Don't clear the codes. The LTFT will start at zero and change slowly as the ecu gathers info.

 

I smoke test all my BMWs. This Jag is the first where I found vacuum leaks that were not detected by the smoke machine.

I couldn't find an adapter large enough to seal the air cleaner end of the intake tube, so I had to cap it with a plastic plug and inject the smoke at the oil fill hole.

In any case, yes. The engine should be at idle and the brake cleaner will cause the engine to stumble if any is sucked into the intake stream.

Personally, I'd clear the codes but that may be optional. I'm not sure if the lean condition codes go away on their own. I've never wanted to wait and see.

 

If fixed, the codes will self-clear if you let them. The MIL will go off sooner (4 or so warm ups). If the MIL is off the codes are harmlessly kept for quite a while but won't affect such as smog tests.

If you clear them you also clear all the OBD monitors (needed to be set by many "smog" tests) and they can't flag lots of things until they set again. (And they won't set if the wrong sorts of faults are present, yes Catch-22)

 

it’s a 4.2 they have different issues

brake booster vacuum fitting. cracked pcv seam and leaking timing cover are the usual suspects

 

I have not had much luck finding leaks with flammable solvents on the 4.2L cars. But if you use brake cleaner, be sure it is flammable. The popular CRC Brakleen that I use for general cleaning work is non-flammable.

To find all the leaks on a 4.2L with a smoke machine requires injecting the smoke from multiple points at sufficient pressure. I typically go to about 10 psi when testing an air intake. If the smoke machine is set for testing the Evaporative Emissions System, the pressure may be regulated to just 1 psi, which is not enough for testing the air intake.

The first thing to look for is any point where oil is leaking out. If oil can leak out, air can be inhaled under engine vacuum.

In addition to the points xalty mentioned, off the top of my head, some of the places I have found leaks on the 4.2L are the O-rings for the full- and part-load breather hoses (or cracks in the hoses themselves), cracks in the accordion pleats of the main air intake pipe, the oil filler cap seal, the oil filler extension pipe if equipped, the two O-rings on the crankcase vent valve ("PCV valve"), cracks in the Helmholtz resonators on the main air intake pipe (especially the seams where they are ultrasonically welded on), the Variable Valve Timing solenoid seals, the intake manifold gaskets, etc.

Cheers,

Don

 

You can use plain water in a spray bottle and get a noticeable difference in idle speed just as easily as using a flammable spray, but no danger of catching anything on fire. Not to mention, water is pretty cheap.

Z

 

I finally got my smoke machine and tested the intake system. No leaks found. I capped the intake pipe from the the air cleaner and used the smoke machine to test. I think that tested everything from the air cleaner to the throttle body. No leaks. Next I did the test with brake cleaner spraying everywhere including the small EGR hoses while the engine was at idle which should produce the highest vacuum - nothing! Live data continues to show negative Short term trims So I deduce that there is no leak from the air cleaner to the throttle body and spraying around the same areas confirmed that. I am a loss as to where to go next.

 

It sounds like you have the air side of the mixture pretty well diagnosed... have you addressed the fuel and ignition side? Weak fuel pumps (or a failed secondary or primary pump), bad or clogged injectors, fuel filter, type of gas you're running... coil packs, plugs...

 

I should have added I also changed fuel filter! Also the DTC codes I am getting are both P0171 AND P0174. So it seems to be something having an affect on both banks.

 

Have you changed the MAF sensor with the correct OEM Denso and made sure that the intake is sealed where it enters the quarter panel?

 

If cleaning the MAF sensor does not help, you are
left with the reasonable choice of changing it .


note: it took 3 or 4 very long sessions with the CRC MAF spray to get my MAF Sensor to function properly. You have to use spray liberally. Let the sensor dry and repeat the cleaning. That worked
for me.

 

Agreed. I posted previously in this thread that there is also a difference in the XK8 and XKR MAF sensors. For what it's worth I have an experimental parts XK8 that has identical codes. I replaced the MAF with a generic cheapo equivalent and the same codes came back. I don't care to fix that issue on this car, but was curious to see if a $12 MAF could solve the problem. It did not. I did note on this junker, the wiring harness to the MAF looks to be heat damaged and the contacts are suspect. If I was to continue troubleshooting, I would repair that harness and make sure that the ECU and MAF was happy. Also... making sure the ECU and fuse block connectors are intact and tight is not a bad idea.

 

I did replace the MAF sensor a year ago. I have cleaned the replacement twice. The seal appears good as evidenced by the spray test. Also live date confirms that MAF sensor is reading correctly

 

It might be worth checking the fuel pressure. You could also take the car somewhere that can check the lambda reading at the tailpipe to see if it matches what the car is seeing.

 

Fuel filter replaced. fuel pressure at 2500 rpm is 381 kPA or 55 psi. MAF is 5 gr/sec at idle going to 17 gr/sec at 2500 rpm. I just don't see any problem there.

 

For reference on my 2001 4.0 XKR the MAF reads 5.1 g/sec at 650 rpm and 10.4 at 1500 rpm. Ideally you would want to compare against the same car as yours to be absolutely sure, but as you say your figures look credible.

How are you reading the fuel pressure? From an external gauge or via the OBD?

 

at this point get another MAF

if there’s any real oil leaks on the timing cover rear main or valve covers it will never have perfect trims but if everything else is sealed they won’t trigger lean codes

 

Problem SOLVED! I re-did the smoke test using a better plug for the intake pipe and as was suggested by Don B, the moderator the air leak was in the seam of one of the Heimholtz resonators! Using about 19 psi the smoke poured from the crack. Thanks to all who responded!

 

At 19psi smoke would pour from my crack too. Congratulations! Scary that such an irrelevant appendage to the exhaust system would cause such an issue.

 

Well done....