Hello Everyone,
could someone please help me with the normal ranges I should see for the O2 sensors and MAF?

The bank 1 lean issue I have been having is now leading me towards looking at the live data and understanding what reading is normal and abnormal (replacement needed) For these two items. My short term fuel trim is -1.5% and all leaks, injectors, tubing, MAF cleaning, connector cleaning, and air filter has been throughly checked. Only line vacumn, compression, and intake main gaskets have yet to be gone through with these two sensors for acceptable readings.

Thank you

Mat

 

What is your long term fuel trim? More importantly, are you seeing any differences between left and right bank figures?
Also, year, model, and engine size would help.

 

I looked through the posts under your name and found several threads, each with a different name for a differnt line of troubleshooting
i would highly recommend starting your own thread with your problem ( don't piggyback onto another thread since it may get skippead over due to the thread title). Put all your previous psts into that thread so that the fine members here can get the whole story.
You will get much better support that way, trust me.
I will be glad to post OBD numbers from my car if it will help.

 

Matt:
The STFT numbers are way less important than the LTFT trims. The STFT will bounce between +-3-5% as you disturb the "system" with things like throttle opening and closing and load changes. The STFT is integrated to produce the LTFT. The o2 sensors should bounce betwen high and low at least every few seconds. Bouncing is good! AJ 26 and AJ 27 engines have different upstream sensors and the AJ27s are more linear and do not bounce so much- So, be sure to baseline against the same system. The MAF should, of course, vary with throttle opening. There are SOME readers that do not read SOME jaguars with the correct range for MAF, so it is probably better to observe the feedback lead with a DMM

 

When I have had lean codes, the long term trim is up around 20%, which is the limit of fuel trim usually. Basically the O2 sensor readings are used by the ECU to try and correct for another problem, like a bad MAF, or vacuum leak,etc.

 

I have attached the diagnostics from my 3130 Innova: Really stumped on how to read this data.

Mat

 

Mat:
Your fuel trims are extremely high positive (LTFT and STFT). That means the system is detecting a lean condition that requires adding lots of fuel to compensate. That is either because the sensors are reading too little oxygen, when,in fact there is enough, or that the engine is running lean. You need to loofor a large air leak in the intake plenum, the part load or full load breathers. The other possibility is a bad MAF, which is detecting too low airflow and the fuel map is cutting the fuel back. The 4.17 gms/sec is a little low from my baseline numbers airflow, but as I said, some scanners read low values from Jaguar system.
The test not complete indicates a reset of the OBD codes. What codes sere there before you reset them?

 

Spaerkenzap is correct. I have had this on two cars, both times the fix was to clean the MAF with contact cleaner spray. The airflow went up in both cases, and the fuel trims went back to normal.

What engine do you have?

 

My car today, a 98 XJ8 with a 4.0 litre unsupercharged, with the airconditioning off, gave these numbers:
644 rpm
21.2% load
5.46 g/s air flow
4.5 degrees timing advance
short term bank 1 = 0.8%
long term bank 1= -7.0 %
shot term bank 2= 0.0%
long term bank 2= -3.9%

The O2 sensors upstream of the cats switched between 0.8 volts and 0.1 volts (normal)
downstream they both read around 0.12 volts.

I'd say you have an overall lean condition, not just one bank.

 

You really should add your car year and model to your signature so others know what car you are talking about.

Attached is a graphic with nominal MAF sensor flow readings for what I think is your engine. Just be sure to take the 'in drive' readings in an open area like a parking lot, and hold the brake very firmly.

Cheers,

 

Hello Gentlemen,
I continuously see a lean P0171 after driving for about 15-20 minutes. The Bank 2 Lean code P0174 shows up rarely. During the drive the Bank 1 code resets to off and then shortly back on again.

When I listen to the top of the engine I hear air movement in the top center area of the engine possibly the Intake Manifold (Black). I can't see or feel any crack or opening. I was thinking of asking a garage to perform a smoke test on the engine this week. I think I could remove the top intake manifold but would ask for guidance from anyone that has already performed this tasks. Would I need to take apart the fuel injector rail and injectors for the 4th time this month to remove the Intake and are there gaskets to replace?

I have cleaned the MAF three times already and carefully checked all connections when I reassembled them. Do the readings for the MAF look fine? I tapped the MAF for malfunction indicators due to vibration or problems in the electronics with no result in engine behavior.

Thank you

<<<Mathew>>>

My wife has lost all confidence in the car when after I fix one anomaly that another appears or has always been present.

 

Mathew:
Do I remember correctly that you have had the fuel injectors out to test? If that is right, I suggest you take the manifold off, and the fuel injector assemblies and check for a pinched o-ring or gasket. It will go much quicker the second time you do it and cost much less than the garage will charge. And it will probably lead you to the problem. Another method to find a \leak is to watch the stft numbers while "spraying" the gas from an UNLIT propane torch around the intake plenum. When the engine begins sucking propane instead of air, the trim numbers will take a dive down. The O2 sensor voltage will rise.

 

Response:
Just to confirm that my readings shown below are the same readings you are comparing with your own shown in this earlier post:
Short Term Fuel Trim-Bank 1 % 25.00
Long Term Fuel Trim-Bank 1 % 19.53
Short Term Fuel Trim-Bank 2 % 25.00
Long Term Fuel Trim-Bank 2 % 19.53

How do I tell from the scanner about when the O2 sensors switched states?

Thank you

<<<Mathew>>>

 

I will modify my signature to have the vehicle's specifications.

1999 VDP XJ8 non-aspirated 4.0

 

Mathew:
I assume your scanner has a live data mode. Yhe lambdas should switch between lo and high in a second or two or less at idle. Low is below ,2 volts and high is generally above .8 volts.

 

Response from Mathew:
Yes, it is the Innova 3130 and the scanner can replay live data. I believe those data points are in this section shown below:
Bank 1 - Sensor 2 V 0.03
Bank 1 - Sensor 2 % -1.56
Bank 2 - Sensor 2 V 0.04
Bank 2 - Sensor 2 % -1.56

 

So your sensors are stuck on lean (low voltage) That is either because the engine is running lean due to exra air, running lean due to the MAF indicating low air flow and calling for too little fuel, or bad sensors saying it is low when you are (by now, due to the trims) running VERY rich. Does the exhaust gag you and smell like gasoline? If not, you are probably actually running very lean and the ECU cannot get enough trim to correct. Make sense?

 

Response from Mathew:
No smell from exhaust at any time and engine always starts and never stalls. I just have this "stumbling" idle where you can see that the engine shakes intermittently ever so slightly.

Would you rule out the two sensors and lean more toward a vacuum leak?

I have had to many trial by replacement repairs in the past and looking for mentoring as to what looks fine by the data. I have attached the O2 test data which I believe shows the switching ranges.

Thank you, Sir

<<<Mathew>>>

 

My understanding of these codes is that the engine is running lean (for whatever reason), and the o2 sensors pick that up. The ECU tries to "trim" the fuel, adding up to 20 or 25% more fuel, depending on the car. If it is still running lean, then it trips the codes, since there is an obvious problem.

 

I agree- You are almost certainly running lean due to a vacuum leak, although I would not yet rule out thw MAF. Try using propane to find it.