Poor fuel economy - where to start?

[solitaire]

Hi All,

I have a '94 celsior with a first gen 1uz. I used to get about 11l/100kms but its currently around 12.5/100kms, my driving style has not changed and the mileage/trips are the same (its my daily and I only ever drive to work or tootle round orewa).

Plugs, cap & rotor were change about 20,000ks ago, probably less than that. Oil changes are frequent, its just had new coolant and tranny gets drained and refilled when i do oil changed, have also changed tranny oil filter - I have tried running 91, 95 & 98 and cover the same distance with them all (about 550k/s per tank). It's running a K&N oiled filter right now although I am thinking of binning it as i heard that these karman vortex mafs dont like them?

this time last year i was getting 650kms easy with 91.

Could someone be kind enough to advise a troubleshooting/maintenance process? i.e. check this first then replace that etc etc etc.

Points to note: it seems to miss/buck/get generally pissed off at 50% throttle when under load intermittently, it is fine at 25% throttle or at wide open throttle. It does not happen all the time though. It started doing this when i changed the cap, plugs and rotor.

[headshotnz]

Im no expert, but maybe you upset the timing?

[strx7]

does it still feel like it has the same amount of power it used to?

[Jonno2002]

thats not bad economy try 17L/100k round town in my jz
try unplugging the oxy sensor or better yet replace it, and check stupid shit like tyre pressures, brakes arent sticking etc etc

[edwagon]

yep, def watch the AFM with any type of greasy/oily shit - they have mirrors in there that need to stay clean, and not smeared with K&N oil etc

Also, be careful cleaning them - plenty of stories of people buggering them with the wrong cleaning technique

Thats great economy for an auto uz in a land yacht - I kept my uz surf in really sharp tune and even nursing it, would return 15L/100 or so - but then, you gotta pay the cost to be the boss!

[Bling]

Same amount of driving while it's warming up? I get bad economy in my daily as it's 50% spent warming up. Not ideal but i'm not walking to work!

you gotta pay the cost to be the boss!

Nice

[BlakeNZ]

02 sensor is the first suspect.

[thegreatestben]

02 sensors.

I think there are 4 of them hahahaha

[gmacrae]

the miss/buck is something you wanna look into, probably something to do with the timing like mentioned.

My ucf20 uses 9.5L/100k on the open road, but about 15-17 around town - your 12.5L is pretty good assuming its open road and city driving mixed.

[solitaire]

Awesome suggestions, thanks - found that denso sell universal o2 sensors that will work but its all ex usa with insane postal charges... anyone on here a denso reseller? don't want hookups, just reasonable retail.

Stupid question, how to i do the timing on a 1uz? I cant find any reference to it, and i cant remember seeing the dizzy cap being adjustable... and there are two dizzy caps so do i set the timing on each bank separately?

Sounds like i need to get the trueno out of the garage and have a 1uz love weekend.

[Mr.Phreak]

It started doing this when i changed the cap, plugs and rotor.

Did you do the leads at the same time??

[gmacrae]

I'd get the car scanned for codes, i bet the ecu is complaining about the cam angle sensors (dizzys) being out or something

[solitaire]

It started doing this when i changed the cap, plugs and rotor.

Did you do the leads at the same time??

No I did not, didn't quite fit the budget at the time - you think this could be a contributor?

You raise a very good point, they did look a bit tatty - I would have thought leads would either work or not work? Or can they produce intermittent faults too?

[solitaire]

I'd get the car scanned for codes, i bet the ecu is complaining about the cam angle sensors (dizzys) being out or something

Is that the same as bridging the two terminals in the diagnostic plug? if so its not showing any codes on the check engine light - not that I put a great deal of faith in the on board diagnostics on the ecu - they have never helped me with any gremlins on the mr2

[edwagon]

It started doing this when i changed the cap, plugs and rotor.

Did you do the leads at the same time??

No I did not, didn't quite fit the budget at the time - you think this could be a contributor?

You raise a very good point, they did look a bit tatty - I would have thought leads would either work or not work? Or can they produce intermittent faults too?

Leads can make a huge difference

They affect the strength of the spark greatly

They can partially break down - and you'd be hard pressed to pick up a small/intermittent weak spark misfire on a smooth/quiet v8

But it could def cost you a litre or two/100km

[gmacrae]

yours is a ucf11 right? not sure if the OBD1 computer will tell you more with a scan tool than the dash light would. It's the first place I'd start anyway. Leads are another good possibility though. They'll be pretty brittle after 18 years so changing the caps etc could've stuffed them

[solitaire]

Leads can make a huge difference

They affect the strength of the spark greatly

They can partially break down - and you'd be hard pressed to pick up a small/intermittent weak spark misfire on a smooth/quiet v8

But it could def cost you a litre or two/100km

Ok cheers, sounds like i need to stop being a cheap C&%T and spend some money on the old girl.

Ill check the timing, do the leads and clear out the pcv thing, then ill have a look at the o2 sensors - sound like a plan gents?

[solitaire]

yours is a ucf11 right? not sure if the OBD1 computer will tell you more with a scan tool than the dash light would. It's the first place I'd start anyway. Leads are another good possibility though. They'll be pretty brittle after 18 years so changing the caps etc could've stuffed them

yeah ucf 11 - ok so maybe I need to get an OBD1 tool anyway, cheers.

Thanks for all the great suggestions everyone

[Mr.Phreak]

A scan tool won't tell you anything more than bridging the terminals and watching the disco show on the gauge cluster.

The other thing I'd check is to make sure the spark plug wells tend to catch water (especially if the leads are a bit old) and can create a few issues.

Some of the earths can get a bit scabby too, but that usually shows up when braking more than anything

You can measure the leads......but if they're old, you could find out it's fine, then break it when you put it back in. Genuine leads cost a bomb though, but come with all the plastic clips so you don't have to worry about lacing them up neatly.

It's pretty hard to mess with the timing on these, I wouldn't get too worried about it.

[solitaire]

Ok well I did a few things.

I had a look on http://www.lexls.com which had a few good ideas and tutorials.

I was getting some weird fluctuating resistance readings from a couple of the leads and I "think" they might have been the leads that came with the car, they look like they have done more than 80,000k's which is when the cambelt was last changed.

I have now changed the leads, I had sent away a few requests for pricing but everyone either didn't come back to me or couldn't stock anything, in the end I got some eagle leads from appco as the genuine article was a bit too much for me to stomach (yes im cheap)

I also changed the pcv valve and fuel filler cap gasket as i noticed it was not sealing any more. I also cleaned and re oiled the k&n, being carefull to spray and wipe any excess off so as to avoid over oiling it.

I then pulled the efi fuse for 5 minutes.

Its probably all in my head but the engine sounds meaner when i rev it now... placebo most likely.

Will report back with my fuel results

ps. I also got a new fuel filter but $&#$% doing that on the driveway in the rain, i will wait until the trueno is out of the garage.