This has now happened twice, both times at idle and yes I have the typical symptoms (fuel trims show such at idle and 2500 rpm) of a vacuum leak (out of the blue, of course)..

The first time it happened I went through the left turn signal into a parking lot and pulled out my small scanner I keep in my glove dept. and it showed p0171 and p0174. However I could rev the engine up to 4500 rpm, which told me that I was not in restricted performance. I found the air filter box was open on the top, re-closed it, cleared the codes and they had not returned until today. Again sitting at idle and it flipped in restricted again. This time I just drove normal- it shifted through all the gears and I got the car up to 50. Got home looked at the freeze frame and it said I had only a P0174 and the LTFT was at +19.5 when it flipped the code. I also thought that the car would have to be at +25 to cause a p0171 or p0174???

So what gives? Why is the restricted performance not putting me in a real restricted performance?

Relative to the lean code, it is my understanding that the most common cause is the brake booster vacuum line. Any other suggestion other than the more than 500 posts I have read on the forum about these codes?

Thanks

Tom in Dallas/Plano
2005 S-Type 3.0 127k

 

You wouldn't usually get restricted performance for a lean condition.

I thought it would be +25, too. There may be other criteria, though. Some/all are in the extensive Denso PDF but is it even worth hunting through in a case like this...

 

It depends and I had the exact same thing happen on my old 2005 S-Type R. When the car has a fixed vacuum leak at idle this is a very large percentage of the total engine air flow. So the system see's this and sets restricted performance and/or other error codes. However when the engine is revved up the vacuum leak is now a very small portion of the total engine air flow so it's no longer in restricted mode.

This behavior really confused me because I could drive the car fine and only when sitting at stop lights did the check engine light come on as well as restricted performance. Then when the light turns green I hit the gas and both lights went out.

My issue was the PB booster vacuum line leak from the induction elbow which is very common to the SC 4.2L V-8.
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Great observation! Maybe this will help the next guy when troubleshooting.

 

Thanks.I assumed I was not the only person on the planet that had the issue. I saw where Brutal indicated that the PB booster cable is the most likely suspect. I assume that the induction elbow is where it enters the back of the engine?

Thanks

Tom

 

Yes.
Here is my long thread on that problem. I was unhappy as I had just done the very hard under the SC coolant hose and when the car was back together I had codes and restricted performance immediately!
The pictures will help explain better than me!

SC Elbow Vacuum Leak
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I have the 3.0 not the SC. Is it the same or different?

Tom

 

No under SC hose to leak for one! But yes the 3.0 has it's own set of issues.
The 3.0 gets it's vacuum from a different setup compared to the SC V-8.
If you read that thread I think you need to find where the vacuum leak is. There are a number of places it could be and on the SC engines a very common point is the PB vacuum line. But I would monitor fuel trims and start spraying around the engine to see if you find anything?

Maybe a leaking PB booster? Just a guess and that's not common at all so I would NOT suspect it. Just something to check and rule out.
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I taking it to a shop to run a smoke test on Monday. Tried the spray thing on al the lines that Rick showed in his color photo and the engine did not change. I could not look at the scanner at the same time, so a touch limited in what I could do. I don't have the time to hunt and peck for it. So for $133 bucks, easier to have some pros do a smoke test.

The other area could be the all the vapor junk they have attached with the bolts for the driver's side shocks.That is such a flimsy attachment, but all the main vacuum lines seem easy enough to get at.

My first fallout was with a 0171 and 0174, although they both appear to be reading the same. The second time was just 0174. Does that lead your common sense to anything special that could be the cause?

I did not have this before I took it in a shop, very fine one, to change the upper control arms so they were in that area on the driver's side. It showed after then, but since I had not done a look at the fuel trims before I have no idea as to where they were and it could very well ave nothign to do with them. Looking at the PB vacuum line, mine appears to be in very good condition, but a touch hard to see behind the upper manifold, but it looks like to me, that once the engine cover is off, that it s not difficult for someone in the know to reach behind from the driver's side of the car to remove and replace.

Thanks

Tom


UPDATE from today:

I finally got my scanner where I could spray down the system and see how the fuel trims would function at the same time- nothing from the brake boost line or any of the vapor stuff or pcv. the only time it spiked was when I sprayed down the throttle body area However none of he vacuum lines attached responded. I took a dropper and bit oft carb cleaner in drops to isolate and not really anything. I took off the air cleaner outlet tube and re-seated in and it appeared to bring the fuel trims (LT) from 19.61 to 11 or 12. When I sprayed it down again the it did not jump to negative 20 as they did before but I was still seeing movement to a neg 8 or so for a short time when I resprayed around the throttle position sensor. However that is not involved with any vacuum is it? The air cleaner hose is fine -nothing wrong with the bellows.

Does any of that make any sense and what in the area would cause a leak that is not hose related. The throttle body has been on for a long time, however it does not appear to have any leak where the gasket is.

I am stumped

Tom

 

Thanks for the added info about when the problem started. Yes the vacuum stuff they had to remove could be the problem. I can't remember all what is on there and I thought some of it was for the EVAP system? But you have no EVAP codes so that's no help.

As you know the drivers side upper control arm is a SOB to get at some of the nuts! I really fought that repair! It's somewhat intertwined with all the PB stuff on that side since we have LHD cars.
Nothing looks out of place over in that area?
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One minor consideration with the brake booster: The leak can be where the pushrod enters the booster, facing the firewall. You can spray all around under the hood yet miss this potential leak, as it’s actually drawing air through the firewall from the cabin.

It’s not always practical to spray that area above the pedals. If the vacuum line is not hard to undo, it’s often easier to disconnect and plug that line. See if the trims respond. Obviously don’t drive like that, but it’s fine for troubleshooting while parked.

One more thought: What are you using for spray? Old-fashioned carb cleaner works well, as both the liquid and propellant were mildly flammable (but not dangerously so). The fuel trims respond immediately to this extra “fuel” drawn into the engine. But alas, some newer eco-friendly formulas are non-flammable. You might get lucky and have this inert stuff momentarily plug a vacuum leak. But that’s it and the change in trim will be minor and fleeting. A spray that acts as extra fuel will be much easier to notice. I do not care to discuss how I learned this…

 

I went to a quality shop that charges more per hour, but wanted it done correctly. Spraying down everything ii the vapor area revealed a big zero as did the brake booster cable..

TBB

 

Would pressing the brake pedal not cause a notice in the fuel trims if the push-rod is involved? Would the purpose of discounting the line on the brake booster be done to rule out the brake vacuum line? If I can getting no vacuum pressure, then what does the brake booster do and how would that prove a leak in the push-rod area?

Tom

 

Good questions. I'm not 100% sure how the fuel trim responds to cycling the pedal with a good booster. Through a check valve, the booster holds enough vacuum for two or three brake applications with the engine off. With the engine running, this internal reservoir is kept full. With no leaks and brakes not in use, there's no refill action so no change in fuel trim.

When you apply the brakes and some vacuum is consumed, the reservoir gets refilled. I don't know if this happens when you step on the pedal, or after it is released. You'd see a brief change in fuel trim when this happens. But without a known-good booster for comparison, this change would be easy to misinterpret.

How would a leaking booster affect trim? Could be a bad shaft seal that only acts up as the pushrod moves. Or it could have a constant leak elsewhere. Makes my head spin trying to think how it would show up on a scanner.

That's why I suggested comparing with the booster disconnected and line plugged. If it's easy to disconnect the line from the manifold, capping the source there would take both the booster and line out of the picture.

Don't get drawn too far down this rabbit hole. Just be aware if the booster is sucking air from the cabin, you won't find the leak testing under the hood.

 

I know where her is at least one leak and get the FT to -21 very quickly when I spray in that area and for the life of me, I cannot figure what is wrong unless thee are some sort of micro fractures in the rubber that is causing the problem. It is not the TPS, but it the rubber bellow attached to the throttle body. When I spray on that side toward where the bellow connects (in front of the TPS, from left to right, the FT go immediately to -21. I have looked at the inside and outside of the rubber an all appears fine. The clamp is on as tight as I can make it without breaking it. However I still get in the same area the rise in FT.

Is there something wrong with the clamp although it looks fine. I have the connection up to the stop posts on the TB. The clamp is on evenly. This is strange - any suggestion short of buying new air bellows . Would a new clamp help at all. I can't think of anything I could put on the throttle body to make connection tighter
Thanks

Tom

 

Are you talking about the duct between the air filter and throttle body? If so, see posts #32 and #36 in this thread.

https://www.jaguarforums.com/forum/s...2/#post1934812

 

That is good info, but have no hole there. It is right were the hose connects to the TB and on the side of the TBS blowing carb cleaner on it. I will look again, but I am pretty certain when I last changed the air filter and had all of that off there was zero wrong with the resonator. I can't figure out what is wrong with it- be it the rubber connection or the clamp. It is on tight all the way around and I was very restrained in specifically using carb cleaner on small places at a time.

Tom

 

I ddid not have to take it off. Right in the same spot is a hole. Now I have found my vacuum leak This is new in the last few weeks.

Thanks

Tom

 

Thanks ALL.

Problem found and fixed. Until I get new bellows and resonator I used 3m metal tape and sealed up like a fish in a bowl. Watched long term FT go from +19.6 on both banksdown to -1.78 on bank 1 and +2.45 on bank 2. ST float from -1.78 to +1.78 on both banks.

Now i am going to be curious if this does anything to help mu AC issue. I id ntoice when the compressor came on today that the cooling fan did not auto speed up to max. Temp is 69 degress today so not a great temp to test at.

Be that as it may, the place on the resonator that blew out on mine and teh one that Rick showed is about the same place and it does not rub on anything at that spot. What would cause a semi-outward type breakage or tear? That s very strange. Does the resonator build up that much pressure. It also can cause air temp in the system to go up as it passes uo the first IAT in the MAF.

Thanks again-


Tom

 

Hey I knew you would find it!
Repaired and done.
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