I'm hearing a leak in this hose, possible vacuum leak? The hose is extremely brittle. Does it connecost to the throttle body?

 

Update. As I now believe I've uncovered a vacuum leak (see previous post). Everytime I drive the car and hook up the scanner, it's throwing me these codes p0174 & p0171. There is no visible engine light, but I can connect the scanner and it will give me these codes, which I then erase. They come back after a short drive. I believe I have a vacuum leak in the area of the below photo. That hose is extremely brittle. Could this leak be causing this?

 

Yes, the most common cause of the P0171 and P0174 codes is an air leak.

I forgot you had a knock sensor code, but if you'll look it up you'll probably find that the most common causes are problems in the wiring harness such as a loose or corroded electrical connector, a short in the wiring, etc. The sensors themselves are fairly simple and robust (and hard to get to).

Regarding the new FPR, is it an aftermarket brand, and if so, would you mind sharing which brand it is?

Cheers,

Don

 

The hose you are referring to is the Part Load Breather and that hose leads back to TB and yes over time they become heat hardened and brittle and usually have a crack in it somewhere.
The whole thing needs to be replaced or you can jury rig a crappy repair.

 

Chasing the vacuum leaks is a real PITA. If your high frequency hearing is good, you will hear the vacuum leaks when you let off the throttle and or coming to a stop as a high pitched squeal similar to letting the air slowly out of a blowup party balloon. This throttle condition is one of the times when the Emission Vapor Purge Cycle is triggered.

I will add that those vacuum hose plastic are really a poor design. I am surprised they lasted as long as they did on my XJ8, but I am not in a nasty climate. Mine hold vacuum and pressure when removed and tested while being bent around and are not crumbling or damaged, but as a precaution I rubber coated each hose, then wrapped each one with self vulcanizing silicone wrap. As a added precaution I also replaced and greased all the O Rings at each connector to engine and cleaned out the inside of each engine side connector..
To spend $100 to replace all three of those hoses - Full Load, Part Load and Injector Air pressure with 10-15 year old OEM new/old shelf stock is getting questionable due to the age and condition of the parts stored on the shelf - unless of course the ones you have on your engine now are indeed crumbling to bits, then definitely replace these hoses with NOS parts sealed in plastic bags or NEW manufacture if you can find them as NEW (doubtful) current production.

There is nothing special about these OEM hoses other than being form fit with matching connectors, and they are very problematic.
If anyone knows where the connectors can be sourced separately with the barb ends for vacuum hose, these hoses can be easily remade using standard reinforced automotive vacuum line for probably less than $10 that holds up better to the conditions and jostling in an engine bay.
Having said that, removing the vacuum line to the Fuel Rail FPR and throttle Body base to Purge Valve hose, on mine those hoses were brittle enough that they cracked immediately upon removal - remember to replace those - without breaking the tiny plastic nipple off the Purge Valve. The Purge Valve is all plastic too and gets brittle, and that valve itself is also a potential source of a vacuum leak.

There is another set of critical vacuum connections that need to be checked for cracks and leaking:
- the connection hose from the Throttle Body base to the Brake Booster - this is smooth rigid pre-bent plastic, sealed in the Throttle body base by a quick disconnect barb and two internal O rings
- the rubber ring from the air intake to the Throttle Body base
- the Intake Air muffler
- the entire air intake plastic and flexible parts itself.

Speaking of leaks, replacing the coolant thermostat housing and filler neck with updated aluminum replacements is surely a great idea!

Cheers!

 

Here are my 2001 XJ8 Part Load Vacuum and Injector Air flex hoses, rubber sealed and silicone wrapped, curing in the sunshine. THE OE style just seemed a bit too fragile for the application, even the New Old Stock hoses just do not seem robust enough. Now these feel more substantial, and dragging them across surfaces I am not worried they will get damaged in use.
I worked in the automated hose manufacturing process for Gates Rubber and Gates World Trade, so I don't consider this a jury rigged or crappy repair, rather, a significant improvement solution to the OE corrugated thin Plastic.
I may see about sourcing the various NORMAQUICK connectors to do those hoses in reinforced rubber vacuum hose on my 2000 XJ8.
My OE corrugated plastic hoses were not cracked, crumbling or damaged to the eye, and "did not appear" to have leaks applying both vacuum and pressure, but as a precaution after inspection I degreased and cleaned them, sealed them in rubber coating and wrapped them with silicone self vulcanizing hose tape. The hoses appear to be quite a bit less fragile feeling more flexible and pliable now, the rubber coating or silicone self vulcanizing tape did not seem to add significant thickness to interfere with anything. Remember to replace and lubricate the O rings in the NORMAQUICK V2 style plastic couplings, and clean out the mating surfaces to effect a complete seal. Full Load hose is next.

It is definitely easier to work in that area with the TB removed - 4 bolts and 4 connectors and it is out of the way and off for a rebuild at ASI - feedback on that later.


Foreground is the Injector Air Hose, back is the Part Load Vacuum hose.

 

After several weeks of running, and repeated propane/butane tests around the intake and hoses, all leaks are fully resolved on my 2001 XJ8 and no lean codes on my 2001.
So the rubber coating on the corrugated hoses seems to work well with all new O rings and o-ring grease.

Now to determine why I am not getting any Fuel trim F/T 1x2 and F/T 2x2, and STFT1 & 2 % readings on Torque Pro on my 2001 XJ8 when I have it very actively graphed - exact same templates, on my 2000 Xj8...

Cheers!

 

This question has been asked by others and I find no answers anywhere on the forum to the question:

What is this a photo of ( circled in yellow ) and what is its part number? It exists on many Jaguars, is in the fuel line BEFORE the fuel rail (upstream) connected to the fuel rail input, has NO VACUUM LINE connection and I cannot seem to locate it in the JTIS ...

and on my XJ8 there is ALSO a vacuum operated Fuel Pressure Regulator on the EXIT of the Fuel Rail that IS vacuum operated near the Schrader valve that looks like this:


Are there TWO fuel Pressure Regulators on the 4.0 liter V8? If yes or no, what is the part number of the upstream device feeding the fuel rail, and what does it do, and where is it described in the Manuals?

It is connected and disconnected from the fuel line with quick release round fuel line connector tools.

Cheers!

 

Looks like fuel 'pulse-damper' to help with injector noise.

bob

 

Hi StagByTriumph,

Those pulsation dampers are typically integral to the fuel lines and as far as I can recall, Jaguar has never offered the dampers separately, thus, no part number. To replace them you have to purchase the entire fuel line. On early XJ40s a failing damper caused a "helicopter sound" that was audible in the passenger compartment but not in the engine bay.

Cheers,

Don

 

Motorcarman and Don B,

Thanks for that input.
I would have never guessed that was the function of that regulator looking device.
A "pulse damper" in my field of Process Control engineering is in reality, a regulator, either incorporating a spring/diaphragm, expansion chamber and/or check valve. That device looks to be a spring/diaphragm assembly, could also act like a check valve.

With no part number, there is no pinpoint test to determine if it is defective somehow or impeding or checking flow, other than verifying fuel rail pressure remains at the correct pressure through full acceleration?
The other part might be detecting "fuel injector noise" into the cabin - which is one of those touchy customer subjective area. Noise can be dealt with, but impeded fuel flow might be an issue affecting performance depending on how it might fail.

It is odd it is not sold separately as it very easily detaches from the fuel supply line and fuel rail input , literally it comes off in 30 seconds after depressurizing the line. Does that Pulse Damper sort of act like a check valve, requires a bit of pressure to open?

 

Hi StagByTriumph,

I'm sure you're correct that the damper uses a diaphragm of either rubber or metal, supported by a spring of metal or possibly compressed inert gas. I don't believe it includes a check valve, since I have never seen this indicated on any of the fuel system diagrams in Jaguar service documentation. I also believe the damper is always open and does not require a minimum pressure to open (like most check valves). From what I read many years ago, I believe the purpose of the damper is to absorb pulsations, or oscillating waves, that are created by the recurring sudden decrease in fuel pressure each time an injector opens. Wherever the fuel lines are attached to body panels, the vibrations resulting from these oscillations can be transmitted into the passenger compartment. A patent search would probably answer these questions definitively.

Cheers,

Don