Hi all,

I bought a 1998 XJ (x308) Executive, V8 3.2l. Can't get past through MOT due to very high CO emissions (15-20 times more than allowed).

The seller said the car was in a garage for about a year, not being ridden. I can clearly see that the fuel is too rich. There's quite a lot of white smoke coming out of the exhaust, I can also smell the petrol from the smoke. I've put some fuel additives which are supposed to reduce CO emissions but it didn't reduce the amount of white smoke coming out.

The engine is a bit rough at idling, however no problems when driving it, the acceleration power seems accurate. The fuel consumption is extremely high, I've ridden about 50 miles and that used up about 30 liters of fuel.

I was quite sure this must be the oxygen sensors failing. Took it to the Jaguar dealer for a quick check - they did not find anything and also said that the oxygen sensors are working fine (I still don't believe them). With the computer plugged in, they saw the same diagnostic trouble codes as I did with my ELM327 plugged in. The codes are:

P0102 (Mass or Volume Air Flow Circuit Low Input)
P0112 (Intake Air Temperature Sensor 1 Circuit Low)

At the other service they checked the engine compression and said it was OK. However they have no idea what could be the problem either.

Does it make sense to:

1) Replace the spark plugs to original ones?
2) Replace the Mass Air Flow sensor?
3) Replace oxygen sensors?
4) Replace catalytic converters?

What else could the problem be? A total mystery!

 

Welcome jagggernaut, please introduce yourself in the New Members section under General Jaguar Forums, (site rules) and review everything there.

As for your issue, try unplugging the MAF first. It should go into default and give you a code. By going into default it should give you the opportunity to see if the smoke persists and either claim it as the culprit or eliminate it as such. I'm surprised the dealer did not do this if they hadn't.
I would at minimum check the plugs, smell them and be sure of proper gapping and look for a nice grayish white ash on them. If the motor is running as rich as you say, those plugs should have a dark or blackish ash on them. Be sure to annotate the color of each plug cylinder.

For codes, put Jaguar in front of any of your P**** codes searches, especially P1***, to garner more specific per vehicle info. if available. The P1*** show maker specific issues, but even the basic P**** codes can have specificities.

 

Sounds like a bad connection at the maf, if I remember correctly those were the codes mine threw when I turned it on with the maf unplugged. Does your scanner show live data, and if so do the air flow and iat readings make sense? They probably won't with those codes pending. Also are there any other codes? How do the stft and ltft look?

 

That certainly sounds like the MAF to me. Same thing happened with one of my BMW's. Constant white smoke, smell of fuel in the exhaust, stumbling idle, and high fuel consumption. Tried everything to get it through emissions. Borrowed a MAF and it passed with flying colors. As stated above, check your wiring as well. My obd2 scanner will do live data and give the MAF's output signal. I would verify that value changes with RPM consistently, or at all.

 

+1 on the live data check.
And enclosed are some data of the MAF reading.
They are for a 4L, but your 3.2 should not be too much off those values.
I added a screenshot for which gauge you are looking for.

 

It's cold here - is it just condensation (often called steam)?

You have codes so test/clean/replace the items. Generally avoid changing other parts in hope - gets costly, tends not to be a fix.

 

Thank you all for suggestions. I've sat down for another OBD test and this is what I've found:

MAF airflow rate values seem to be normal and they do change with RPM. However, I've noticed that sometimes signal disappears for 15-30 seconds and then appears again. Not sure if the MAF is failing or the OBD scanner is not stable? The values are jumping quite a bit (see attaced screenshot on the bottom).

Intake air temperature was 8 degrees at idling, after some revving it became 50C - is that normal?

Short term fuel % trim (banks 1 and 2): 19.53%
Long term fuel % trim (banks 1 and 2): 14.84%

Oxygen sensors 1 present: no data (I assume my ECU does not support O2 sensors? Why does it say that only 1 is present?)

After clearing the codes, this one is still persisting:

P1797 (CAN TCM/ECM Circuit Malfunction)

It also says GEARBOX FAULT below the speedometer. Could this be related or is this a completely different issue? The gearbox seems to be working fine.

Going to wash the MAF sensorand try unplugging it to see if there's any difference. Also I've ordered a set of new original spark plugs.

P. S. I've asked what were the results of the compression test and was told that all cylinders had value around 12 so looks like there is no mechanical fault in the engine.

That's what I initially thought before MOT, I hoped just to warm up the engine, do some revving and the smoke would disappear, however that's not the case since the CO emissions are very high.

 

Your fuel trims are high positive, indicating a major air leak. If they were negative that would be rich. It may be that the ecu is dumping in excessive fuel to overcome the air leak, resulting in poor combustion.

I don't have any experience with intake air temp, but I don't thin it should jump to 50C.

 

They should both be pretty stable, it's all digital comms so a weak connection at the scan tool shouldn't cause only certain values to disappear if I remember correctly.

While monitoring, you can try tapping on the MAF and wiggling the connector to see if either causes any change in values.

 

These values basically rules out the MAF as the culprit alone, and to me something is going on further down the (air/fuel mixture) line.
If you are sure the MAF readings are somewhere within the range, check the connector of the MAF carefully.
There all small pins on the sensor, and they sometime bend.
I had problems with this connector seemingly fine, but making errratic contact, and very wrong trim readings as a result.
I carefully bent all pins slightly up, used contact to grease to reconnect, and it is fine ever since.

If not, a rather massive vacuum air leak further down the line can cause these trim levels as well.
Should be quite a leak though, and can perhaps be detected by just listening, surely by doing a smoke test.

If it is not vacuum related, I should concentrate on the following 2 items:

- the working of the air intake temperature sensor.
This one has a input to fuel trims. I presume your 8C degree reading was also your outside ambient temperature? The reading will increase if the engine warms up, but 50C in a jump indicates a possible cause.

- the working of the coolant temperature sensor.
This one also has a direct input on fuel trims. You did not mention the reading, and I presume it is ok, but just in case.

With all of above ruled out, I should concentrate on the ECM, the CAN and its connections.
This will be a very complex one , but you might have a problem with the ECM itself, or with its connections if lucky.
That might be indicated by your erratic temp sensor, and your remaining code.

Question to that: does your engine switch from open loop into closed loop?
From a cold start, it should change after some minutes, and can be checked in your diagnoses.

 

+1 air leak

I think I'd fix that first and see if the P1797 persists then hunt that (may be harder to find).

 

I hope you're not driving the car. All that unburned fuel could easily overheat the cats and destroy them. Find the air leak and fix it.