The Unhappy Kitty – Jaguar Check Engine Light On
This is a great study of dedication, and a solid illustration that logical thinking, some “detective work”,
and understanding of how automotive systems actually work, make all the difference in service outcomes.
In other words, “knowing”, rather than just “parts changing”.

It’s also a cautionary tale that “scanning the computer” and use of fault codes, does not fix cars, it may or may not give an indication of the area in which to investigate, but unless there is true knowledge of how the system operates, it can lead to unnecessary work and parts replacement. Knowing, not just doing, that’s the secret to a skilled technician, and a good outcome.

The Car
Recently we had a very nice Jaguar XK8 with the 4.0 liter V8 engine in for service. Seems it had a Check Engine light that was chronically on, and from looking at the car, it was clear that this had been the case for some time. The fault was for a camshaft timing issue, something that can be very onerous, indicating possible deep engine problems. The camshaft timing on this car, like most modern vehicles, is dynamically controlled by the engine computer, to minimize emissions and to peak performance. In other words, the camshaft timing is advanced or retarted to fine tune engine operations, and make the engine purr. Purring it was not, in fact it was stumbling, running rough, hesitating, and then there was that glowing Check Engine light, telling the world it was one unhappy kitty.

Background
Clearly another shop, likely more than just one, had had a go at it. In an effort to correct the problem, they had run new wires from the engine computer to the oil control solenoid for the camshaft timing, assuming I guess that the wiring harness somehow had a problem (it did not). A case of guessing, rather than actually measuring and testing the wiring. On a hunch I called our local Jaguar dealer to check service records and history, but they told us that they don’t work on any Jaguar or Land Rover more than 10 years old.

The previous shop had replaced oil control solenoid, which was not a bad idea, given that they do commonly do present problems. Unfortunately, this was not the cause either, but likely not a bad idea to rule things out, it’s good to have a baseline to start with. They had also removed the camshaft covers, probably to check the camshaft timing and chain guides, which can be problematic on some cars. These were found to be fine on our inspection. In short, they likely tried everything that they could in an effort to extinguish the light, and then they gave up. And though some meandering, the car found its way to us.

Our Turn
Initially we did our standard process of evaluating and confirming the actual issue. We then checked for Technical Service Bulletins (TSB) from Jaguar and in our technical information database on pattern failures. We did find some TSBs, which suggested changes in oil viscosity, which we carried out, but to no avail. So we started from the beginning, checking engine oil pressure – the camshaft timing is operated by means of an adjustable sprocket moved by engine oil pressure. The engine oil pressure was found it within specifications, both cold and warm. One of the challenges with this problem was that the fault would not reoccur immediately, one could drive the car for some time, before the fault reoccured, which makes diagnostics more challenging.

We did get the fault to repeat, and noted a change in engine performance when this occurred. For baseline, we switched in a known good solenoid valve for testing purposes, and reran the test. After a drive period, the light would come back on, as the fault would reoccur after the car was driven a few times, but only after the engine became warm. Going high tech, we then checked the signal to the solenoid valve from the engine computer, with a digital oscilloscope, just to rule out and engine computer problem. We observed the waveform pattern looked proper, and the computer was clearly trying to dynamically adjust the camshaft timing, but was not reaching the correct point and was still calling for more adjustment. A quick comparison to the other engine bank, confirmed this, nice thing about having a V8 engine, one can compare each half of the engine to the other. Jaguar has limited technical specifications and data on the operation of this system, so having the comparison was invaluable.

The Finding And The Solution
Our tech then made the bold decision to remove the front upper timing cover, and check the camshaft sprocket itself for a defect, thinking perhaps the spiral adjustment system have be sludged up, or clogged, and that’s when we found it. A very small, perhaps 3-5 millimeter piece of the aluminum bracket, used to feed oil to the oil pressure operated camshaft sprocket, was either worn or broken away. This small piece allowed engine oil to bypass the seal, and preventing enough oil pressure from operating the adjustable camshaft sprocket when warm. When the engine was cold, the engine oil pressure was high enough to overcome this internal leak, but once the engine warmed up, and the oil pressure dropped, the camshaft sprocket could no longer adjust, and the fault occurred.

The repair was simple, replacement of the casting (really the housing for the camshaft solenoid), with another part, and replacement of the rubber seal. The engine was reassembled, road tested both cold and hot, then drive overnight, with no check engine light, or registered fault. Boom, problem solved. Happy customer, and happy kitty, runs and purrs like new!

Easy, no, it was not easy. Repairable, yes, with some hard work, thought and skill.
Rewarding, correctly solving the “unsolvable” problem, you bet!
That’s what we do. Day in and day out here at the Atlantic Motorcar Center.

Final
Not a simple repair, yes, but one, if done correctly, will last the life of the car.
That’s our goal, fix it right the first time, and prevent problems from happening in the first place. 30 years of service experience have well taught us that “an ounce of prevention is worth a pound of cure.” Be cured, once and for all, and give us a call, we’re happy to answer any service questions you might have on your auto, be it an Audi, BMW, Mercedes or an unhappy kitty (Jaguar).

Earning Your Trust, Every Time You Turn The Key…that’s what we do…every day…for the last 33 years.
Click here see what our happy customers have to say about us and our service at AMC Customer Reviews.

If you have questions, or if we can be of further assistance, just call us at (207) 882-969, we’d love to meet you, and your car!

Warmly,
Bruce and the AMC Service Team