sv51macross

iTrader: (1)

Check sig for model/aspir. With normal (70% max throttle, below 3800) driving, the last several fillups have been averaging 12 mpg. Granted, this is almost entirely city driving, but still, shouldn't I be getting at least 15 or more?

Lucy has no mods to her. Recently pulled intake system to fix leaky PD, mileage seemed to take a bit of a dip. O2 sensor circuit does not work. Tired to retrofit the 4-wire from a 94 Camry V6...didn't work to say the least. However, Aaron Cake told me that the O2 sensor should not be the culprit in such low mileage.

I'm not as anxious as before to go probing for voltage drop, but if anyone has any ideas I'd be open an welcome to them. Probably going to replace the ***-ahem, AWS coolant hoses soon, so the Plenum/UIM can come back off to do what I need to.

Thanks for the time.

nycgps

iTrader: (4)

your car needs oxygen feedback for cruise and some operation. but yea it shouldn't cause it to drop so much

when was the last time u replace ur spark plugs? last thing to check is your engine compression.

P.S: I like Elfin Lied, such a sad story. I even bought the DVD-Set from Japan.

MadScience_7

Even if the bad O2 sensor isn't the crux of the problem, it sure as hell isn't helping. The standard single wire sensor is pretty cheap, no need to try ghetto rigging something else. Or is it a problem with the ECU?

LunchboxCritter

iTrader: (9)

Pull your plugs and look at them. If it's rich then I would suspect the O2 sensor.

I wouldn't argue with Aaron Cake, but an operational O2 sensor is OEM equipment for a reason, and therefore should be in proper working order.

They are only $18.00 on www.advanceautoparts.com. Also, definately get an oxygen sensor socket.

Cratecruncher

I'm getting the same crappy 12mpg. The car used to get 18 on average.

I suspect I might have dirty injectors after 180k miles and some stale gas now and then.

I'll be interested to hear opinions on this one.

_Mac_

iTrader: (9)

I feel ya on getting 12ish mpg. Almost made me sell the fc but I'm hoping I can figure it out push a few more mpgs out of the thing.

sv51macross

iTrader: (1)

About dirty injectors, does fuel injector cleaner do anything, or do they need to be sent out to be cleaned? (I have a bottle of Lucas) And is injector cleaner going to interact negatively, or be lessened in efficacy by 2-cycle oil?

About the O2 sensor, awhile ago it wasn't working and replacing didn't help. I did some resistance...maybe I should check that wiring for voltage drop instead, but for only 1v?-Anyway, ECU-O2 was fine, but O2 bung to -batt was a very high resistance. I cannot access the manifold bolts(to reground the manifold) and the only way I'm willing to to go in there enough to do so is if i have some stainless-steel to replace the thermal reactor.
Anyway, I thought replacing it with a 4-wire narrowband would work. But the fuel economy got even worse with it plugged in, I think the 94 Camry used widebands...

@NYCGPS, it might be compression. When I dove in to replace the leaky PD, I accidentally broke a couple of the OMP lines at the injectors. It was only while replacing the lines that I discovered that the #1 and #3 lines were broken near the pump and the previous owner 'repaired' them with little ribber sleeves...that rotted-out 6 months later...several years ago...I found the source of my oil leak though!

Cratecruncher

I ran a bottle of Techron through mine but it didn't do anything frankly. My plugs looked good when I replaced them just recently. For only $18, I'm planning to replace my O2 as Lunchbox suggests (thanks for the heads-up on potential grounding issue too). I also might send out my injectors to Witchunter but it's almost $100 for 4 injectors shipped.

The thing I don't get however is that I'm using about 50% more gasoline to do the same amount of work yet my plugs are clean? Where does it go? I can smell a rich idle but my v-8 wouldn't be able to run at all that rich.

Bamato

iTrader: (6)

How does the car drive? Does it stutter, hesitate, etc?

Cratecruncher

Mine doesn't. It's never been a speed demon being an '87 stock na. I replaced the block about 15 years/40k ago. It has a bit of "throat congestion" at around 1500rpm if I let it hover there and will occasionally "pop" at the muffler. Otherwise, it sounds good at idle and above 1500.

calpatriot

the O2 sensor may be the problem... or one of the problems. Inop O2 sensor will definitely decrease mileage, as the engine will run rich all the time.

Also, check the cat converter. If the O2 sensor has been inop for any length of time, the cat will overheat, melt internally, and (potentially) act as an exhaust restriction.

Quick way to check for exhaust restriction is to *remove* the O2 sensor, and leave the hole open; if performance/mileage improves, the exhaust is likely restricted.

sv51macross

iTrader: (1)

Will the cat overheat without prolonged high-level driving? Or is 80 on the freeway enough to do it?

sv51macross

iTrader: (1)

(Sorry for the double-tap, damn forum takes away the edit option after a little while)

Actually...I wouldn't be surprised if the cats are kinda clogged...there was a period of time where, due to a [horribly] botched engine swap by the previous owner, at least one injector was dutied full-open at idle...And all this time with the O2 out.

On the topic, what's a good, high-flow cat? Because I was thinking of getting a pair of universal high-flows and linking them in series, spliced into a OBX header-back (already have it, was a birthday gift), but 250 apiece for Bonez 3" units is a bit much. And what issues with fueling would need to be accommodated with the extra flow?

Cratecruncher

Until this thread I never appreciated the relationship between short cat life and O2 sensors. Live and learn I guess. My sensor has never been changed and the car is an '87 so chances are it hasn't worked in years. I just checked with my neighborhood O'Reilly's. They have a Bosch O2 sensor 11027 in stock for $20. I'm on it!

Back in '95 the car wouldn't start which was eventually traced to a collapsed main cat. I removed all the catalyst from both the cat and pre-cats at that time so everything is free flow. When the exhaust rusted out a few years ago I replaced it from the cats back with a used system (yes, I was cheap). Since I don't know the history of those mufflers I'll also try running a couple gallons through without the sensor and see if there is a change.

jimmydanny

Wonder if I can throw myself in here.. My car got the S5 TII, but it might seem as the car doesn't work as it should, and the engine was swapped 5 years ago, and the car wasn't touched for the two last years.

When the engine was swapped, so was the exhaust, so the cat must have been okay then. Should I presume the O2 might be the guilty here? Feul economy on a wankel is a no-no anyways, thats not my issue, but it seems a bit rich on the exhaust sound and idle (I know it is supposed to be rich on idle, but it sounds too rich, without me measuring it)

walken

iTrader: (6)

the s5 sevens I've owned would never get more than 12mpg unless all the factory emissions equipment worked.

BomberMan

iTrader: (4)

Am I talking out my *** or do does a dirty fuel system (injectors/ filter) mean that you would actually use LESS fuel due to restriction?

I'd change the O2 sensor first and if mileage doesn't improve also check the fuel pressure regulator and pulsation dampener for faults. Exhaust restriction will effect fuel consumption too, but it shouldn't matter that much...

porsche4786

I'm not surprised if I see 13mpg out of my 89 n/a. But last time I filled up I got 15.45mpg. Which was good for me.

sv51macross

iTrader: (1)

O2 sensor was replaced; no change. PD replaced; no leaks. 2nd fuel rail also replaced, works as it should.

And a clogged filter would lower fuel pressure. Lower pressure means poorer fuel atomization, ergo less burned/more wasted, ergo increased duty-cycle, ergo more fuel overall dumped in.

Justen

iTrader: (12)

buy a prius

Marck

iTrader: (2)

mine was averaging at 8 mpg.. i looked around and i saw that my ecu temperature sensor on the bottom of the radiator snapped so i just connected them together and some how im managing at 15mpg.

bumpstart

while there is many reasons for bad economy
common ones are

faulty 02 sender
the neutral switch on gearbox is disconnected
lack of trailing spark
drifting calibration in the AFM ( or its trim pot in s4 )
or in the coolant temperature sender to ECU
or in the cabin atmo sender or engine bay map sensor
( which incidentally may just be a missing /pinched/failed vac hose )

and yes,, faulty injectors can worsen economy,, they may leak-down after shutdown
and they may spray a pattern poorly and therefore demand more throttle
( and hence injection period ) from the user for power
and not to rule out that they may be poorly atomising due to lack of purge air to the injector atomiser cups
( again a pinched/failed hose in nest issue )

calpatriot

Quick way to check the O2 sensor and the closed loop feedback system all at once is to hook up a 12v LED to the two center pins on the test connector (S4 cars). At a steady 2000 rpm the light should go on and off about 8x per 10 secs.

I have some posts on here from a while back that you can search for with pics on how to do it. The LED should be on (rich) at idle (once warmed up); on during acceleration; off (lean) during deceleration, and flashing during steady rpm cruise.

If the O2 sensor or its feedback circuit have been out of operation for any length of time, the cats will self-destruct, whether you get on the freeway or not. They can then become exhaust restrictions, which might help explain the poor fuel economy.

While u are messing with wires and LEDs, why not make a $3 trouble code checker (two leds, wires, 2 resistors, 3 spade lugs) and check your car for trouble codes. If the O2 sensor is out, it should throw a code 5. The same test set can double as a throttle position sensor adjusting kit.

_Mac_

iTrader: (9)

Found one of my spark plugs were loose so hopefully that helped a bit? Would I benefit from deleting 2 of the 3 cats? Waiting for a volt meter so I can check my sensors.

jjwalker

S5 NA. 5k miles on engine, new injectors, new fuel sock, new fuel filter, nice clean K&N air filter. Only mod is larger exhaust ports.

I get 10-12mpg and I don't drive my car hard. All city.

Suggestions?