Air & Fuel Filter Restriction

[manxann]

After many years working with carburettor engines and the problems caused by the above, I have yet to see any clear facts on how air & fuel filter restriction affects engines with fuel injection and engine management systems. It would appear that the EMS must compensate, presumably by reducing power output to maintain correct exhaust gas balance.
Is anyone any better informed?

 

[GregLocock]

Air filter restriction will be compensated for because all EFIs measure manifold air pressure.

Fuel filter restriction might flag an error code due to low fuel rail pressure, but other than that would not be compensated for so the engine would run leaner than expected at high power. I suppose the flag could be used to force the engine into a limp home mode with a reduced red line but AFAIK this is not done on ours, since we don't measure the fuel-rail pressure. Persistent lean running might flag an error, but I doubt the mixture is checked at WOT since it is open loop. Cheers

Greg Locock

 

[TheBlacksmith]

When the vehicle is closed loop, the O2 sensor would probably increase the injection slightly to compensate for the clogged fuel filter. Other than WOT, there may be little or no noticeable power loss. EFI systems seems to have a wide tolerance to compensate for poor maintenance. I had a hard case student that though he could detect a missing spark plug at idle. We pulled 5 plug wires off a V-8 before the idle became unsteady. It even restarted (hot) on 3 cylinders. Power however was lousy and you shouldn't try this at home!

Blacksmith

 

[manxann]

Thanks for the foregoing answers. My curiousity has been stirred to wonder, in a worse-case scenario, do you end up with an engine running at idle and no more? I did have a two-stroke boat engine that reached that state but that was due to carbon build-up on the piston covering 85% of the inlet port!

 

[TheBlacksmith]

More likely you will end up with a "code" and limp home mode due to a mismatch between RPM, throttle position and manifold pressure in either case. (The diagnostic algorithm just compares the three values to see if they are tracking and the engine is responding accordingly.) Plugged air filter = manifold pressure too low, plugged fuel filter = throttle position too high.

Blacksmith