High fuel consumption '88 Carrera

[drohrer]

This '88 Carrera is getting 260 miles per tank compared to recent 400 miles. Recently did the following: plugs, rotor, dist. cap, ignition wires, fuel, air and oil filters, Oxygen sensor, brake pads, brake flush, front wheel bearings, tires, alignment, 2 intake spacers and gaskets, value adjustment and new CV joints, Techtron fuel additive. No fuel leaks. Any suggestion on where to look next?

[db_cooper]

Could be the cylinder head temperature sensor. I don't have have the specs, cold and hot. Easy to check with a multi meter. Be sure the connector is good on the air flow meter too and the throttle switch is working properly. If the change was sudden after the tune up, check to make sure something was not bumped and causing a problem, like the vacuum hose knocked off the pressure regulator. If the tune up was done because the mileage was poor, look at the easy parts first.

[billybek]

Lift your right foot!!!

[old man neri]

Maybe you got a defective 02 sensor.

[drohrer]

The head sensor sounds like the best place to start. It's running rich. Perhaps because of a faulty sensor.

[ZOA NOM]

I would re-verify everything you listed in your post. Whenever you discover a change in the car's performance, it almost always came from something you did.

[rusnak]

you should be getting well over 400 miles per tank. Do you notice a loss of power, gas smell in the exhaust? If you have a copy of the Bentley manual, then you should go through the checks of the fuel injection system with a multimeter that are outlined in the manual. If the car has a fluctuating idle, then you might have a vacuum leak.

Off the top of my head I'm thinking you might have to redo the valve adjustment, but if it were that far off, the car would be barely running.

[JeremyD]

Originally Posted by drohrer

This '88 Carrera is getting 260 miles per tank compared to recent 400 miles. Recently did the following: plugs, rotor, dist. cap, ignition wires, fuel, air and oil filters, Oxygen sensor, brake pads, brake flush, front wheel bearings, tires, alignment, 2 intake spacers and gaskets, value adjustment and new CV joints, Techtron fuel additive. No fuel leaks. Any suggestion on where to look next?

Did you do the work and then started getting the crummy mileage, or was the work done because you were getting crummy mileage?

usually it will run like crap with a faulty cht sensor.

is the car stock?

[Rot 911]

I too suspect the O2 sensor. Either defective or you didn't get the wiring connectors completely connected. If the O2 sensor is disconnected the DME will go into a rich gas condition.

[cgarr]

Do you have the old parts you can start putting back on? one at a time? engine only! Do your front wheels turn freely?

[livi]

Welcome to the forum!

All great advice of course and as stated, trace back every part you changed or tuned. Anything from said O2 sensor to ignition wires faulty or mixed up.

Good luck!

[3.2Carrera]

how is your driving style? I can get over 400 miles to a tank when i am going on road trips, but when i am driving around town i get anywhere from 260-350 miles per tank.

[drohrer]

All great opinions and feedback. I started getting poor milage and needed the tune-up anyway. I also failed to mention that I replaced the "DME brain" relay and regulator.

My milage was consistantly 400 miles in city. 20 miles/gal. Highway better than that. I'm going to double back on the O2 sensor and put a meter on the CHT sensor.

Front wheels do turn freely.

Maybe it's just my light-footed driving style. One friend suggested jumping on it at least once a day to burn out any carbon build-up (160K miles). As mentioned, I have used the techtron stuff a couple times at 4-5K mile intervals.

[Eric Coffey]

As mentioned, check the O2/CHT sensors and vac lines. Also, just to be safe, I would also check for leaking rear (rubber) fuel lines. The 3.2's are notorious for developing pin-hole leaks in the rear fuel lines over time (replaced one myself on a `88 a few years back). They tend to become brittle from the engine heat over the years. Usually the leak is only detectable when the engine is running (operating fuel pressure).

[drohrer]

I wanted to see what would happen if I disconnected the O2 sensor. Nothing. Not knowing where something would happen I just suspected that since there was no change that the O2 sensor was bad. So I put the old one back on and things changed immediately. Better mileage, engine temperature increased to operating temp quicker and heating systems got hotter quicker. So thanks for the opinions. The O2 sensor may have crapped out due to a leak that caused a short from the rear wheel well adjacent to the connector or it was the wrong "1985 Bosch" version. not sure what, everything ok now. Cheers. D

[drohrer]

I wanted to see what would happen if I disconnected the O2 sensor. Nothing. Not knowing whether something would happen I just suspected that since there was no change that the O2 sensor was bad. So I put the old one back on and things changed immediately. Better mileage, engine temperature increased to operating temp quicker and heating systems got hotter quicker. So thanks for the opinions. The O2 sensor may have crapped out due to a leak that caused a short from the rear wheel well adjacent to the connector or it was the wrong "1985 Bosch" version. not sure what, everything ok now. Cheers. D

[stlrj]

Your air flow meter might be out of adjustment.

If it were my car, I would pull the AFM, pop the cover and reset the pointer to lean out the mixture which would be equivalent to the 3mm allen CO adjustment on a CIS engine.

Cheers,

Jose'