Just bought a lil ole lady bone stock 94 Z28 with only 64k miles.Previously had a 95 Z28 M6.The city fuel mileage is much worse on the A4.Is this normal.Drove both the same.Lil stomping here and there.With such low mileage and completely stock I am disappointed.The 95 had a bigger TB and some other minor mods and had much better throttle response.I did put in new tr55 plugs-what a real pleasure trip that was-and replaced the hoses,flushed coolant,new rad cap and a hypertech 160 t-stat.Another thing I noticed is car runs cool in city but temp is 1 step below red on highway-basically needle is at 11 o'clock on the gauge.I do know the radiator was replaced 2 years ago.Just bought a fuel filter that am replacing today.The car is 17 years old and was a southern California car.I have not had it scanned.The ses in not on.The car runs like new so hate to replace wires and opti if not needed-on the other hand I know electronics do not fair well after sitting a lot.Also added a high flow air filter-not cai.I have read o2 sensors can hurt mileage but wouldn't they trigger the ses light.Any advice appreciated.

 

The "high flow filter" could have contaminated the MAF with oil.

Higher temp on the highway than in town sounds like an electric waterpump but given the rest of the description probably not so I would look and see if the lower airdam is missing or cracked so it is folding over.

Far as wires, if they pass a spray bottle test at night you might leave them alone but if the cap and rotor are original far as you know I would put an MSD cap and rotor on it. The MSD cap and rotor will convert it to vented for you, and a cap and rotor are wear items.

Far as the hypertech stat, did you do that without reprogramming? Why?

O2 sensors are critical to fuel mileage and are not quick to code even when they are going bad.

 

Scan it. There are numerous codes that do NOT turn on the SES light.

Is it possible the A4 trans is slipping? That would explain poor throttle response and poor fuel mileage.

Misfires and exhaust leaks before the O2 sensors create a "false lean" condition, causing the PCM to add fuel the engine doesn't need. Check for misfires and exhaust leaks.

 

Sprayed wires and seem fine.The opti is completely original and was planning on upgrading when I eventually replace the water pump which does not leak-yet.I did not know msd was a vented opti-I thought the venting required the "open" cam sprocket.When I replaced hoses decided to replace t-stat.Got a bad Duralast 180 t-stat that I believe was not as long as the factory stat.I read a few posts boasting the improvement of a hypertech 160.Do plan on reprogramming.Just surprised that engine does run cooler now in the city which is 80-90% of my driving.It has not run hot on interstate but is much hotter than in town.The car was loaded with leaves when I got it and I suspect there may be leaves between a/c and radiator creating obstruction.Have not checked that yet.

 

No slipping or misfiring at all.Tranny is 4l60e and extremely tight.Not trying to mislead-throttle response is very good but my m6 with the cai was incredibly more responsive.

 

Do not have a scanner.Do not believe autozone has obd1 either.Was going to jump the obd1 ports to see if will flash codes.

 

The MSD cap has vents built into it so no need to swap to the GM vented components.
The MSD opti is a bad bad thing, do not assume such things are an upgrade, a LOT of parts are designed to take your money more than offer you anything.

A 94 will NOT flash the codes, it is an advanced OBD1 that requires a scanner that displays codes. Most of use use a laptop with cable and software for such, there is even free software that will scan codes for you.

 

so would changing to an msd cap and rotor give me vents without going full msd opti.I also wonder,since car was always in california,do they use a different fuel mixture there.I know they are famous for being ahead on emissions and perhaps they have more or different fuel additives in their pumps.Just a thought.

 

The computer should be re-tuned for a colder thermostat, or go back to stock 'stat.
I agree with Caprice, and that you should probaby clean the MAF wires with alcohol and a q-tip or 2. It is too easy to over-lube the airfilter. It will allow some of that oil to pass through, fouling the MAF.

 

Cleaning the MAF may help but don't actually touch it while doing so. Clean it by spraying with a MAF cleaner....CRC makes one.

Touching those fine wires increases the chance of breaking them....

 

I guess I live dangerously. I used a q tip to gently brush them. They seemed to be strong enough. I got more grime off of them doing this, after I had sprayed them.

 

I would that that the opposite would be the issue, the car should want to overheat in the city but do well when you are getting good airflow from highway speeds (as opposed to idling at a stop light)

City fuel mileage should be about the same between a A4 and M6 car (I've owned a '94 Z A4, '97Z M6, and '97 SS M6) but will vary based on your driving habits. If your getting significantly worse, then you might have an issue that needs to be fixed (slipping tranny, o2 sensor, etc.) M6 cars do get quite a bit better fuel economy on the highway with double overdrive though. But then again, who buys a f-body for the fuel economy?

 

Dwayne's comment reflects a common problem that many run into. In traffic or stopped at an idle, the cooling fans come on and handle the airflow chores, keeping it cool. At speed the airflow comes mostly from beneath the car, directed into the radiator ducting by the air dam. If the air dam is missing or broken, it can't direct the air up and the car runs hot. His other comment about the electric water pump may or may not apply, depending on what has been done to the car.

As for fuel mileage, I have had both an M6, which I have now, an an A4. The fuel mileage around town was considerably worse which I attribute to the cars as my driving style doesn't really change. 16 mpg for the A4, 19mpg for the M6. I assumed from the post that the OP is seeing a much bigger difference than that....

 

We have an A4 '97 and an M6 '95. When we drove them both up to Carlisle, last year, I had to fill up the A4 one more time than the M6, my son drove. We didn't calculate the milage, but it was clear to us, the manual was much better on fuel. We did check the milage on the trip to Oshawa, this year (only drove the M6). It consistently got 27 mpg. I'm lucky to get 21mpg in the auto (when I've checked it).

 

Same tuning, same tuneup parts at the same time, fresh O2s in each? The convertible is going to be heavier so there would be a minor difference.

I get high teens including racing out of my car with the weight/power/3800stall/4.10s I have for you to only get 21 says either you drive like a complete maniac or something is wrong with the car.