2002 Buick LeSabre – Code P0172 – What Next?

I would get your O2 sensor checked.

The clues in your original post, especially the oil smelling like fuel, tells me that you might have one or more leaking fuel injectors on cyl 1, 3, or 5, since the code is for Bank 1. A vacuum leak usually causes a lean condition since unmetered air is entering which dilutes the fuel mixture, so I am not sure looking for a vacuum leak is called for at this point. Rich code means too much fuel or not enough air is throwing off the fuel mixture to the point where the computer cannot adapt. Normally I would suggest testing the O2 first, but since you indicate a fuel smell in the oil, that sounds like too much fuel is being applied. BTW, if you are wanting to do more repairs on your own car, which is fantastic, do yourself a favor and get an OBDII scan tool. You can get USB or Bluetooth devices that pair with a PC, tablet, or smartphone for around $25-30. A worthy investment. These will let you not only read codes, but also monitor live data to show you the real-time functioning of things like the O2 sensors and fuel trims. One that I like to recommend is the ElmScan 5.

Ok, here’s a little basic automotive chemistry for you. In chemistry, there is a term called “stoichiometry” which refers to a ratio of one thing to another. In automotive work, we also use the term stoichiometry to refer to the ratio of air to fuel. On gasoline engines, the stoichiometric ratio (or stoich as it is usually shortened to) is 14.7 parts air to 1 part fuel (usually written as 14.7:1).

The computer attempts all means possible to keep that stoich. It does this by adjusting the fuel injectors (fuel trims) and air admittance (usually through IACV). To do this, it uses sensors. The O2 and MAF mostly. The MAF sensor produces a voltage (or sometimes a current) that is proportional to the amount of air passing through the intake. The pre-cat O2 sensor(s) produce a voltage proportional to the amount of oxygen to hydrocarbons present in the exhaust stream. This data is the primary feedback that the computer uses to adjust stoich. There are other sensors that contribute as well, so it isn’t really as simple as I just described, but that is the basic info.

When there is an air/vacuum leak, there is air in the system that did not pass through the MAF, so it is not accounted for in the computer’s calculation. This typically causes a lean condition. The O2 responds to this and the computer enriches the mixture (positive short term fuel trim) to compensate. On the other hand, something such as a leaky injector will apply too much fuel. The O2 indicates a rich condition and the computer then tries to remove fuel or add air, reducing fuel injector pulse width (negative short term fuel trim), or maybe opening the IACV, or some other strategy, again trying to achieve stoich. If it is unable to provide stoich through the adjustment strategies it is programmed for, it sets a rich or lean code. If the compensation results in stoich, no code is set, and the new values are written to memory (long term fuel trim). This is called the “adaptive fuel system.” Only when the computer fails to compensate and produce stoich is a code set. This is the idea Eric was talking about in the video.

If you have a fuel issue large enough to make the oil smell of fuel, it is probably too large for the computer to compensate for, and will set a rich code.

Just because a code is set, it does not point to a particular component as faulty, although faulty components can cause codes to throw (quite often they do). It is important to understand how the systems work, and what each component does and how it contributes to the system, to be able to accurately diagnose faults. Learning to use your scan tool, and getting some books on engine management systems will take you a long way toward this goal. The idea is to become a diagnostician rather than a parts-swapper.

[quote=”Aldon” post=137453]A couple of days ago I took your suggestion and changed out the Fuel Injector O-ring seals. [/quote]
I apologize if you misunderstood or if I just wasn’t very clear. When I mentioned leaking injectors, I didn’t mean the O-rings, I meant leaking on the inside such that the pintle is damaged or isn’t closing all the way (due to obstruction or mechanical failure) and pressurized fuel is able to escape past it into the cylinder and run past the rings into the oil. Also, that may or may not be the problem, as on my side of the internet I cannot see what you see. If it were my vehicle, I would pull all six injectors and send them out to an injector service for testing and cleaning (about $25 each), then you will get confirmation if each injector is working properly, and it will be professionally cleaned (they will return the injectors with a performance report).

Also, when tightening up the nuts to put the fuel rail back on, I snapped one of the screws I was putting the nut onto. It didn’t even get very snug before it twisted off… The fuel rail is secure and doesn’t wobble, but I’ll still want to change this bolt however I don’t know how to get to it. So help on this would be appreciated as well.

It got cross threaded. I would remove the fuel rail and use vice grips to try to grab onto what’s left and twist it out. Once out, use a thread chaser or tap the same size and thread pitch (be certain of this!) and repair the threads before inserting a new bolt. If it cannot be twisted out, drilling into the center of the bolt and using an extractor (or drilling it out and re-tapping the hole for a larger bolt) may be the next option.

[quote=”Aldon” post=137458]Ah okay. But if the inside of it is leaking it still would have to go past the external O-rings to get into the oil right?[/quote]
No, the fuel drips out the nozzle into the cylinder where it runs into the combustion chamber, then drips past the ring gaps in the piston rings, and continues past the rods and crankshaft into the sump where it mixes with the oil. The lower o-rings keep the intake airtight and the upper o-rings prevent fuel from leaking out of the rail.
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Maybe the nut got cross threaded onto the screw and then twisted the screw so that it snapped off?

Yes that it what happened.

I was thinking I would have to take it apart to unscrew it from the inside. But if there is no head to these screws it would be awesome to just be able to extract it. How far do you imagine that I can drill into the screw? I don’t want to damage anything on the other side.

They do not have heads. These aren’t screws, they are studs, which are basically threaded on both ends. You should be able to unscrew it. Before attempting it, though, put penetrating oil on the broken one and let it sit while you’re getting the new stud. Then you should be able to twist out the old one, install the new one, and reattach everything. If you wind up having to drill it, and you’ve never drilled something like this before, you may want to find someone to help who has. You can look at your new stud to see how deep the thread go, but you shouldn’t have to drill it all the way through, just enough to get the old one out. A shallow hole and a screw extractor would probably work. Honestly, you could probably just leave it alone and it would be fine. While you have the rail off, pull out the injectors (from both sides) and send them off to the cleaning service. That way you can reduce the number of times you have to remove the rails. Also, while waiting for the injectors to come back, it might be a good time to change the oil and filter.

[quote=”Aldon” post=137581]Do you know anything about this cleaning service;I was looking at sending them out to these guys (Injector RX). (If you have an alternative suggestion, let me know). I’ll be able to send them out at the end of the week when I’m back home. Also, I wanted to quickly double check: Are my injectors the “Standard Top Feed Fuel Injector”? I’m pretty sure they aren’t a “Direct Fuel Injector” or GDI. Thanks again for all of your help and patience. I’m definitely still a newbie when it comes to fixing cars.[/quote]

You’re welcome. I don’t make a practice of recommending businesses, especially service businesses, since someone else’s experience can vary so dramatically from mine. However I will make an exception in this case. In the past I have used, and been extremely satisfied, with the service from WitchHunter Performance. I have never used InjectorRx, but after some brief research they seem quite legit. I would say using either would be good. InjectorRX seems to have a faster turnaround and is a few dollars less per injector than WitchHunter.

You have standard injectors. The way you can tell the difference is by where they mount. GDI (gasoline direct injection) injectors mount to a port that opens directly into the combustion chamber, whereas standard injectors mount to a port in the air stream between the intake and combustion chamber. As such, the direct injectors have a metal body, and usually a longer nozzle extending from the body, where the standard injectors have a plastic body and short nozzle inside the body.

Port injector (standard):

Direct injector (GDI):

That was a pretty good adjustment in flow. The test report doesn’t really have a place to show if they were leaking, because they don’t test for leaking before the cleaning is done. But, that would have been added as a comment AFTER the service (in the notes section) if one was still leaking. Dirt can get between the seat of the valve and keep it partially open where fuel can leak past. The cleaning service removed any dirt in them. If it was leaking before the service, it isn’t now. What I would do now is clear all codes and drive the car for a bit to see if any codes return. As for the fuel sender, it could be bad without the pump being bad, they are separate units, even though they come together to form one assembly. I do not think (yet) that your fuel pump is the problem. If the check engine light comes back on, check to see if is the same or a different code. The next test to run would be a fuel pressure test now that we know the injectors are clean and are not leaking. This test will also tell you if the fuel pump is up to par. The pressure should be 43-49 psi, and the needle should be fairly steady and not fluctuating.