1995 Previa Poor Mpg

[95previa]

Hi guys,

I'm getting very poor mileage on my 1995 2.4 previa. I'm doing around 13mpg in the ciry and 15mpg on the hwy. Any help would be greatly appreciated.

TIA

Henry.

[miti-babe]

Henry

without some extra info, your gas-guzzling could be down to almost anything...

How many miles has your bus covered?

Recently serviced?

If not, try replacing the spark plugs and air filter at the very least... poor sparking and a blocked filter will cause poor fuel economy... My 13 yr old Previa has 160k miles and I've just replaced ignition leads & plug caps, dist cap and rotor arm... it has made a significant difference to starting & fuel economy...

Good compression?

If not, could be down to valve recession leaving the valves slightly open... this will definitely cause poor fuel economy...

Lots of around town, short journeys?

This will cause oil emulsification and heavy combustion by-products in the oil... this in turn is dragged up the PCV System and is deposited as a grey/brown sludge in the throttle body... removing the throttle body for a darn good scrub (about every 30k mls) will be more than worth the trouble of getting it off the car...

If none of the above helps...

You may be suffering from any (or all ) of the following:

Leaking fuel injector(s) - rare, but definitely causes poor fuel economy...

Defective gearbox... you'd have surely noticed if it was still i first on the highway...

Malfunctioning air/fuel system... Air-flow meter, throttle position indicator and exhaust oxygen sensor are favourite (in that order), not a cheap option to replace any of them

My first suggestions are ones that you can try yourself...

You could take the bus into your local Toymota dealership and have them run a diagnostic routine on the ECU (probably won't see any change from $150 just for the test...) or you could buy a Haynes manual which shows you how to link out the ECU and use the dash indicators to tell you fault codes (worth it's weight in Hershey Bars...) The manual cost me £16.99 inc shipping, so you should be able to get one for about $20 - 25.

Good luck!

[95previa]

miti-babe,

Thnx for the reply. Here's some background of my car:

- almost 70k miles

- spark plugs are 1 year old

- new air filter

- new fuel filter

- recent oil change

- new air-con compressor

- new engine mounts and accessory shaft mounts

- recently serviced

- the CO content in the exhaust gas are WAY over the limit (according to my mechanic), my mechanic suspects leaky injectors

- my mechanic has checked the compression and he said it's ok.

- no codes from the ECU

Yes, my car is mostly a city driven car, 99% of the trips are around town/short trips with feather feet.

Is there a way to check those 3 sensors to see if they're working correctly??

TIA.

Henry.

[miti-babe]

Henry

70k miles seems darn low for the injectorators to be giving up the ghost... You running it on sand?

The air flow meter, throttle position indictator and Oxygen sensors are all electrical components that can be either tested in isolation (the home mechanics choice), or subjected to dynamic tests as part of the Toyota Diagnostic routines... (Not so easy and a damn sight more costly...)

You'll need a fairly good quality electrical multimeter and a set of feeler gauges. All the tests are outlined in that Haynes manual I told you about (no I'm not one of their agents...!) Manual No. 2048 covers the 2.4 Petrol previa from '91 thru '95.

The TPI is checked after removal from the car, which also allows a visual inspection of the condition of the Throttle Body itself (mine was absolutely horrendous.. and took half a day just to clean it...)

Similar situation with the Air Flow Meter as you need to remove it to do all the static checks, but you can crawl under and do the tests on the O2 sensors in situ...

Another thought... Did your mechanic test out the fuel pressure regulator? If that isn't releasing at the right pressure and dumping fuel back into the tank, you'll have a seriously overpressure fuel system... it's more likely that this one component may be faulty, rather than all 4 injectors at such a (relatively) low mileage...

And here's another one from my own (recent) experience... My Previa is dual fuel (autogas) and normally only runs on petrol from start-up and when she's cold... However I found that the petrol was being used at an alarming rate and that after a few highway miles, she developed a kind of "allergy" to the autogas and would only run cleanly on petrol....

I'll cut to the chase 'cos it took me over a week to get to the bottom of this...

Turned out to be the charcoal filter in the evap emissions circuit... The 3-way valve at the top of the canister had "bought the farm" and was allowing inlet manifold vacuum to be presented to the fuel tank breather system... not a problem normally, but when she's running autogas, 100% of the gasoline is returned to the tank via the regulator dump valve... Much of this returning gas is vapourised and was sucked directly into the charcoal canister where it condensed and soaked the filter... this eventually filled up and allowed the throttle body inlet tube to draw neat fuel into the throttle body... drowning the engine in fuel...

The result was the canister overflow venting neat gas onto the pavement and the car refusing to run autogas...

The cure...

Remove charcoal canister and ritually dispose of same...

Block (uneccesary) Evap breather from tank with 8 mm bolt and hose clip (there is already a substantial breather from the tank to the gas filler, this second one is one of them tree-hugging green thingies...

Block throttle body evap inlet pipe (to prevent air leak into throttle body)...

Resume discounted autogas driving...

Have you noticed a smell of gas as you get out of the car Henry? Check to see if you've any drips of gas coming from the tubular cross member just under the oil filter, 'cos that's where the charcoal canister vents into...

Why didn't I replace the canister? £143.00 plus 17.5% tax, that's why! (You do the £/$ math on this one...)

Let me know if I covered your fault when you get it fixed...

Jeff (miti-babe)