Air Flow Meter + car problems

[avos at cochlear.com.au]

     From what I can see, my car does not use a Bosch system or air-flow 
     meter, though I must admit I have not done alot of research into it, 
     as it has always performed adequately (until now - see below). My car 
     does however use a single hot wire element type air-flow sensor, which 
     I think is the same system used by Bosch, so I imagine that similar 
     principles apply.
     
     Recently my car has been performing badly at low to medium revs as 
     boost comes on. It seems to fiddle around with settings when you 
     initally put your foot down until it decides what it is going to do (a 
     few seconds sometimes) and then it runs great. It is annoying under 
     hard acceleration, as it will hesitate and then hit you with an 
     almighty boot in the back. I am sure that this is not good for my 
     engine, and have lowered my boost level to ensure that I will not 
     damage anything. I have replaced the fuel filter, oil and oil-filter, 
     spark plugs, and cleaned the air-filter in the hope that it may be 
     some blocked filter, or bad spark, but all this with no success. I am 
     starting to wonder whether a sensor is working incorrectly on my efi. 
     I have several other ideas before I narrow it down to the efi - fuel 
     pump (not supplying enough pressure), fuel pressure regulator (Does 
     anyone know how to check the fuel pressure is constant under engine 
     load on a 4WD car for which I do not have access to a 4WD dyno), 
     fluctuating boost (though this is not apparent from my boost guage), 
     blocked injectors (though I have run petrol additive injection cleaner 
     with no effect on the problem). If all this fails I will no know where 
     to start - Does anyone have any ideas on what could cause such a 
     problem. The weird thing for me is that it seems to run fine once it 
     has started to sought it itself out and reached high revs, which seems 
     to me to rule out the chances of it being a fuel delevery problem?
     
     Any advice will be appreciated, I am starting to my pull my hair out. 
     Note that my car has had no modifications done recently, and ran fine 
     for a year with the modifications that it has, so I doubt that it has 
     anything to do with any modifications that I have done.
     
     Adrian  


______________________________ Reply Separator _________________________________
Subject: Re: Re[2]: Air Flow Meter
Author:  diy_efi at coulomb.eng.ohio-state.edu at INTERNET
Date:    05/5/97 17:31


----------
> From: avos at cochlear.com.au
> To: diy_efi at coulomb.eng.ohio-state.edu 
> Subject: Re[2]: Air Flow Meter
> Date: Monday, May 05, 1997 12:09 PM 
> 
>      My Subaru turbo 2.0L has a Uni-Filter cone filter. These filters are
     
>      slightly more restrictive than the K&N versions, as they are an 
oiled 
>      foam type filter, though apparently they filter better. Mine also 
has 
>      much greater surface area than the K&N versions so probably flows 
>      better anyway. This filter bolts directly to my air-flow meter, and 
>      immediately the throttle response and max top-end power of my car 
was 
>      improved noticable with no other modifications done at this stage. 
>      Since then it now has a larger exhaust and more boost, and I can 
only 
>      imagine that the difference of the filter has been amplified though 
I 
>      have yet to change it back to standard to see. One thing I will say 
>      that is different between the Uni-Filter and K&N is that the 
UniFilter 
>      has a machined alloy trumpet which they claim achieves more laminar 
>      flow by swirling the air into the air-flow meter. This may be a 
ploy, 
     
 I spoke to soon in my reply post to Kevin. I should have read yours first.
In most BMW kits they use a basic K&N filter element and then each company 
has its own adapter which attaches the mouth of the filter to the sensor. 
     
>      but it may support the theory of turbulent flow upsetting the 
air-flow 
>      meter. The K&N filters have no such mechanism of enhancing laminar 
>      flow that I know of. The trumpet is probably about 3 inches long and
     
>      exponentially (approx) brings the diameter of the filter (~5 inches)
     
>      down to the diameter of the air-flow-meter (~2.5 inches). 
>      
 There is one BMW kit which uses a K&N "cone" attached to a 6inch pipe
which goes to the air flow meter. I would imagine that your 3inch trumpet 
saves space and works even better than that idea. Just curios, does your 
Subaru use a Bosch engine management system with a Bosch air flow meter?
     
     
>      Adrian
>      
>      PS- I think the Uni-filter brand is Australian made though I am sure
     
>      there are equivalent versions made elsewhere. 
> 
 Know if they sell in the good 'ol USA?
> 
=-=-=-=-=-=-=-=-=-=-=
Steve Meade
smeade at deltanet.com