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Fuel Economy Drop Since Manifold Replaced

C

Caboose

New Member
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Location
Dublin, Ireland
Car
05 Accord 2.2 iCTDI
Hi All, great website and great resource!

If you guys could give me a hand with the following problem I'd be chuffed!

Back in November I had all the tell-tale signs that the manifold was cracked (fumes in cabin and knocking noise). I had the manifold replaced under warranty in November in my Honda Garage. I also had the car serviced at the time (filters and oil). The car has 93,000 miles on the clock.

I have filled up the car about 5/6 times since then and have noticed a sharp drop in the fuel economy from getting about 530 Miles out of a full 55 Litre tank to about 470 miles out of a full tank ( right down to end of reserve tank).

I'm wondering has anybody else with replaced manifolds experienced this loss in fuel economy? If not, what could it be? The car has been great otherwise and I have not noticed any loss in power.

Cheers for any help :)

Caboose
 
Didn't notice much change after mine was done.

Could be a failing sensor? this is a job for CJM. ;).
 
Its more likely down to the cold weather and ecu relearning. Welcome by the way.
 
As the guys said and welcome Ken
 
F6HAD said:
Its more likely down to the cold weather and ecu relearning. Welcome by the way.
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Do you mean that the ECU has to relearn after the new manifold install or the weather? :) We've had a mild winter over here. It hasn't dropped below zero excluding a couple of nights before Christmas.

Do you reckon I will see a return to the same fuel consumption?
 
my fuel economey has dropped off during winter because of the added fuel consumption for heaters / seats / lights.
 
The ECU is constantly learning, but a manifold change will knock it way out. Shouldn't take more than a couple of tanks to get things straight though.
 
Caboose said:
Do you mean that the ECU has to relearn after the new manifold install or the weather? :) We've had a mild winter over here. It hasn't dropped below zero excluding a couple of nights before Christmas.

Do you reckon I will see a return to the same fuel consumption?
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They need to disconnect the battery during manifold install, and that causes the ecu to reset its learnt parameters. Also the ecu will have slowly adjusted to compensate for the lack of backpressure due to leaking manifold, and now that the backpressure has restored, it will need to re-learn again.

just give it time and wait for the weather to improve, it all contributes to economy.
 
As Fahad and the others have said.


Mixture of the reduced temperatures (whilst still quite mild for the time of year) the ECU relearning and also probably more queuing in traffic due to Christmas traffic etc.

Another thing to check is your tyre pressures as pressures can drop significantly with lower temperatures see this thread Check your tyre pressures

I have noticed in my time here, though that quite a few people notice an initial drop in fuel economy after the manifold change, so it most probably mainly due to the ECU relearning.


Personally I've also noticed a slight drop in economy recently, although not quite sure whether it is also partly due to a change in tyre brand as well as the temperature.
 
ive noticed a drop too on the diesel. I have put it down to the temp
 
Thanks for the reassurance all. Obviously a drop of approx 60 miles per tank is not something to worry too much about. Hope to get many many more years out of my baby.

I'll share a shocking fact for Irish pre 2008 Diesel Accord owners... Since the engine capacity is 2204cc, we pay €960 for road tax each year !! Enough to make you puke!

Post 2008 they have started to charge road tax on Carbon Emissions, which I think would cost about €250.
 
I've just worked out im getting 31mpg on pure town driving... Wtf!? surely this aont right??? had manifold done over a month ago. other than a service, what can i check?
 
rx7ali said:
I've just worked out im getting 31mpg on pure town driving... Wtf!? surely this aont right??? had manifold done over a month ago. other than a service, what can i check?
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What sort of driving do you call town driving.

I.e is it lots of stop starts, waiting around etc or is it constant steady motoring with just plenty of traffic lights, but you manage to get through them on each turn ?

How have you calculated the 31 mpg and do you always fill up at the same filling station ?

Is it a noticeable drop from before the manifold change ?
 
CJM said:
What sort of driving do you call town driving.

I.e is it lots of stop starts, waiting around etc or is it constant steady motoring with just plenty of traffic lights, but you manage to get through them on each turn ?

How have you calculated the 31 mpg and do you always fill up at the same filling station ?

Is it a noticeable drop from before the manifold change ?
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I dont fill up at the same place tbh, i just always fill up to the top.

I havent had the car long enough to say whether the manifold has made a difference tbh, I've only had the car since end of december.

I worked this out having reset my milage at a FULL tank, and then writing down the milage after filling up to full. I dont have the exact numbers in front of me but it was something like 370 Miles on the clock and i managed to squeeze 54 Litres into the tank.

This is driving around Milton Keynes, so all 1/2 mile drive, roundabout, 1/2 mile drive , roundabout, 1/2 mile drive , roundabout, 1/2 mile drive , roundabout, 1/2 mile drive , roundabout. no real trafic to speak of, no sitting around. Just lots of roundabounts :p

Bare in mind i was getting something like 26mpg from an old 2L petrol mondeo in the same driving conditions, i would have though that i should be getting 36/37mpg from the Accord.

Other than a service, what can i do? Is there a sensor, or component that could be to blame? I'm happy enough to working on the car so can and will do anything to try get some extra miles out of my juice.
 
rx7ali said:
I dont fill up at the same place tbh, i just always fill up to the top.

I havent had the car long enough to say whether the manifold has made a difference tbh, I've only had the car since end of december.

I worked this out having reset my milage at a FULL tank, and then writing down the milage after filling up to full. I dont have the exact numbers in front of me but it was something like 370 Miles on the clock and i managed to squeeze 54 Litres into the tank.

This is driving around Milton Keynes, so all 1/2 mile drive, roundabout, 1/2 mile drive , roundabout, 1/2 mile drive , roundabout, 1/2 mile drive , roundabout, 1/2 mile drive , roundabout. no real trafic to speak of, no sitting around. Just lots of roundabounts :p

Bare in mind i was getting something like 26mpg from an old 2L petrol mondeo in the same driving conditions, i would have though that i should be getting 36/37mpg from the Accord.

Other than a service, what can i do? Is there a sensor, or component that could be to blame? I'm happy enough to working on the car so can and will do anything to try get some extra miles out of my juice.
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In total is your trip around 2 1/2 miles if so with that sort of mileage a diesel wouldn't work out any more economical than a petrol as the engine won't have reached operating temperature.

Another problem you seem to have (not your fault but road planning) is that you have constant roundabouts that will mean that you will be braking/ slowing down and then re-accelerating to come out of the roundabout, whilst the engine is cold.

This could also be affected more by how you drive i.e pretty much accelerating up to the roundabout, firm braking then accelerating back out swiftly. The most fuel efficient approach would be to de-accelerate in good time to negotiate the roundabout, using the highest gear, the car is comfortable with and trying to get around with offending roundabout with as little loss of momentum as possible, then gradually increasing the speed again.

You may of course do this already, which should then rule out driving style.

Best bet is next time you are going on a longer run, say 50 miles or so fill the car up., reset the mileage and top up again at your destination. Ideally you want to be doing something like motorway driving at 65 mph max.

Once we know what sort of MPG that returns then it would be better to say that there is something not quite right, otherwise it could just be down to short journeys with lots of roundabouts.

You could of course check that things such as the air filter are nice and clean, no obvious binding of the brakes , tyre pressures etc and of course that there are no puddles of diesel on the driveway when it rains.

Another factor could be the weather, especially if it has been cold, down your neck of the woods.

Do you have any other issues, like excessive black smoke on acceleration or anything ?
 
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