Folks,

Thought to share an experience with the AJ27 engine in my 308, MY 2001.

Was driving me mad with an intermittent restricted performance issue, which then became permanent.

Uncharacteristically, I had approached this like a bull in a china shop: rationale was that the engine needed seeing to, and I had put the cash aside to do it, so what the heck?

Anyway, usual suspects, knock sensors replaced, throttle body cleaned and metal gasket replaced, TPS aligned, inlet manifold smoke tested - OK here. No avail.

Wild goose chase continued: petrol feed system check from tank onwards - all pipes, evap valve, carbon canisters and fuel pump all tested OK. O2 sensors live readings and sensor tests OK.

So I gave up, and left it for a while - actually, a long while, going through the annoyance of the British winter revving at less than 2800, and living with the tin cans-***-cars on the motorways taking advantage of the situation meantime .. grrrr.

Few days ago, we had a lovely couple of glorious summer-type days. Bone dry, temperature in the high 20s, and so I told my equally Jag crazy older brother that today this problem is going to be sorted out.

I was getting a P0328 and P0329, which are knock sensor circuit high codes for Bank A and B respectively, so started there - right at the sensors, and here's the sequence of tests, which lead to a resolution (at long last):

1. Ohmic tests: these sensors give a stable 200 KΩ ±10%. Both sensors returned an abnormally high 5.6 MΩ - problem 1 identified.
2. With (1) in mind, I replaced the sensors with 200 KΩ resistors, cleared the codes, started the engine - same probelm. Restricted performance and the P0328 and P0329 codes returning. Weird, ha?
3. Next, disconnected the large buk head connector, traced the knock sensor wires back to that connector and did a continuity check. Tests successful, which indicated no breakage in the wiring loom between the connector and the knock sensors
4. Same checks between the other half of the connector and the ECM. Tests successful, so no breakage in that part of the wiring loom either.
5. Next, cleaned the connector with some contact cleaner, reconnected and torqued the centre bolt holding the two connector halves together
6. Next, continuity checked from the wires from both knock sensors to the ECM. Success - all looked well, so time to clear the errors and recheck.
7. Connected the 200K resistors, cleared the errors, started the engine and BINGO !! success. Engine revs all the way across the range, and I'm a happy man.
8. Two new knock sensors installed (P/N LNE1692AA) at £68 from SnG and the cat's purring again.

My next port of call: hacking the SCP-a-là-J1850PWM network to map out the messages flying back and forth between the BCM, the instrument cluster and other nodes on the network. I have a wicked idea to implement a gateway which is in the making - watch this space

L8r folks ..

 

Do you have the electrical system guide? Not the wiring diagrams, but the one that goes over the networks and communication protocols and some other things that could be useful for trying to tap into the SCP. If not I can try and find it for you, don't think it's in the large files section but I have it tucked away in my stash of useful jag documents on my other computer.

 

It is one of those two.

 

https://www.mediafire.com/?oc5ad7qbl2j6t
The workshop manual is a MUST!

 

That would be a find and half pal. If you can do that, then I'll be ever so grateful.

 

Much obliged. I'll have a read of both right now.

 

Checked them out; one is basic training for Jag electricians - not much use. The other is some other fellow's experience debugging earthing and the starting and charging high current loom. Mildly interesting.

What I'm looking for is a bit more involved: I'm looking to map out the messages on the SCP bus (otherwise known as the Ford J1850PWM). This is part of a project to construct a gateway for the X308 and X350, starting with the X308. Once I'm done with the SCP, then I'll turn my attention to the CAN bus, which is a much simpler affair - I have a good CAN interface and sniffing utilities I've cut myself to map out the messages.

As usual, the pain is mapping out the Jag-specific PIDs, which identify nodes on the network - I've not found it in any Jaguar-issued documentation and don't fancy paying in excess of £40K just to get a diagnostic tool manufacturer subscription from Jaguar.

Thanks all the same by the way, and thanks for sharing what you have.

 

The service guide is the one I was thinking of, but I guess it was more hardware oriented than I remembered. The only other thing I have is someone's results on trying to reverse engineer the ACP, so the signals between the head unit and phone module, and the data going from/to the CD player and I guess the amp on later years. Not very related to the SCP though.

 

I attended several Jaguar Training courses in the late 1990s to the mid 2000s that pertain to this and have PAPER copies of the student guides. Someone might have had them converted to .pdf.

I might have had sections converted but I don't know. I'll look though some files.

You might look (on the internet or Gus's site) for MXAD and 6AD (circa early 2000s).

MXAD is the Multiplex Systems Diagnostics.
6AD is the Advanced Body Systems Diagnostics.

Both are for network description and diagnosis.

I found portions of some documents.

bob

 

Much obliged for this. I'll have a look.

 

ahmedalalousi,

That was a nice bit of troubleshooting on those knock sensors. It raises a question regarding the codes. My codes list indicates:
P0328 - Knock Sensor 1 Circuit High Input (Bank 1 or Single Sensor)
P0329 - Knock Sensor 1 Circuit Intermittent (Bank 1 or Single Sensor)
Does the "P0328 - Knock Sensor 1 Circuit High Input" indicate the resistance of the sensor is high (in this case 5.6MΩ)?

The reason I ask is because I get code 0332 - Knock Sensor 2 Circuit Low Input, often when it is damp outside. The resistance measures 186kΩ. It is still within tolerance of 10% of 200kΩ but perhaps the ECM has a different tolerance (perhaps 5%). By the way, when the engine warms up, the code disappears. I'm going to replace the knock sensors. I was just curious if the low and high input error codes relate to the resistance of the knock sensor. It seems they do.

Anyway, I'm glad you fixed the code problem. It is just plain aggravating to have that Restricted Performance indication all the time.

Was the price (£68) for each sensor or both? What/who is SnG? I'm trying to find 2 sensors at a decent price. Thanks!

Pete.

Edit: I found out who SnG is. I'll have to order their catalogue.

 

Thanks

This is exactly what I discuss in the thread. First of, you need to verify that no breakage exists in the engine bay wiring loom, particularly the splice which carries knock, crank and cam position sensors and the ECM. What I did was to verify connectivity between the knock sensors and the bulk head connector, then connectivity between the bulk head connector and the ECM, first and before doing any further diagnostics

Resistance checks are to only be done once you have verified the wiring integrity, otherwise they are extremely deceptive and can get you on a wild goose chaise.

186kΩ is border line by the way, unless it is consistent under both cold and operating temperature conditions.

My advise: don't replace anything until you have verified connectivity. And when you do, disconnect the sensors and replace them with 220kΩ resistors. Clear the codes and drive the car. Check codes again. If they don't come back, then you have your culprit in the knock sensors and then can change them knowing that they are faulty.

You can say that again! try having some smart A boy racer trying to overtake you on a turn, and then engine restricts at 2800 leaving you look like a fool

More seriously, it is a hazard to drive with restricted performance engine, particularly on the motorways.

Each.

Glad you did. For completeness, they are SNG Barratt and their web site is SNG Barratt - The Ultimate Jaguar Parts Specialist

Obviously, I have no affiliation with SNG Barratt in any way, shape or form.

 

Sage advice indeed. Thanks very much for taking the time to reply.

I thought the same thing; 186K is borderline.

I presume 1/4 watt resistors will work. I have tons of those in my parts kit, but very few larger ones.

I agree, replacing the sensor with 220K resistors will isolate the problem quite handily. The OBD II will detect a high or low input as soon as the ignition is switched to position II. It's a great way to test the continuity of the entire wire run. Removing the resistor will generate a high input error. Putting in a 50K resistor will generate a low input code. It isn't even necessary to drive the car with the resistors in the loop.

 

Interesting reading. My problem is the car going to Restricted Performance at higher altitude, above 6,500 feet, with no DTCs or warning lights; not even a loose gas cap advisory. All of the evap hoses from the gas tank to the canisters have been replaced as well as the vacuum lines under the bonnet. I'm about to go out and check the plastic hoses for leaks as I'm having the same problem with the A boy racers ...


BTW, mine is an 02 XJR

 

Ah. Had this too, and the problem is usually a MAP sensor - not a fault, but simply a spec issue. Air, as you know, gets thinner at higher altitude, as well as pressure dropping, so if you're going to be driving regularly at height, I'd consider either a wider range MAP sensor or replacing the sensor as appropriate - kind of a winter/summer tire exchange chore.

Always good to check for leak hoses, though wouldn't replace anything without a definite diagnostic; but that's pedantic me .. you might have a different take


BR,

Ahmed.