Full disclosure. I think I did something really bad.

I have a 96 XJS with the AJ16 engine.

I recently replaced both of the exhaust manifolds. I did something stupid. I had some trouble getting the down pipe donuts on, so I smeared on some silicone paste.

This is it here,
Although I was not able to get the proper torque on the two nut attaching the down pipe to the rear manifold, (I was able to get the torque on the front one) I cannot feel a leak at the joint.

Now when I start up my car, its all lumpy. I hook it up to a laptop and I do get voltage readings on the four oxygen sensors, but there is no change ever to the fuel trims.

The STFT is locked at 0, and the LTFT hangs at 8.43. Doesn't matter what the car is doing.

I now learned that O2 sensors and silicone do not like each other. The O2 sensors (NTK brand) are about 6 months old. Did I kill them? Did I kill all four of them?

I did pull a P1315 and P1316 code last night, but only using the IDS, not a standard OBD2 code reader. I cannot complete an oxygen sensor orientation. It begins, but it abruptly fails me after about 70% through.

Is the voltage reading from the all O2 sensors fixed, or is it constantly varying? If fixed, I'm inclined to think you killed 'em. Killed 'em good!

Cheers
DD

The front ones move between 0.06 and 0.09

The rear ones move between 0.10 and 0.12

While diving with the laptop plugged in, the fuel system PID says that it is in open loop due to insufficient engine temperature. The ECU is reporting a proper coolant temp of 180F. What else tells the ECU what the engine temperature is?

The silicone paste I used have a flashpoint of 570F, do you think it's all been cooked off?

Seems to me that you should be getting a lot more voltage variance. From memory (I haven't looked in ages) I think mine vary from something like .4 volt to 1.2 volt.

The ECU is probably relies on the coolant temp sensor as much s anything else in switching to closed loop but not seeing enough activity from the O2 sensors might prevent it from happening.

What are the P1315 and P1316 codes? I can't remember.

As far as the silicone burning off....I don't think that's the issue. I think the silicone damages the O2 sensors from a chemical standpoint.

Others will chime in.

Cheers
DD

The codes are miscellaneous misfire codes, nothing that specifies a specific cylinder. I may have had the O2 sensor connected backwards.

I jumped the CTS and the idle is better. Haven't plugged it back to the laptop though. I'll see if I got it out of open loop.

As far as the silicone, I was trying to figure out if I have to clean anything out? I'd hate to put in new sensors and foul those up too! I'm hoping its all been burned out by now!

I'm inclined to think your 'full disclosure' could be on the mark. Oxygen sensors of all types are easily destroyed by silicone/silicates, even in small amounts. The industry learned early on, that even the small amount of silicate the engine drew in from the valve cover sealer they were using at the time was enough to take out O2 sensors. That small amount was what gassed off and was drawn in through the breather system, made it through combustion and got to the sensors. I'd guess your silicone grease was a heavy hit.

You say the engine is lumpy at start-up. Is that IMMEDIATELY on a cold start?? If it is, then you need to check things that are not related to OBDII. Immediately on cold start, the O2 sensors are not involved because they are not at a temp they can operate. For the same reason, you need to ignore any fuel trim readings. They are meaningless until the system is up to temp, the O2's are operating and the system is in closed loop. So, Doug is right that you probably can't complete the O2 orientation for some reason that is preventing closed loop.

It is very hard to re-use the exhaust donut gaskets as they are similar to a compression union, in that they are compressed when installed. Getting a compressed gasket off such that it can be reinstalled is pretty tough. You really need new ones.

P1315 on the AJ16 generally means a persistent misfire has been detected and the associated cylinder's injector has been turned off. That could explain your 'lumpy' engine. P1316 is indicating a random misfire detected.

You got your work cut out for ya!
Good luck!

Do you think the silicone has burned off or do I need to go in there and clean anything out?

Is it safe enough to swap out the sensors? I've probaby put 100 miles on the car since the silicone went in

I've moved this thread from the General Tech section to the XJS section for greater visibility and response from members/techs more familiar with this model


regards,
Steve