Air pump - everything you wanted to know...

[Brett]

A TII will pass the emissions with a DCAT exhaust - assuming it still has the air pump.  :yes

[marco]

I really must be hard of thinking at the moment, can someone just confirm/ disprove the following for an FD?

the airpump provides a pressurized air supply to the ACV, which then provides it to one of the following:  to the cat, into the exhaust port, or re circulates it back into airbox (or induction system). above around 3.5k rpm the pump cuts out and does nothing, and if you want you can always unplug it. If you go for an after-market exhaust, then the supply from the ACV to the cat is removed, however if the pump is plugged in then at low rpm (i am thinking idle) the ACV directs the airpump air straight into the exhaust port. this would explain how cars that have been decatted but still have a functioning airpump and ACV sail through the MOT, as un-metered air is pumped straight into the exhaust. also you cant get away with removing the air pump and fitting a breather on the ACV, as there has to be a positive pressure so as to overcome the exhaust pressure.

Is this right? i ask as i am bout to remove my airpump and acv, mainly out of spite as i have lost a lot of knuckle skin on the pipes between the two. at the moment the car has an aftermarket exhaust and apexi pfc, and when i plugged the pump in for the MOT it sailed through. after they completed the test i unplugged the pump and asked them to do a sniff, and the emissions were sky high. I originally put this down to the fact that i had given the car a good spirited drive to the garage and asked them to do emissions straight away, and once the car had sat for a while the emissions had increased. No i am starting to think it was the port air, and as such i should leave the pump well alone. Anyone else got an opinion on this? I know i could go down the route of fiddling with the apexi settings, but just how in depth is this?

[Prof]

I know the yanks have taken off the mechanical air pump, on both FC\'s and FD\'s (FD one has electric clutch in it)and there is a mod to fit a Corvette Electric Smog pump feeding into the ACV.  That was to get through emissions tests in California.
 
At idle, the volume of exhaust gas is not that great, so the air pumped into the exaust ports must be enough to dilute the emissions down below the limits.  It must be possible to plumb in an air feed into the exhaust system at some point, using a check valve and electric air pump to get through those MOT\'s.  It\'s either that or play with the ECU and cut some fuel and risk a lumpy idle - although you can fail on that as well.

[marco]

oh well, i guess the pump will have to stay on then, was hoping the \'rag it and quickly sniff\' would help get it through!

[doddy]

to get through those MOT\'s.

My next MOT is tomorrow at 16:10 (you may know that we have a centralised MOT system rather than MOT approved garages...).  Since my air pump is still plumbed into the exhaust I\'ll get some benefit from it.

Is there anything I can do to ensure that it really is pumping well at idle?

[Brett]

Nothing you can do really - its fed from the airbox same as the intake.  Just make sure its all upto temperature before you take it in :yes

[doddy]

see my TII now legal post :> :> :> :>

[sparkgap]

For me reconnecting the air pump electrical clutch may have been the way to pass the MOT at my local garage.
I was enjoying the better idle, although lifting off at 2000 rpm would always produce backfire even off-load.
I\'m starting to think that leaving the air pump connected may have been a mistake though.
I think that the exhaust gas temperature has been raised considerably with normal city driving.
My O2 sensor is now intermittent and I get more smoke upon startup, more concerning is the overboosting that I have been experiencing.
The A\'pexi is cutting the fuel at 4500rpm WOT and the boost is peaking at 1.1! It normally stops at 0.8.
I can only imagine that I may have damaged a wastegate and the O2 sensor.
Obviously the Air pump is diluting the gas but it also assists burning unused fuel in the exhaust, which will happen in the manifold and turbo before anywhere else.
I thought I could smell that odour that you only get from a new downpipe off any car shortly after but ignored it.
The pipe that fed the removed secondary cat was blocked intentionally, therefore the exhaust manifold is getting that extra air as well.
Starting to think I should have driven 500 miles to WGT and back for the MOT because it passed there last time without the pump!

[sparkgap]

I finally got round to solving the overboosting problem.
My fears that I had somehow overheated the turbo were unfounded, it was just a split silicone air line from the secondary control solenoid. Happy days.
Air pump remains disconnected now.