Clutch problems? Fuel system problems? Please help me start a diagnosis...

[naujcdl]

All,

Here is the subject and its issues:

1998 CSVT, at 126780
NO mods, EVER, fully maintained with syn, never EVER ridden hard or abused.
Always premium.

So here is the issue:
As of about three months now the car has been getting terrible mpg, whether city or highway. I used to EASILY get 350-360 mpT, aka, this car would be driven more hwy but when it comes to city it got around 21-24 on a great day or normal clutching, etc.

Now the car has been getting AT BEST 280-290 mpT which is lame IMO for how it is driven, etc. That translates to a mere 17-18.5 mpg, tops, if even my numbers are correct.

Things i need to make sure are out there:
Needs a clutch, it is still grabbing but i can take out the clutch and non gas pedal pressed and the car would still run w/o issues.
I know the clutch and flywheel are bad, will need replacing.
Original Fuel filter, FPR and injectors.
Had an UIM/LIM done back in August 2013 and all gaskets replaced.

I will take out the spark plugs and check for white(lean) or wet/black(rich) condition, although the FP is working w/o issues.

What do you suggest based on your experience with this platform or similar symptoms?

Am i starting to see a dying engine? It DOES NOT burn any oil, ever. Do i have a serious FS issue or just how this car runs on certain weather/time?

Thanks for any help.

 

[gmorrell]

If the fuel filter is indeed original, it needs replaced, as it's way past the service interval, but that's not likely the MPG problem.

Don't know where you live, but if you're seeing a lot of winter and cold weather, this will affect fuel economy. Additionally, as the ethanol/gas ratio changes (ethanol content is generally increased in cold weather), this will also negatively affect fuel economy. Ethanol has lower BTU/pound than gasoline, and as the winter blend leans towards more ethanol, the energy goes down and fuel economy drops.

Other things to check:
1. Coolant thermostat stuck open, this makes for cold coolant, PCM reads this and thinks the engine isn't warm, adds more fuel for cold enrichment, fuel economy drops.
2. If the upstream oxygen sensors are original, they're done. As O2 sensors age, they switch more slowly and their outputs head lean, and this causes the PCM to add more fuel, fuel economy suffers. 60K miles is a good life for an O2 sensor.
3. Fuel pressure too high, maybe a bad fuel pressure regulator, only way to check this is with a fuel pressure gauge.
4. Have a look at a few of the spark plugs, that's a good idea.
5. No check engine light?

You have a few things to check, let us know.

 

[naujcdl]

Hi,

Excellent suggestions to add to the list of to do's.

Yes, i live in wonderful cold Chicago, arg.

1. While engine is warming up nicely and there is no heat issues or coolant issues, it is time for a new thermostat.
2. Upstreams and dowstreams, I ALWAYS get them confused, upstreams are the ones past both CATS or before the cats? Which o2 to install, bosch from AA?
3. I will check the fuel pressure gauge and compare against manual from library and report.
4. Yep.
5. None, i will post tomorrow a simple but hopefully enough for all to see how torque pro is reading all the o2's and coolant, vac and throttle response.

 

[gmorrell]

Upstream O2's are the two sensors closest to the engine, they are before the pre-cats and are the primary parts of the fuel mixture control feedback loop.

The downstream O2 is used to monitor catalytic converter performance.

Bosch O2's are good products.

Search around here, there is a how-to on swapping the upstream O2's. The rear bank one against the firewall is a real knuckle buster, you'll invent new cuss words changing it. Stock up on Band-Aids.

 

[naujcdl]

I did change one on my first SVT back six years ago, that was a PITA. Should be easier now as I have done some mechanical work but never hurts to be aware and prepared, thank you.

And thanks a lot for the o2 explanation, it makes sense now and it is better understood.

Will do.

 

[BrApple]

From my observations when the upper O2 sensors start to go it will cause a decrease in fuel mileage, at least 50 miles per tank, before the CEL comes on for the sensors.