This is about identifying vacuum leaks to help others find them faster.

'07 XK Base coupe, 80Kmi. So, my Long Term Fuel Trim Bank 2 was around 20% at idle. Much better at 2500, of course, but still higher than I'd like. Classic indication of a vacuum leak, particularly on a 13 year old car kept in New Mexico for most of its life. There can be many small leaks on a car this age, but ya gotta start somewhere, eh? Also, manifold absolute pressure is about 6 psi, where the manual says 7-11 at idle.

So I hauled out the smoke tester:

1. Examined the air intake. Found a couple of leaks at the hose clamps, not major. There are four (!) between the MAF and the Throttle Body. No surprise, two minor along the stream. Cleaned mating surfaces and reseated them all with new hose clamps (old ones were bit twisted). While there, cleaned the MAF. Weirdest damn place to put a MAF I've ever seen. Cleaning it improved my grams/sec data from 4-5 at idle to 5-6. 15-20% difference in airflow accuracy is a pretty good improvement.

2. Next, the gasket at the bottom of the oil fill was dried out and cracked. Couldn't find a separate gasket, so $25 for the part. Also, smoke exited around the dipstick gasket. $3.00 for the oring on ebay. See the pic. My guess that these are likely to fail on most older XK's.

3. Further, a slim puff of smoke from Bank 2 injectors area. Not clear: could be the injector, the intake or the valve cover gasket. More work needed. I'll probably re-gasket all of the injectors just be because they're 13 years old. Easy job. Need to get some higher pressure smoke into the valve cover to test it as well.

That brought the LTFT down to 13-15% at idle. So, more to find. Voltage is OK on the O2 sensors, so I'll get everything tight before considering them.

So, here's my "ask": what other specific locations have you seen that are vacuum leaks on the NA 4.2 engine? I'll test them and let everyone know my results. Thanks!

Best, Panthera.

 

Dipstick o ring, oil filler neck o ring - which you covered.

PVC PCV valve o rings and lines.

Full load breather and o-rings.

Throttle body gasket.

Intake manifold gaskets.

EGR valve gasket.

Brake booster vaccum line and o rings.

EVAP vacuum line and o rings.

And whatever intake parts that connect to the throttle body. Not sure on N/A but on S/C the T-piece is known to get shredded and cause air leak.

My smoke test revealed much of the same as you... I ended up replacing that rubber coupler, and pretty much every o-ring and it took care of my P0101 issue.

 

The oil fill is a common leak on both the NA an SC cars. I was able to find just the o-ring instead of buying the whole part.

Nice job diagnosing the issue instead of just throwing parts at the problem.

 

Thanks! Great info, that will give me a very helpful focus. Do you happen to remember the ones that made the biggest difference?

 

Also the vacuum line that goes to the FRP sensor.

The ones that made the biggest difference were the ones that were leaking. If it wasn't leaking, it shouldn't make any difference if you replace it - it would just be a preventative thing.

 

07 XK NA 4.2 80Kmi. OK, finally got back to the vacuum leaks. Fixed the smoke tester and hooked it up. Note my last work took the LTFT bank 2 down from 20+% (code trigger level) to less than 13%. So, progress.

Two specific failures. First, the EGR assembly had a significant smoke exit up and around it. To test to see if it was the gasket, I cranked down the bolts somewhat to see if smoke reduced. It didn't. Question: If you've replaced this unit, is it possible for the gasket to fail rather than the EGR itself? In other words, is it worthwhile to put in a new gasket first, or should I just do both the gasket and the EGR? Also, is the EGR gas transfer pipe (runs from the EGR under the intake manifold to the rear of Bank 1) a likely fail point? The EGR is pricey, so trying not to throw a part at it.

Second, one of the Bank 2 injector gaskets was leaking at the intake. I'll probably pull them all on Bank 2 and do an oring job on them. Anyone have any advice that isn't in the manual?

Some confidence that these two will correct the problem. As usual, we'll see.

Many thanks for the advice so far!

Panthera

 

A failed EGR pipe or valve would throw a code, so I wouldn't worry about replacing those unless they are damaged.

You can clean the valve and pipe mating surfaces while its out. Then just inspect the pipe for any cracks, etc..

If removed, the gaskets need to be replaced as they are metal and deform during installation.

Be sure you align the gaskets correctly when replacing - making sure the hole in the pipe is centered with the hole in the exhaust manifold.

 

THANK YOU

 

Thanks -- gaskets on their way. Got them online for $17 plus shipping (pretty typical). Called up my local dealer, Ft Lauderdale jag since they're nearby. They wanted $50+ for the three.... Dealers amaze me, sometimes....

 

I hate to say this but it’s still possible that your EGR valve is the source of the leak without drawing a code for a faulty EGR valve. When I replaced the valley hose on my STR I put it all back together and I was still getting lean codes. smoke test showed leaks all over the place and the one that is relevant here is that my EGR valve was leaking from the solenoid portion of the valve because I had some part of the EGR valve seal give out. The solenoid still function correctly but I had a vacuum leak. So I had to replace my valve. AlsoYou’re about to find out that getting that EGR out to replace the gasket is a pain in the *** and you might wanna just have to do it once and replace the valve at the same time I know my valve was leaking

 

Thanks. The smoke was coming up around all sides of the EGR, so my first reaction was bad EGR. But I also wanted to avoid replacing a good part, by replacing the gaskets first. Hadn't heard of anyone having a bad smoke test from the actual EGR without codes until your comment. Thanks for it -- I may just do the EGR as well as the gaskets at the same time. By the way, why was it a PITA? Looks straightforward in the manual for a NA car -- was yours a R? . I appreciate any advice that makes it easier. Again,Thanks!

Panthera

 

Where in NM? I'm in Roswell.

 

I bought it out of Tucson. Never been there myself. Heard it's pretty.

 

Below is a screen grab of a drive cycle yesterday. It's "EGR Error %" vertical is error; horizontal is the time of the drive cycle.

Note there are no EGR error codes, but I do get smoke exiting from around the EGR valve during a smoke test. Likely is a gasket, and unclear if it's exiting from the EGR itself.

I'm going to replace the EGR, but I'm looking for experience as to what a typical EGR drive cycle should look like. Is the below typical, or a failure mode?

For those interested, this is "Car Scanner Pro" on Android, through a cheap bluetooth OBD link. The Datalogging mode is incredibly useful. Of course, it doesn't pick up Jag-specific codes, so I use SDD for that.

Panthera

 

The EGR valve on the NA 4.2 was a PITA because of the upward facing bolts on the unit. Get a 10mm flat ratchet wrench, the kind that has a pivot on the ratcheting side. A regular 10mm won't work -- not enough room.

You should assume you're going to remove all the varied coolant tubing around the unit, so you can get enough room to move the wrench. I pinched off the coolant lines, but found the the small amount of coolant drained into the engine, so was able to remove both ends of two of the lines to get the room I needed.

Also, there is a very small grey vacuum line from the side of the throttle body that goes down to the vacuum tank on the Secondary Air Injection system. This plastic line is extremely fragile from heat and will likely break unless you carefully remove it and set it to one side. Be prepared with regular flexible vacuum line to replace the broken part of the line if it fails. It likely will.

Once everything is cleared out around the base of the EGR, you'll be able to get the 10mm ratchet wrench up underneath the EGR with the wrench at a slight angle and get a firm grasp on the two bolts. Remember you're reversing out an upside down bolt so get your direction right. Also, you may need a small breaker tube around the wrench to break it loose, because there's not much room for hand leverage. Once loose, it's an easy replacement..

The rest of the job is as explained in the service manual.

BTW, I ordered the EGR from RockAuto for $190. They actually sent me an OEM Denso unit, exactly like the one Jag installed at the factory and wanted $400 for.

 

Where can the EGR valve on the 5.0L be found?

 

Go to the sticky at the top and download the service manual for the 5.0. Search for EGR and you'll find illustrations for the EGR location.

Regards, Panthera

 

07 NA 4.2 engine. Below is the identification for this part. PN is C2P11447. Incredibly fragile when aged. You can rebuild it using regular black flexible vacuum line, but the unit is available for $39-50 from alternative sources if you want to use original part. Directly attached to the throttle body, and if cracked or broken, will be a strong vacuum leak. Oddly placed and difficult to see. Note that there is a check valve in the middle.

Also: As far as I can tell, this is the only vacuum interface to the AIR system. If anyone has found another, please let me know. Part of diagnosing VL's is clearly understanding the boundaries of the engine vacuum envelope.

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Had a rough idle on 2010 xkr, and found mice had eaten my old filters, causing the leak. Even had a few acorns inside. Went with k&n filters because of wire meshing on both sides. And put a rodent repeller with audible hum under the car. Oh the joy.

Let me also say, it's better to leave cabin climate control in auto mode. Ran much better on auto, ie ac on. Perhaps a voltage issue since supercharger pump was also down. Maybe having pump and ac off doesn't kick on the alternator, or low voltage issue.