Saab C900 ITG 'TriFoam' Air Filter Project

Compiled by Craig Dewick

February 2005 - March 2005

A standard type of air filter is a flexible assembly made from folded heavy-duty filter paper. This type of air filter is very in-efficient and is prone to clogging and decay from all manner of contaminents with extended use.

Induction Technology Group (aka ITG) in the UK makes a range of high-performance air filters. Their signature filter products use a special three-layer combination of filter foams secured around a stainless-steel gauze former which ITG calls their TriFoam System. This provides a better level of filtering than paper-based filters but most importantly has a greatly reduced impact on air flow through the filter (which contributes to an engine that 'breathes' easier). The opportunity to buy one from a UK-based Ebay seller came up in December 2004 so I decided to buy it and try one out!

Note that this was a very short 'project' (just one day in February 2005 to actually install it) but it's highlighted a couple of things which are only really best-described in pictures.

Preparation Work to Remove the Old Paper Filter

DISCONNECT THE BATTERY NEGATIVE BEFORE COMMENCING! Fuel vapours will be present and are a serious fire/explosion hazard!

ITG 'TriFoam' air filter with air filter box still assembled under 'snail' Top view of air intake, throttle valve and fuel distributor Air 'snail' removed from filter box and throttle valve

View inside throttle valve (left) and air/fuel mixture control assembly (right) Close-up view into air intake side of throttle valve Top of air flow sensor plate (connects to fuel distributor via a linkage)

Close-up view of the condensate (oily mixture) on the airflow sensor plate Something to note:

The oily condensate contamination on the top of the airflow sensor plate shown in these pictures is a concern - it's coming from the hose connected between the crankcase breather nipple and the throttle valve (top port into the valve assembly as confirmed by the pictures showing inside the throttle valve)

Preparation Work to Remove the Old Paper Filter
DISCONNECT THE BATTERY NEGATIVE BEFORE COMMENCING! Fuel vapours will be present and are a serious fire/explosion hazard!
ITG 'TriFoam' air filter with air filter box still assembled under 'snail'	Top view of air intake, throttle valve and fuel distributor	Air 'snail' removed from filter box and throttle valve

View inside throttle valve (left) and air/fuel mixture control assembly (right)	Close-up view into air intake side of throttle valve	Top of air flow sensor plate (connects to fuel distributor via a linkage)

Close-up view of the condensate (oily mixture) on the airflow sensor plate	Something to note:
	The oily condensate contamination on the top of the airflow sensor plate shown in these pictures is a concern - it's coming from the hose connected between the crankcase breather nipple and the throttle valve (top port into the valve assembly as confirmed by the pictures showing inside the throttle valve)

In order to open up the air filter box, the fuel filter (attached to the intake port of the fuel distributor by a short braided hose from the outlet of the filter) has to be removed from it's bracket, and the hose connecting to the charcoal cannister (which is part of the ELCD - Evaporative Loss Control Device - system) needs to be disconnected either from the top section of the air filter box cover or from the charcoal cannister unit.

The top of the air filter box with the Bosch CIS mixture control unit (airflow sensor and fuel distributor) is secured to the body of the air filter box with six screws. The close-up view of the airflow sensor plate above shows four of the six screws around the top cover. When the top cover is in place it holds the air filter element securely in position centrally inside the air filter box.

Charcoal cannister (part of ELCD system) with hose from air filter box removed Close-up of connection to charcoal cannister Loosening the fuel filter so it can be moved

I found it easier just to pull the special elbow with small plastic gauze filter out of the charcoal cannister. The elbow or hose must have been broken or damaged at some stage due to the electrical tape covering it. That's how it was when I bought the car and over time I'm starting to understand how the ELCD components are meant to work. 8-)

Removal of Paper Filter and Installation of ITG Filter

Holding airflow sensor + fuel distributor + fuel filter out of the way ITG filter placed in position ready for re-assembly Paper filter that was removed

Stainless fasteners securing fuel filter bracket Note about fuel filter bracket securing:

<--- You WILL need to do this eventually. The fuel filter bracket on Saab C900's is secured with two pop-rivets and nothing else. The bracket is just a piece of formed sheet steel right? Well yes, but the fuel filter the most critical element that your engine relies on to ensure it's fuel supply is as free of contaminents as possible!
The rivets holding the fuel filter bracket were loose when I got the car in 2003, and it had always been my intention to replace them with proper fasteners. I sourced some bags of miscellaneous metric-sized stainless-steel fasteners and have been steadily using them to fix up things on the car.
Do your car a favour and secure the fuel filter bracket properly before it comes off completely one day and leads to a potentially hazardous situation developing while you are driving along with the fuel filter bouncing around

Removal of Paper Filter and Installation of ITG Filter
Holding airflow sensor + fuel distributor + fuel filter out of the way	ITG filter placed in position ready for re-assembly	Paper filter that was removed

Stainless fasteners securing fuel filter bracket	Note about fuel filter bracket securing:
	<--- You WILL need to do this eventually. The fuel filter bracket on Saab C900's is secured with two pop-rivets and nothing else. The bracket is just a piece of formed sheet steel right? Well yes, but the fuel filter the most critical element that your engine relies on to ensure it's fuel supply is as free of contaminents as possible! The rivets holding the fuel filter bracket were loose when I got the car in 2003, and it had always been my intention to replace them with proper fasteners. I sourced some bags of miscellaneous metric-sized stainless-steel fasteners and have been steadily using them to fix up things on the car. Do your car a favour and secure the fuel filter bracket properly before it comes off completely one day and leads to a potentially hazardous situation developing while you are driving along with the fuel filter bouncing around

Replacing the air filter is a simple job to do, but remember to be extremely careful when moving the top part of the air filter box with the airflow sensor and fuel distributor out of the way. You will need to use a lot of force to keep it held up enough to wiggle the air filter in/out of the base of the air filter box - this is because of all the fuel lines, etc. that attach to the Bosch fuel distributor and also because the fuel filter (which connects via a short hose to the fuel distributor) has to be moved too.

The small fuel lines are easily damaged and if they're quite old they could become brittle and might split or break, so be careful and lift the airflow sensor and fuel distributor slowly and carefully. If a fuel line does develop a split or break, try to avoid getting fuel on your skin if possible, and wash your hands immediately if you do spill any fuel on them.

It's not advisable to disconnect the fuel lines, but it is ESSENTIAL that the battery negative is disconnected BEFORE doing this job because of the fuel vapours that will be present after removing the 'snail' between the throttle valve and air filter box.

If you'd like to contribute any additional or updated information for this page, please let me know.

If you would like to discuss this page and it's contents with other Saab enthusiasts, please visit the Saab C900 Technical Forum at Craig's Classic Saab Workshop.

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