Crappy fuel economy, crappy power?

[ericem]

Hey guys, I really need to get this issue fixed. To start its a 94 turbo legacy. Now fuel economy is pretty crappy at 300km to 50+L. Doesn't matter how I drive it either :S Really there isn't much power in boost, you don't really feel the boost. It hits 8 psi. What I have noticed is when I floor it, if I let off the pedal it will start accelerating much faster, almost seems like the engine is bogging when I floor it.

 

What has been done, spark plugs (coppers), fuel pump (walbro 190), swapped injectors, knock sensor, cleaned MAF, BPV checked for vacuum leaks, engine seems to idle pretty nice. Recently did the timing belt, idlers, oil pump, water pump didn't make any difference either.

 

History of what has been done on this car, replaced the engine and tranny with one from another car since it was easier to swap the engine and tranny together. Previous engine I could easily get 400km to a tank, 350km at its worse.

 

This is what I am thinking about doing, swap over intake manifolds since my old motor has a better condition one, and at the same time I can replace the intake gaskets (TB, IAC, and head to manifold). I am thinking maybe a gasket is broken or cracked, and when I hit full boost it leaks.

[GLCraig]

What I have noticed is when I floor it, if I let off the pedal it will start accelerating much faster, almost seems like the engine is bogging when I floor it.

 

That sounds like some kind of an exhaust restriction. Sometimes the catalytic converters will break apart and clog up the exhaust system down stream. Disassemble your exhaust and shake out the sections. Also do a visual inspection of the cats.

[heartless]

That sounds like some kind of an exhaust restriction. Sometimes the catalytic converters will break apart and clog up the exhaust system down stream. Disassemble your exhaust and shake out the sections. Also do a visual inspection of the cats.

 

would have to agree here - a partially clogged exhaust will cause these kinds of symptoms, as could a bad/lazy O2 sensor. would check it out before going thru anymore engine stuff.

 

also - is the "check engine" light working? (should come on breifly when key is turned to the "on" position. if it doesnt, it needs to be fixed) is it throwing any codes?? check for stored codes. '94 should still be using the black & green connectors under the dash for checking codes.

[ericem]

No CEL, I am running a non catted downpipe, but the mid still has the stock CAT. On a hot day, cold start I can see white smoke! I figured the o2 sensor has no affect till I am cruising. The o2 sensor is dented, and the wiring insulation is cut up a bit.

[heartless]

No CEL, I am running a non catted downpipe, but the mid still has the stock CAT. On a hot day, cold start I can see white smoke! I figured the o2 sensor has no affect till I am cruising. The o2 sensor is dented, and the wiring insulation is cut up a bit.

 

technically speaking, it is true that the O2 does not come into play until the car is fully warmed up - but - if yours is in that bad of condition, I would change it, regardless. It is amazing the difference a new O2 sensor made on my car!

 

Advance Auto has a direct fit replacement Bosch unit for under $100 (US) versus $150 for a dealer unit - it works fine, just put one in my car (yours takes the same part number) (stay away from the "smart link" one!)

 

White smoke on start-up? that sounds like either a small amount of coolant getting into the cylinders - or - possibly fuel seepage into the cylinder overnight (have a lawnmower that will do that - huge cloud of white smoke when it finally fires)...what do your spark plugs look like??

[GLCraig]

If you O2 sensor is indeed bad, your fuel mixture is going to get really rich and that second cat is not meant to see that much unburnt fuel. This can cause the cat to get too hot and melt or break apart. If changing the O2 sensor dose not make a significant improvement, you next step should be inspecting that second cat.

[ericem]

Hey guys, how much does the TPS play a role with things? I think I want to retune the TPS and replace the o2 sensor.

 

Still questioning the intake manifold gaskets though hmmm.

[Fairtax4me]

Hey guys, how much does the TPS play a role with things? I think I want to retune the TPS and replace the o2 sensor.

 

Still questioning the intake manifold gaskets though hmmm.

 

A bad TPS would show symptoms of throttle sticking or not responding. Very simple devices and they don't generally go bad. If it were that It would surely throw a code, although this is OBD1 we're talking about. The engine would have to be on fire before the ECU noticed something wrong with the TPS.

 

Had one go bad on a Chevy Corsica I used to own, even just the slightest touch on the throttle pedal would make the engine redline. NOT fun to have the car try to run away in rush hour traffic. Two feet standing on the brakes and the best I could do was keep it from accelerating more, but it sure wasn't slowing down. Nuetral, Key off and coast across 4 lanes of heavy traffic... not much fun either!!!!

[ericem]

Yikes, I am thinking in terms of Throttle position sensing might be off lol.

 

BTW this tank 53L and 280km. WOOT!!

[Fairtax4me]

I'm gonna guess that if you don't have a ruptured FPR, you probably need an O2 sensor.

[heartless]

seriously - check the car for stored codes. There are many instances where the car can throw a CEL but it may not STAY on full time. The only way to know for sure is to check for them.

 

When my O2 sensor went bad it would throw a CEL only breifly (a few seconds) and then back off again - it would be easy to miss it as it was not on steady.

 

not sure if the '94 is read the same way as the '90 version, but I had to connect the black connectors, then turn the key to the "on" position (do not start) the CEL would then flash any stored codes. In my case it flashed a 32 - 3 long flashes, 2 short, pause, repeat.

32 = O2 sensor inoperative

 

After changing the sensor, clearing the codes and going for a test run, when i checked for any possible codes again, it flashed the "all clear" which is a steady flash, pause, flash, pause, etc, at 1/2 second intervals.

[Jes1991]

tried replacing the fuel filter? it helped on my Subaru.