dgi 07 -> Apology accepted.

I kinda like being called a DB. But Read On , Holmes!

OK, so I bought a couple of those 8 x 125mm bolts to fix the Exhaust flange, tightened everything up, but threw the damn codes. Its funny that I can now guess EXACTLY when that code will pop up on my dashboard on a test drive.

I have been working on this for over two weeks now. Driving me nuts (and the wife too). Went to bed thinking all I need is a little sleep.

Woke up this morning and decided to get one last look at the intake manifold before I put the POS up on Craigslist. Got the handy porta-light out and this time, I got right on top of the manifold looking down.

WTF! - there is about an 8mm hole right on the manifold top. I grabbed one of those 8mm x 125mm bolts (for the exhaust flange) and it threaded right in. Pic is attached - shiny bolt head on upper middle of manifold.

I turned the key and was immediately surprised that she started right up on the first try (usually took 2 - 4 time of cranking). Kinda makes sense - if its a manifold leak, it would add additional air to the air that the IAC adds upon startup...

Anyway, I then cleared the P0171 / P0174 code and went around the block. It ran like normal - gave it a bit of a workout...but eventually the P0171 / P0174 pending came up. A bit disappointed, but hey, she now starts on the first try!!....so I pulled in my driveway and went to clear the code, but went to SENSOR DATA first to check... oh noes, don't say it!! Don't even think about the LTFT again!

Wow, It had gone down from 25 (max - for the past couple weeks) to 18 with a simple, but spirited drive around the block. The P0171 / P0174 codes are "pending" due to the LTFT still being high, and until it drops to zero or some lower limit, the pending code will continue to pop up.

I have a wedding to go to tonight that is about 60 miles away.and will have to see if I truly have to drive / learn down that LTFT to finally rid myself of these codes.... How's that for a coinkidink?

So what the hell is that hole? My DIY "plug" is a tiny bit loose - it is tapped...thinking of putting a rubber washer under it. But what the hell is it? The two other close by manifold bolts (above and below this one) have shoulders that will not fit in the "valley" of hole...anyone?

Don't pay any attention to the duct tape - grandkodiak suggested pulling all wires out of the loom and check for shorts and other problems - just gotta put them all back.

 

The hole on the intake plenum shown in the first picture is normal. To be sure, I checked mine during my Saturday morning under-hood fluid checks. I have the same hole on my plenum also. I'm not sure why it is there, but it is normal.

 

If you look at the pic of the underside (from an ad on ebay), the bolt hole goes clear through the plenum, indicating it is bolts onto the lower intake manifold...you have no bolt either??

Is there a vacuum there?

 

Yeah I don't have a bolt there either. It's never given me any troubles to my knowledge. I'm not sure you're supposed to plug it up.

 

Don't know what purpose it has if not plugged - maybe another engine model vacuum connection, like the PVC connection - seems same size and tap as that plastic threaded vacuum nipple on the PCV connection on the intake end.

If you look at the underside pic, if you loose that gasket seal (which I could have done when I cleaned out the intake with Seafoam), you could easily spring a vacuum leak from the main intake chamber to atmosphere.. Mine apparently did....

Just took the 8mm bolt out and put a lock washer under it. Just need to tighten, but its so tight that the socket can't get on the bolt head. Its hand tight - better than no bolt, I guess...

Can you guys without bolts feel a vacuum there?

I will search for pics of the head to see if there is a point for this bolt to thread onto...this is getting fun!

 

I just checked- no vacuum from that hole in the plenum with engine running. If yours has vacuum from that hole with engine running, it sounds like your plenum gasket has been compromised.

 

and another pic of a disco II manifold without plug... from ebay...

You know, this has me thinking - in the oil refining industry, a long time ago, before we "retired" piping and vessels by obtaining thicknesses using ultrasound (and a couple other methods), they put in "century holes". They basically drilled hole a certain depth into the pipe or vessel, and when the pipe / vessel corrosion allowance was eaten away, the tell tale "century hole" would spring an intentional leak.

Maybe this is a leak detection port?

EDIT - lordmorpheus - we cross posted...sounds like it is some kind of plenum leak detection port...

Also - lordmorpheus, you may want to try revving the engine up and checking for vacuum leak - I never got that P0171 / P0174 lean code on idle, just when I drove it... and especially when I jumped on the throttle...although it was difficult to start meaning it was affecting operation at low revs too - nevermind.

 

One more pic of the intake manifold, which the plenum bolts onto (not the heads as I said earlier) - doesn't really show a bolt hole, but still looking for a real pic...

 

Land Rover Discovery 2 Lower Intake Manifold 99-04 | eBay shows no hole in the lower intake.


Edit: Lol, Earlier, I walked past a junk engine to pop the hood of my vehicle to look at the hole, start it, etc.

I just checked the junk engine, which has the plenum laying loosely on it. The hole on the plenum goes straight through the 1/4" of aluminum, down to the lower intake, where there is no hole.

If you have vacuum at that hole, either the plenum gasket is damaged, or your plenum is warped.

 

OK... no need to further research - I now know what my issue is (leaky upper manifold gasket) and have the problem under control.

I guess I am done here - I thank you all.

dgi 07 - Really, thanks for your help.

EDIT - I have attached a pic of the lower plenum, as when that ebay auction is over, that pic will be gone...