Ford Forums banner

P0420 and FRP odd reading

2K views 6 replies 3 participants last post by  for(d)life 
#1 ·
Hello everyone!

2003 Grand Marquis LS Ultimate Edition 4.6L

Been getting P0420 code about 3 to 4 times a year, all in the summer time. I know what the code is, but don't know the cause. No other codes.

Got a scanner tool and it has live data. Now, this is what's strange about it. The scanner will read FP/Vac (psi) live, (fuel rail pressure relative to vacuum) and most days will hover around 39 psi steady, give or take 2 psi. Lately, when the wife takes the car to work, after she gets home, I'll wait 15 minutes and check FP/Vac (psi) live while hot, and it hovers at 58 psi. It's happened twice, when it's 90 degrees out, and the ECT is about 190 degrees.

20 psi difference :surprise:, and a high fuel pressure CAN cause a P0420 code. WTF?? Is this normal? Do I need a new FRP sensor?

Please help!
 
#3 ·
Thanks Bert for the link.

This may explain it.
I found it here: >> Under Pressure: Maintaining Ford’s Electronic Returnless Fuel System

"While running, the PCM is attempting to maintain 40 psi of pressure at the injector nozzles. The PCM will raise its target above that pressure if it “sees” the fuel temperature rise high enough to cause vapor pockets in the rail. The higher pressure counteracts vaporization."

My theory is; the code may mean the catalyst is on the threshold of being bad and the extra heat of the Summer throws the code. It will go the whole Winter without tripping the P0420 code.

Thanks again,
Laters!
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top