Jaguar Forums has been a Godsend for me. Never had to post a specific question before but can't quite find the solution to this.

2004 xj8 - check engine light came on followed by restricted performance. Used a reader and codes 171 and 174. Cleaned the MAF with contact cleaner and reset codes. 150+ miles and no new codes. Running rough but actually doing good mileage But it keeps "blowing" off the air intake from the manifold. Of course it runs badly then. Replace the hose and tighten down the clamp and it stays on until hard accelaration. Any ideas? Thank you for suggestions.

 

Hi blairth,

The most common cause of simultaneous P0171 and P0174 codes is an air leak somewhere between the MAFS and the cylinder head. Cleaning the MAFS may have helped, but more likely you may have sealed up the leak when you reinstalled the MAFS and did any other work on the intake plumbing.

You can download the full DTC Summaries manual with explanations and likely causes of each code:

https://www.google.com/url?sa=t&rct=...03388427,d.cWw


Your sense that the air intake pipe is being "blown" off of the manifold is very interesting. Could it possibly be simply slipping off? Are the inside of the pipe and the fitting on the manifold clean and dry, or contaminated with oil or grunge? Is the clamp in good condition and tightening correctly?

If the pipe is truly being "blown" off the manifold, there would have to be some source of back pressure. Off the top of my head, a remote but possible scenario would be a broken intake valve spring. With the intake valve not sealing properly, combustion chamber gasses could blow back into the intake manifold. We would think that they would simply blow all the way out through the air filter, but with the rest of the engine sucking air in the opposite direction the point at which the two pressure streams meet might very well be the union of the air intake pipe and intake manifold.

Can you detect any unusual knocking or rattling sounds from the areas where the valves are located on either cylinder head? You can use a long screwdriver or socket extension as a "stethoscope" by placing one end at various places around the tops of each cylinder head and touching the other end to your ear.

Cheers,

Don

 

"blowing" off the air intake from the manifold.

Suggest you post a picture of the area in question.

 

Thanks for the replies. I will post a picture a little later to clarify. It's the 2" plastic/rubber tube that conects the air filter to the engine. I cleaned it all up and made sure that it was not just "slipping" off. I have tugged and made sure it is secure, and it is still coming off.

Replaced the air filter yesterday cause it was a bit dirty. The inside shows dirt so I assume that is probably from some kind of misfire or such.

The codes 171 and 174 have returned so I am betting (hoping) it is a vaccum leak as opposed to something more sinister. I dont hear any knocking but its hard to tell. I have seen videos of smoke testing but have not figured out where to hook in on this engine. Any guidance?

It seems to be coming off during hard accelaration and runs worse once the engine warmed up. When it is cool it runs pretty smooth.

Thanks for any additional help. Just got thru a wild goose chase for smog passage and really tired of it not running well. BTW, all O2 sensors are about 3 months old. I have seen that can mess with these codes occasionally.

 

Here is the TSB Jaguar offered a decade ago.

bob

 

I have experienced that although the clamp seems to be tight, it is actually binding on the thread and screw head and not actually tightening. Engine torque rotates the engine, and it pulls off.