16 MPG?! Smells like gas fumes all the time?

[darklotus42]

So 1st off- 95 CS 3100 144k

And as the title says I'm only getting about 16mpg. And while it's running and shortly after shutting it off there is a strong odor of unburnt gas fumes. Could this be related to my EGR or EVAP system? My live stream data says the EGR solenoids apparently never cycle. Also I'm getting a stumbling with during acceleration that I'm assuming could the be coil packs altho I still need to check the vacuum system. Any thoughts how to fix?

[Human]

I have a similar phenomenon with my '95 CS Convertible, but raw gas odor mainly manifests when I first fill the tank, and is usually gone by the time I've driven 20-30 miles. Fuel economy, as near as I can estimate, averages around 18mpg, but the engine runs smooth as silk, no stumbling at all. Also, filling the tank can be tricky, as it doesn't always automatically shut off the pump. When it fails to shut off, gas will eventually spill out onto the ground from under the passenger side, opposite of where the filler is. It does not overflow from the filler neck itself. My (admittedly imperfect) solution is to put 10 gallons in when the gauge falls just below 1/4 tank. I'll put up to 12 gallons in, if the needle is down in the red one, but I never try to top it off.

[darklotus42]

Yeah that is weird. However on mine it isn't the odor of raw gasoline. Its similar to how it smells with a rich mixture but I would figure you wouldn't be able to smell that after the car has been shut off. Somebody suggested I could have plugged catalytic converter. I know I've bottomed out a few dozen times (bad suspension) so maybe that's the problem?? Idk I just wish I could hook a scanner up and it would tell me but OBD 1.5 sucks

[Schurkey]

10 hours ago, darklotus42 said:

95 CS 3100 144k

 I'm only getting about 16mpg. And while it's running and shortly after shutting it off there is a strong odor of unburnt gas fumes. Could this be related to my EGR or EVAP system?

Not EGR.  Could be EVAP.  More diagnosis needed.  At 16 mpg, you can probably bet that your catalyst is ruined.

My live stream data says the EGR solenoids apparently never cycle. Also I'm getting a stumbling with during acceleration that I'm assuming could the be coil packs altho I still need to check the vacuum system. Any thoughts how to fix?

The Usual Three:

1. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. TBI systems don't hold pressure when the pump stops running, but the other fuel injection styles should. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.)

2. How old are the usual “tune-up” parts and procedures? Inspect/replace plug wires, spark plugs. Use quality parts sourced from an authorized seller (NO COUNTERFEIT PARTS FROM AMAZON, EBAY, OR OTHER SKETCHY SELLERS!) Be sure the ignition coils will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper electronic spark advance. Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”.

3. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims during the time that the vehicle is not running properly. “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle.  1995 "OBD 1.5" is NOT a problem for any REAL scan tool.

[Vegeta]

A cat would be plugged from poor operating conditions, and you would have no power.  See if the fuel pressure regulator has fuel in the vacuum line.  Thats my shot in the dark.  its not gonna be evap at 16 mpg.  You have either bad ignition, stuck injector, bad fuel pressure regulator.  See what your BLM/INT are at.  LTFT and STFT would be the same thing, fuel trims.  

[darklotus42]

What kind of parameters should I look for?

[Vegeta]

Fuel trims.  I dont know your computer to say if its INT and BLM or if its labeled STFT and LTFT.  int/blm would be 128 nominal, and LTFT and STFT are % based from 0% fuel trim.