While my car is idling, I remove the oil cap and the vehicle d now. I'm testing my crankcase vent valve. I know that I'm creating a vacuum leak but before it would just idle roughly and never die. I removed the CCV, and plugged up the crankcase vent valve port and also the hose That connects to the crankcase vent valve, the vehicle was running and it didn't die or run roughly so that would point towards a crankcase vent valve, correct? I keep getting pesky PO171 and p0174 codes

09 xf 4.2

 

it looks like you have an XF and you have posted this in the s-type forum.
regardless removing the oil cap or the pcv pipe will cause an engine shut down , as that is not just a vacuum leak its a MEGA monstrous vacuum leak .. in fact it would be hard to find a larger one on the cars vacuum system . and the computer can not offset this amount of counter acting with fuel . so it should shut down . this is no way to test for lean conditions and far from conventional . try using fuel trims and ether after you have watched a demo on youtube . or smoke test or any other conventional way of testing .

 

I have a 4.2 which is the same as the pre 2009 other models with the 4.2. I'm fully aware of which forum I posted it in. If it's an engine question with the 4.2 I normally have better luck as there are more members with the S-Type or XJ with the 4.2 as they only made the XF with the 4.2 for 2 years. We've already smoked tested it, changed the upper and lower intake gaskets, re smoke tested and the smoke was nowhere to be seen, we changed both oxygen sensors before the catalytic converter and a mass air flow sensor with a OEM. There's really no way to test the crankcase vent valve as the diaphragm inside of it closes at certain pressures that I can't manually do. The oil cap removal prior to me thinking it was the crankcase vent valve would just cause a unsteady idle and not kill the engine. We manually blocked off the crankcase vent valve ports and the crankcase vent valve hose and the vehicle maintained idle. Vehicle did not die. All signs are pointing towards crank case vent valve. At idle my LTFT are steady + 3-5 percent. At wide open throttle or anything above 2000 RPMs the long-term fuel trims can reach double digits up to 20% on both banks. Fuel pressure is okay. New fuel pump and fuel filter less than 12,000 mi ago. We installed OEM parts for that as well. No exhaust leaks. It's been a real doozy to figure out. I ordered a crankcase vent valve and will try it on Friday.

 

Ok , understood.
the pcv valve is only $60 max .and is a eventual service requirement any ways .
i replaced mine because the o-rings were done .
have you ruled out the MAF ?
what are your MAF readings ?
.
also
don’t rule out the fact melted/blocked cats
can throw your trims .
some times caused by a a bad MAF ,
Normally with quite blocked cats you will get a
pinking sound with acceleration .

 

A MASSIVE LEAK.

Of course it will stall or go mad.

 

I'm clueless of the intake channel on the XF, but more than one member here has reported exhausting all their ideas unsuccessfully chasing lean codes....only to find a small hole in the silencer cavity between the air filter and the throttle body. Might want to take a hard look at the entire channel between MAF and throttle body?

 

Do you think it's possible that a fuel injector could cause a lean code on both banks?

 

Humm..

Doubtful. Injectors are bank specific so chances are one injector would set a code for the bank it is on.

Also..I'm thinking that if an injector was leaning the codes enough to set a code..you would also have a misfire on a single cylinder.

 

That's my thinking as well. I wasn't sure if the jaguars had a tune port type set up or not. I installed the new crankcase vent valve. My long-term fuel trims do not go above 20% on wide open throttle anymore. My old ccv was bad for sure. I could not get the diaphragm to close inside while sucking on the port. I was able to get it to close on the new one that was OEM. What's normal LTFT readings? I'm about 5-7 Percent

 

LFT's do not have a specific number..They are a correlation related to SFT numbers.

We're chasing a possible vacuum leak here? Do you have a way to remotely monitor your trims while the engine is running?

 

Yes I do!

 

Hot engine, at idle, are they within 5 of zero?

If not, follow the many posts about checking for air leaks.

 

Cool..

You need a propane torch (unlit) and a piece of rubber hose that fits over the end of the nozzle on the torch. Most times the correlations will be furthest apart at idle,

Set up to monitor the trims on both banks with your scanner.

Point the hose at possible vacuum leak areas. PCV/Oil filler/Dipstick and the press in vacuum line that connects the brake booster to the air horn etc. The trims will change almost instantly when the propane enters the system.

 

+1

LTFTs will show if there may be a leak, STFTs with the above go wild at a leak. (Not all possible leaks can be found that way e.g. EVAP-related ones.)

 

I noticed that my long-term fuel trims change instantly upon acceleration. Is that normal? I was under the impression that it took about 5 minutes for them to change

 

If you're trying to diagnose a problem that's not as far as I can see any help. What is it you're trying to do?