I keep getting this damn check engine light and restricted performance notice every 3-4 weeks. I clean the MAF sensor and it seems to go away after a day or two...runs fine for a month and back it comes. I know its coming cause the transmission starts shifting harder.

Cannot nail this down.

 

have you pulled the codes and it says MAF????

 

No, but it keeps saying its running rich. So this is the procedure i've been doing for a year now after getting it check from the dealer and they couldnt find anything.

 

Prince Marko,

If I understand correctly you're running too rich, which means the computer tries to reduce the amount of fuel injected. Means negative trim, can you confirm?
My XJR has the odd tendency to go to -15.6% LTFT and stay there, no idea why exactly this number.
I cleaned the MAF and it returned to zero, only to creep back down I'm the next few days.
So I took a look at the car whilst it was running, I wiggled the MAF connector and it made a gulping sound, the air flow on my OBD changed from 7g/s to 5g/s and the fuel trim normalised to zero.
I think the contacts are just a bit oxidised.
Might be worth trying on yours? It seems unlikely that your MAF gets filthy every couple of weeks, or is the filter also dirty?
Do you have OBD scanner on to read the trims? Is it negative and are both banks same?

Also I'd appreciate if anyone knows the significance of -15.6%, as min never triggered a Check Engine Light, I was worried about the fuel usage 21 l/100km and hooked up OBD to read the trims.

Cheers

Lincoln

 

When its running rich, it means it has too much fuel being pumped into the system. I can smell it upon startup occasionally. I'll look at the MAF connector and did try cleaning the connections around a year ago.

So now the restricted performance is gone and the check engine light is still there, but its shifting smoothly now. It will go away and reappear in 3-4 weeks like clockwork.

I'm wondering if it has anything to do with the dirt and grime collected inside the fender where the airbox is pulling the air from. The filter does need to be changed, but in the past that didnt stop this issue from occurring.

 

What are the actual P codes that appear when the EML light comes on?

Oxidised connections on the MAF sensor plug have been known to cause this fault.

The fuel trims are also controlled by the front Upstream O2 sensors. The heaters can fail on these causing loss of sensor signal, so the ECU defaults to a basic fuelling map which uses more fuel.

 

princemarko,

I just read & replied to your other thread about the brakes on your car.

From what you say here about the engine management problems, and what you say on your other thread about the brakes on your car having poor performance, I think that both faults could be connected...

There's a thick vacuum hose on the brake servo-if this has any air leaks then it will reduce the power of the brake vacuum servo & also leak excess air into the inlet manifold, which will upset the fuel metering.

I'm repeating myself here I know, but have a look at your brake servo hose & also your brake servo itself-there may be a vacuum leak somewhere from the inlet manifold connection to the brake servo connection.

You can check the brake servo for internal vacuum leaks by disconnecting the pipe from the inlet manifold connection, cleaning it & then sucking it. After a while it should 'feel' harder to suck air out the servo if it's sealing proeprly & holding the vacuum.

 

but if it was a leak somewhere, why would the system clear all the codes and run smooth for 3-4 weeks and then re-occur? If it was a leak, it would consistently run a check engine light and restricted performance right?

 

It was just an idea-something to check if you've tried everything else. You mentioned poor braking performance as well as the engine management problem-the only thing that links these 2 systems is the vacuum supply from the inlet manifold to the brake servo.

It's also an easy & quick thing to check...

The fault could be intermittent & if the brake servo has an internal vacuum leak then it could depend on the type of brake useage.

I once did a repair to a Diesel BMW & accidentally broke a small vacuum pump sealing stub, which caused the braking performance to become much worse as the vacuum to the brake servo was reduced.

You say your brakes are performing poorly & you've got this engine management fault, so I just thought the two faults may have 1 common cause...

The standard XJR brakes are pretty good & the brakes on my XJR haul the car down from high speeds very well, so I'm wondering if your poor brake performance is caused by the brake servo not receiving the full vacuum level.

It's possible any vacuum leak could be intermittent as well-giving these variable results. More than that I can't say-apart from the fact that it's fairly easy to check so could be done just to eliminate the possibility...

 

Ok, thanks. Will get it checked out.

 

If the brake pedal feels 'hard' & 'dead' and the brake performance is bad, then that's usually a sign that the brake vacuum servo is not doing it's stuff-either because it's own internal diaphragm is worn out & leaking internally, or there's a vacuum leak in the supply pipe from the inlet manifold.

Just a thought, as you suspect the brake performance & have the engine management faults-the one thing that could cause both those faults together is the brake servo air & vacuum system from the inlet manifold...