When i start the car first thing on a cold morning it has a definate loud banging /knocking noise coming from the front of the engine compartment.

It probably lasts 10 -15 secs and disappears. It is loud enough to hear inside the cabin too. It happens randomly in the cold, but ONLY when its cold.

Any ideas?

Also the 30f temps have bought the low vehicle and air suspension failures codes back which don't concern me currently as I am unable to drive.

 

That does sound scary. Usually means a starvation of oil until pressure builds up. Oil pump up to snuff? As a reference, I have a ticking noise on my engine from the valve train when I first start the car. After it worms up a bit, the noise goes away. Blaming it on worn lifters. I can live with that.

Loud banging noises are not cool. Keep us posted.

 

You need an inspection from all sides at the front, so I'd get it to a shop asap. It might be something on the exhaust system, if the car runs perfectly OK when hot, or a loose cover or heat shield.

 

Is it coming from the front right (passenger) bumper area? If so, that is the Air Injector pump or some valve for it. More of a loud tick/thump than a bang. My car did the exact same thing last winter whenever the temp was below 40F. The pump only runs for the first 20-30 seconds on cold starts.

 

When my XJ8L plastic thermostat housing broke, this was the sound I heard. At the start, kind of cold weather. It then would overheat when stopped, but showed no sign of failure when driving. So, the cheap plastic housing broke, partially blocking/leaking the inside passages (which you cannot see from the engine bay, i.e. there was no coolant leak).

 

I think it's the air compressor too.

 

I have the air compressor ring kit. I shall have to dig them out and have a look at the compressor and change the rings I suppose.. I had thought this may have been the offending article.

I will let you know.

 

when my 1997 XJ8 sat too long, the plugs were fouled - had to be removed and cleaned. I was told that this was typical on thismodel

 

It dropped below 30f last night and the Jag has dropped and I have the low vehicle and suspension fault warning lights on. Dang, I thought changing the compressor piston ring set may have resolved the issue (and tightened the brass connector on the compressor air line). Ah well.

I definately heard the front left air strut throwing a hissy fit and sank pretty much immediately on start up. That looks like the culprit.

I will be checking the connector with bubbly water and see if it is that, if not then just wait until the weather warms up a bit before driving it (and the snow and ice has dissipated). which will probably be tomorrow (knowing Texas weather!).

I also had the knocking again on startup in these cold temps. I will diagnose this now as the cold conditions will allow me to have the knock more often.