Also, is there a way to keep the throttle butterfly open during the smoke test?

 

Had a go at smoke testing it today. First I tried it with the smoke entering through the PCV line in the intake hose and capped the end off with a rubber glove.





I had a few attempts but couldn’t find any leaks. I managed to get a bit of pressure in there, but nothing.





I had the ignition on with a brick on the throttle but I don’t know if that was actually opening the throttle butterfly so I had another look for somewhere else to test past the throttle body. I found this little vac line on the back of the charge cooler manifold, so found some smaller diameter tubing and connected to that (pic is upside down).






At first I though I’d found a leak on the gasket between it and the top of the supercharger (albeit on bank 1 side) but I think it was just smoke tracking under the inlet pipe that was coming out of the vac line stub in the photo above that I’d connected to as the seal wasn’t perfect. Other than that, I could find no leaks. And I tried several times.


I had a play about with some items on bank 2 with the car running and the scan tool attached. I lifted the dipstick, made no difference to bank 2 fuel trims as they are already maxed out but bank 1’s increased, then dropped back when it was pushed back in. The O ring on it was quite perished so I replaced it but no change. I unscrewed the oil cap with the engine running which made it run slightly rough and again made bank 1’s fuel trims increase. Once it was back on, bank 1’s trims fell back to near 0, so I can assume it’s not that (bank 2 still maxed out). I pulled the little vac line off in the pic above with the engine running and had the same results as the oil cap, with bank 1’s trims increasing, then falling back once it was back on and bank 2 remaining maxed out throughout (what is this vac line for?).


​I’m at the point of giving up with it now, I’m not prepared to go through the battle of pulling the supercharger when I can find no obvious fault. I can’t really think of anything else to try.

 

Don't forget to check the power brake booster for leakage.

IIRC, there's a check valve in the big vacuum line to the booster. If doing a smoke test, the check valve will stop the flow towards the potential leak.

If doing the spray/fuel trim test, douse the seal from inside the cabin where the pushrod passes through the firewall. This potential leak area is often overlooked.

Another option is to disconnect and plug the big line to the booster. Don't drive like this, as your brakes will have no power assist. See if the fuel trims improve.

 

Thanks but surely this issue would not be isolated to bank 2?

 

Who knows? Maybe you’ve got a combination of minor faults. Something like a marginal coil on bank 2, and a vacuum leak affecting both sides. The computer flags bank 2 because overall conditions are a little worse on that side.

 

It’s a bit more pronounced than that though. Conditions on bank 1 are nigh on perfect and bank 2 off the scale. I’ve already swapped all the coils from bank 2 over to bank 1 and vice versa to check the coils but it made no difference.

I’m going to get an endoscope because I’m starting to think it can only be either a crack or leak on the exhaust manifold that I can’t see.

 

I’ve left this alone for a bit as I’ve just stated a new job and didn’t have the mental bandwidth!


Just been out and had another mess with some brake cleaner and a straw trying to find this air leak. It’s only affecting bank 2 so can only be the upper manifold gasket or gasket between charge cooler and head, if it’s an inlet leak rather than exhaust. The only time I got the short term trims to deviate from between 24.2 and 25% was if I aimed the straw in between the supercharger and chargecooler on bank 2 as far down as possible and kept my finger on the trigger for about 10s. This would cause the STFT to drop to about 20%, then creep up again once I stopped spraying.


This would fit with an air leak between the charge cooler and the head, however I would have expected this to have a more dramatic effect on the short term trim, as in I would expect it to nose dive if it managed to draw in the brake cleaner. I repeated this 3x and each time got the same result as above.


What do we think?

 

You have done good troubleshooting and at this point you do have a specific area that does repeat 3 times showing changes in the fuel trims.
I think you need to dive in and see what's going on. Not many intake leaks reported either but these are now old cars and really anything is possible after 20+ years of driving!

If the SC is pulled don't forget that crummy under the SC hose too!

Has the SC ever been taken off? The gaskets are sometimes reused but I recommend new even for those expensive intake/charge cooler gaskets. Just thinking out loud on this one?
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Im not convinced. Youve sprayed so much theres no telling where the spray has gone. It could have been sucked into the air filter.

using carb spray isnt effective bc the car will almost instantaneously adjust the fuel mixture as soon as it gets it first whiff. So a change after a period of time doesnt add up. Youd see a momentary spike then itd would readjust.

do a smoke test. Youve got a leak but carb cleaner wont help much

 

My first guess would be a fuel injector oring. They can leak after they get old a hot and harden. The injectors can vibrate which would assist in making the leak. Gaskets, once sealed by the compression are typically pretty robust if the torque was correct.

maybe see if any of the mounting bolts are loose. And try wiggling the injectors a lil bit. While watching the trims. Maybe youll see a change

 

one method i have used to check for induction leaks is a propane torch. unlit of course. just hold the button down/in. then you can point the propane around various areas of the engine and see if it smooths out. this is how i found a leaking intake manifold gasket on my XJ8 4.0. one advantage of this method is that there is no flammable liquid being sprayed whch is always risky around your painted surfaces. for more hard to reach places slip a length of vacuum hose on and tape it to a dowel or coat hanger. you can direct the flow of propane exactly that way.

 

Don't expect to hear any engine note change - use OBD to watch STFTs and they go wild.

 

I agree listen to JagV8. I had a very similar problem on my old 2005 S-Type R. Tried all what your doing with no change or help at all. JagV8 told me to get a scanner that can show fuel trims in real time and BINGO!
I found my vacuum leak in the elbow of the SC going to the PB booster. Engine sounded exactly the same.
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Yep the PCM adjusts the fuel mixture so quickly When it senses the propane gas that you don’t hear the traditional stumble that you used to hear in the past