typically larger gaps give greater results, since that increases the firing voltage. 40+ mpg sounds great, but if you don’t actually see the fuel in the filler neck between fills you really won’t know if thats an accurate number, since one can dribble feed up to 2 gallons of fuel after the pump clicks off.
rob
yeah I realize that, my method isnt super accurate and around 32 was what i got with the atx, but doing this even with mostly 70mph hiway driving i got those #'s, I was impressed especially with the 98mtx’s shorter fifth gear
what size tire was on the car?
you should try filling the neck between fills and see what you’re getting… it would be valuable info to see where you might be at.
205/40/17
40 psi i think
well your speedo/odo should be accurate then for testing since 205/40-17 has the same diameter as the stock 185/60-15’s.
it started with the 14 alloys in my case:)
but yes still accurate
Hmm I wounder if that T-stat is having a issue with open loop and closed loop and not gaining you better results.
no open closed loop issues - but if the pcm reads a coolant temp less than 175 degrees foran extended length of time then it will throw a code and light up the Service Engine Soon lamp.
rob
well - back to the topic at hand… the MPG project car…
I sold the car to a work buddy who needed a commuter car for work. I told him I have a couple other small items to do to the car before I hand over the keys.
I seemed to have hit a plateau at 37.5mpg so I tried adding a 180 thermostat to replace the 170 I had previously installed, and added a ZXtuner upper intake tube and larger TB elbow to the stock intake, as well as a MAC air filter (think K&N drop in filters). Still around the same number.
So… I’ve decided to add 19 lb injectors to the car and see if perhaps I’m running too lean to begin with. I hope to do the run in the next couple of days. I already installed the injectors and the car did pick up a little more balls so I may be on to something here 
Rob
aren’t stock injectors 19 lb?
no, 17lb is stock
A recap from page 1:
Run 1: Car is as purchased, with 10w30 wal mart oil and fram oil filter, and almost new Goodyear Integrity tires on the base model steelies. Tire pressures were 30lbs, front and rear, and the trunk and passenger compartment were free of any additional weight items… I consumed 2.64 gallons. and ran the car at dusk, turning the headlights on about halfway thru the trip (34.1 mpg)
Run 2: Weight removal bits… I removed the spare tire, jack, false floor, and carpet pad from the trunk. Under the hood I removed the motor mount dampers and engine lift hook, and inside the car i removed the steel sandwich plate inside the glovebox… about 50 lbs total. I also upped the air pressure to 38lbs in the front and 34 lbs in the rear. Headlights were on the whole time. Consumption was 2.58 gallons (34.88 mpg).
Run 3: Added 14x6 motegi alloys, installed lowering springs in the rear only to improve stance (sits level looking now instead of that Dodge Neon kicked in the ass look of the stock springs), and installed a zxtuner ultra udp while replacing a noisy idler bearing. Headlights were on and consumption was down… 2.44 gallons (36.88 mpg)
Run 4: Switched out oil to 0w30 Mobil 1 and a motorcraft oil filter, added a 170 degree thermostat, reset the pcm, and removed the lower resonator from the stock intake. I drove the car for about a week to get the pcm to start learning its parameters again. Headlights were on and now I saw 2.40 gallons used (37.5mpg)
Run 5: I added a hi flow elbow to the TB end of the stock intake and ran again… Hot day, no headlights, and 2.41 gallons used (37.3 mpg).
Final Run: I added the 19lb orange top injectors, filled the tires to 36lbs all around, put the spare tire and jack back in the car (it’s going to its new owner today), and went to the same Mobil station for all the other runs and filled up the tank to the usual gas in the neck level.
The weather was sunny and warm, 91 degrees and 30% humidity according to weather.com. I drove without the a/c on (as all the other mpg runs). I ran during the day (no headlights on) and I had both windows fully rolled down vs.3/4 rolled up on all previous runs.
Upon return I fit 2.33 gallons into the tank before the gas was once again visible in the neck. Thats 38.6 mpg! for my final run, a 4.5 mpg improvement over the stock first run.
The car runs better than ever, with the new injectors smoothing out the engine vibration and improving torque and hp as well. The car is considerably quicker than stock, and driveability is excellent as well, eliminating a/c compressor engagement surge as well as low rpm powerband flat spots.
Rob
Hey - any interest in me trying this same little project on an atx equipped zx2? i have one at my disposal (bought a complete parts car - a 2000 atx zx2 w/ cruise and sunroof)
i am curious to see how much difference there is between 5 speed and atx, using the exact same parameters.
Rob
Always interested in more info - never know when it might come in handy.
Question on the 19# injector change - did you have to tune for them - I didn’t see it mentioned one way or the other.
It’s plug and play on the 19lb injectors - the change between 17 and 19’s is enough that you can do them without a tune. In fact they just might work best without a tune (if not juiced or boosted).