after a timing chain broke in my 1999 XK8 and caused a heavy damage to the engine, I decided to replace the engine with a newer 2001 AJ27 model, with cast iron liners and updated tensioners. I do not have facility to do it myself, so I let a local, reputable garage to do the swap. They did for 1300 dollars, but results are disappointing: low coolant level is constantly on despite the tank being full,
the car needs 5 minutes to warm up before it takes off without significant hesitation and backfiring,
P1646 is comes on all the time,
the car hesitates when throttle is applied and seems like to have a 100 HP less than before.
Engine idles smoothly and all cylinders are firing...

Before the engine catastrophy I had no problems whatsoever...
any hints of help will be appreciated

 

There was a recent thread on thermostats and air bubbles in the system. Might help.

Good Luck.

 

The P1646 says that the A right bank o2 sensor is not happy. Check connections and/or replace the upstream sensor.

Did the shop change the thermostat in the replacement engine? If not, it appears that you might have to.

The coolant sensor in the bottom of the overflow reservoir might need replacing. About $25 for the sensor, easy replacement.

 

I agree with Test Point try a new thermostat.

 

Will the newer engine work correctly with the original ECU or did you change that as well? I am new to the jaguar, but have a little auto knowledge, wish you luck in the diagnoses.

 

The coolant sensor fixed - a droplet of Superglue on a broken off connector end...

1646 still coming after resets - sometimes after a few yards of driving, sometimes after 5 miles. but the car does not have any power.Accelerates very slowly, as if it would be fuel-starving. Although, instant fuel mileage gauge shows hefty gasoline flow. Could the oxygen sensor malfunctioning influence performance that much?

 

Yes it could. Find the source of that problem and re-evaluate.

 

The code you have is not for the sesnsor, it is for the ECM circuit to the sensor, it is related to the ECM. You need to get it evaluated and be sure the ECM is programmed to work with the engine. The reason you are low on power is that this problem inhibits the throttle to 30%. You need a pro.

 

It may be the ECM, but I think that is less likely. When I had P1646 on my S-type, I replaced both the upstream and downstream O2 sensors on the right side and the problem was completely erradicated.

Also check the O2 sensor wiring and connectors on the right side.

If it was an engine/ECM compatibility problem, I would expect to see both left and right sides with this error (P1646 and P1647).

 

Unless the tensioners were replaced with the aluminum bodies 4.2liter engine tensioners you are not home free on them. Sorry but you should know. The updated "rev 2" plastic ones are not fullproof". How many miles on the replacement engine?

Somebody correct me if I'm wrong.