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Proper steps before emissions test after P1111 code?
I've been chasing a solution to P0171 and P0174 codes on my '02 Super V8, USA spec. I removed all of the intake and cleaned it and checked for leaks, cleaned the MAF sensor and the throttle body, replaced the fuel filter, and ran a bottle of sea foam in the gas tank. I also did a primitive home smoke test and couldn't find any leaks. I cleared the codes once after cleaning the throttle body and MAF sensor and the CEL eventually came back with the same P0174 and P0171 codes.
After replacing the fuel filter and trying the sea foam I continued to drive the car, and recently the CEL light went out. The current pending code is P1111 and stored codes are P0171 and P0174. I don't know if the fact the CEL is not lit up actually means the problems been fixed or not. I need to get the emissions checked to be able to renew the registration. Do I need to clear the codes before the test and will that likely result in P1000 replacing the P1111 code, resetting the drive cycle?
I've attached a photo of the I/M Readiness test from today. Thanks for any input. The more I've researched this issue the more confused I've gotten.
Have you driven it for about 30-40 miles above 40 mph most of it? This is the process for OBDII emission codes so the system can read and determine if the fault has been fixed.
To first answer your question, yes, if you clear the lean DTCs, P1111 will be reset to P1000. And P0171 and P0174 will not typically reset themselves, even if the Check Engine Light extinguishes. If you decide to try clearing the codes, as Highhorse mentioned there are Jaguar-specified drive cycles you can perform to help accelerate completion of the readiness monitor tests so P1111 will trigger.
Just thinking through your symptoms, since the oxygen sensor readiness monitor tests passed successfully (one of the requirements for P1111 to be achieved), the ECM must find the O2S signals plausible. The most likely explanation of the persistent P0171 and P0174 DTCs is that you have one or more leaks in the air intake and/or crankcase breather system somewhere between the MAFS and the intake manifold gaskets, or a fuel delivery issue such as clogged injectors or a failed fuel pressure regulator. Have you checked your fuel pressure with a mechanical gauge?
If your scan tool has Live Data capability, it is helpful to monitor the Short-Term Fuel Trims (STFT) with the engine warm and at idle, at 1,500 rpm, and at 2,500 rpm. This will give you an idea of how significant the leaks are and whether they are likely small vacuum leaks or large intake leaks. There are many resources online that explain fuel trim interpretation.
It is also possible your MAFS has drifted out of range. Again, if your scan tool can display Live Data, you can view the MAFS signal. A general rule of thumb is that at idle, the MAFS signal will in grams-per-second will be about equal to, or a little higher than, the engine displacement in liters. So for a 4.0 liter engine we would expect a MAFS reading of around 4 g/s or a little more. Your tool may display the MAFS signal in different units, such as pounds-per-hour, so you may have to do some conversion. As the engine speed is increased, the MAFS signal will also increase. For some Jaguar models, the Workshop Manual or Technical Manual may give a chart showing expected MAFS readings at different engine speeds, so it would be worth checking the literature for your model year and engine.
Smoke testing for intake and breather system leaks requires higher smoke pressure than the 1 psi typically used to test the EVAP system. I will typically use at least 5 psi and sometimes as much as 20 psi when testing for intake and breather leaks.
Also, you have to inject the smoke at multiple points to test for all potential leaks. I start by removing the MAFS, propping the throttle plate open, and injecting smoke into the main air intake pipe. Then I plug the air intake pipe and inject smoke at every crankcase breather hose port, the oil filler port or neck, the brake booster hose and other vacuum hoses, etc.
Many leaks can be found by visual inspection alone. If you can see oil leaking from the cam cover gaskets, spark plug tube seals, oil filler cap gasket, VVT solenoid gaskets (on engines so equipped), crankcase breather hose O-rings, etc., or fuel leaking from injector O-rings, these are leaks that can lead to lean running. If oil or fuel can get out, unmetered air will get in under engine vacuum.
I see you have a Cen-Tech OBD reader; it has a live data mode that you can use. Check the STFT (short term fuel trim) and LTFT (long term fuel trim) boxes and see what the numbers come up as. They should be close to 0.0 but will generally be a bit above that. If the numbers are in the 10-20 ranges you definitely have a vacuum leak somewhere. These cars are notorious for leaking vacuum somewhere. Besides all the little plastic hoses, make sure you have a tight O-ring on the oil stick and the oil cap ring is intact. ( I finally replaced the cap on one of my cars and it significantly reduced the trims after trying everything else.) Also, those little vacuum hoses have o-rings on the ends. You might try getting a box of metric o-rings at the auto store and replace them all. It take a bit of patience!
Thanks very much to everyone for your input. The good news is that I chose not to reset anything and took the car for the emissions test and it passed.
After the test, I did check some live data info with the engine fully warmed up as I would like to understand what issues i might still have. I got the following readings:
So I think those readings would indicate I have a vacuum leak somewhere. When I was trying to diagnose the issue weeks ago, I did do some visual inspections for oil leaks and tried to find any vacuum leaks. I couldn't see or hear anything, but I didn't check the spark plug wells or remove the supercharger to get more access. I bought a replacement part load breather hose to install as a possible solution, but haven't installed it yet. The car doesn't drip oil that I can see. I recall checking the gas cap and dip stick. I don't recall checking the oil filler cap. I remember seeing a little oil discharge at the filler cap in the past, but not in a while. I will check the oil cap again and might take the car to a local specialist I use for a proper smoke test.
Those LTFTs at idle are quite large but below the threshold for flagging codes.
That could mean that your car would fail UK test (done via tailpipe) but if you're in USA and no tailpipe test then probably will pass smog and you can fix the issue after.
07-20-2024, 06:16 PM
Proper steps before emissions test after P1111 code?
