How much petrol did you put back in the tank when you say running almost dry? 50L+? And only getting 415-430.
 
I'm going to check my own fuel economy over Christmas and report back, you have gotten me curious.
 
Out of interest what spark plug leads did you end up getting. I ordered a set of OEM from Amayama but they emailed back saying they are now discontinued. Considering going through Lithia but $50USD for postage has me waiting until I need to buy something else to make it worth it.

Never ended up buying any, I kinda assumed they weren't the issue / don't wanna fix what's not broken

I almost always run it till like 1 tick left (but not fuel light) then fill up with 98 and that'll get me 400-415km.  Always reset the trip meter as well. So I'm guessing if it let it run completely dry, maybe I'll get 430-445km max?

I feel like mr2y is on to something regarding the cat however so I'll pop into an exhaust shop.  I've kinda done everything I can really.. apart from replacing the O2 sensor and spark leads. Even if the O2 was dead, I should be getting a CEL

Did some more research because I'm interested myself, yes a blocked cat causes more back pressure and causes some engines to run richer to compensate (not sure why exactly). Also, good exhaust shops should be able to test it. If you can get a readout of the O2 sensor you'd be able to see if it's running rich 100% of the time, but I'm not sure how you would do that, sadly Mr2s dont have ODB.

mr2y
Did some more research because I'm interested myself, yes a blocked cat causes more back pressure and causes some engines to run richer to compensate (not sure why exactly). Also, good exhaust shops should be able to test it. If you can get a readout of the O2 sensor you'd be able to see if it's running rich 100% of the time, but I'm not sure how you would do that, sadly Mr2s dont have ODB.

Yeah my mechanic said good luck finding a reader for it haha

I asked for some info on the MCM Brisbane page regarding inspecting a suspected blocked cat, how much a replacement should be, etc. and all the feedback I've gotten is "smash the honeycomb out". I swear I'm one of the few people my age that actually cares about car integrity

Hoonsy
Never ended up buying any, I kinda assumed they weren't the issue / don't wanna fix what's not broken

I almost always run it till like 1 tick left (but not fuel light) then fill up with 98 and that'll get me 400-415km.  Always reset the trip meter as well. So I'm guessing if it let it run completely dry, maybe I'll get 430-445km max?

I feel like mr2y is on to something regarding the cat however so I'll pop into an exhaust shop.  I've kinda done everything I can really.. apart from replacing the O2 sensor and spark leads. Even if the O2 was dead, I should be getting a CEL

If I run my car to when the fuel light turns on I will fill up with about 42L of fuel. That leaves 13L still in the tank (55L tank). If we go by the 10L/100km stated in that other thread, I should have travelled 420km. If you are filling up even before the fuel light turns on you would have even more in reserve but travelled less distance, 400km might be not far off the mark (assuming 10L/100km)? Have you worked out your actual efficiency of your car yet? (Litres used X 100) / km travelled = Litres per 100km.

I'll fill the car up tomorrow and run it over the next few weeks or so till the fuel light comes on next. I haven't used that actual formula to figure it out, I've just kinda guessed it. I run the trip meter, it gets to roughly 400km give or take 10km every time before I top back up (which is usually 40-ish litres, depends how low I let it go). 

Just by looking at the numbers and guessing, I can say that my best is usually 10L/100km, but I'm usually getting worse than that (previously filled up to half tank on the spot, been driving to work the past few days. Trip meter says 150km and it's already used almost all the fuel put in, hence I have to top up tomorrow)

I will calculate mine too, curious to find out. I need to fill up tonight, so I will start my trip meter. You don't need to take it to the fuel light, that was just my example when remembering how much I filled up the other week. Just keep note of distance travelled and litres used when you top up. 

Hoonsy,
you need to take your car to a mechanic, experienced with MR2's, that can check over your car, replace what's worn out and tune it correctly. We have two experienced mechanics and MR2 experts in Brisbane Club (Scope & Nate) who you could contact.
You should be getting 165 - 175Kms per quarter tank ie approx 550 to 600 before fuel warning light comes on. On refill once light comes on you should need 40 - 44 litres. These figures are for suburban driving. That's around 7 litres per 100Kms. On an open road trip you should be able get <6 litres/100Kms using 98 Octane. Falcon from Qld Club has been able to get down into low 5's!!
cheers
Steve

Lumix: Oh fair point. I'll give it a go then and see how I go? I'll keep that formula in mind, thanks buddy

Groper: Trust me, I'd honestly love to get one of the boys to get a proper look at it. I remember seeing that "tech day" but couldn't go - would love for another opportunity like that to swing by. Just not sure if I could afford proper professional help either unfortunately.. I mean, I can afford the check up/inspection at my mechanic, and he's good, but he doesn't seem to do a thorough enough job as it's more of a "car in, car out" kind of workshop (your average workshop I guess). 

Hoonsy
Lumix: Oh fair point. I'll give it a go then and see how I go? I'll keep that formula in mind, thanks buddy

Groper: Trust me, I'd honestly love to get one of the boys to get a proper look at it. I remember seeing that "tech day" but couldn't go - would love for another opportunity like that to swing by. Just not sure if I could afford proper professional help either unfortunately.. I mean, I can afford the check up/inspection at my mechanic, and he's good, but he doesn't seem to do a thorough enough job as it's more of a "car in, car out" kind of workshop (your average workshop I guess). 

You should send Scope a PM and see if he can help you out Hoonsy.

I think because you do all short trips in city traffic, that is why your fuel economy is the way it is. 

I know my car had a worked head and an exhaust and intake, but it was still averaging around 400km in city driving. And lets be honest, we do like to put our boot into it every now and then. 

On my trip down to Sydney, I got nearly 600-700km out of a tank (cant remember exact figure).
It may be more conditions based. It's easy to worry about things with these cars, but in my 4 years of ownership I have learnt that they will run for a looooong time as long as you keep changing the oil haha.

I flogged my old engine every day of its life and it still made 130RWHP.