A "dead" one would, but there are plenty of failure modes other than complete no signal. BTW, I am realizing you have several mods to your car and maybe the fuel trim issues are related. So far I understand you have KN filters (often debated to cause MAF and fuel trim problems, lowe temperature thermostat (will cause car to never go into closed loop if too low), some sort of exhaust change ( where are the lambda sensors mounted?). Any more that don't you don't think might be involved in this?

 

Yes I have a K&N panel filter installed, but I cleaned the MAF sensor to check that the oils off the filter hadnt made the MAF dirty. I do have an aftermarket exhaust, which pritty much the same as the standard system using the same amount of silencers. I also have 200 cell sports cats installed, which I was told wouldnt cause the car any running problems when fitted. As for the Lambda sensors these are still installed in the same locations as standard and are seated in the same position.
The thermostat is an OEM replacement like for like.

Do you reakon any of these would cause feul trim issues? If this is the case then I guess Ill have to live with it, at lease I'll know where the problem lies.

 

Also another quick update had another emissions test done, they passed at 3000rpm after a minute or so, at idle still terrible.

 

No, if your lambdas are relatively in the same position, they should not screw up the fuel trim. Ditto for the KN filters, as long as the MAF is clean. I assume that the car is in closed loop, so it isn't the temperature. I was just wondering.

I gotta tell you, it sure seems like an air leak or some plugged injectors if it is not the MAF.

The fact that your numbers get better at higher rpm further indicate an air leak. I suspect you have an intake gasket or injector o-rings leaking like mine were.

I will say that on a SC engine, it is dangerous to run it lean. Ask Waterdragon!

 

Thanks for your help sparkenzap, how can I go about checking intake gaskets or injector orings?
When I had the head gasket work done don't you get new intake gaskets in with the kit, there was hell of a lot of gaskets in with the kit for all sorts of things. So perhaps if this is new then it cant be a leak from this location which narrows it down a bit.

What happens when you run it lean, I suspect mine has for quite a while.

 

What happens when you run lean is that certain cylinders- the ones leaner than the others, can run hot and have preignition that the knok detection system cannot handle, resulting in burned valves, blown head gaskets, and even holes in the pistons. For real!

 

So it went to see the jag specialist today. He ran a ECU test with no errors found, checked all lambda sensors all where ok, did a smoke test and found no leaks, he also cleaned the MAF sensor which I had already done. When I picked it up he said the only thing left which would cause high fuel trims when everything else seems ok would be a faulty MAF, so I'm going to replace this in hope it sorts out my issues.