Dear all - hope someone can help me out.

I have an X300 4.0NA which runs pretty well, I have replaced a whole lot of sensors and cleaned the MAF, put in new Coils and plugs. I have a number of OBDII readers and all are telling me that the LTFT on banks 1 & 2 are at +52.2% while STFT hovers between about -10 and +5%. I have got the LTFT's down as far as +47.7% with a second MAF I have but nothing will budge it any lower.

As both sides are exactly the same readings (Even when replacing the MAF) then I am assuming that it has to be a single sensor like the MAF, or the FPR or fuel pump? My rationale is that if I have injectors that are not giving enough fuel on duty cyle it is highly unlikley that these values would be the same accross banks 1 & 2. Using similar logic, I doubt that a both O2's could be out by excatly the same amount. Could this be a issue with fuel pressure - either the filter being blocked (I did change it not long ago?) or the pump not providing enought pressure to the FPR or the FPR being out ? Is there a way to check these ? I understand that there is no easy way to check fuel pressure at the rail on the X300? Any advice appreciated thanls Matt

 

There are 2 different MAF sensors for the AJ16 engine , one for the supercharged version and one for the normally aspirated

The normally aspirated is a labelled Lucas # I will have to look at mine in the morning

Search Genuine Air Delivery System Components Parts For Jaguar Xj 1995 - 1997 (from 720125 To 812255) Classic | Jaguar Land Rover Classic Parts

The MAF sensor output to the ECU at the proper idle speed should be 1.2 volts DC on the X color wire

See page X

There are intake vacuum leaks and exhaust manifold leaks that can effect your target STFT of 0.0 , but not being perfect , + or - 3.0 is OK through all of your throttle / load range.

See page Y

Editing

 

Hi Parker thanks for the reply - are you suspecting the MAF ? I have 2 from non Supercharged 4.0 AJ16's one is the original one for the car and another from a wreck.

Ill check both for their voltage

When you say page X and Y what doc are you referring to please?

Matt

 

WiFi going in and out so let me try

 

www.jagrepair.com/images/Training Guides/801S - 2000.pdf

 

Checked my MAf 1.26v at idle so ever so slightly high but not enogh to have LTFT over 50%?
Am I reading the LTFT incorrectly maybe ?

Matt

 

Your late 94.5 will be the same as the 96 with a more complete wiring guide

See page 60 for the MAF connector Green / Pink wire , the connector needs to be stayed installed to power the MAF

jagrepair.com/images/AutoRepairPhotos/jagxj1996.pdf

 

The vacuum lines are on page 60 of the 801S doc

There are 2 systems , a single vapor canister and a dual

if you have the single you will have the one vapor canister on the left fwd of the rear wheel and the dual has one on each side

 

!.2 is good enough and / but this only looks at the idle range but it proves the MAF is alive

I''m not so use to looking at the Long Term Fuel Trim

 

Other then vacumm leaks a cracked manifold or a worn or loose donut gasket on the joint between the manifold and the down pipes can cause problems and someone simply found the stud nuts loose

There is a trick to one of the 4 studs and best gotten to from the bottom with a 15 mm

 

And then there is some simple things to clean up the O2 sensor connections and there is a cheaper Bosch equivalent sensor if to that point

The engine coolant temp sensor may not be seeing above 88 degree C on your reader and this would keep your engine regulation from being in a full closed loop looking at your O2 sensors

The EGR valve and EVAP valve should be closed at idle and the smog pump should only run for 60 seconds with a check valve involved

The EGR has a error signal on your reader and the EVAP is an easy 9 volt battery test for closure

 

I had the same [apparent] problem with my X300/XJR. I was never able to fix it; drove the car that way for years. I inserted "apparent" because I came to believe that the LTFT readings were an anomaly of Jaguar's less-than-stellar early efforts with OBDII. At the time (years ago) a couple Jag techs here agreed that my notion had some merit.

You say the car runs "pretty well". What problems are you having?

Personally, I would suggest going after the symptom rather than chasing the LTFT reading.....although, depending on the nature of the problem, there may not be much difference in either approach. But, if you get the engine running well, don't fret over LTFT readings.

Just my two cents, and I know not particularly helpful. I'm not disparaging other advice being given.

Cheers
DD

 

The sensors on the engine are usually powered by a reference 5.0 volts from the ECU but 1/2 of the sensors are powered by the ECU control Relay ( 12 volts) which includes the MAF

the pic is for the SC engine but yours is the same with only 1 fuel pump

The large relay right # 5 can be swapped with the same part # relay for a headlight or A / C

This on the basis that the relay is closing but has burnt power contacts inside limiting the current to properly run your MAF , fuel injectors , and ECU

You can probably still see 12 volts on the output of the relay and this relay is the 2nd power to the ECU used at all times

Now would be to clean the ground studs in the engine compartment including the large ground strap on the starter mount bolt and the dedicated ground strap for the case ground on the ECU

 

Doug thanks for your input. I am also beginning to suspect either my obd2 reader or the data flow. We know that the X300 MAF reading is out and needs the decimel point moved. Maybe 52% is 5.2%. I was of the opinion that if combined stft and ltft exceeded 25% the mill would come on with associated codes. I have no codes at all and no mil light. I think I’ll change the FPR anyway as the one I have is original . Cheers from AUS

 

The ELM - 327 technology is patented to a company in Canada and is pirated by Chinees manufactures of their devices

You would expect that they would have proofed their software before putting the product out but ...............

The display range of the STFT is + or - 25.2 % but then that would depend on who monkied with the master software that was stolen

The only error that I'm aware of is a disciple movement on the mass air flow rate as a grams / second unit which should be a hair above 4.0

Your 1.26 volts as a meter reading is close enough on the retrn signal to the ECU to compute and this depends on the correct idle speed

 

The LTFT for the 1995 OBD2 cars are historically inaccurate. If you search around you’ll find many posts about owners that have the LTFT stuck on 99!

For some reason the 96 cars don’t have the same problem.

 

Have the O2 sensors been eliminated from consideration? When they fail, te ECU seems to default to running rich. Car runs like a charm, but has a particular thirst. What sort of mpg are no managing?

 

What sort of mpg are you managing?

Yea what he said but if your fuel trim reading of 5.2 ( being a decimal off ) is not too far off and may be acceptable even though the target is 0.0 with 3.0 being common from reading others

You already have a pretty much agreement on the MAF voltage out of 1.26 but this variable is not a direct measurement of fuel efficiently but is used in its regulation to get you there

O2 sensor connector and grounds clean ?

You can easily check that the heating elements in the O2 sensors are intact and there is only one relay for all sensors heat before they will function properly