When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Today I’m going to simplify, stoichiometry, fuel trims, OBD codes P0171, P0174. So put down the credit card grab a tube of gasket maker. Newer cars run on a closed emission system and if the system is not closed you may experience knocks, pings, compromised MPG, transmission problems, engine lights, etc., grab a tube of Permatex High-Temp Red RTV Silicone Gasket Maker. If that doesn’t work change the mass airflow sensor first, in some cases it can give a false P0171 and P0174, you will get different codes for your O2 sensor etc.
Between the gaskets getting older and the plastic fatigue little gaps are letting in air and causing your fuel trims to run rich. Grab a tube of gasket maker and take a couple of hours on a Saturday, you’ll be glad you did. P.S. I am not selling anything except knowledge.
Bad MAF is fairly uncommon but usually causes RICH codes (P0172 & P0175).
Rather than a dubious RTV fix I recommend finding the leak and doing a proper fix. (Watch fuel trims, spray some burnable stuff like propane or carb cleaner - see the many threads where people have done this and as I say done a proper fix.)
Those are some very creative modifications you have come up with, and quite a bit of work! You photos and captions are very nicely done as well.
However, I do have to question some of your assertions.
Jaguar's definitions of Diagnostic Trouble Codes often do not always mirror the generic definitions you will find on the Internet or in generic OBDII manuals. You don't mention the year and model of your Jaguar, but you can download the 2004 X350 DTC Summaries manual here:
At the bottom of this post I am attaching the Technical Data Sheet for Permatex Red RTV Silicone, which specifically states that it is not recommended for use on plastics or painted surfaces. Also of concern is that the TDS does not state that Red RTV is suitable for use in air intakes or that it is safe for O2 sensors. Some silicones will foul the sensors, turning a "cheap" fix into an expensive problem. Based on the information provided by Permatex, Red RTV does not appear to be a suitable product for use in sealing air intake components.
Another area of concern is that the typical maximum operating temperature for PEX (cross-linked polyethylene) is 180F/82C (marked right on the hose). The absolute maximum rating is 210F/99C, according to the document at the link below. Sitting on the top of your engine, that hose will continuously experience temperatures in that range and higher, so you may not be able to expect the hose to last indefinitely.
I am aware of a couple of X350 owners who have replaced their MAFS, but not because they had actually diagnosed a MAFS fault. It's certainly a good idea to clean the MAFS periodically with an appropriate product (I do it at air filter changes), but as JagV8 mentioned, MAFS failures seem to be rare on these cars, and would be one of the last things I would suspect to trigger the P0171 and P0174 codes. Note how far down the list the MAFS is in the Jaguar diagnostic recommendations in the right column of the charts above.
In my experience, maybe 8 times out of 10, the P0171 and P0174 codes are triggered by an air leak in the intake plumbing between the MAFS and the intake manifold gasket, and following the procedure JagV8 outlined is the fastest way to suss it out if you can't find it by visual inspection. Given that the parts are available from Jaguar and most of them are not expensive if you shop around, I have to agree with JagV8 that the best approach is to diagnose the actual problem and either properly refit the loose parts or replace the faulty part.
But I have to applaud your creativity and ingenuity.
The first picture shows the round fixture attached to the crankcase breather. What is the name of and purpose of this part? I have a lot of air noise coming from that area and I'm not sure if it's supposed to be loud. I do not have any codes or idle issues though.
The first picture shows the round fixture attached to the crankcase breather. What is the name of and purpose of this part? I have a lot of air noise coming from that area and I'm not sure if it's supposed to be loud. I do not have any codes or idle issues though.
Hi Torrid,
That round flat part is the "crankcase vent valve." The original part number is AJ83695 and the latest superseded number is AJ87773. It's not a PCV valve since there is no valve inside. I think it's more of an oil separator.
Since it's part of the crankcase breathing system, it does pass crankcase gasses, but it's not loud on our car, so you may want to check for any leaks or issues with the valve or its connections to the cam cover or breather pipe.
That round flat part is the PCV valve, or in Jaguar terminology, the "crankcase vent valve." The original part number is AJ83695 and the latest superseded number is AJ87773.
Since it's part of the crankcase breathing system, it does pass crankcase gasses, but it's not loud on our car, so you may want to check for any leaks or issues with the valve or its connections to the cam cover or breather pipe.
Cheers,
Don
I don't feel any air around it. It sounds loud and mechanical getting near it. It makes me wonder if it somewhat amplifies the sound of the cam/lifter assembly.
Edit - I just looked into this further. It looks like if it was actually leaking I'd have pretty bad idle issues and that due to the design it has a fairly turbulent design that does cause some air sound that could be mistaken for a leak. Seems it's normal.
You are correct about the plastic tube. I live where it is usually cool to cold (Pittsburgh PA) and don't drive very often I have had any issue with the plastic, also I think that is the first time I have placed a tube over the engine. I will go back to copper to make sure there is no issues. I lurked around the forum for the past few weeks and was steered in the wrong direction way to many times trying to get my 2005 XJ8L to pass emissions test but the advise I received (or read) was misleading but this simple fix was cost-effective and got me through inspection. I appreciate your fantastic follow-up and I am an artist and don't think like everyone else. I am one to make a repair once for the life of the car and don't like to breakdown. but the plastic pipe is going to ripped out tomorrow morning. Great input.
09-13-2015, 10:43 PM
123 fix, P0171, P0174 all modern Jaguars.
