MAF sensor and O2 sensor bad?

CaliLee · Mar 4, 2021

Not sure if this is the same thing here but I just had to do one MAS and the purge valve.

My wife had the engine light come on one evening and we dropped it off at the Indy we use. They called me and said the fuel trim was way off between sides and they would need to figure out why. Called me back the next morning and said it was one MAF and the purge valve, we had them replaced.

That was in January and we’ve had no issues since then. Looking back over the last year we’ve had them look at it for a weird shudder at low speed on steep hills. They weren’t able to reproduce it at the time though.

I’ll have to go see if I can reproduce it now.

Michael Gain · Mar 9, 2021

Quick update. In tank fuel pump and filter install went well and may have solved the problem (knock on wood). I finished the work on Saturday and did a short drive to the gas station on Sunday. LTFTs were high (~10%), but STFTs we low (~ -4.5%). O2 sensors read well. However, coolant temp sensor #2 read 11C while #1 read 47C.

I am attributing the mismatched coolant readings to not being warmed up. I am reasonably sure that the #2 coolant sensor would heat up once the thermostat opens.

Anyway. Monday's drive to work showed a little bogging when coming to red lights, but, driving home, it was not present. Likewise, on this morning's drive, there was no idle bogging.

I cannot rule out environmental factors though. It's been warmer the last few days... I'm going to keep an eye on it this week and report back.

jlglr4 · Mar 9, 2021

I believe one coolant sensor (located in the lower radiator hose) is measuring coolant coming out of the radiator before it goes through the t-stat, and the other is measuring the hot coolant leaving the engine. So, I would expect a big difference in temps. I seem to recall seeing about 80F on one and 120F on the other at some point (summer). Your seeing an even bigger difference, but not sure how long you were driving, weather, etc.

Somewhere (manual?) I read that one coolant temp sensor is used to make sure the other is working. Not sure how that whole system works when you’re measuring the hot/cool side of the system, but I suppose there’s a way to do it.

PoppyAnn · Mar 14, 2021

Michael Gain said:
I had a little time this morning before work and thought I would troubleshoot an annoying idle issue (bogs slightly when coming to a stop, and occasionally will vibrate the steering wheel when parked).

Using my handy iid tool to log live values, this what I see:

View attachment 12547

I can lack common sense sometimes, but I see the driver side maf is under reporting and the engine is adding even more fuel (stft) to its learned value (LTFT). Does everyone concur that driver side maf needs replaced (it's already been cleaned a couple of times since ownership.

Also, I am confused by the o2 sensor readings. These are the o2 sensors after the exhaust manifold o2 sensors, but before the cats. One is super positive and one is super negative. What is this telling me?

Thank you as always for your wisdom and guidance!

Hi there,
Before you start buying expensive parts try swapping your 2 MAF sensors over and take a look at the readings did the readings swap over as well if they did you then know that one is faulty if you can afford it replace both that way you will know that the one you thought was good was not faulty for me when there are two of the same sensors on a engine I always change both together just like when you change a tyre I always change both that are on the same axle as this is the only thing that you have to depend on for your life.
Good luck in finding the cause of your problem.

Regards Poppy Ann.

PoppyAnn · Mar 14, 2021

Michael Gain said:
With consolidated airflow, I am with you. No way that each bank's measured air molecules makes it into that bank's cylinders, through one throttle body, and churned up by the supercharger. But, I wouldn't be surprised if a land rover engineer thought it was a good idea...

Ignore the rpm at the top. It never changed... at a stop light, I actually logged rpm as well. Must have been a glitch.

Thank you for the comparison offer. I think the low reading MAF is at fault, but I will replace them both. I also have all the parts necessary to replace the exhaust manifold gaskets. I am not sure of a leak there would cause a rich or lean reading at the o2 sensor though.

I already smoke tested the engine once, but will do it again to rule out a vacuum leak.

Michael Gain · Mar 14, 2021

Still experiencing some bogging at idle, and some vibration at part throttle. So, I decided to pull the spark plugs; verify their condition, gap, and install torque; and check for vacuum leaks again.

Spark plugs looked good, but the gap was a little too close. I adjusted and torqued them to spec upon reinstall. More to follow.

Baby was napping so smoke test (air compressor) was not used. The purge valve is closed as it should be when not energized. The rest of the lines were tight and sealed.

However, the line going into the back of the intake manifold is loose. It connects fine, but slides easily on its post. I am thinking that it's internal o-ring is shot. On a side note, the check valve seems to work. It's open under manifold vacuum and closed under boost.

I typed its printed code into Google to no-avail. So, I sent a not to the parts website I normally use.

While I wait for the parts place to get back to me, does anyone know if the internal o-ring can be replaced without replacing the hose?

jlglr4 · Mar 14, 2021

Sorry to hear the fuel pump didn’t fix your issue. That line on the back of the manifold is loose on my car as well. Connects fine, but slides in and out a bit, and I’ve been a little suspicious of it, but I did wiggle it around while watching fuel trims and it made no difference. So, I haven’t done any more with it (and don’t know the answer to your question). Just wanted to let you know that mine is the same.

Michael Gain · Mar 14, 2021

jlglr4 said:
Sorry to hear the fuel pump didn’t fix your issue. That line on the back of the manifold is loose on my car as well. Connects fine, but slides in and out a bit, and I’ve been a little suspicious of it, but I did wiggle it around while watching fuel trims and it made no difference. So, I haven’t done any more with it (and don’t know the answer to your question). Just wanted to let you know that mine is the same.

Thank you for the sanity check! The only other weird thing I saw today was the passenger side MAF connector. It doesn't look corroded, but definitely like it could use a cleaning. I couldn't figure out how to release the terminals though. More fun for me tomorrow I guess lol

jlglr4 · Mar 14, 2021

Just read back through the forum - you mentioned before that your actual fuel rail pressure is lower than commanded. Is that still true now after the LP fuel pump install? Wondering how much lower, and whether you’ve considered the HP fuel pumps as a potential problem.

Michael Gain · Mar 14, 2021

jlglr4 said:
Just read back through the forum - you mentioned before that your actual fuel rail pressure is lower than commanded. Is that still true now after the LP fuel pump install? Wondering how much lower, and whether you’ve considered the HP fuel pumps as a potential problem.

I believe that it is still low, but I did not take a screen shot when I measured it... It's a great point though and I will grab some data tomorrow.

I do have another theory. The air intake sensor is on the back of the intake manifold, right next to the vacuum line that I just removed. I am not sure if the timing correlates, but I did use some of the CRC "intake valve and turbo cleaner" through that vacuum line. Maybe, the cleaner fouled the temp sensor? Some of the symptoms would make sense.

I plan on pulling the sensor tomorrow and spraying it down with MAF cleaner. I may replace the o-ring as well depending on condition.

MAF sensor and O2 sensor bad?

CaliLee

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