Removing stutter when pulling off (MPI, guide)

[wiredsoftware]

Quick guide, no pics I'm afraid, of how I fixed the stutter that I was experiencing when pulling off in my MPI. Basically, I've cleared out the internals of the air box snorkel. 

 

- remove the air box snorkel, its attached to the air box with a single + head screw. There is a tube underneath it that goes to the manifold to feed warm air, pull this off (easiest to do at manifold end).

- using a screwdriver, prise the snorkel apart into two halves along its length, at the lugs. 

- Once inside, you'll find lots of plastic obstructions, and a primitive valve which is supposed to ensure warm air is fed when the engine is cold, and cold when it's up to temperature. Unfortunately, it seems to mostly get in the way, and mine was quite stiff. 

- Pull out the flap/spring

- Using a dremel, cut out any remaining plastics that used to house the flap so that the tube is empty. Finish by sanding it smooth, and optionally coat with a suitable plastic paint to smooth out any imperfections. 

- put the two halves back together by pushing them back into each other. 

- refit using the screw, and plug in the warm air hose (you could always run a cold air hose from the front of the car, if that's your thing). 

 

Result: much smoother pulling off, the slight bogging down is gone, both when hot and cold (was always worse when cold). Power is the same, no change to MPG. 

 

I suspect the flap inside was not functioning to its full potential, so restricting airflow. I've left mine now sucking both warm and cold air, working fine for me, although others have removed the snorkel altogether and attempted a cold air intake. I'm dubious of the benefits of this - because MPI not race car. This also has the advantage of looking 100% stock. 

 

Incidentally, I tested that this might have been the problem by first running the car without the snorkel altogether. This fixed the issue, but this car is not made to go bwarp, so this solution has made it sound stock again. 

 

This is may not be suitable in extreme low or high temperature climates, but we get neither in the UK. 

 

Comments welcome. 

Edited 7 February, 2017 by wiredsoftware

[TMB]

My air intake is standard but it doesn't bog down when pulling away. Maybe it's because my hot air flap thingy is working OK though.

[wiredsoftware]

Could be. I'm not convinced that flap is a good design, when closed the air is forced to come from the manifold, up a relatively narrow pipe, and then completely double back on itself to get to the air box. When open, it's always partially obstructing the inlet tract. 

 

Probably a triumph of efficiency over engineering. 

Edited 7 February, 2017 by wiredsoftware