What should the mass air flow grams per second be for the RPM ranges? Is there a chart handy?

 

I guessed maybe you were asking about a mercury outboard ?
So I looked at your profile, as you have not been specific. It says 2011 xj .
which is still far from specific .and puts you in the in correct forum .
Though these figures will be identical to S-types regardless .
The 4.2 v8 supercharged is supposed to be between 5.2 and 6 g/S at idle /650rpm.
i have no idea about the diesel or v6 variant . I assume the 4.2 na would not differ by much if any .

 

Thanks Andy..

I was searching the workshop manual but didn't have the engine size to reference. Thanks for taking the time to go to the OP's profile to try and help. I hope Gary can take less time than you have trying to help to go to his profile page and lets us know what we are dealing with?

JMHO

 

Sorry. It's a 4.2 N/A xf. Idle was good but I wasn't sure what the mass air flow reading should be during 2500 RPM. 3500 RPM. I keep getting the pesky PO171 and PO174 codes. Changed intake gaskets upper and lower. Smoke tested it twice after and no leaks like before. Changed mass air flow sensor. My long-term fuel trims are reading 8 and 12 sometimes. I'm leaning towards a crankcase vent valve in which case I've ordered a Land Rover one or possibly oxygen sensors. Unless the Delphi mass air flow sensor isn't correctly reading which is what I'm after.

 

Hello Gary and thanks for the added details. I was searching through the S Type repair manual to find an answer to the MAF flow chart question. You mentioned you have an XF? I'm not sure if anyone on this subforum have downloaded that to help you?

 

I assume that the 4.2 in the XF is the same as the 4.2 in the other models. That was my thinking anyhow

 

Ok . It should be as close to 5gs as poss at 650rpm ,
that’s the rule I read , any higher and it’s getting richer .
the MAF’s are designed to richen as the fail not lean . As a safe guard !

my question would be did you buy genuine replacement MAF .
or are you trying your luck on a generic reproduction one ?
as we all know were that will lead you .

you should monitor your fuel pressure via OBD2 and don’t rule out a fuel filter replacement also .
also check the 02 sensors are functioning correctly I.e voltage via obd2 .
Just remember its not always an air leak just because the code says lean .

 

The freeze frame data will show what else is happening when the code flags.

 

I bought the mass airflow on Amazon. It was a brand new Delphi which is a very respectable company. It's Logging right around 5 g/s at idle.

Fuel filter was changed by the dealer 12,000 miles ago along with the fuel pumps.

Oxygen sensors are another thing that I bought. Ended up getting all four denso's. Probably just going to change them as they have 176,000 on them as a precaution.

 

Amen brother! Preach it! Glory be! Can I get another amen!

As mentioned, you could also be looking at tired O2 sensors. So many fueling decisions are based on what these sensors are reporting. However, we mere mortals have little way of knowing how accurate these readings are. Unless you've got a freshly calibrated tailpipe sniffer at your disposal, the O2 sensors could be quite inaccurate and you'd never know.

From what I understand, the values have to be way out of range before a corresponding sensor code is generated. I consider O2 sensors to be normal wear and tear parts, like spark plugs. I'm not suggesting to just throw these expensive parts at the car (Pull!) in hopes of a fix, but do keep them in mind if nothing else helps.

Re: The smoke test. While very handy for troubleshooting, make sure you're aware of the limitations. No apparent leaks is not always conclusive. The network of vacuum lines will have check valves and electrically operated solenoids. You're sending smoke in the opposite direction of normal vacuum flow, so the lines beyond any check valve will not be tested. Same with any solenoids that are normally closed with the engine off. For a valid smoke test that covers everything, you have to be aware of these check valves and solenoids and bypass them as needed. I do not care to discuss how I learned this...

 

I hope you don't mid if I add this to my sig?

 

You'll know if you look at the fuel trims!!

If the O2s are out then so will be the trims!

Now, if the trims are out you don't instantly know if the O2s are to blame (though there are multiple of them so think!) or (say) the MAF (only one so again, think!).

 

I'm not following your line of reasoning at all. Reading between the lines, it's almost like you're implying I'm less correct than usual. There MUST be some other explanation, at that makes no sense at all...

Actually, I totally agree with you. I had just wanted to point out that O2 sensors can drift out of calibration without necessarily setting a sensor-specific code. Both here and in other forums, I've seen one camp that treats an O2 sensor as infallible, and it can never be wrong. You're not even allowed to entertain the thought. Then I've seen others that blame the O2 sensor for any and all faults, and change 'em out at the first hint of trouble. I think the truth is somewhere in the middle.

I take it this is something of a philosophical thread by now, but certainly don't mean to hijack it. What would happen to the long term fuel trims on a high mileage engine, with normal wear and tear? Let's say compression is down evenly, just enough to reduce performance a little but not be overly noticeable. And for the sake of argument, the O2 sensors are brand new and confirmed accurate with a freshly calibrated tailpipe sniffer. The guy running the test was wearing a lab coat and holding a clipboard, so you know he's good. With reduced compression, would the computer increase the fuel flow to try to compensate? Is long term fuel trim compared to fuel scheduling on a new engine? Maybe I'm a little confused about the terminology. Mostly I'm just curious what happens with long term fuel trim as an engine slowly ages.

 

They definitely can and do drift / misread. It then shows in the fuel trims.

You'd expect an O2 to do that with old age (though misfires won't help) so you'd not expect 2 or more to do it at the same time. That is one reason why it's a good idea to keep an eye on the trims (say annually or every 6 months) as you can see something's going wrong before it gets serious enough to damage a cat or flag a code.

I mention the cat(s) because if you think about a misreading O2 the PCM is tweaking the fuel to what is in this case the wrong amount (i.e. to what the O2 is saying).

 

I can confirm that the 197-6030 oxygen sensor does not read correctly in our vehicles. Double digit lean FTs.