EFI vs Carbs economy, are u having a laugh.......!

Hi all. I just thought i'd share my experience of this so far.... I had a 3.9, with a holley carb, in a defender. It was regularly doin 19-20 mpg on the motorway, ran a little rich, but no big deal.Obviously sounded amazing.

Every forum i read said switching to EFI would give better fuel economy, more power though out the rev range, no flat spots etc etc.

Well i've fitted i 14cux system to it, spent weeks making sure its working correctly. ////runs like a dream, starts perfectly everytime, alot more refined (if you like that sort of thing).

But.......

Now i'm only getting 11 mpg!!!!

does this sound right?????

I have seriously soke up this morning wondering weather to just sell the whole Hotwire system and go back to omething like a weber 4 barrel.

What do you guys think....?

bendelaurence said:

Hi all. I just thought i'd share my experience of this so far.... I had a 3.9, with a holley carb, in a defender. It was regularly doin 19-20 mpg on the motorway, ran a little rich, but no big deal.Obviously sounded amazing.

Every forum i read said switching to EFI would give better fuel economy, more power though out the rev range, no flat spots etc etc.

Well i've fitted i 14cux system to it, spent weeks making sure its working correctly. ////runs like a dream, starts perfectly everytime, alot more refined (if you like that sort of thing).

But.......

Now i'm only getting 11 mpg!!!!

does this sound right?????

I have seriously soke up this morning wondering weather to just sell the whole Hotwire system and go back to omething like a weber 4 barrel.

What do you guys think....?

Click to expand...

i'll give you two kit kats for it

What was wrong with Holley, your MPG sounds great - what was the performance like?

I get around below 15 to the gallon with my carbs - but then I do drive like a tart!

Ditch um both and get the Weber got one on my 2a superb carb get about the same mpg as you on the motorway though with the carb that is.

The obvious answer is - Are you running it open or closed loop with the correct tune resistor ?

robrennie said:

What was wrong with Holley, your MPG sounds great - what was the performance like?

I get around below 15 to the gallon with my carbs - but then I do drive like a tart!

Click to expand...

Performance was good low down in the rev range. Plenty of torque. But seemed to top out at about 4000 revs? That mpg was in the motorway, round town it certainly dropped.

The problems with it were:

The auto choke was rubbish!!! It used to run at 3000 revs when cold, 3000 revs everytime u start it warm untill u blip the throttle.

It ran too rich. Couldn't adjust it out. Probably needed re jetting.

The long and short of it was, I wanted it to start more consistently without the cold start revs, I wanted better mixture, more mpg and more power. Seemed like the way to go, but now I'm not so sure......

eightinavee said:

The obvious answer is - Are you running it open or closed loop with the correct tune resistor ?

Click to expand...

It's running without lamdas with the correct tune resistor. So I'm guessing 11 sounds a bit low? Maybe I've got a faulty AFM, or injectors? I install one of thoughs fsi powerboost valves from Rpi 2 weeks ago, that just made the situation worse.

how are your plugs - are they normal looking?

installing the FSE just increases fuel pressure and will result in more fuel being used.

check your AFM is working

Fuel injection

also have a search on The V8 Owners Forum - :: Index

bendelaurence said:

It's running without lamdas with the correct tune resistor. So I'm guessing 11 sounds a bit low? Maybe I've got a faulty AFM, or injectors? I install one of thoughs fsi powerboost valves from Rpi 2 weeks ago, that just made the situation worse.

Click to expand...

I managed to get 18 mpg on the motorway on a run on my 3.9 hotwire and about 8-12 round town. I do use a loud peddle a bit too much but most of the time that was being nice.

The plugs were perfect too and its a non cat so I am not sure really that hotwire is the best for fuel economy. I have only done about 30 miles on my 3.5 with carbs and I had a fuel leak (now fixed, mostly lol) so the jury is still out on my own carbs v hotwire trial.

Couple of things I'd add - First off you really need a few mins on Testbook to see that all is well re sensor readings etc,or it may "seem" OK,but be running say half way up its warm up cycle etc.(Or that the coolant and fuel temp sensor plugs have been swapped - it does happen.)
Second thing is where did the CUX system come from,if its been sat for a long time,esp if its been removed from a car it may not be in top nick.The injectors might need cleaning,pressure reg might be sticking etc.
That its running open loop wont help either,if you were running oxy sensors you woulod have live data to help work out what,if anything is wrong.(Plus you would get better consumption too.)

Thanks fett for the figures, so I'm sure i should be able to get 18mpg sat at 50 on the motorway.

Eightinavee, where can i get a copy of Testbook.

I've fitted a new FSI Raising rate regulator from RPI. They said it should help economy.....? Its currently set at 30psi with the fuel pump on and engine off.

The CUX system came from an old RRC. I don't think it was stood long before i got hold of it. But apart from that i have no idea of its history. I've run some STP Injector cleaner through the tank. Maybe i should get the injectors out? Are they cleanable by the likes of us, or should i send them off?

I'll get some oxy sensors if you think its a good idea. But I've read a few places that they run better in open loop because of compromises made to suit emissions laws.....

Let me know what ur thinking.

Cheers lads

nah it was more like 70 (ish )

i cant help but noticing how much my 92 disco uses btw.

it's old enough not to have cats or lambdas.

it stinks and makes your eyes water in the workshop, the plugs are just about ok however, certainly runs just fine. have to say ive never known if its ever run spot on though, but the sensors all checked out with a multimeter about a year ago.

remember that 14cux fires 4 injectors at a time, so its got poor economy designed in from the offset (it wastes 3 squirts for every 1 that it uses)

cheers

Mr Noisy said:

i cant help but noticing how much my 92 disco uses btw.

it's old enough not to have cats or lambdas.

it stinks and makes your eyes water in the workshop, the plugs are just about ok however, certainly runs just fine. have to say ive never known if its ever run spot on though, but the sensors all checked out with a multimeter about a year ago.

remember that 14cux fires 4 injectors at a time, so its got poor economy designed in from the offset (it wastes 3 squirts for every 1 that it uses)

cheers

Click to expand...

That it bank fires rather than injecting sequentially makes only a small difference.The injectors firing against a closed inlet valve does not mean the fuel is wasted,it is just drawn in on the next inlet stroke.Your engine should be fine without oxy sensors,but it would be better with them.
Just be thankful its not running on the old 4CU flapper system - that really was a lottery....

hi mate

yeah im happy with the 14cux generally, im glad it aint flapper, and in all fairness its been trouble free for years.

im still not seeing though how bank firing the injectors makes a small difference, it squirts out 3 times more than is necessary every single time. and yeah its drawn in when the valve opens, but it shouldnt be there anyway. engine would run cleaner without the extra!

mine does better mpg without the lambdas so how does that work?
at a guess i would say gumed injectors or afm is the dissy ok
rpi fpr is a waste of money and increase fuel pressure across the whole rev range.
as eight in a vee says ecu test first port of call

if you think how fast engines turning,its not hanging about for long before been dragged in ,none is wasted they are sill lean burn

Still expensive to run thou!!

thats my point, no matter how long it is hanging about, fact is the system squirts out more fuel than it needs to.

i know its old and simple, its just annoying that its so simple that it bank fires.

thats a reaon why megasquirt gives an instant mpg improvement - only squirts when needed!

cheers anyway

it dosent squirt more than it needs just as much as needed, but just as is multi point at port better than single injector at opening of manifold true sequential would be better