I checked the wiring already and the sensor looks new, Is it possible the O2 code is because of the rich condition?

[GLHNSLHT2]

yes I guess it could be possible. Fix the map issue 1st, then reset the codes and see what comes back.

[the.palmetto]

I am having gas mileage issues with brand new plugs, wires, coil, and O2 sensor. I've been having the issues even beforehand. With an R/T I should be getting at least 20mpg city but I am getting more like 16, but I was getting about 13mpg before the tune-up. My exhaust smells exceedingly rich. It doesn't make sense because I just switched out those parts last week. And no, I don't have a lead foot problem it is not my driving habits. I am currently breaking in a new clutch so I have been driving like a granny and still getting crappy mileage. One thing out of the ordinary is a code 53 logic module internal fault. Think that could be the culprit? There's no reason I can think of as to why it is this bad.

[NAJ]

Repair the vacuum circuit to the MAP, clear the codes and drive the vehicle.
Code 51 is "Lean Exhaust Indication" and may be a result of the Code 13.
Always start with the lowest code #, correct the condition, clear the codes, road test, recheck for codes then move to the next lowest code # if any are present.

DR-2A Fault Codes 13 &/or 14 MAP Sensor Circuit

Turn ignition switch Off, then connect a vacuum gauge inline with map sensor vacuum hose.
Start engine and observe vacuum gauge with engine idling, then observe gauge while snapping throttle open and close.
If vacuum gauge reads manifold vacuum with engine idling or vacuum gauge reading drops to zero when throttle is snapped open and closed, proceed to Test 2 step B.
If vacuum gauge reads zero at idle, repair vacuum line to throttle body.
If vacuum gauge reading slowly drops to zero when throttle is snapped open and closed, repair restriction in vacuum supply line to MAP sensor.

DR-2B Check MAP Sensor Circuit In SMEC

Connect diagnostic read-out tool to engine test connector, then disconnect MAP sensor connector.
Place system in Sensor Test Mode 08.
If display reads at least 4 volts, proceed to Test 2 step C.
If display reads zero volts, replace SMEC. Before replacing SMEC, ensure wire in terminal No. 1 of 60-way electrical connector is not shorted to ground.

DR-2B Check MAP Sensor Circuit In SMEC
Notes

Complete Driveability Test 2, Step A before proceeding.



Connect diagnostic read-out tool to engine test connector, then disconnect MAP sensor connector.
Place system in Sensor Test Mode 08.
If display reads at least 4 volts, proceed to Test 2 step C.
If display reads zero volts, replace SMEC. Before replacing SMEC, ensure wire in terminal No. 1 of 60-way electrical connector is not shorted to ground.

DR-2C MAP Sensor Signal Circuit

With diagnostic read-out tool connected to engine test connector, MAP sensor connector disconnected and system in Sensor Test Mode 08, connect a jumper wire between dark green/red wire and black/light blue wire of MAP sensor harness connector.
If display reads zero volts, proceed to Test 2 step E.
If display is not reading zero volts, proceed to Test 2 step D.

DR-2D MAP Sensor Wires to SMEC For Open Circuit

With diagnostic read-out tool connected to engine test connector, MAP sensor connector disconnected, and system in Sensor Test Mode 08, Connect a jumper wire between dark green/red wire of MAP sensor harness connector and negative battery terminal.
If display reads zero volts, locate and repair open circuit in black/light blue wire of sensor harness connector to wiring harness splice.
If display reads 5 volts, locate and repair open circuit in dark green/red wire of sensor harness connector to SMEC.


DR-2E Checking 5 Volt Supply to MAP Sensor

With ignition switch in Run position and MAP sensor connector disconnected, connect a digital voltmeter to violet/white wire of MAP sensor harness connector and ground.
If voltmeter is reading at least 4 volts, replace map sensor. Before replacing MAP sensor, ensure terminals in harness connector are making a good connection.
If voltmeter is reading zero volts, locate and repair open circuit in violet/white wire.

[specialK]

great information! thanks! I am off tommorow and will do those tests.