when i first got my rx7 i was getting 9 mph. like 140 miles a tank. i mean it was bad. SO i did a few things. main problem was my precat was plugged. that blew out at high rpm one day while i was driving. another thing was my timing was off so i fixed that. got a new air filter, took the sparkplugs out and metel brushed them got new wires, also adjusted the Plunger thingy on the Uim that Somewhat controls fuel thats coming in and. Im sure there were other things.. but after i got done messing with everything i then saw like 20mph.. Plus More power

 

Few things.



1. Your probably using an autometer gauge w/ the stock O2 sensor...this isn't a reliable tuning device ..it's good, but I've found them to be off by as much as 1 or 2 points easily..



2. A streetported motor (depending on how extensive) is going to use more fuel then a stock motor. Your taking in more air, so your stock ecu TRIES to compensate by adding more fuel. This brings me to #3



3. Get a S-AFC or alternative fuel control device. The stock ECU does not understand a lot of what is going on w/ ported motors..and a fuel controller will allow you adjust most of it's imperfections. Especially at idle and WOT.



You should be able to get about 17-18mpg on a normal SP w/ the right tuning. I would still check/replace the o2 sensor and check your timing.

 

what does it have to do with then...it may not be a/f ratio but i know it isn't idle. it doesn't change the idle at all when i adjust it.

 

It leans and richens the fuel AT idle, out of idle it has no effect on anything.

 

The stock ECU runs the tuning a little rich across the board, there are some minor variations from unit to unit, but for the most part it stays to the rich side of things.



A true streetported motor isn't going to produce huge power gains and create huge fuel demand, but it can effect the readings of the input and output sensors throughout the engine, not to leave out that one or more of these sensors could be operating below recommended spec or not operating at all.



An S-AFC and a wideband O2 will help to tune in the engine and get the AFR's to a reasonable level, but first the other sensors and systems must be functioning properly.

 

By true streetport, I'm assuming your meaning a port job that doesn't affect streetability.



My streetport was huge...didn't really affect streetability, but did affect gas mileage...and that was w/ no emissions, etc too...

 

I suppose I should have added "generally speaking" in front of the streetported motor part, but yes there are variations in styles of streetports. Most of the time its some clean up of the runners, a little teardrop work and some oil and cooling mods, everything else remains the same, in otherwords the port job won't surpass the limits of the stock systems.



If you step outside that realm, of course, there are an endless amount of recommendations for upgrades, but in this case, without knowing exactly what the details are in this particular engine I was speculating that it was a "small" streetport, and while 12 mpg seems low, I was actually getting 8 mpg in my streetported engine and increased it to 16mpg after fixing some sensor related problems.

 

Sorry about jumping into the thread



i've got the same problem with my 86' FC, just got a rebuild with streetport by Atkins Rotary and the mechanic i'm going to can't seem to figure out why the car keeps dying out after idling for a while.



the previous engine also ran really rich and kept dying out and refusing to start for the longest time but it had close to 200K miles on it. The mechanic recommneded a new engine but the same problem still exists. The car runs really rich still (white smoke out the exhaust and smell of gas) and the mechanic kinda gave up on trying to fix the problem so he told me to bring it to another shop



i'm going to another mechanic right now and the new mechanic tells me that if this problem existed before the engine swap it might have been a bad sensor to begin with. the new mechanic also tells me that i might have been jerked around by the previous mechanic who didn't bother to do a proper engine diagnosis before recommending the swap.



well i'm $3000 poorer right now and still without a working car.....please help!

 

12MPG is fine. Some people have it worse. (8MPG madness)

 

Am I alone here in getting 29+ MPG freeway?



S5 TII stock turbo, stock ports, E6x......



Road trip from Phoenix to Minneapolis With the car completely loaded, because I was moving, and still amazing mileage. I averaged out every tank so im sure thats accurate.