jaytc2003

iTrader: (1)

I average between 180 and 200 miles in my my93 classic this is no matter how it is driven. I can drive it off boost but it doesnt seem to make any difference

The car has an induction kit, exhaust (cat back) and VTA dump valve but I feel that this is quite poor fuel consumption.

Is there any way of checking to see if something has been added to the management or sensors to fool the ecu into using more fuel?
The engine is sweet and has done less than 70k doesnt burn oil or anything like that.

mgcvk

VTA might be factor in higher mpg although I'm sure others will contest this.

scoobfan

VTA would make no difference to consumption, it simply keeps the Turbo spinning.

I would get a diagnostic check done, it will bring up things like a dodgy
lambada sensor which could and does affect consumption if it's shot or
on it's way out.

Rob

jaytc2003

iTrader: (1)

I have done a check myself by using the black connectors but everything was okay. Could it be that the lambada is just sending wrong signals to the ecu?

I have a lead under my induction kit that isnt connected, it originates from the drivers side wing, and then on the connecting wire that is braided and seems to run to the exhaust. If I connect this I get a light on my dash lighing up, this is 3 along to the left of the check engine light (which doesnt light up)

JohnS

iTrader: (1)

The VTA would make a difference to fuel economy. Each time you change gear/lift off, the engine measures more air coming in through the MAF sensor and adds more fuel to compensate (ie you'll run rich for a short period of time). The reason for this is that the ECU isn't expecting the air to be vented (it assumes the standard re-circulating valve is in place) and calculates the fuel incorrectly.

If you do a lot of town driving, where you change gear a lot, then the effect on fuel economy could be quite noticeable.

You have to remember also that the earlier cars only came with a 50L fuel tank, and 200 miles isn't that bad, depending on the type of driving. If it's lots of urban, or fast country road driving, then 200 miles is probably about average. If it's all contsant speed motorway driving, then I'd expect closer to 240 - 250 miles from a tank of fuel. If you are on track, then I'd expect about 50 - 70 miles from a full tank.

John

jaytc2003

iTrader: (1)

It is mainly motorway driving with a bit of urban.
So it is far to assume then that the recirc type dump valve is the better option to have? Is the standard one good or something like a baileys recirc type?

blackdown

I too have a my93 and get close to 250-260 miles to the tank doing a bit of urban but mainly motorway.

The car has HKS induction, decat straight through exhaust.

mrfuzzyfelts

i get 150 - 200 in mine!

aint that just scoobies 4 ya?

jaytc2003

iTrader: (1)

just ordered a new standard recir type from Graham Goode (along with a set of coloured dials so I will now know what speed I am doing!!)

scooby_matt

How much did it cost mate?

jaytc2003

iTrader: (1)

The dump valve was £55.32 + vat so not to bad. Will miss the old dump valve noise but if it helps with performance and economy then its a small price to pay!

scoobfan

John - Can you elaberate a little more please.

I'm interested in this one, are you saying that more fuel is used as the
turbo keeps spinning more freely, creating a greater cycle of air through
the system hence more fuel is required.

I was under the impression the only air flowing over the MAF was from
the induction side not at the end of the cycle by the DV.

I must admit it sound feasible and it wasn't something i had thought about

Rob

jaytc2003

iTrader: (1)

Rob, think it could be something similar to this

If you think of it as 5 litres of air going through the MAF at a constant rate, then with the recir type DV that air assuming it hasnt been used by the engine as combustion is always going to be in the system. The ECU by means of sensors, knows approx how much air hasnt been used so adjusts fuelling to match what it already has, and also by the constant supply still going through the MAF, basically putting less fuel in as there is still some unused in system.

Now if you have a VTA DV then the MAF Fuels for this air but when you make the gear change you obviously lose this. So the ECU has already added the fuel for this but then thinks that there isnt any air in the system so it adjusts the fuel using the signal from the MAF by enrichment, so in effect your getting more fuel being injected decreasing economy.

Is that about right John?

JohnS

iTrader: (1)

Pretty much correct

Tha MAF measures the volume of air taken into the engine. The ECU calculates the amount of fuel to use for an amount of air (taking into account temperature etc). If you eject some of this air to the atmosphere, then more air is drawn in when you are back on the throttle again. This is measured by the ECU as extra air, and adds more fuel to compensate.

The standard re-circulating dump valve does just as good a job of keeping the turbo spinning as a VTA (unless you are running close to 400bhp+), but the excess air goes back into the intake side after the MAF sensor. The ECU knows this volume of air, and doesn't add in extra fuel.

OK the volumes of air are quite small, but ti does make a difference. This is why many cars with a full de-cat and VTA produce flames on the overrun, due to the extra fuel being injected. Sometimes this extra fuel doesn't burn fully, and hence you can get flames at the exhaust!

You'll often notice that cars fitted with a VTA are more "sooty" around the exhaust area/bumper due to the car running rich for a small period of time on a regular basis - that's if the owner doesn't wash their car that frequently.

John

peachy wrx

i need a stiffer spring for my bailey dump valve,getting 120 miles to a tank full!