I honestly thought I was going to need to buy a set of O² Sensors, still might if the codes come back.
After 2 cans of starter fluid I never got any rpm variation at all. However, I could hear what sounded like a leak around the Fuel Regulator and Flying Saucer that runs vacuum between the left (facing windshield) valve cover and the intake manifold. I've been working on a CAI and also noticed I had the other side connected between the MAF and throttle body instead of the filter side.
I never did actually diagnose a leak but it all smoothed out after I replace both of the large hoses @ the valve covers and put fresh o-rings on the fittings. 1/2" & 5/8" Heater Hose worked perfectly. I guess the nylon house had just worked loose and was leaking around the barbs + hard o-rings....
I honestly just had a hunch, and that hissing sound that comes from the left side does a great job of disguising any other audible leaks in that general area.

One question though, does anyone know what's inside that flying saucer? Is there a diaphragm? I would love to delete the fittings on both sides and install a set of NPT to Barb fittings. Thread the openings an then never have to worry with it again. I did this on a GM f-body tensioner pulley that had heater hose fittings integrated into it. The hoses were crazy expensive. I've never been a fan of the hard nylon lines.

Anyway, just wanted to say thanks and let ya know what I found. I'm really glad it all got sorted before this Wednesday. The new exhaust mods are getting installed and I wanted to know what was up before I tore into that project.

By the way, my ELM is still showing some crazy Air/Fuel #s. But no codes or even pending codes. I'll post if there's any change when I drive home tonight.

Thanks
-James

 

I've wondered about the same thing James. I'm not sure what is inside the crankcase vent valve, I'd agree and guess it is a spring balanced diaphragm. My old 2004 XJ had plenty of blow-by at idle, the one I am servicing right now seems to have much less. In both cases (previous and current cars) I hear the loud sucking sound. Personally I think the sucking noise is caused by the corrugations in the nylon tube, not a result of a leak. Did yours quiet down with the smooth hose installation?

What I can say is that I experienced intermittent lean codes on my previous 2004 XJ8, particularly during cold weather here in the northeast. Starter fluid never garnered a reaction BUT spraying brake clean around the intake manifold gaskets yielded an instant drop in RPM (almost to the point of stalling her out.) Don't ask me why I tried brake clean vs. starter fluid, I think I just had a can sitting on the floor and decided to try it out of frustration. The vacuum leak issue / random lean codes and limp mode were driving me nuts.

I'm glad I did because I've been using brake clean to find tricky vacuum leaks on these cars ever since. Probably not great for the sensors but a shot here and there in a pinch shouldn't hurt anything. My leaks were almost entirely related to the gaskets that sit between the lower manifold aluminum extensions and the plastic upper manifold housing. Technically these gaskets aren't considered serviceable, Jag wants you to buy a whole new intake... thankfully someone has reproduction molded gaskets made up and they are selling on eBay for ~100 bucks. A little shoddy with some flashing to clean off but they worked fine. I got sick of the intermittent lean codes and did a complete intake rebuild on my old '04 a few months before an idiot rear-ended me on the parkway. Lean codes disappeared permanently and the fuel trims fell to nearly 0%, both long term and short term. Unfortunately the car was running great when she got totaled.

My new project '04 XJ8 hasn't seen an open freeway in 3 years. Hoping to change that in the next couple weeks. Knock on wood... intake gaskets seem tight, will see what happens when winter rolls around.

Do you have a scan tool that allows you to view your fuel trims? Even if the lean codes are not present, if you are seeing numbers in excess of 3 or 5% on the long term you probably still have a vacuum leak someplace.

 

I'm using a ELM Bluetooth and Torque Pro to keep an eye on things. I drive an hour each way to work an starting off things didn't look good the trim was at 25% by the time I got here they were pretty close to zero.
I still don't like the volt readings from the O²s. They'll do fine for a bit and then suddenly drop off or increase within one sampling., Like 0.8 to .2 in less than 1 sec.
I'll log the drive home tonight and post a link. Also, I think the AFR can't be correct. Does anyone else run Torque and have a AFR measured # with no codes? Mine says 9.43:1 an that can't be correct, it would be blowing the top out and it's not. It's running better than ever, an no knocking... I think the equation in the app is screwed up somewhere. Wish I knew how it got it's number...

 

https://drive.google.com/file/d/1-51...w?usp=drivesdk


You can filter it with the top row of the document. It was a definite improvement but I wasn't totally convinced that I had actually sorted the leaks or put a band-aid on them. I hate to have to do stuff twice. So I did some looking and researched a couple things, and here's what I know. My flying saucer is just a basic oil separator. And it doesn't do a very good job at that. There's nothing inside diaphragm wise. So I deleted it. I believe the housing is leaking bad either way.

In it's place I tapped a 1/2" NPT Thread into the opening. I applied some TruBlue Thread Locker & Sealant to a 45° stainless fitting w/a stub pipe nipple. Blue will cure rock solid, it's resistant to pretty much everything and it's never failed me on anything for nearly 5yrs now. I put a 1/2" NPT to 1/2" Barb into the 45. I angled it facing straight forward at the headlights. Attached 1/2" heater hose and routed to the front of the engine cover and then back to the fitting just before the intake manifold. The hose is longer but should be fine. I applied a dab of blue on the fitting and popped it in.
Left side done.

The right side has a street 90° 5/8" NPT to Barb w/Blue applied. On this one I installed a small house clamp around the plastic nipple to prevent it from cracking while I tapped the connection.

So no more large nylon hoses. On either side. I'm allowing everything to set-up an cure overnight before I attempt to go any further an start'r up.

I didn't have to drill out any of the openings inorder to run a tap thru the openings. But keep a shop vac handy for sucking up shavings, while threading the 2 covers.

I see no reason why this shouldn't work as a solid fix. I'll button up in a few hours when it's light out and post some pics and results.

Materials used:
US Pass.Side -
½" 45° Pipe Fitting
½" X 2" Threaded Pipe Nipple
½" NPT to ½" Hose Barb
15" long ¾" Heater Hose

US Dvr.Side
⅜" NPT to ½" NPT - ⅜" into cover
90° ½" Street Elbow
½" NPT to ½" Hose Barb - The ⅝ hose will fit and be tight.
12" x ⅝ Heater Hose.

* I then ran the other end of the ⅝ hose to a Barb I had on the filter side of the MAF.

I'm whipped, and gonna get some sleep. I'll update regardless of the turnout am since I didn't have to drill out the openings I can still use the OEM parts with some Blue to seal them in, but I can't get the vacuum parts off the shelf so I decided to give it a try. Oh yeah, I also added a clamp to every remaining hose and fitting. It felt like a totally different car driving home with no codes tonight. She wanted to run, but the cops were hot. All goes well I'll wined'er out on the way into work tomorrow.

I hope the hiss is gone now....
BTW I logged every sensor.... Not says it's a baseline but no lights or codes.

James
Hillbilly Hydrographics





***If you attempt this, BE CAREFUL. YOU CAN CRACK YOUR VALVE COVERS.

I'm an industrial mechanic so I do this for a living. Just don't put the stainless parts in crooked or in a bind. The plastic will lose.

 

The NPT fittings did the trick. I posted some pics in the other post and I'll attach a Torque log later today. Perfect AFR, no codes 😃