Ultimate Cefiro said:
i have a friend driving the 3.0L as well n he has downgraded to 2.5L....exactly like wut u ask......v 3.0L wiring, ECU and gearbox........n here comes the nightmare....1stly he convert due to higher roadtax and the engine oso not in gd condition......den he decided to take the engine KOSONG lar.......(bcoz cheaper compare 2 h/cut)........n insist dat all the thing would b the same including wiring etc..........then the main prob is, with the 3.0L ECU, u will get higher fuel injecting level compare to 2.0L bcoz IT IS for 3.0L which definitely will need MORE fuel if both engine achieve same RPM bcoz of higher capacities......then his car acceleration is HEAVY like hell due to this problem and oso lower Top speed due to larger gearbox dat is hardly for a 2.5 2 push.........n then his car is juz like a skunk due to the heavy fuel load......he said he will b fainted if he drive the car too long coz of uncombusted fuel.........so my fren, dun u ever try it.......the car maker usually do the best to design n match all the things n if u spoil it up, u might end up v failure........... (like my car now runing with VQ30DET injector in a VQ30DE, accel. very heavy, wuhuuuuuuu i wanna cry but im gonna install my turbo later, ONG soree yar dun cemburu yar.... :D but nehow i know u r a slow driver....)
Technically, this should not happen...
a) The amount of fuel injected is a function of the amount of air going into the engine. The amount of air is measured by the Mass Air Flow meter, this signal goes to the ECU, which triggers the injectors to inject fuel.
The metering of fuel is determined by the period of time the injector is turned on. The injector is basically a simple open/close valve. The ECU supplies current...the valve opens...fuel is under pressure, so it sprays out. No current, the valve closes. The time period is refered to as the injector timing pulse width.
Since the air flow meters of the 3.0L, 2.5L and the 2.0L are identical (I know since I am using a 2l one in my car), we can conclude that the signal for a given (constant) volume of air is identical.
Since both the 3L ECU and the 2.5L ECU are reading from similar devices, it must receive the same information for a given volume of air.
It will then provide the correct pulse width according to it's programmed fuel maps to accomodate the fixed volume of air.
Here is where it gets complicated....
A 3L ECU expects to find BIGGER injectors...hence, it should provide a shorter pulse width. A 2.5L ECU will expects to find SMALLER injectors, and hence, it should provide a longer pulse width.
So, it is likely that the motor should run lean, and not rich. BUT car makers have thought of this in the design of their platforms...
When at low speed/rpm, the motor runs in what is called a "closed loop" operation. This means that there is a feedback mechanism that sends a signal back to the ECU telling it if the mixture is too lean or too rich, and the ECU adjusts subsequent injections accordingly.
This feedback mechanism are the two O2 sensors you have on your outlet manifold...right at the bottom near or on the cat converters. It will detect a rich or lean mixture, and send it's readings back to the ECU for the ECU to interpret and take subsequent action.
So, in normal driving, some simple tuning should be enough to offset the fuel mixture issues.
However, at higher speeds, the ECU will stop relying on the O2 sensors as the engine is running too fast for proper interpretation of the feedback signals. Hence, the ECU will switch to an "open loop" operation i.e. injecting fuel according to pre-calculated values as determined by it's internal fuel map. In this situation, a 3L ECU (with 3L injectors) in a 2.5L motor will run rich. As the difference in capacities is 20%, it would be simple to tune this out with an SAFC 1.
I find this to be unnecessary as in my current configuration, I am running a fuel pressure (coupled with a high flow air filter) that basically guarantees at least 20% additional fuel availability in order to generate the additional power at higher engine rpm's.
It is more likely that somewhere in the conversion, some sensors were damaged, or the sensors on the 2.5L were out of order. The only reason the engine would run so rich would be :
a) Mass Air Flow meter no longer metering correctly. Can cause engine to run over-rich or over-lean. Unless the signal stops completely, this would not cause any warning lights on the dash.
b) O2 sensors not functioning correctly or functioning intermittently. In this situation, the ECU would run in "safe" mode and basically dump fuel and reduce engine timing in order to protect the engine. That would explain the "draggy" feeling when taking off. This would not trigger any warning lights on the dash, though if the sensor were really badly damaged, a "check engine" warning may occur, and an error code would appear (needs to be read with a special tool).
c) Water temp sensor damaged or burnt out. If the water temp sensor provides a "engine cold" signal to the ECU, higher fuel consumption would result as the ECU would increase injection in an effort to warm-up the engine. This would not trigger any warning lights on the dashboard.
d) ECU damaged. Timing retarded. If something has shorted out in the ECU, there is a fail-safe "map" that retards the motor and dumps fuel to keep the engine running safely. This is the "safe" or sometimes irritatingly referred to as the "limp" mode.
The wire harness differences are marginal for the two vehicles. There are some minor differences in plugs (easily solved by dismantling the plug...taking out the copper pins soldered to the wire and slotting into the "other" plug). Also some minor differences in the number of earth wires and earthing points on the motor.
This means that basically, the designs of both wire harnesses are identical.
One other possibility....
There is apparently a difference in the capacities of the fuel pumps between the 2.0L and the 3.0L. As I have never had the opportunity to see a 2.5L fuel pump, I cannot determine if it is different. It may be that the fuel pressure in the 3.0L is slightly higher than in the 2.5L. It is also likely that the 3L fuel pump has a higher flow rate than the 2.5L fuel pump...which may account for the rich air-fuel mixture.
