Found cause of P0172 & P0175 DTC's

[Jordo]

The car had to make it "too rich" to run correctly??? Just thinking out loud.

[m5james]

Basically, yes...it sprayed extra fuel to compensate for the extra air.

[Harley Monster]

But why did it spray so much it caused it to go Rich.

My hunch and it is only a hunch is that in the DME there are limits on the fuel quantity for certain RPM & Manifold Pressure and this quantity of fuel was exceeded to make the engine run normally not that the engine was actually running rich.

I would like to know the real answer, just because I would like to know the real answer.

[m5james]

It's unmetered air, so the only reading your getting for air/fuel ratios now is the precat 02's, and considering that they're probably due for their 80-100k replacement as well, they weren't giving 100% readings back to the ECU. Basically the MAF and 02's were fighting, so play it safe and spray more since we know there is an issue.

[Harley Monster]

M5James...I have a question on the O2 sensors.

These are original (118,000), is it best to change them out before failure or is it best to wait until they do?

My dad used to say, "If it aint broke, don't fix it..."

Will the failure of the O2 sensors leave you stranded? Or does it start out with an SES light?

I guess it is OK to hijack my own thread.

[m5james]

They don't usually fail, they're just like spark plugs or MAF(s) where after time they get more resistance and start reacting slower. I've yet to see one fail, but I've fixed customers vehicles who had specific "slow reaction" codes coming from the 02's. It's one of those things where replacing them on a regular interval will just help the car run that much better with just that much more power. I've experienced for myself, customers and read of people suddenly having more power, better gas mileage, etc by replacing these wear items. At 118k, I'd replace the precat (don't worry about the post cats) 02's and spark plugs if you're looking to wring every drop of power and gas mileage out of your X, both of which can be found at Autozone for far cheaper than the stealership. The 02's in my 7 cost me $70 a piece and the plugs were around $7 each, Bosch and NKG's. Replacing the 02's require that special socket that you can get there as well, and the 02's can be seen from the engine bay at the top of the headers, with the rear one being the hardest to get to.

I understand the term you're referring to, but cars we're made to last longer back then as well. I've got a 90 S10 Blazer that is my winter beater...271k, runs like a champ and hasn't cost me even CLOSE to anything my BMW's have cost me over the years. Nowadays they're made to be more consumable with the advent of technology telling us what to replace vs back then they just had to last otherwise people wouldn't buy them. I'm just getting on my soapbox now.

[Harley Monster]

Thanks James!

[m5james]

Glad to help, sir....keep us posted.

[Harley Monster]

M5James, you sound very experienced, do you have any suggestion in changing out this Y pipe? Bill K earlier in this thread had some good suggestions, do you have anything to add? It is really tight in there.

[m5james]

I'm a BMW indy with 4 BMW's I maintain regularly within the family...my advice is to have smaller hands than mine

Seriously though, I don't really have any good advice other than lots of lighting and a decent set of tools, but it doesn't require anything special, so don't worry too much. The tradeoff of being the I6 vs the V8 is that your engine is quite long while the V8 is wide. It can be done, it'll just require taking off various bits to get it to as Bill suggested. I've used a very long flathead to remove the hose clamps around the ICV, but that doesn't always work and it eventually kills my back if the screwdriver keeps sliding off.

Clean the ICV while it's off...you can flip it in with your wrist in a turning motion, it should have a little valve that flops around. I usually spray them with carb/choke cleaner and 9 out of 10 times it flushes back out with black soot. Just something to do while you're in there. Carb/choke cleaner has a tinge of oily residue, so it'll act as a lubricant as well, meaning don't use brake cleaner. In a pinch, I've even done it with WD40 and then shook the hell out of it to so it doesn't have standing puddles inside of it before re-installation.