I just had CEL on 2004 xtype 3.0 with 110,000 m yesterday and hooked up my Bluetooth OBD and pulled codes. It says P0171 and P0174. I've researched lots of posts on here that point to vacuum leaks in the PCV hose, brake booster hose, or IMT orings or bad O2 sensor. I am hearing it's prob low fuel pressure or too much air entering past MAF sensor so fixing one of those issues is solution. So I checked the hoses and it looks like the previous owner recently changed the brake booster pipe and it still has jaguar label tags. Looks very new. The PCV hose also looks in good shape. For good measure I took out MAF sensor and sprayed it with MAF cleaner. It was dirty and needed it (weird thing is my MAF has Toyota and Denso labeling) I didn't take off IMTs yet and am going to Jag dealer for two orings in a few minutes. Figure that's cheap insurance and won't hurt to replace those needed or not. I went ahead and reset the codes and cleared CEL. Car idles and runs great by the way even when code came on

So here is my question - my scanner measured fuel pressure at 55 +/- and the vacuum pressure measured 19-21. I am not sure what the spec should be on those two measures. Can anyone provide what normal readings for fuel pressure and vacuum should be? Thank you

 

RobinGA, both the fuel pressure and vacuum are right about where they should be. The vacuum might be a little low, but with the codes, I would expect that.

I know you said you inspected the PCV hose, but did you look at the underside of the hose? That is where the damage will be if you have any. Granted, this all assumes you have a smooth PCV hose. If you have a ribbed PCV hose, then the splitting is not an issue.

As for finding a vacuum leak, there are two options that you can use:

1) using a cigarette or cigar, gently blow smoke into the engine bay while the cooling fans are not running. Blow the smoke in the general area of where you think the vacuum leak might be. Watch the smoke as it wanders through the engine bay. where the smoke makes a sudden change in direction (will seem like it is disappearing), that is pointing at the vacuum leak.

2) using ether/starting fluid, spray the joints where you suspect that the vacuum leak may be coming from with the engine running. When the engine RPMs speed up, that is where you vacuum leak is. Just make sure not to spray directly on the hot exhaust manifold.

 

Thanks Thermo. I do have the round rubber PCV breather hose so I am going to order new one which does look like they changed to be ribbed.-part C2S40863. I am going to do the smoke test. I am thinking about using one of those fireworks punk sticks I have to produce the smoke and move it around the joints and hoses.

The readings I took were at a cold idle also. I am going to drive around a little now and monitor the readings with my ODB which is Bluetooth to my phone and see what they are at speed. I did reset the codes so I also expecting the CEL to come back on possibly over next couple days. This car gets driven about 10 miles or less a day.

 

The punk idea worked great to produce constant smoke. But I think there was a bit of breeze outside today. There was no area on the usual suspect parts that was sucking in any of the smoke so at this point I'm not sure if I have a vacuum issue or not. But I will try it again inside the garage when I get the trailer and golf cart out of there.

 

Thermo - so I took the car out on the road. It drives and runs great, no issues at all. I watched in real time my fuel pressure and vacuum readings. Fuel pressure stayed very constant around 55 at all times. The vacuum at idle stays around 19. Upon acceleration the vacuum drops right away sometimes going below 5 on hard acceleration but on normal driving it dips to around 8-10 and then seems to stay at around 14-18 when at 55 miles per hour. While the throttle is being applied vacuum stays under 20 but as soon as I let off to coast or prepare to brake it rises to 20 or above briefly. It looks to max out at 24.0 which it did a couple times when I took foot off gas pedal. I didn't drive far but that pattern was consistent. Does this vacuum measurement seem proper?

 

RobinGA, just to ask a silly question, but did your fuel pressure go up and down with your vacuum (ie, went up when you were hard on the gas and down when you let off the gas)? The fuel pressure should have changed some (a few pounds) with where your foot is on the gas pedal. The fuel pressure is designed to maintain a constant differential pressure between the intake manifold and the fuel line. THis ensures the fuel gets properly atomized and the computer knows how much gets sprayed in every time. If the pressure is not changing, then I would look at the plastic lines on the underside of the intake near the throttlebody. There is a white line and a green line as I recall. With age, these plastic tubes can become brittle and crack, leading to your vacuum issue. This would also explain why your fuel rail is up at 55 psi (which is slightly on the high side, but not out of tolerance). Ideally at idle is should be at 48-50 psi. Under hard acceleration it should go up to 55 psi.

 

I will specifically look for fuel pressure tomorrow with a road test. I thought fuel pressure was fairly constant but admit I was watching vacuum level

 

Why not watch fuel trims to see if it is an air leak or not...

 

Friend of mine has a supercharged F150 Lightning, he just picked it up cheap a few weeks back because the check engine light was on and the owner was clueless about fixing it.

Yep it had P0171 and P0174 along with the CEL. Fuel trims were off the charts at +25% on both banks LTFT and the STFT's were also very high at idle.

He spent hours searching for a vacuum leak, and in the end, he couldn't find one.

I hooked up my IDS to see if it might give some clues, and it gave a list of likely culprits.



No fuel pressure sensor in this truck so we put in a new fuel filter just to rule it out, the old one was so choked up I could not blow through it, and a dirty brown sludge came out of it.

Seemed to make some improvement, but the trims were still off the chart.

So he chucked a bottle of injector cleaner in the tank and filled up with a high-ethanol content fuel. Drove it around for a couple of days and it slowly got better & better, it sounded better, it drove better, and after clearing the codes, they haven't come back since.

So it was blocked up injectors and fuel filter that was causing the P0171/P0174, not a vacuum leak.

Not saying this is your problem, just sharing some recent experiences.

 

Good info - but did you do the usual thing with suspect fuel trims? (i.e. see them high at idle, rev to 2000-2500 and see if they drop) With what you report you'd expect them NOT to drop, thus confirming NOT an air leak.

 

JagV8 I just now did a road test as my wife drove and selected STFT1 and LTFT1 as measures and they are showing up as %. Both of those measures were moving around a lot as the car was driven and also at revs while in neutral. I really don't know what I was supposed to be seeing but the values changed quite a bit and the STFT1 value would sometimes go negative. The LTFT measure when car was turned off shows 12.5% and the STFT1 shows -9.4%

The fuel pressure psi stayed around 55 at all times. When the engine was rev'ed in neutral it didn't fluctuate much at all. I did notice it went up to 56 during the time while I monitored the values. The lowest the fuel pressure went was 52.2 psi. It really stayed very constant even when revving engine. It did not drop suddenly as engine rpms dropped after revving.

The vacuum showed similar movement than yesterday by moving down under 10 in/Hg while accelerating and then stayed steady around 15 in/Hg at cruising speed, and rising sharply to above 20 in/Hg when foot taken off accelerator.

I found another measure which was Intake Manifold pressure and it stayed fairly constant around 13-15psi but did seem to fluctuate in correlation with accelerator usage.

 

A positive number means a lean condition and a negative
number indicates a rich condition.**If you have a scan tool you can monitor this before you begin repairs to get base line
readings. After the repair you can use these readings to confirm the validity of the repair. The long term fuel trim in a perfect
world would be at 0%, and the short term fuel trim would be fluctuating from approximately*‐.8 to +.8**After any repair attempt
test drive the vehicle for a while then check the long term fuel trim.**If you fixed the cause of the concern it will be moving
towards “0”. It is important to note that this is a learned value so it will not just magically go to “0” on its own you will have to
let it relearn by driving the car to see the new numbers.

 

Maybe instead you could do what I posted?

 

JagV8... I finally comprehended what you meant by fuel trim test after reading some other threads and doing more searches. Here are the results that I just tested. One test right after cold start and then again after the engine had warned up to temp. By the way I could not rev the engine to 3,000 as it started stuttering or missing just under 3,000.

On cold start
Idle was 920. LTFT1 19.5 LTFT2 19.5 STFT1 0.8 STFT2 3.1
At 2,500 rpm LTFT1 12.5 LTFT2 15.6 STFT1 11.7 STFT2 8.6

After warm:
Idle was 728 LTFT1 19.5 LTFT2 19.5 STFT1 -2.3 STFT2 3.1
At 2,500 rpm LTFT1 6.2 LTFT2 7.0 STFT1 14.8 STFT2 11.7

I found it interesting that at either engine temp the idle LTFT1 and 2 were both dead on 19.5. As soon as I pressed accelerator that measure would change but when the engine settled back at its own idle it pegged at 19.5 every time.

Also now at idle if I tap the accelerator there is a slight sucking sound before the engine rpms increase. Kinda sound like the noise I remember making when siphoning fluid through a hose

Thanks for any feedback you can offer. I already have upper and lower gaskets sets as well as new spark plugs in hand that I will change on Wednesday on a day off from work. I just changed fuel filter, air filter , and replaced IMT orings last week.

Codes P0171 Bank 1 and P0174 Bank 2 showing up still

 

AFAIR P0171 and P0174 pop up when respective LTFT hit 20.
Looking at these values and since you hear hissing noise, it seems like you have a HUGE vacuum leak.
What you hear is probably your engine sucking air through a hole in intake system.

Check if your PCV hose is still intact. And brake booster hose (especially the valve in the middle of it).
And every single hose that could be loose (for example there is a rubber hose near pcv valve/hose, just before throttle body coming from the left side into the rubber)

Get somebody to accelerate while you inspect engine hissing.

 

As LTFT drop when revved you look to have an air (aka vacuum) leak. If an accessible part you can find it by a smoke test or cautious spraying of a burnable gas (STFTs go mad when found).

DIY or any competent tech can do these.

 

So I have changed several things on my Jaguar 3.0 some last week and then major stuff today. Fired up the engine seemed to be smooth and pulled codes in Torque Pro only to find LTFT1 and 2 still pegged on 19.5. Dang it! I have a new Vacuum Induction tube in transit which I will change out soon as it arrives. That tube is one that attaches to a nipple at rear of intake has a thin red tube covered by flexible conduit and other end connects to fuel rail. I have done a smoke test and also carb cleaner test. As far as I can tell those tests aren't showing up evidence of rpms changing speed around a leak.

I have replaced:

PCV hose
IMT orings and inspected them again today while intake was off
Fuel filter
Air filter
Spark plugs
Lower manifold gaskets
Upper manifold gaskets

A couple observations. The inside of the intake manifold was very "wet" and not hard crusty carbon. I cleaned the lower manifold really well on all mating surfaces and also the interior of each opening. Old gaskets didn't look too bad but there was lots of wetness on them as well. I am going to buy new PCV valve. I have to think that wetness is oily residue being introduced through breather hoses.

As before I did the intake job today, the engine will slightly stumble if I tap the gas to rev it up. If I slowly apply pedal it's not so noticeable, but if I tap it sharply I can reproduce this stumble every time. I also hear a noticeable sucking sound during that stumble then it catches and revs up fine. Does that indicate maybe the throttle body?

I am stumped on what to try next other than just go ahead and buy the two other vacuum hoses that attach to upper intake. The smoke test and carb cleaner test on those two didn't show a leak though. Where else should I be looking for on a vacuum leak which LTFT 1 and 2 show I still have?

 

Maybe there is insufficient amount of fuel injected, causing mixture to be far too lean.
But this is far less probable than a vacuum leak.
Especially if you hear hissing/sucking noise.

 

Update on my engine conditions --
So I was able to get someone to tap the throttle pedal and make the sucking sound for me to listen to under hood. I can clear it very well and it is coming from the hard rectangular box that attaches to air inlet hose right before throttle body part #C2S9587. That hard plastic box is where I can hear the sound and it must be the throttle body air sucking in that I am hearing. Maybe this is normal noise and I am just now hearing it. It's not a constant sucking sound but starts as throttle opens up.

Another thing I want to ask your help on. I disconnected the battery for about an hour. After I reconnected everything I cranked engine while looking at real time measures on ODBII tool. The engine was very smooth. Both LTFT1 and 2 were at -0- and those stayed that way while I let it idle. I'm thinking great I've solved the vacuum leak changing the intake gaskets and just needed a hard reset to clear everything. I test drive the car and LTFTs are rising but staying around 6-10. It's running fine. I bring it home. I started it a couple more time and let it idle for several minutes and when I came back to check my LTFTs are back to 19.5 again for both. CEL isn't on yet but codes are showing up real time as good ole P0171 and P0174. At idle I get LTFTs at 19.5 and when rpms go to 2500 they come back to low single digit numbers like 4-8.

Could my MAF sensor be bad and causing this? I tried disconnecting it and cranking the engine and it would not start with MAF disconnected

 

Please post picture with marked place where you hear the noise.

Vacuum leak doesn't matter much at higher-than-idle rpms and load, because there engine is sucking much more air through intake manifold and small leak doesn't make much of a difference.

So, it's almost certain that you have vacuum leak.