Z18XE sudden drop in conomy

**rowano** · 28th February 2012, 11:24

Hi all. Looking for some advice. I was getting 420-440 miles from a full tank in 57 plate vectra c. Didn't drive it for 2 weeks, when I came back to it I've been getting 340-380 miles to the tank. It's done about 7000 miles since then, I've changed air and oil filter filter, new oil, new plugs, no brakes dragging and not sure what to try next. Got a fault code 0165 which is starter relay circuit voltage, no idea what this means. Any advice please?

**rich r** · 28th February 2012, 12:39

Is it getting properly up to temperature (ie around 85-90C)? Z18XE thermostats seem to fail very frequently, which will affect the fuel economy.

Starter relay low voltage could indicate that your battery isn't holding charge very well, so it's voltage is dropping quite a bit when the engine isn't running.

**rowano** · 28th February 2012, 13:01

Cheers Rich. Gets up to temperature OK, usually takes about 5 minutes or so to get there.

I'll get the battery tested and replace if needs. Wouldn't expect this to effect economy though?

**rowano** · 28th February 2012, 13:01

Cheers Rich. Gets up to temperature OK, usually takes about 5 minutes or so to get there.

I'll get the battery tested and replace if needs. Wouldn't expect this to effect economy though?

**rich r** · 28th February 2012, 13:28

That sounds about right for the temperature. Not that then.

I wouldn't have thought the battery would have much effect on economy - nor a failing alternator for that matter.

Are you judging fuel economy by the trip computer or by how much fuel you put in? It could be that the trip computer needs a reset.

**rowano** · 28th February 2012, 13:41

Done by distance travelled on a full tank. Always fill up when petrol warning light comes on, takes ~55 litres. It does seem like the first 1/8 of a tank gets used up a lot quicker than it used to - I used to get about 50 miles before the fuel gauge needle moved, now after 50 miles it's reading 1.8 tank gone. I'm thinking this is probably just the gauge needing recalibrating though.

**Das** · 28th February 2012, 14:26

Take the MAF off and spray it with electrical contact cleaner, do not touch it with anything though. May just be dirt on the sensor causing a poor reading and a higher fuel consumption.

**rowano** · 29th February 2012, 12:48

OK DasArab - I'll give that a try over the weekend. The MAF sensor is the one on the air inlet, just after the filter housing yes? Do I just take it out, unclip the wiring and spray inside in housing?