p0175 2001 Crown Victoria Police Interceptor HELP PLS

Sup gang... Im at my wits end.. thought Id try here.

2001 Ford Crown Victoria Police Interceptor
4.6 L engine
470w (I think) Auto Tranny
82k Miles

Keep getting p0175 with the occasional p0172 at the same time. Mostly just p0175. The following items have already been replaced:

Coil Packs
Spark Plugs
EGR Valve
EGR Valve Solenoid
Fuel Pressure Regulator
Fuel Filter
MAF Sensor
IAT Sensor
all 8 Injectors
air filter
coolant flush
engine coolant temperature sensor
2 x Trottle Body Service
2 x Injector Flush

After all that, the fuel trims are STILL at -23. Ive troubleshot the car as much as I could... fuel pressure is at 30 PSI. Vacume checks out OK. I found NO vacume leaks as far as I can tell. The engine does have a slight misfire type miss to it at an idle but nothing really bad. the car runs great besides the little hickup at idle. used Snapon Shop key to troubleshoot the TP sensor, IAC sensor, and the PCM. all seem to be working correctly according to the shopkey.

what am i missing?

thanks in advance

Kevin

EDIT: I swapped CATs and O2 sensors with another vehicle. Didnt put new ones on, just swapped out. Still no change.

Looks like you covered all the bases. You still need to reset your KAM(keep alive memory). The PCM still uses the LTFT to regulate the current injector flow. Even though the problem is likely fixed, it's trimming negative because of it's previously set memories telling it to run negative. Reset KAM
If your scanner won't reset it you can disconnect the batt. for 10 minutes and that should do it.

Then run vehicle while monitoring O2 sensors. If the o2 sensors are working fine but the LTFT starts going negative, then there may be a problem with the PCM. It may need a reflashing( the dealer would know more about that). Reset KAM first andpost back .

Hope this helps you out. Ive been there!

Disconnected the negative cable for about 3 hours today. (had to make a trip so took the opportunity)

before I started the vehicle after reconnecting I connected the MODIS and pulled up the LTFTs and STFTs and monitored them from the start. they started out pretty good but shortly came to a high negative reading, around -19 to -21.

I did notice something kinda wierd today. I decided to ditch the MODIS and use my trusty DVOM to manually check some of the outputs on the sensors. The ECT was reading at a very high voltage (5.4) at around 194 Degrees F. It was climbing up to around 6 volts and change as the temperature increased to around 210 before the fan came on. As the fan came on, the voltage dropped to around 5.10ish as the fan cut off.

I thought ECTs were on a 5 volt ref signal. How can it increase above 5 volts?

Thanks in advance

Kevin

vaccum leak from the intake gaskets!

I thought vacume leaks only cause a lean condition?

Any word on why I am getting a high 6 volt reference backprobe signal at the ECT?

Thanks in advance,

Kevin

the over fueling that the pcm strategy attempts when it senses that the engine is staying lean can be what throws the rich code! I don't know about your voltage question, haven't looked into it, 4.6's are known to have issues with intake gaskets though so you can take it for what it is!

If the fuel trim is negative double digits it is because the PCM sees way too much fuel and is attempting to take fuel away until the proper threshold can be reached for proper O2 sensor operation. If there is a Rich code in the computer, it is because the PCM COULDN"T TAKE AWAY ENOUGH FUEL TO BRING THE AIR/FUEL RATIO DOWN. It is still running rich. Period.
Fuel trims are minute adjustments to compensate for aging injectors, inperfections in engine castings, etc. When the proper air fuel ratio is reached the PCM will hold there for proper engine operation. When it can't compensate enough and reaches the threshold's limit it sets a code, so, no your engine is NOT running lean, with a rich code.

I think the ref. voltage is something like 5. 8 Volts. It may even be 6. If it's 6V ref., I wouldn't get excited about it.
LIke I said, if you reset the KAM and start up the engine and the trims start creeping negative and the O2s are switching properly, then you've got a PCM problem or an unresolved enrichment problem(I think it sounds like a PCM).

Thanks to all who have replied and given their input.

Unfortunately, we cannot reprogram new PCMs in our shop cause of the lack of Ford Specific tools. So we are evacing the car to the Dealership to have it hooked up to their computer.

Just for information's sake, as soon as I get a response back, I will repost here with the information incase someone else has this problem so they can read all about it.

Great assistance from the people and this site.

Thanks

kevin

Hope it all works out and let us know what the problem is, definitely!

would it be the same scenario for a 97 crown vic lx 4.6L with the civillian package (non-interceptor)? let me know...thanks.

No, not necessarily(not likely either). What diagnosis have you done so far?