I have a 1996 Daimler 4 litre, and from one or two threads it seems that the air injection system can cause a few problems. Mine's been damaged through a ham-fisted mechanic (not me !!) before I bought the car recently. Can it be removed with any benefits, or is it required for computer etc calibration and need to be repaired ?
Second question is the fuel consumption. I've no codes showing, but at a steady 100 kph (60 mph) it sits at about 18 mpg until the car has done at least 20 miles. Then sometimes will go up to 27 mpg which seems far more acceptable. No roughness or missing at all, although the temp gauge is a needle-with or two below centre. Any ideas?

 

If you remove the secondar system it will put the MIL on, but the engine will run OK.

Fuel consumption will vary significantly with engine coolant temperature, so I'm not surprised by the different instantaneous figures that you have seen.

 

Many thanks for that - much appreciated and I guess that Mr Jaguar, as usual, got it right. Will look for a replacement unit and enjoy the drive.

 

They're supposed to warm up fairly quickly. Mine was slow to warm up and it turned out the stat was opening at 70 degrees instead of 90 degrees.

You can check exact engine temperature with an OBD-II scan tool as the temperature gauge is designed to make you feel better, not report engine temperature. Like the oil pressure gauge.

 

I took mine of completly no mil light where are you at kiwi td as I removed my air pump and put it in the shed when I looked through the service history the previous owner had only replaced it before I bought the car

 

Hi Doc.
Am in Waikanae, New Zealand - thanks for your note and I might take the pump off and see what happens. It could also be the temp as suggested - mine too is a little slow to warm and after 350 km yesterday with very gentle driving at no more that 100kph and few hills the average consumption was 20.9 mpg, which seems a bit heavy. Shall look at borrowing an OBD11 reader so time will tell. Many thanks for all the help and merry Christmas from NZ at 30 degree celcius.

 

I should have realised from your username that you weren't in the US. On an NZ spec car removing the secondary air injection system shouldn't cause a diagnostic fault code. It would also remove a potential source of a possible air leak into the exhaust, which might accoundt for your poor fuel consumption. If you cruised at 100kph for 350km, then I would expect the fuel consumption to be nearer mid-20's. I assume that the auto gearbox actually goes into 4th and the torque coonvertor locks up. If not, that would really reduce your fuel economy too.

 

Many thanks for the replies; will remove the injection pump in the next few days and report back, although a bit hampered at the moment as a set of stairs on New Year's eve bit my ankle rather nastily. The last full tank with only very easy driving and no short runs returned less than 20 mpg, so not too good yet, although the smiles per mile are still OK.

 

The temp runs fairly high on these cars
I have searched for a lower temp thermostat still not found one
My car had a problem with a one way valve under the back seat it had something to do with the emissions and was allowing raw fuel to go into the engine past the electronics took a lot of time a and money to figure it out
Someone else on the forum might know what the valve is called something to do with the vapours from the fuel tank /charcoal canister

 

Hi Doc,
You are referring to the Rochester valve. It is operated by manifold depression. If the valve fails it could provide an un-metered air leak into the intake system.

 

Fitted another air injection pump that came at a very good price, and a small improvement in the fuel consumption over 200 miles. The old pump doubtless was leaking air - crack was hidden underneath out of sight. Work continues ...

 

Got my hands on an OBD11 reader. Long term fuel trim both banks 39.2, and short term mostly about 24, but will drop to -24 at times. All at idle. Revving without load drops the LTFT a bit. Clearly a large air leak somewhere, but why the change in one bank's STFT? Utterly bamboozled by this one.

 

On early cars the OBDII softeware did not correctly transmit the long term fuel trims to scan tools. If you see values larger than about 25% + or - then you will just have to ignore them because the values are rubbish. If your short term fuel trims are at the limits of + or - 25% and one is + and one is -, then this suggest the two sensors are connected back to front. Try swapping the two connectios to the harness the other way round. If the snesors are back to front that will have a major effect on feul economy. If both short term fuel are in the same direction them you have some other problem. Really you want both values to oscillate around zero.

 

Many thanks again. It looks like the O2 sensors are the original ones, so have them on order and will swap next week - the readings are suspect on one. When these are sorted I'll fit your new timing bracket that I think is a work of art !!

 

Would it be possible that a faulty air injection pump would cause the engine to stall (while at low rpm) when the pump engages? This seems to happen to my 4.0 XJ6 occasionally, after a warm restart. I will also check the purge system valve under the car. Thanks for the good info.

 

This might sound stupid, but is the air injection pump the electric motor above the alternator? I've only ever seen belt driven air pumps.

 

Tim:
Yes- not yes it is a stupid question; it is not. But yes thats the air injection pump!