well sorta, put a "restriction" in the MAP vacuum line and it has leaned out the mixtures a tiny bit

my reason behind this was as they run rich from factory it may help trying to lean it out a tiny bit. there has been a very slight power increase but as i usually run it on ultimate and im on shell this time its hard to make a good judgement.

this may be of more use when i put an exhaust on as im pretty sure it will get richer.

anyone think there would there be any down falls to doing this?

car is a EB 4L

mm nice idea, the only down side would be that it may run to lean and hole a piston or 2!!!

well i forgot to say, i hooked up an autometer a/f gauge beforehand. its not running too lean and unsafe, but just a tiny bit less rich...

Wouldnt the ecu relearn whats happening through the sensors in the exhaust? Like if you try and set the throttle? same thing happens?

The pressure difference between both sides of the restriction would take a little longer to reach equalibrium, thats about all due to a reduced flow rate. I cant see this hurting any thing however I cant see any advantages of doing this mod either. I think that it would be very hard to vary the amount of restriction to set it to any form of calibrated spec. Can you actually feel the difference through the seat of your pants or is it a mystery like the 3kw gain from a performance air filter.

Technically the mod should actually richen the AF mixtures up a bit at partial throttle while at full throttle it will stay exactly the same. You also throw out the timing curves by doing this which could lead to problems, although the factory timing curves are fairly safe.

would u be able to explain a bit further as it would be good to know the operation of the MAP. what i thought was - "it will be gettin a weaker signal causing less fuel being injected".... just a guess though.

also if possible could you explain the effect it does to timing and why. would be great if ya could.

Okay heres my understanding, the MAP sensor is used to calculate engine load with idle being around 20-26" of vacuum (from memory) and full throttle being close to 0". Obviously the fuel maps go from an AF ratio of around 14.7 under light loads to around 12 (sometimes richer) under full throttle or 0vac. Putting resistance in the MAP vac line will make the MAP read less vacuum under light loads resulting in a richer AF ratio, in effect the EEC thinks you are placing more load on the engine than you actually are. When you are at full throttle there is no vac in the map sensor therefore the added resistance will not do anything. IMO the changes would probably be very little but from my understanding any changes would actually be the reverse of what you want. Also, if the added resistance is too much, it will make the MAP readings quite slow to change which could cause problems.

Same goes for timing, where the EEC calculates the load of the engine to determine the timing advance. Like fuel the EEC thinks you have more load on the engine so pulls more timing out.

This is also the reason why I6s with larger cams tend to run richer. Large cams generally produce less vacuum, therefore the EEC calculates a higher engine load and makes the engine richer.

i see what u mean, but the only thing i dont understand is how there is less vacuum at full throttle than at low throttle eg. if i were to put my hand over the intake snorkel at idle there would pretty much be no sucking but if i gave it a rev i will feel air being sucked in.


I dont understnad this either, it sounds like if i were to take the MAP vac line off the sensor, the engine would still run as there is no vacuum there so its in its std position.

also where do the wires go from the MAP sensor?

cheers 4 ya help

Okay you are talking about the air being sucked into the engine, not manifold vacuum. The vacuum measured by the MAP is the vacuum inside the manifold compared with normal atmosphere. This is created by the engine trying to suck air into the engine but the throttle limiting that flow therefore creating a vacuum inside the intake itself. So when the throttle is closed, the engine is trying to suck more air in than the throttle is allowing causing a vacuum while at full throttle the throttle is fully open so the engine can have as much air as it needs meaning that the intake pressure is the same as normal atmosphere.

The wires from the MAP sensor go directly back to the EEC where the voltage is analysed and engine load is calculated.

now its all coming together... thanx for tellin me that stuff, makes a lot of sense.

also i mean with the MAP sensor wires which individual one goes to where and what ie. ecu, earth.etc (and also from what i "know", the MAP sensor doesnt giv a voltage out but a frequency... or is it related?)

I don't know if anyone read my last message, but ignore it... I've realised the difference between the MAP hose and the PCV hose.