Pertol Consumption Wayyyyy Too High

[LowRed]

First of all Merry Christmas to one and all :D

I think this year i may get a card from the Petrol Suppliers that keep my Monster running.

I have had 2 Sport Cats fitted to my LS400, with a complete system Stainless Steel.

The Fuel Economy was never toooo good but i expect for a old V8 it is gonna be nasty.

But since the Exhaust fitment with Cats I'm doing about 215ish Miles to a £74 Full Tank.

Bad I know i use to cry when i would do about 260ish before.

My main driving is Local City driving, is there anything i can check or do or adjust to decrease the Fuel she drinks or have I just made a Greedy Basteward a bit Greedier????

Answers on a Postcard Please, you may make my Crimbo :D:D:D

Regards

LowRed

[cleverdick]

And a happy new year! :P

Now then. Forgive me for asking, but with the greatest respect, why did you have this mod done? Personally, I just don't get it when people try to modify their LS400s in an attempt to improve performance. Aren't these fantastic cars quick enough already? It's not a sports car and it's not meant to be (even though it'll p*** on most).

As for fuel economy, you should expect high 20s at least on a long run, obviously much less on an urban cycle, particularly with the a/c on for demisting etc. I think that 30mpg from a 4 litre V8 motor this size is pretty damn good, particularly when coupled with this level of refinement and reliability. Certainly nothing to complain about in context.

These cars are among the most highly developed in the world. Toyota did their job thoroughly. So why try to reinvent the wheel? If you deviate from OEM stock, you'll upset the balance and something's gonna give.

In your case, it could be something as simple as an O2 sensor that they forgot to reconnect (not sure if this would throw an error code) or something like that. I really do hope so. Might be worth getting an emissions check done on the same machine as on your last MoT, so that you can make a comparison.

Good luck...

[LowRed]

Thanks for the speedy Reply

The reason I made the Exhaust Upgrade was that the original Cats gave up on the car and broke down internally.

I had a fair bit of corrosion through the Exhaust due to being originally from a coastal area. Plus from Lexus the Cats are a rediculous £400 each, so for 2 sport Cats and a Stainless System, I paid £900 for the lot. Hence being cost effective. The Note is rather sweet and sounds like a V8 should ;)

But the Fuel is drinking now big time, I will have the Emissions tested and Oxy Sensors monitored to see if something is not right, I may need to tweak the other OEM parts to get it running better. The Car seems to be running a little too rich for my liking, but onwards and upwards :)

[BarneyTT]

Thanks for the speedy Reply

The reason I made the Exhaust Upgrade was that the original Cats gave up on the car and broke down internally.

I had a fair bit of corrosion through the Exhaust due to being originally from a coastal area. Plus from Lexus the Cats are a rediculous £400 each, so for 2 sport Cats and a Stainless System, I paid £900 for the lot. Hence being cost effective. The Note is rather sweet and sounds like a V8 should ;)

But the Fuel is drinking now big time, I will have the Emissions tested and Oxy Sensors monitored to see if something is not right, I may need to tweak the other OEM parts to get it running better. The Car seems to be running a little too rich for my liking, but onwards and upwards :)

In theory you have made the exhaust system less restrictive which should make the gasses escape quicker which in turn should give added performance, but as the system is less restrictive I would have thought mpg should have slightly increased not decreased also.

I'm not very technically minded but those sort of mpg figures don't sound right to me, I would expect mpg to be higher than you've quoted even for a LS with an aftermarket exhaust system.

[ROYT]

Just my twopennorth, but have you tried some injector cleaner?

If any are not perfect and do not spray a nice cone of fuel, i.e are they leaking, or over fueling, this will waste fuel.

[maneesh]

it seems you're getting around 13mpg, compared to around 16mpg before. i'd say fitting a freeer flowing exhaust and the sport cats probably gave you a bit more performance with higher fuel consumption too!

have u checked, is there a leak in the exhaust anywhere, near the cats?

[peter026]

Bung some Red Ex in Chris and see what happens It might improve the mpg slightly, although, another make, I think it called Millers, is supposed to be very good, I'll pop out to the 4x4 in a minute, I have some in there, and check the name

Edit

Well been out and checked and Yer tis

[Mike_B]

In theory you have made the exhaust system less restrictive which should make the gasses escape quicker which in turn should give added performance, but as the system is less restrictive I would have thought mpg should have slightly increased not decreased also.

Not quite - the amount of back pressure in the exhaust system has an impact on the amount of fresh fuel/air drawn in during the intake cycle. If there is resistance on the exhaust cycle then obviously slightly less burnt gas will be pushed out, meaning there is already a higher pressure in the cylinder when it starts to draw the next charge in - hence, less fuel/air is drawn in and consumption is reduced at the expense of performance. Unless you have a fully open throttle, the inlet side runs at a considerable vacuum (this is where the servo gets it's vacuum from) so any residual exhaust gas in the cylinder has a big impact on the total amount of fresh charge drawn in.

For an extreme example of exhaust tuning, take a look at a 2-stroke motorcycle engine. Usually, the exhaust balloons right out close to the engine to help with scavenging before closing back down to a small bore again by the silencer. But then, in most 2-stroke bikes fuel consumption is irrelevant... :winky:

[lutonmatt]

it does sound quite bad on the fuel but you should my trans am around for a week a 6.6 v8 that sounds like a v8 should and drinks the juice like a yank does i can put £20 in on sunday morning run a couple of miles to a meet and up to buger king in the week and its gone i have never worked out the mpg but its not good i do 20/30 mile to 20 quid but you dont hang around in it

but cant wait to get my 400 back on the road plan to have it back by the end of jan

[LowRed]

Thanks for all the comments people :D

Guess I will be trying the Oxy Sensors, Injectors, Throttle etc etc lol

Will let you know if I can reduce the Fuel Glugging

Merry Christmas All :winky: :D

[Mat]

Hey low red

16 mpg is what im getting around town! normally i get about 19!!

Did you sort the problem?

Mat

[ibby]

putting a free flowing exhaust will most likley lower economy

na engines rely on back pressure from exhaust..

[LowRed]

Hey low red

16 mpg is what im getting around town! normally i get about 19!!

Did you sort the problem?

Mat

Well its been a while since I had Money, so not yet due to that lol

now I have a Missfire like half the Spark Plugs are jumping.

Will look into both now but guessing they may be related :S

Suggestions on a PostCard:D