Sudden Increase in Fuel usage

[mal58 Junior Member Find all posts View Profile Close mal58]

Hi,
My Prado 90 has clocked up 205K. It has regularly been serviced and at 201K had the belt, spark plugs, air filter etc changed.

It has always returned around 500-550km from the main tank of petrol when driven around the suburbs. There has been no change in pattern of usage.

Recently and I would say within the last 1500km this has suddenly dropped to 450km per tank.

The engine runs OK, no sign of hesitation, plenty of power, no smoke on acceleration and no ECU warning lights.

There have been no mods in this time and the only work was that the second battery and charcoal cannister were removed to repair the rust developing on the battery tray. The charcoal cannister was just moved out of the way, not disconnected.

The exhaust does smell as though the engine is running a bit rich.

Any idea of where I should look before I go talk to my friendly mechanic ?

Cheers, Mal

[RanJ Avid PP Poster! Find all posts View Profile Close RanJ]

Get the timing checked. Especially if it's just had the timing belt changed. Couple of teeth out of alignment wil do that.

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

lift it up in neutral and check if wheels can spin by hand, perhaps a brake caliper is seizing up

[mal58 Junior Member Find all posts View Profile Close mal58]

HI,
Thanks for the suggestions so far, don't think it is brake binding as all the wheels are only slightly warm after a drive.

With regards to checking the timing, would that be as simple as using a timing light, or would I have to take the front cover off the engine and align the timing marks on the pulleys etc ?

Cheers,
Mal

[RanJ Avid PP Poster! Find all posts View Profile Close RanJ]

Yep. Just a timing light. Off the top of my head you'll need to short out two pins on the diagnostic connector. There is a sticker in the engine bay that tells you. If yours is missing let us know and someone can fill you in.

[mal58 Junior Member Find all posts View Profile Close mal58]

Sorry for the delay in getting back to you on this topic but I have been away.

I checked my Prado a couple of days ago and I am not 100% sure that I did it correctly.

My understanding is that you check the timing on Cylinder No.1. However, the No.1 spark plug is covered by the ignitor pack and to get it out requires removing half the air cleaner and all the peripheral items including vacuum hoses, sensor plug for the air flow meter etc.

Reading the Gregories manual (because thats' what I have), it suggests that you use the lead marked 1, which in fact goes to cylinder 4.

When I connected the timing light I could not see the timing mark on the pulley until I put some white tape either side of the mark.

The timing mark appeared correct when I shorted out the terminals in the diagnostic connector, but it was not very clear, because I suspect that the spark for cylinder 1 and cylinder 4 are fired at the same time, so there is a rotation where the timing light flashes and the pulley is not at the required 10 btdc, because every second fire is for cylinder 4. Does this make sense ?

If I am correct, then I think the timing is correct.

I still have terrible fuel economy, so my next investigation will be into the various sensors etc, as who knows I may have disturbed something when I fixed the battery tray for the second battery.

[Toopy Member Find all posts View Profile Close Toopy]

Get some crc maf cleaner from an auto shop and give your maf a good clean, let it dry reinstall and see how it goes

[RanJ Avid PP Poster! Find all posts View Profile Close RanJ]

Nope. You got it right. Your timing is correct.

[mal58 Junior Member Find all posts View Profile Close mal58]

Hi,
Sorry for the delay in getting back to you all. (Being sick in bed for the last few weeks with the flu did not help).

After some further investigation and remediation, the fuel economy has improved back to what it used to be. I found two things.

1) The small vacuum hose that goes onto the air cleaner and across to some sort of solenoid on the inner guard was disconnected.
2) Another small vacuum hose that runs across the top of the motor and into the metal pipes had a split underneath. It looked perfectly OK from the top.

There were no obvious sucking or air noises, so it was hard to detect without visual inspection and following each of the hoses.

Cheers,
Mal

[RanJ Avid PP Poster! Find all posts View Profile Close RanJ]

Sorry about the flu but good to hear about the easy fix!