Ok then, I still wanna know if you replaced the downstream oxygen sensors.

The coils and oxygens sensors share a White Brown wire back to the EMS Power Relay, which I believe is in the passenger knee bolster. I think it’s hidden behind other relays. I wonder if that could be the problem.

BTW, Ive smoke tested my engine before and a leak I had at the intake manifold would not reveal itself. Only one out of three shops I took it to was able to find that intake manifold gasket leak…not saying it’s your issue, but that could still be out there. My problem was smaller than yours, so I’m not convinced it could be the problem because I’d assume your intake manifold leak would be larger than mine, thus easier to check.

 

Fuel Injectors all have a Black Yellow wire that goes back to an ECM Controlled Relay.

That’s located in the same area as the EMS Power Relay.

Both relays are the light blue kind and are highly recommended (by TSB even!) for replacement. They go bad.

This might be the culprit!!!

 

Alright sweet. A picture or diagram of said relay would help immensely. I've only owned domestic (GM or FoMoCo) vehicles and I'm learning about getting around this vehicles wiring system more and more every day.

Can this relay be swapped out for something like a headlight relay? And when you say passenger bolster, are you talking about the kicker panel on the front passenger foot well or the cover to the rear passenger foot rest under the seat? THANK YOU!

 

I forget, I'm in the x300 forum. I have an XJS. (same engine and wires) I apologize, I thought the engine harness would be very similar.

You'll want to go to jagrepair.com and download the wiring diagrams. It'll show you where these two relays are on your car.

I just looked at your wiring diagram (Fig. 04.1 for a 1996 x300?), it seems that only the ECM Controlled Relay is tied to the injectors. Its a BLG colored wire. Says it's a black relay, in the right hand engine bay. You could swap that out with a known good relay and see if anything changes?

 

Here's an attached photo from JagRepair.
I've actually swapped the ECM controlled relay for the headlight relay already with of course, no change.
I'll try again and swap out the ignition coil relay as well.

 

Swapped relays and nothing changed.

 

It was worth a shot.

 

Have you ever replaced the downstream oxygen sensors?

 

No, is it important they are swapped? I thought they don't regulate mixture.
no CEL for catalytic converter.

 

LTFT for both banks is -10.5

 

The downstream O2 sensors defiantly regulate mixture after the coolant temp reaches 88 C

Have you checked the 1 fuse that is the internal heaters for the 4 sensors to read correctly ?

 

Yes that fuse was changed as a precation.

 

My ECM looked perfect inside as well. Only when I pulled the plastic cap from one of the main EPROM's off I had the impression it could gotten hot the way it looked.

 

You initially stated that you changed all oxygen sensors, twice? I wish you had specified you only changed the upstream ones. The upstream ones are only there to trigger a fault when the downstream fail....but if the downstream, ones are just going bad, you'll experience what you are experiencing. These cars are so frugal with codes....

You really ought to change the downstream sensors...I almost hope that it isn't the cause now, since you have spent so much time and money chasing the other sensors. This is a textbook symptom of failing oxygen sensors.

 

Okay so before I'm labeled as a doofus, I wasn't aware that Jagaurs Ho2s system operated differently then most manufacturers? If the two o2's pre cat definitely monitor fuel mixture then the ones after also monitor catalyst efficiency and fuel mixture? If the downstream ones are bad then it could throw off the mixture table?
Im learning! Also it hasnt been that expensive. Most of this stuff could probably stand to be replaced anyways.

 

Surprised me too. From the factory "1995 Technical Introduction."

I as well thought basically all emissions systems only use the downstreams for catalyst monitoring.

 

If this is the actual problem, I'm driving this car off a bridge.

 

From a Jaguar Service Training Manual, "Four oxygen sensors are installed on the exhaust system, two upstream and two downstream of the primary catalysts. The two downstream sensors are used by the ECM for closed loop fuel metering correction. The upstream sensors are used for OBD catalyst monitoring. Refer to Catalytic Converters on page 48."

Go to Page 81/360

http://www.jagrepair.com/images/Trai...20-%202000.pdf

 

That link doesn't work for me, try sending a screenshot if possible. Also, just so we're clear, the oxygen sensors the closest to the exhaust manifold monitor the catalytic converter? And the ones after monitor fuel mixture? How does that work?

 

Hows this? It's a large file, so it might need some time?

Jaguar Training Manual

I am not the engineer, but according to the manual, "The resistance of the sensor element varies greatly with the partial presence of oxygen in the exhaust gas. The change in resistance is converted to a voltage output to the ECM via a constant voltage source and variable sensor resistance. Whenever the fuel / air mixture ratio passes 14.7:1 (Lambda = 1), the sensor delivers a voltage swing: Air / fuel mixture leaner than 14.7:1 – reference voltage high (maximum 4.89 V) Air / fuel mixture richer than 14.7:1 – reference voltage low (minimum 0.015 V)"