Subaru Forester Owners Forum banner
1 - 6 of 6 Posts

·
Registered
1999 S/Turbo SF5 Auto
Joined
·
93 Posts
Discussion Starter · #1 ·
I have pressurised my exhaust system (~20 PSI) and used soapy water squirted onto joints etc. to find any leaks.
This is what I found:

1] 1 manifold gasket and 2 cross-over pipe gaskets producing small quantity of bubbles - so small leaks.

2] Good hissing leak on turbo where the waste-gate actuator pivot rod comes out of the top of the turbo - the bush is obviously worn, because if you manually press the operating lever to open the waste-gate, the leak pretty much stops completely - so leak under no boost condition.

My question is could any of these leaks cause poor MPG? I understand why leaks on the headers can allow air into the exhaust and give a false reading to the oxygen sensor, but these leaks are pretty small. Yet the bigger leak on the turbo unit is more likely to see a continuous pressure as it is on the downstream side of the waste-gate and turbine, and so unlikely to allow air into the system.

I would much appreciate any comments on this.

I'm going to replace the gaskets - just because its only going to get worse and its quick and easy.... the turbo sounds more expensive to fix :-( :frown2:
 

·
Registered
1999 S/Turbo SF5 Auto
Joined
·
93 Posts
Discussion Starter · #2 ·
So I have a unique problem then ;-):wink2:
 

·
Administrator
2007 Forester Sports XT 4EAT
Joined
·
41,240 Posts
An exhaust leak near the front O2 sensor could cause the sensor to detect a lean condition, causing the ECM to richen the A/F - Air/Fuel mixture = reduced gas mileage. I'd also expect to see a P0420 CEL code from the rear O2 sensor.

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 

·
Registered
1999 S/Turbo SF5 Auto
Joined
·
93 Posts
Discussion Starter · #4 ·
Hi Bobby, thanks for your reply.... My '99 SF5 only has one o2 sensor, so no fault code possible as described. I understand how the o2 sensor would cause a rich condition if there was a significant leak - I just wondered if my very small leaks would cause a noticeable difference?
 

·
Administrator
2007 Forester Sports XT 4EAT
Joined
·
41,240 Posts
On the models with a second O2 sensor that monitors the efficiency CATs, it only takes a pinhole to trigger a P0420 CEL code. :icon_eek:

I'm going to guess any exhaust leak, near the O2 sensor, could be problematic. :confused:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 

·
Registered
1999 S/Turbo SF5 Auto
Joined
·
93 Posts
Discussion Starter · #6 ·
Ok, a pin-hole is pretty tiny - it must be quite sensitive then :surprise:
I'll continue, and replace all the gaskets from heads back.... 18 year old rusty nuts and bolts here we come :rolleyes:
 
1 - 6 of 6 Posts
Top