This morning I went out- warmed up the car and ran an idle test and 2500 rpm.
On idle the LT fuel trims are -10.2. and -11.7 (out of the range of 10%)
At 2500 rpm the LT are -2.3 and - 3.9.




I then at idles took the oil dipstick completely out and nothing changed on ST (where you would first see it)and nothing in LT.
I then put the dipstick back in and unscrewed the oil cap and the short terms shot up to + 10.5 and +14.3- so I got some indication of air introduction affecting the ST as it should. But that is not nearly as high as the ST and LT go when just cruising down the road at any steady speed from 10-80 mph.

The 02 sensors fit within voltage limits and were graphing as one would expect.

The MAF was .80 lb/m


The only other mention of anything that is strange and this is one of those things that is hard to describe. When you start the car you immediately hear a single click sound coming from dead in the center of the engine. When running at 2500 rpm I could here, albeit at a lower level due to engine revving. After driving the car and it is stopped you will hear a number of these clicks coming from engine center as if something is try to work and not getting there. It is NOT the pure valve by the fender- that has been replaced and I can put my ear and stethoscope at that exact spot and that is not making the noise. The closest sound I can refer to is the opening and closing of the DCCV solenoid on my 05 S-Type, but much louder and more metallic. That may or may not mean anything, but I do not think that is a normal sound and it is dead in the center of the engine.

Any ideas?

Thanks

Tom

 

I've worked on a couple of SC jags but never drove them extensively. There is a flap of some sort in the SC itself that opens and closes, something to do with demand, I think. One of the members must know what I'm talking about, or maybe i'm lost.

The negative trims at idle and high positive while driving make me suspect the MAFS. What happens if you disconnect it?

 

This means the car runs rich by default (fuel has to be removed to run right).

Could be a bad air flow meter, or something to do with evap. If the purge valve is stuck open, the fumes from the gas tank/charcoal canisters are constantly being dumped into the intake, over-enriching the mixture. The feedback system has to then compensate with negative trims. You might want to try and see if that is what is happening. Trace the hose from the purge valve to the throttle body and plug it as a test. Then check the short term trims, they should go positive quite a bit to correct the mix. Also, I believe the purge valve is actually operated by PWM, so you should hear it clicking rapidly, on and off, in cycles of 30 sec (or is it 60sec?). From memory, the long term trim are corrected by the average of the short term trims every 2 minutes.

 

If you are referring to the purge valve under the fender on the drivers side- that has been replaced in the last 3500 miles.
The evap system- the part on the back might be suspect. I think Bob Graff posted 3 TSB about it. That I might suspect and he as thrown at a cruising speed of 55-60 two P0455 codes, but none of that appears related to the causes of the 0171/174. He has not in the last 3 years ever gotten the evap system to complete- just shows incomplete along with the ccm (of course).
Are you referring to the servo Pulse width modulator? (PWM)

So it runs obviously rich by default and then just driving a constant 20 miles an hour it runs extremely lean. Does that really make sense? I don't know- but that keeps pointing to a sensor for me?

Tom