Does anybody have a good diagram of the vacuum lines? I'm getting P0171 and P0174 errors. I have replaced the air intake (which did have holes) but still getting these errors. I'm thinking a smoke test is in order too but will give a good manual inspection first.

 

Richy, I've traced so many air leaks in my car, I was actually planning on doing a checklist and diagram showing all of the various hoses, norma connectors, and gaskets where unmetered air can get into the manifold...I just haven't done it yet. Sorry...but I'll try to work on it soon.

In the meantime, check these

1. Throttle body norma connector and o-ring
2. part load breather norma connector and o-ring, and hose. check its opening while you've got that connector off too (instructions in the FAQ also)
3. clean your MAFS (check the FAQ thread for instructions)
4. make sure your air cleaner cover is sealed properly, its easy to get the back corner jsut a little off-center when getting those goofy clamps to snap on right.
5. the oil filler neck is screwed on in my 4.2, make sure yours is tight if its the same
6. o-ring on the oil dipstick, should be there right at the base of the handle
7. if the 4.0 has a PCV valve, make sure its norma connect o-ring is not deteriorated and the line isn't crispy like potato chips...nitrile o-rings are higher quality than regular rubber.
8. the clamp and seal for the air-pipe to throttle body is not rolled and its good and tight.

 

Good info. Trying to remember if this started happening before or after I changed the oil. Is there a generic "replace all vacuum seals" kit available or is it a piece-by-piece thing?

 

Piece by piece, I"m afraid. You could spend $30 or so on parts and do all the lines and o-rings in one shot though, if you wish. I'll try to give sizes, type of material and such in my upcoming report.

 

my 2001 xk8 has p0171 &p0174...dealer replaced breather hose...cel back on 100+temp day 2 days later....car was run without water 3 years ago...all fine but maybe heat damaged a seal....any ideas

 

If you've got some throttle body cleaner in your garage, using the straw to direct the spray, try shooting a little bit at each hose connection, even along the hose if you feel it could be compromised (those plastic ribbed hoses are easy to crack, and never see it by eye), and listen for idle speed changes. Even simpler if you can watch the data live on a scanner, your short term trims will drop (towards the negative side = rich) 5-8% within a couple seconds if there's a vacuum leak there, check out this video of me hunting a throttle body gasket leak.

 

cleaned MAF and throttle body,added SEafoam to gas,replaced air filter, cheked dipstick o-ring....still have cel....will this eventually shut off?

dealer is inept...keeps fixing problem with no result.....dealer is only game in town.

not sure where all the vacuum lines are to do carb cleaner test


2001 XK8 conv....90000 miles...owned since new...beautiful car,fun....but tempermental

also have 2002 XJ8....50000 miles.....beautiful and reliable

 

Just under the coolant reservoir on 4.0 is a vacuum pipe before it disappears behind shielding on inner wing. My pipe hard hardened & cracked from heat at back of engine/ exhaust.

Regards
John

 

New here. Did the vacuum leak write up appear? Keep looking for leaks but can't find it. Seems to be intermittent too. Car doesn't stumble when revved in park only under load.

Does this model have the imt o ring issue I've read elsewhere? Or brake line o ring seal issue?

Frustrating that I can't find it....appreciate any help

 

No IMT on your XJ8, but you do have a brake booster line into the TB

 

Wow! Well done, Matt! Perfect illustration of a leak detection method I use almost daily.

Also a perfect example of something I try to convey to people all the time. Unless you are in the middle of a fueling diagnosis of some sort, forget the short term fuel trim; pay attention to the long term fuel trim. The short term will ALWAYS bounce around during normal engine operation. The long term fuel trim is what is telling the overall story.

Cheers,

 

Thanks Steve!

 

Recently I replaced the gaskets at the water fill/ thermostat neck and of course, had to remove the intake manifold. I cleaned the intake manifold and engine surfaces and replaced the intake gaskets . Now that it is repaired, the car does not leak water and is also running better than I remember. Did it that fix a vacuum leak? I have done about everything to repair vacuum leaks with O-rings but this has been a huge improvement.
Dave Warner
2000 VDP Red/Tan. 250K Mi.

 

Yeah, there is a big gap between an engine running nicely and getting a diagnostic code for fuel trims. Long term trims should probably not be much above 5, but the code comes in at 25. Best is to read the trims. A cheap eBay/Amazon ELM327 can get them.