Fuel fail 44,, will not clear. I just replaced o2 sensor, all the wires are solid, nothing broken, bulkhead and intake manifold grounds are clean and intact, engine ground strap is in place and intact. It has a newer purge valve, and coolant temp sensor. The ECU was replaced,, but not because of the FF44 issue. MAF sensor checked out OK. Fuel pressure is steady at 36 psi,, and 46 psi when the regulator is disconnected. Fuel injectors are about 2 years old,,, I'm HOPING they do not need to be replaced again. I removed the fuel rail with injectors intact and pressurized the system,,, they all hold pressure,,, except one might dribble a little fuel out,,, but i don't think that it is significant enough to create a rich fuel issue.

Is there a separate ground wire for the o2 sensor somewhere? This car has the 2 wires for the heater and one signal wire that goes to the computer.

Something that occurs that might be related; as the car is warming up, the engine will stumble/hesitate, as if it wants to shut off. This lasts for a few seconds and always works its way out and then the car runs perfectly afterwards until the next warm up cycle. When this happens i notice a little black smoke coming out of the exhaust, which i believe is a rich fuel mixture.

Thanks for any input!!!!

1991 XJ6 Base model
160,000 miles

 

Hi 92calijag,

The O2S sensor Lambda element references the same ground as the heater, which is the one attached to the intake manifold at cylinder 2. The grounds connect inside the O2S.

Are you following the diagnostic procedure on pdf pages 108-109 of the manual at the link below?

Jaguar AJ6 Engine Management System / OBDI Diagnostic Guide

Have you checked the O2S wiring for supply voltage, ground, and no shorts?

A failing coolant temperature sensor (CTS) can lead to rich running - have you checked its DC resistance when cold and hot and compared those measurements to the chart in the above manual?

The purge valve references the ground on the left inner fender - be sure that is clean.

Do you have the ability to watch your fuel pressure while driving?

Measure the resistance from the engine block to the left inner fender ground point to check the condition of the engine ground strap (I don't think that either the O2S or purge valve use that ground path, but the spark plugs do).

What is the condition of your battery?

Please keep us informed.

Cheers,

Don

 

Hi Don,
Yes Ive been using the diagnostic charts/flow charts for diagnosing this issue. All voltages and resistances have been checked utilizing a volt ohm meter, and per the procedures listed in the guides. The battery and charging system are ok. The battery is 2 yrs old and has about 13v before i power up the car and the alternator puts out about 14V. The coolant temp sensor is new. I did a resistance check on it when cold, and at normal operating temperature and based on what it ohms out to, the coolant temp is at 195F.

I wasn't able to monitor fuel pressure while driving, but at 2000 rpm its holds between 34-36 psi.

It failed smog due to a rich condition, which relates to FF44.

I appreciate your response!!

 

Just to go through the basics of what can cause rich running or cause the O2S to report rich running, off the top of my head:

Clogged air filter
MAF misreporting actual air flow
Fuel Pressure Regulator (FPR) diaphragm failure (fuel leaking through vacuum hose into intake manifold)
Throttle body constricted due to gunk buildup
Incomplete combustion due to weak spark (plugs, distributor cap/rotor, wires, coil, amplifier)
Sticking/leaking injectors (see how I cleaned mine at home in my photo albums)
Purge valve stuck open
Throttle Position Sensor (TPS) misreporting position?
EGR pipe/port under intake manifold clogged?
Problem with secondary air injection (if fitted)

The rough running at startup suggests the problem is not the O2S, since it is ignored by the ECM for something like 20-40 seconds to allow the heater to bring the O2S up to full operating temperature before the ECM goes into closed loop fuel metering.

Cheers,

Don

 

UPDATE
So I ended up having to go through each component related to the O2 sensor circuit, including running through the flow charts and checking/verifying that everything was working properly. When I got to the coolant temp sensor, the voltage was at about 7.5 volts, when it was suppose to be around 5. I ended up running a jumper wire directly between the ground wire at ECM and the negative battery terminal, which corrected the voltage to 5 volts. No more FF44 !!

 

Hi 91calijag,

Thank you for reporting back with your success!

I understand that a high voltage signal from the CTS would cause rich running, since the ECM interprets 4.05 volts or anything higher as representing coolant temperature of 14F/0C or colder. A CTS voltage of 0.55 volts represents coolant temp of 212F/100C.

So if I understand your solution, you added an additional ground for the ECM between one or more of the ECM ground pins (high power pins 11, 23 and 24), essentially bypassing the bulkhead power ground?

Any additional information you can provide will help others in the future.

Cheers,

Don

 

Hi Don,
Basically yes. After i figured out a solution, I left the original ground wire in place between the ECM and the sensor. When I did my initial checks of the ground wire circuit following the flow chart, it checked ok. So by chance, I attached an additional ground wire from the sensor itself to the negative battery terminal which lowered the voltage. Since that solved the problem, I moved the ground location from the battery to a chassis ground point closer to the sensor.

Thanks for your inputs throughout this ordeal!!