96 355 running lean!!??

My money is on Fuel Filter or Fuel Pump....ethanol eats 'em baby Pressure and VOLUME are two different tests. Do the filter first but its more likely a pump. Could be lots of other things but that's my guess. Did it run perfectly for awhile after the major or is this problem right out of major? Did it sit all winter?
The 40% load reading could be a MAF, but its just odd to me.
Any codes?

 

What kind of scan tool are you using? I would like one that can read engine load.

 

I was plundering around a 355 engine last week and noticed the fuel injector plugs looked just like the ones on another car of mine. Got a vibration in this car and it turned out to be corroded fuel injector fittings.

Maybe this is the cause.

 

I would guess fuel pump as well. I've seen this on a Ducati that was in our shop. Ran lean at high RPM, but ran great at low RPM. If we choked off the air supply it would run well at all RPM.

If you have the ability to do so, I'd try checking fuel pressure when the car is under load, to see if the pressure drops at high RPM and hard acceleration (high RPM sitting still probably won't draw enough fuel to lower the fuel pressure).

 

If one of your tensioner bearings is ceasing up, it will do the same thing...loss of power above 3000 or so rpm. Take a look at your timing belts, there is a spot where they can be seen from the top. If one of the tensioners is ceasing, that belt will show strange striations on it as the rubber on the belt wears but not the cords in it. This is a long shot but always good to check all possibilities.

 

You said you did everything n major so I assume all filters were just changed so they should be good. Did you by chance get the injectors cleaned some do and some don't. If you want to check the maf you could disconnect it and let the ecu use the throttle pot to determine fuelling. According to the WSM if the maf screws up the ecu is automatically supposed to do this. Te throttle pot will give you full fuel when the throttle is wide open. If it acts the same it shows your maf is likely good. And proves you have a fuel delivery issue of some kind.

 

There's no chance a towel or something was used to plug the intake during the engine out and got pushed it and is restricting the airflow?

 

Also is it possible a fuel filter got put on backward to the direction of fuel flow. I did not think this could be done when i changed mine but the WSM says it can.

 

My last suggestion would be to check the fuel pressure adjuster. This is likely the problem what it does is based on manifold suction it allows fuel to flow back to the tank. If the adjuster is not seeing enough vacuume it will not fully open and allow fuel to bypass back to the tank.

 

I still think it might be the fuel pump, however there are lots of things to look over after an engine out. I had a similar symptom on a recently serviced car and it turned out to be a fuel injector connection that looked solid but the tab had been broken in the engine out process allowing it to work at low RPM's but wiggle loose when the speeds increases and cause a power loss.
Look over all the connections and vacuum hoses carefully, even stuff that was not removed.

 

I still think it's the fuel pump. If it can make good pressure at speed, then it's not the fuel pump. I don't have any good ideas on how to measure it while driving though. Might want to seek out someone with a dyno.

You could tape over 3/4 of the inlets to your air filters. If that makes it run better at high RPM, then that would be another vote for fuel pump. On the Ducati I worked on, taping up 1/2 of the air inlet made it run much better when the fuel pump was failing. That bike ran perfectly at low RPMs and smaller throttle openings. Ran like crap on the freeway until I taped it up to test it. The fuel pump fixed it.

 

You can chase this forever and still miss it. A Ferrari SD tester will point to the problem in a few minutes. I think its worth a "sub 4500 rpm" drive to the dealer or even tow it. It's not going to cost much for the diagnosis and once you know the issue you can still say "thank you" and take it to do it yourself.

 

Check your throttle position sensors.

 

Unmetered air could cause you to lean out, any chance you have a bad seal on the intake manifold or somewhere else post MAF?