The Conundrum that is the 1UZ - Fuel Economy and smooth running/flat spot?!

[nathanshnoz]

Hey all,

Ok so i know this has been done to death but i'm trying to work out any other issues with my 1UZ conversion. Fuel economy is around 18/20L per hundred giving it a little bit of stick but not really hard driving. It's in a manual 1993 4runner. I have had ECU repaired/rebuilt, plugs are new, leads are new, dizzy caps new, rotor buttons new, new timing belt, water pump, drive belt, starter motor, O2 sensors, blah blah blah i have replaced the majority of parts. this fuel economy does not seem like it is accurate for a 1uz from what i am hearing of others getting in their conversions.

the motor also doesn't run as smooth as it should and definately has a small flat spot. sometimes at idle it is searching and not constant at one rpm. i have tried to get a tacho signal from the coil but cannot get ANY tacho to work acurately on it. i have absolutely no logical explanation as to why this is. i CAN get a singal. but no tacho can decipher it, not 4 cylinder,V6 or otherwise.

Please help me

[madmont]

You need a 4cyl tacho
Do you have any error codes?
Describe your exhaust system

[George]

You need to use the proper tacho signal first. It's normally output from one (any) of igniters, not coils
what year/chassis is your 1uz? do you run any o2 sensors?

[nathanshnoz]

I have a 4 cylinder tacho. Does not read correctly. I also have a monster tacho set to 4cyl and also that does not work correctly.

No fault codes as far as I know but I will double check tomorrow.

Exhaust is custom made headers into twin 2 1/4 inch pipes into single 3 inch with magma flow exhaust and then single 3 inch into semi baffled muffler and then 3 inch out the back

[nathanshnoz]

Yes I know u get the signal wire from one of the igniters. This is the signal wire I am using and even with 2 different 4 cylinder tachos it will not read even close to accurate.

o2 sensors are new and installed correctly

[nathanshnoz]

Engine is from a 1992/1993 LS400

[George]

so I assume you have four o2 sensors and two cats, right? ECU has four sockets with two rows of terminals? (in 1993 donor, newer ECU may have been installed with four 4-row sockets). Is MAF metal or a plastic made one?

are igniters firmly connected to body chassis, and so does battery negative terminal and engine short block? (you may want to temporarily throw a wire between intake plenum and igniters assembly to check for bad earth)

What voltage do you read at VF1,VF2 terminals of diag. plug? (the one which has these terminals actually installed)

[madmont]

Here is wiring diagram for tacho . Black wire goes to IG- in check connector

In my opinion 2 inch is the correct size for primary exhaust pipes merging into a 2 1/2 inch exhaust but that is just my opinion and many will dispute this
Some people also make their headers far too big and wonder why they do not work well
You may not be interested but here is a phone video of my speedo and tacho 0 to 100ks in about 9 seconds
RN46 Hilux 1UZ ,about 1900kg including driver, auto transmission ,5.28 gears, stock headers, 2 inch primaries and 2 1/2 inch exhaust, non baffled mufflers . Apologies for the poor video quality

[nathanshnoz]

so I assume you have four o2 sensors and two cats, right? ECU has four sockets with two rows of terminals? (in 1993 donor, newer ECU may have been installed with four 4-row sockets). Is MAF metal or a plastic made one?

are igniters firmly connected to body chassis, and so does battery negative terminal and engine short block? (you may want to temporarily throw a wire between intake plenum and igniters assembly to check for bad earth)

What voltage do you read at VF1,VF2 terminals of diag. plug? (the one which has these terminals actually installed)

i have two primary O2 sensors. i do not have sub 02 sensors. i have one single 3 inch cat. picture of one of my ECU's (i have a spare one) is attached so you can see pinout/model of ECU. igniters are earthed to the body and there is continuity between the igniter casing and the negative battery terminal. so earthing should not be an issue. air flow meter is metal casing type.



Voltage at VF1 and VF2 are as below:

Ignition ON, Engine off VF1 = 86.3mV
VF2 = 87.4 mV

Ignition ON, Engine ON VF1 = 2.25 V
VF2 = 2.25 V

Madmont - That is precisely the wire that i am using. But i cannot explain why it won't work. Exhaust sizes are a bit of personal preference i think but the exhaust certainly has excellent flow and is not restricted. mine is manual and 4.3 diff ratios, also around 1,850 kg with driver and fuel. your power delivery in the video looks smoother than what mine is but mine would be similar in speed getting to 100. it also is a lifted (body and suspension lift) 4WD and has 33inch mud tyres. that being said, even on 31 inch road tyres the economy is no better.

there is definitely something wrong

[madmont]

Like I said many will dispute what the correct size is
What diameter and length are your headers?

[nathanshnoz]

Like I said many will dispute what the correct size is
What diameter and length are your headers?

They are 1 3/4 inch I believe Tri y style. Length is very hard to tell without measuring passenger would
Flow better than drivers due to the design of them

[madmont]

I reckon those exhaust sizes should work well at about 7000rpm
My 1JZGE has factory headers with about 28mm inside diameter and are not very long but I have quite long secondaries to give me better torque at low revs. Revs quite freely to the rev limit.
Measure the primaries on the heads you removed from the 1UZ they are probably about the correct size to give good low speed torque
As you can see in my little video my smallish pipes work well. The a341e auto has a first gear ratio of about 2.5 so is a bit slow off the mark and needs torque at low revs

[dumbass]

if u have a tall diff ratio and tall tyres then its always going to use fuel

I changed from 4.3 diff ratio t0 3.7 and I lost 50 kms travel distance for a full tank
1uzs are not what they all brag about on the internet hehee

anyway u need to try an ecu that hasn't been repaired or try your ecu on another car as its hard to get an ecu repaired and make sure its perfect all at same time

unplug air flow meter and see if miss flat spot goes away
maybe u have stuck injector which is common for jap import motors
I would wire up the diagnostic plug that sits under the dash and plug a scanner onto it
makes life much more easier than just guessing
u probably could have bought a scanner with all the money wasted on changing most of the engine bits

[George]

nathanshnoz could you check VF1/VF2 voltages when the engine is heated to operating temp and gradually revved through the rpm range you typically use?
2.25V would indicate either perfect engine condition , or some failure in fuel mixture monitoring. The thing making me believe there's some failure is that both voltages (which indicate fuel trims for bank 1/2) are ideally matched, though in old engines the difference between the banks must build up.

I'd advice that you at least emulate the sub o2 heaters so ecu won't flash sub o2 codes. For some reason fuel consumption is sensitive to sub o2 sensors

[dumbass]

just wire up a diagnostic plug and put a scanner on it

ive got a similar ecu if u want to buy one
part number is 89661 50141
so your ecu is 50142 which must superceed my one
but when I put my ecu part number in toyodiy it says its from a usa ls400 90 to 94 model