2zz - why is my mpg so poor?

cptspaulding · January 3, 2017, 02:36

Just had the 2zz engine swap done & I knew I wasn't getting great mpg. Took until my 3rd or 4th fill up to be confident I could calculate a reasonably accurate mpg figure.

23 mpg.

& that wasn't using lift at all.

I have one fault code, P0135, which is the heater circuit on one of the sensors so that shouldn't have any affect.

The car appears to be running really sweet with no misfires or hesitation. Any thoughts where I should start looking?

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jonbill · January 3, 2017, 08:58

I know nothing about 2zzs, but if you're sure there isn't a leak somewhere I'd be looking at the AFR data. Maybe fit a wideband gauge.

phaeton · January 3, 2017, 11:41

Surely if one of the heater circuits is not working then effectively the sensor isn't working so the ECU will use default mapping, which could well be more fuel than you need, what colour is the exhaust pipe & plugs?

cptspaulding · January 3, 2017, 11:51

Certainly in the 1zz, the heater circuit is only in use for the first minute or 2 from cold, so the car can run entirely unaffected even if all 3 heater circuits are dud.
I would imagine the same is true on the 2zz but I could try a known working sensor on that.
https://vimeo.com/197883884
I also have this little bit hunting on the tachometer when up to temp. Could this point to an leak on the exhaust side?

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normanh · January 3, 2017, 18:05

Heavy Right Foot ? -sorry it has to be said!

Norman

beavisrules · January 3, 2017, 19:04

If it sees no heater, surely it will discard that sensors data assuming it's broke.
I know in theory the sensor section may still be good, but would the car in error state use it?.

Also are your maf & iacv clean?

theredone · January 3, 2017, 19:06

Quote from: "normanh"Heavy Right Foot ? -sorry it has to be said!

Norman

not at all - he`s on a diet s:D

s:D

shnazzle · January 3, 2017, 20:34

Quote from: "cptspaulding"Certainly in the 1zz, the heater circuit is only in use for the first minute or 2 from cold, so the car can run entirely unaffected even if all 3 heater circuits are dud.
I would imagine the same is true on the 2zz but I could try a known working sensor on that.
https://vimeo.com/197883884
I also have this little bit hunting on the tachometer when up to temp. Could this point to an leak on the exhaust side?

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Gummed up IAC?

JoeCool · January 4, 2017, 01:36

Quote from: "normanh"Heavy Right Foot ? -sorry it has to be said!

Norman

I'm err.... not very nice to my 2ZZ MR2.... to be honest I bet it wishes it had never been born. 30 Mpg everywhere. It cruises at 4,500 rpm on the Autobahn, chasing M3's.... - 30Mpg.

Something ain't right. Got to be fuelling rich. Even with the short ratio box and wide sticky tyres you should be able to make 30Mpg for normal/fast road driving.

shnazzle · January 4, 2017, 08:59

And another thing. Once again I think the mr2 is more sensitive to o2 sensors than you think. The heater circuit being broken on one sensor had caused lumpy running on my car and Helen's every time.

As I type this I'm sitting in the car with a lumpy idle after my drive to work and the heater circuit of bank 1 sensor 1 gone.

Had this each time the o2 sensor went.

cptspaulding · January 4, 2017, 11:30

Yh. I'll swap in a known O2 sensor to start with.
What's an IAC?

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ChrisGB · January 4, 2017, 11:53

Idle air control valve. I'd try a new O2 sensor first. Once you know that's OK, try other things if fuel economy doesn't improve.

Ardent · January 4, 2017, 12:31

Cpt.
Proper 2zz ecu or 3rd party? Mapping issue?

PhilMC · January 4, 2017, 13:00

Quote from: "Ardent"Cpt.
Proper 2zz ecu or 3rd party? Mapping issue?

Stewart is on a 2zz ecu, so stock Celica map.

cptspaulding · January 4, 2017, 14:40

Are the 2zz O2 sensors the same as the 1zz sensors.

Thought I best check before I order. (this one IIRC?)

Also since this is into a custom pipe of the exhuast I was considering a bit of instant gasket when fitting to ensure (if there is a leak) that any leak is not at the sensor. Any reason not to?

Essex2Visuvesi · January 4, 2017, 15:17

I remember reading somewhere about not using any kind of sealer on the sensors as it can contaminate them
I could be talking complete rubbish tho

Liberty mkiii · January 4, 2017, 15:22

How long is your average drive?
The reason I bring this up is that I have a 6 mile commute and the car has barely warmed up by the end of the drive. Fuel economy is bad in this scenario

01' MR2 K20 swap, crazy mods to come

Carolyn · January 4, 2017, 19:19

Quote from: "cptspaulding"Are the 2zz O2 sensors the same as the 1zz sensors.

Thought I best check before I order. (this one IIRC?)

Also since this is into a custom pipe of the exhuast I was considering a bit of instant gasket when fitting to ensure (if there is a leak) that any leak is not at the sensor. Any reason not to?

Can't see instant gasket surviving the heat. I'd go for an annealed copper washer. (Heat it up with a torch and let it cool).

ChrisGB · January 4, 2017, 20:22

I'm pretty sure the last two Denso sensors I bought had crush washers on them as supplied. The highest temperature instant gasket material would never cope with exhaust manifold temperatures.

shnazzle · January 4, 2017, 20:23

The densos certainly do

cptspaulding · January 6, 2017, 13:19

So...

Ordered & fitted new Denso O2 sensor. Started the car & checked the codes before resetting. Oddly it showed P0125 & P0135 before I reset it (P0125 hadn't been there before).

Reset with the OBD reader, drove for 10 minutes & P0135 came on again!! Rather than try another sensor in the car I took the new sensor out, put it into Patsy's 1zz MR2 & drove that for 30 minutes. No eml, & no codes on her car with this sensor.

Edit - Just drove it with the sensor disconnected & only threw up P0135. Could it be that the system isn't reading that sensor at all?

Also can someone confirm that the O2 sensors are the same for both 1zz & 2zz? (although the pre cat on 2zz has only one).

PhilMC · January 6, 2017, 14:44

If someone can confirm what pins on the plug going into the ecu are for this O2 sensor you could at least do a continuity check to make sure the wiring isn't at fault?

Huambo81a · January 6, 2017, 15:51

I have a 2zz with a tuned Apexi map, and i get 30mpg with the odd trip into lift here and there.

Alex Knight · January 7, 2017, 19:24

Duff heater circuit is causing this, despite the rest of the sensor working.

cptspaulding · January 7, 2017, 19:52

The sensor is good, Alex. I've checked it. Now run 3 sensors; one brand new, one out of another 2 & still P0135 appears. Rechecked 2 of those sensors in a 1zz & both are fine.
So I suspect that my ECU isn't reading the heater sensor circuit. & If that hasn't been connected correctly on the loom, then it's not a massive stretch of the imagination to think that the sensor circuit itself isn't connected either.
Going back to the swap chap prob later this week to sort my overfilling & another fault.

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