I've recently replaced a lot of stuff on my Formula that I think should have given me optimum MPG's. Here's what I've done/had done:

- Fixed exhaust leaks
- Decarbonized engine
- Replaced plugs, wires, rotor, pickup coil, O2 sensor, air filter, EGR valve & catalytic converter. Everything new except the EGR valve.
- Set timing to 10°

Given all that, I expected the car to exceed, or at least match its best ever MPG, which was 30-33.

This morning I drove to a gas station and filled up. The car was almost up to full temp. I drove about a mile to the interstate, drove ~200 miles, and filled up again. Mileage was 27.8 MPG.

The things that come to mind that were different from when I used to get 30+MPG are:
- I used to be able to get gas without ethanol
- About 1/2 of the trip this morning was with headlights on
- About 1/2 of the trip this morning was through mountains, although I rarely had to use my brakes (that's why I used the Fiero for the trip), but there was a decent amount of up & down hills.

Given the circumstances of this trip, am I expecting too much?

Also, I have an Auto X-Ray scanner that can display real time sensor data. All the data looked reasonable, except the ECT (Engine Coolant Temp) sensor, and the Open/Closed Loop flag. When I was at speed, it usually read 195°-200°, but occasionally it would read around 80°. And occasionally, the Open/Closed Loop flag would read Open Loop. However, the car didn't run any differently when this happened. No increase or decrease in RPM's or roughness, so I suspected that I was just getting a bad data transfer from my scanner. A question... if I had an air bubble in my cooling system, would the ECT read low if was in air? I would expect it to read high. The ECT isn't that old. It's an AC-Delco unit that I installed 4 yrs (20000 miles) ago. When the OEM unit failed, it failed hard. The car would not start or stay running without some throttle applied. With the outside temp around 60 or so, it was reading something like -40°F (I don't remember exactly, but it was Alaska-like temperatures). IF there's a problem with the ECT, it's not like the failure that occurred before.

So go steal one from someone else's duke and see what happens. Sure sounds like it's an idea headed in the right direction. The fact that it says open loop when the temp is off seems to me that its BEFORE the ECM, not in the ECM to monitoring connection.

not sure what thermostat your running,
but the car must have the right temp to stay in closed loop,
few other things to check,
charging system
grounding system,

look at the wiring that is at the plug that clips ON the temp sender. On my 83 z/28 the temp send went south ( at lot farther than miss. ) It was reading -81. the repair included a newer type of senser with a newer type of plug. the old plug had no plastic on the wires.

quote Originally posted by phonedawgz: So go steal one from someone else's duke and see what happens.

I have a Formula... with, um, a V6.

quote Originally posted by phonedawgz:Sure sounds like it's an idea headed in the right direction. The fact that it says open loop when the temp is off seems to me that its BEFORE the ECM, not in the ECM to monitoring connection.

Maybe. I monitored the scanner last night on the ride home. I got some really weird readings, like a vehicle speed of 134MPH... while waiting at a red light. I cycled the power on the scanner, and it seemed to be working right. I seriously doubt that anything changed about the data being sent from the ECM. I'm not completely sure now if my scanner is working properly.

quote Originally posted by ApeMan:not sure what thermostat your running

I'm running a stock 195° stat.

No one really answered the main question I'd most like answered: Am I expecting too much? I don't really NEED an extra 3 or 4 MPG. An accounting of my lifetime Fiero expenses shows that I've spent more on maintenance and repairs than I have on gas. But MPG is good gauge of how well an engine's running, and I want it running at optimum.

This morning it wouldn't crank and stay running without some throttle. I didn't have the scanner hooked up, so I don't know what the sensors were reading, but that's concerning. It finally started idling on its own after it warmed up a bit. I suspect that the ECM is still in learning mode, so maybe (hopefully) it's a temporary thing. I'll take a drive at lunch and see what happens.

On my 3.4 pushrod swap, it was a bear to get started, turns out my cold start injector was leaking and causing all sorts of weird cold issues, and mileage decrease. 27-28 is pretty good, especially for a 22 year old car, but if you're gonna chase gremlins, try unplugging the cold start injector.

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Currently in the middle of my 88 + 3800NA swap

IDK on the mileage - some people get pretty anal about mileage, some just check on trips, some check all the time. If it does't bother you well then there is nothing to fix. Personally I doubt I''d worry about it, but that speaks more of my personality than it does of logic.

Will the cure be worth the fix? ie will your improved mileage be worth the money/time to fix it?

Is there other reasons to fix it? ie you're quite concerned about the enviroment/gas supply/perfect running car?

quote Originally posted by phonedawgz: IDK on the mileage - some people get pretty anal about mileage, some just check on trips, some check all the time. If it does't bother you well then there is nothing to fix. Personally I doubt I''d worry about it, but that speaks more of my personality than it does of logic. Will the cure be worth the fix? ie will your improved mileage be worth the money/time to fix it? Is there other reasons to fix it? ie you're quite concerned about the enviroment/gas supply/perfect running car?

It's more of a... If it's running perfect, then...
- There won't be excessive carbon buildup on the pistons, valves, ports, EGR valve, etc
- There won't be excessive heat in the engine bay
- There won't be excessive electrical stress on the ignition system
- There won't be excessive stress on the cooling system
- There won't be excessive roughness and/vibration from the engine
- etc
- etc

It's more of a reliability issue.

I'm a believer that a lot of big problems are small problems that were not addressed, and were allowed to get worse over time.

For example: Worn engine and/or tranny mounts, leading to... excessive stress on the exhaust manifolds, leading to... cracks in the manifolds, leading to... exhaust leaks, leading to... rich running condition, leading to... excessive carbon buildup on pistons, valves, and ports. A rich condition will also cause elevated cat temperatures, which will cause a premature cat failure, and elevated engine bay temps, which causes premature degradation of ... pretty much everything; ignition modules, alternators, starters, sensors, etc. Excessive carbon buildup can also cause pinging and all the problems associated with that. This chain of events can also be initiated by blown exhaust manifold gaskets.

I felt like, until recently, my Formula was on this path of events. I've replaced a lot of stuff lately, and I hope that I have it running near perfectly, but I don't want to overlook a small problem somewhere that could start this chain all over again.

I'm not really interested in getting the last drop of efficiency out of a gallon of gas(although I'm not opposed to it), but I am interested in getting the peak reliability out of my vehicle. I'm currently using my Fiero as a DD, and I often find myself 200 miles from home. Maybe I should just get something new, but I like the idea of having my Fiero running perfectly as a result of my own work. And MPG's, IMO, are a good measure of how well the engine's running.

Over the years at various times, I've let my Fiero sit for periods while driving it very little. I then think about selling it. Then I drive it again, and realize how much fun it is, and I can't bring myself to sell it. However, it's also hard to justify a DD that I can't depend on to get me from point A to point B any time I need it to. I don't fear a sensor failure costing me a 10% increase in fuel consumption. I fear a failure of some type stranding me 200 miles from home. One 200 mile tow truck call can pay for a lot of maintenance and repairs.

BTW, I drove it at lunch today, and it cranked fine with no throttle. It idled as well as it ever does. It still surges like 70% (or so it seems) of all of the V6's. I'm going to address that next. Hopefully, this means that the ECM is still in learn mode. It hasn't been long since it was reset.

Try to find a gas station that has non-ethanol gas on tap... See what happens when you go from crap to the good stuff (real gas)

quote Originally posted by skuzzbomer: Try to find a gas station that has non-ethanol gas on tap... See what happens when you go from crap to the good stuff (real gas)

It's not available in the Atlanta area. I've been spending some time in the Huntsville, AL area, too, and so far I've yet to find any there either.

quote Originally posted by Formula Owner: 27-28 isn't bad, but some people are getting around 34 or so out of a V6, which indicates to me that mine may not be running perfectly yet. Of course these people may be getting fuel without ethanol, inflating their tires to 40 psi, driving 55MPH....

Only checking MPG while driving downhill with the wind at their back, ect. I found by adding just a 1/2 gallon of lawnmower gas between fill-ups I can enhance my mileage on every tank!