Okay - hey guys - this is for my girlfriends truck.

I have done:
-plugs
-wires
-rotor
-cap
-coil

Fuel pump works - all vacuum lines work.
Replaced catalytic convertor from a 2000 tacoma last night.
Truck runs well, but ***** gas mileage. Also, it does cold start now, but requires alot of patience.

The truck does have an emissions computer - but nowhere in the haynes manual can I find the diagram or any indication that it has an o2 sensor - only for EFI and up.

Also - the truck is getting 250 km's to 40 litres of gas, that is 14mpg. I bought my girlfriend this truck for GOOD gas mileage - shouldnt it get at least over 20mpg?! What gives?

Thank you for your help.

Dave

What year truck and engine?

The O2 sensor will be somewhere on the exhaust, from the manifold to the Cat. 3rd gen('89-95)CA smog equipped 22re's will have two, one on the exhaust manifold and one after the Cat. Lazy O2 sensors will cause a loss in mpg, but wont be the cause of the hard to start issue.

The timing could be off a little bit which could effect the cold start, also the cold start injector could also be going bad. The timing being a little off could also effect the mpg's, but not drop it to 14.

What tranny does it have? Auto's do get significantly worse mileage than their 5-spd counterparts.

What it is the size of tires on the truck? Stock tires are 28's, 31's which are a common replacement are about 11% bigger, which equals a 11% loss in kilos on the odometer.

Have you done a compression check? Stuck/not completely closing valves will cause a loss in power which=loss in mpg. Any white smoke on start-up? A bad/failing head gasket will also cause a loss in power and effect the mpg's

You could have a few little things going on that are adding up to a lot of mpg loss.

The truck he is talking about is the one in question.
1990 22r 2wd 5spd

its a 1990 22r 2wd truck. its on 17 inch rims with 45 series tires - same as stock height (195/70/14?) no white smoke, everyhting runs right. Why am i only getting 14mpg?!

If it has to have an O2 and doesn't the ecu could be in a full throttle or constant warm up mode, and causing it to run rich at idle.

The loss in fuel economy is something else though. I think the carb must just be dumping fuel into the engine to only be getting 14mpg.

The thing i'm confused about, is why does a carb have an ECU and how does it work? Is it for timing/electric choke?

Running rich? AAP on Carb known to go out and dump excess fuel always. Plug the hose temporarily to diagnose.

I only have the FSM for 84, so some things will have changed by 90.
In 84 Calif models, the computer primarily controlled the air injection system via the O2 sensor (Called Air Injection with feedback), sending air into either the exhaust stream or back to the air cleaner to keep the O2 levels optimum for the 3-way cat. The O2 sensor was in front of the cat (manifold, I think), & there was a *temperature probe* IN the cat. So the O2 sensor had no effect on the mixture *into* the engine, only on the amount of O2 fed to the TWC.

84 Federal & Canadian models used an "Air Suction system" without a smog pump or computer control. They also used a standard cat.

Both models appear to have some computer controls on a couple of other emission systems, like the Fuel deceleration cut solenoid,Cold Mixture heater, & evaporative emission control.

It's highly likely that by 90, many of the 84 Calif emission systems were in use in Canada & federal models, perhaps even a few other systems as well(Like timing,elect choke, EGR). Only the FSM for your model year will have all the correct details.

Dave