dropped mpg

hiya

was wondering if can help me please, i done the last tank mpg reading and its dropped to about 21 mpg from about 35 ish a month ago,

got a td4 auto, mainly on motorway, cruise set at 65 , no smoke, synergy box fitted, bosch maf, set on 2, maf compensator off, am i correct in saying when the switch is set on green it ignores what ever the number is set at on the synergy box, use older style toggle switch on green, done the egr bypass, and bmw crankcase filter

may i ask what do u think may cause such a drop in low mpg please, no leaks etc,

its pulls very well, ticks over ok, as per recommendations from ron when i first fitted the synergy put it onto number 2 as it had the auto box, but the number only would come into effect when input it onto the red light setting ?????

would something like a haweye etc tell me if the maf is out of range or is it the case would only show if its faulty or not

just didnt know if there is a particular thing that could make the mpg drop so much,

vcu , brakes etc ok, i know there isnt a crystal ball but didnt know if u would be so kind to tell me what are the main items that can cause this poor mpg

could a performance air filter, ie k and n improve the mpg

injectors, maf, etc etc

thks so much guys and do apologise for asking

gary

That's a massive drop in mpg. Sticking brakes can drop mpg especially on an auto but the drop seems to much for brakes alone. It's an easy check though. Get hold of an old washing up liquid bottle, rinse it out and fill with fresh water. Go for a drive the at 40 mph for a couple of miles then find a quite safe section of road to stop but do it by coasting to a stop, avoid using the brakes as much as possible. Squirt some water at the discs with your bottle and see if the water boils off fast. If it vapourizes instantly on contact then a brake is sticking but if the water slowly bubbles away they are probably ok and something else is causing the mpg drop.

Hiya

Thks for the info most appreciated

I've checked all the brakes, vcu etc, I even checked the rears as well in case the handbrake or something silly like that had stuck

Just don't get it, the performance hasn't changed, no smoke etc

I've cheked the readings 5 -6 times , wondered if the maf sensor has thrown a wobbly or maybe an injector etc

But thought if that was the case would throw out some smoke etc

I've got some diagnostic software that I've still got to load onto my laptop and plug a bluetooth box into the socket but not sure its going to tell me if the maf, injectors etc are faulty

Its like an elm and gives live data, the manufacturers said 100 percent it will work, has a software crack in it

Just really strange and racking my brain in what the main culprits are that could cause the drop in mpg

Thks so much again and will of course report back as I try and find out what's doing it for future ref

Gary

I only do short trips 2 to 3 miles a time mines gone from 32mpg to 26/7mpg over the winter months

Just checked this morning after filling up and I got 26 mpg out of the last tank. I have a 40 odd mile round trip mostly A roads, but with stop start at each end of the trip. FBH seems to be running constantly…

hiya,

thks guys, its the sudden drop that concerns me,

just trying to load this diagnostic software, a autocom cdp pro,

suppose to work with mine being a pre obd2 socket and been assured by the company it will work, time will tell

gary

Not sure if I'm making this up but I thought that fuel stations used a winter mix diesel to stop the waxing in the colder months which resulted in higher mpg. Have you done the other basics like checking the air filter and also tyre pressures ?

The cold weather has definitely had an effect on my MPG. I have just completed a very light footed 600 mile round trip on mainly motorways and my manual TD4 has dropped from 43 to 37 when compared to a similar journey I did last October.
Local short trips are reducing my mileage to around 360 (27/28 mpg) a tankful at present so as said before, this could be a big factor for some of the OP’s problem.

Just read about failed thermostat in the open position affecting mpg - dont know by how much though ... is it running cool ?

hiya

thks guys, most appreciated , the strange thing is its running fine, just the mpg has plumited ,

just through me loosing well over 10 mpg, just wondering if this software will tell me anything, just waiting for it to get a bit warmer, yes i know woose, lolol

temp is fine, pulls fine , no hesitation and doesnt smoke

been trying to read up , alot of talk about a maf sensor, got the bosch one with a synergy set on number 2 but got on the green light setting,

gary

gstuart said:

hiya

thks guys, most appreciated , the strange thing is its running fine, just the mpg has plumited ,

just through me loosing well over 10 mpg, just wondering if this software will tell me anything, just waiting for it to get a bit warmer, yes i know woose, lolol

temp is fine, pulls fine , no hesitation and doesnt smoke

been trying to read up , alot of talk about a maf sensor, got the bosch one with a synergy set on number 2 but got on the green light setting,

gary

Click to expand...

my synergy is set on 5 and i use green light or eco all the time iv still dropoed 6/7 mpg in cold weather