Makes sense, thanks. I misunderstood that SAI actually plumbs to the exhaust side. Will report back after fixing upper gasket.

Cheers,

Brian

 

Here is what I know:

The system is "open loop" when the Land Rover Discovery II starts up first thing in the morning.

The system is open loop as the O2 sensors are not heated yet.
The O2 sensors heat due to internal heaters run by 12 VDC applied via a fuse. The O2 sensors are also heated by exhaust gas.

When the O2 sensors are heated to the proper temperature, then the system will move into "Closed Loop"

The SAI only runs the air pump first thing in the morning when you start up from cold.

At this time, the system is "open loop".

Even if air is added to the cylinders via the SAI - the system is open loop and the O2 sensors are not contributing to the fueling calculations.

Plus

The ECU KNOWS when it activates the SAI pump. So, the ECU would take running the SAI pump into account and probably not throw a CEL code.

If you want to eliminate the SAI - then just disconnect the air injection hose from the SAI pump to the SAI piping.

But, if you disconnect the SAI blower hose - you'll probably get another code sooner or later about the SAI. I had the SAI hose disconnected and
I got a "power train" code after about a week.

I don't think it is the SAI.

Your problem happens when you are "closed loop"

Closed loop involves injectors and sensors

Sensors are:
a) O2 sensors
b) MAF sensor (which is a hot wire detecting air density). When the air runs over the wire in the MAF, the ECU can detect how much more current it takes to keep the MAF wire at a certain voltage/temperature.
The MAF hot wire is indeed a hot wire. This is why not to spray CRC sensor cleaner on the hot wire when the MAF is active. The MAF is active when the
engine is running.

If you have a vacuum leak, then you are getting air in AROUND the MAF and this will make the MAF readings inaccurate because there is air getting in which is not running across the MAF hot wire.

You could get a vacuum leak if the intake manifold gasket was mis-seated.
Or from the brake line
Or maybe those smaller lines.
Also - vacuum is used to suck hydro carbons out of the valve covers.
If you did not put in the valve cover gaskets well - you could get air sucking in to the gap between the valve covers and the gasket.

You would probably get oil out too.. So, I may be wrong with that one.
But, if there is a gap at the top of the valve cover - you may get air in that way.

Or, if your oil cap will not seal.

 

Jared, nice work getting it solved. For the record, mine also turned out to be an intake air leak so x2 on the diagnosis. In this case air was leaking from around the lower injector o-rings. This was the one gasket that I didn't replace during head gasket repair. Its been a week and a couple hundred miles since replacing the o-rings and no check engine light. Hoo-ray!

 

THis is a great read! Thanks for all of your expertise here! My question is (because I also have the 1171 1174 drama): would a break in the rubber line going to the cruise control module cause this? I noticed it the other day when seeing why my cruise doesnt' work anymore but I didn't put the pieces together until now.
Also my 2000 has about 173k on it and makes a noise that sounds like an exhaust leak (around the cat area) when its cold but it gets quieter as it warms up but I can't seem to feel or see a leak so I am looking for a reason to replace the Y pipe. How do I know if the cats are clogged or bad?

Thanks again!

Andy

 

In order to remind folks that many different root causes can give the same effect, I am posting my P1171 P1174 results.

I agree that lean code are almost always a vacuum leak, and that is what I looked for for many hours. I purchased a shiny new smoke machine, which I have been wanting for a long time, but it confirmed I had very little air laeking, just a wisp from the valve covers, barely enough to seep oil.

My MAF sensor was nearly new (13 months, 10 K miles and looked clean). I cleaned it thoroughly. My STFT and LTFT ran in a reaonable range, alternating between + to - 8 or so. My Oxygen sensors cycled fine. But the Disco would not pass readiness and gave P1171 and P1174 after 100 to 200 miles.

I noticed the STFT would go very high, after a few minutes of running at idle. I assumed that my Evap system was leaking, but I confirmed that was not the cause of the O2 ingress by clamping the line closed while the high STFT was showing.

I was getting really aggravated, but no damned piece of equipment is going to beat me! I then started a chart of the MAF, the STFTs and the idle speed. What i soon noticed was that the MAf was reading 800 (units?) at about 800 rpm, but when the idle drifted down to 750 rpm, the MAF was only reading 550 to 600, and the STFT was shooting up. Cause or effect? Well, if the car was leaning out at idle, the RPM would be expeted to rise a little, not fall. So, reluctantly, spent the cash for a real Bosch MA from Rock Auto.

It fixed it! MAF now reads about linear vs. rpm around idle. My conclusion is that the old MAF lost calibration when it was down in the weeds at low rpm. If I had turned on the AC and defrosters, I probably could have gotten it to pass readiness by keeping the airflow up where the MAF was closer to accurate.

Happy, happy, happy!

If a code could in and of itself tell you what to change, there would be no need for dealers, mechanics or auto techs!

Ross
MY 04 Disco II