XK8 Gurus,
You have been so helpful in the past. I hope you can help again.

SITUATION: I have two simultaneous problems. 1) My OBDII port fails intermittently to connect to the XK8. 2) My engine suddenly and intermittently runs "lumpy".

BACKGROUND: I am trying to diagnose my '97 XK8 Coupe AJ26 engine's intermittent "lumpy" mode which occurs with a simultaneous "engine fault" fault message and "restricted performance" message. Also, my OBDII reader intermittently fails to connect to the car and this prevents me from consistently seeing the DTC codes. Sometimes I am able to read the codes below.

Regarding the scanner (Ancel BD200, which has worked well on this car in the past), sometimes the scanner will connect to the car when the car feels like it is running in normal mode without the warning messages. And sometimes I get a failure to connect message on the scanner.

What could be causing the intermittent failure of the OBD scanner to connect to the car?

I don't think the intermittent failure of the scanner to connect is due to a faulty OBD cable, plug, or receptacle because the scanner will connect and reconnect spontaneously without manipulation of the OBD cable. Nor is the problem due to blue connectivity.

Regarding the "lumpy" performance, the car appears to run normally for about 1-2 minutes when started. Then, while idling about 1000 RPM the car will suddenly switch into "lumpy mode" with a drop in RPM to 300-500 RPM, and a few seconds later the car will switch back to normal mode, then 30-60 seconds later the car switches back to "lumpy" mode. The DTC codes, when I do get them, are P0333, P0352, P0353, P0355, P0358, P0405, P1000, and P1368. I have not worried about the P1000 code. The P035X codes come with a message "Ignition coil 'B' (or C, E, H) Primary control circuit/open...". I have learned that these codes refer to "Group 2" cylinders 3, 5, 2,and 8, two on the right bank and two on the left bank.

QUESTIONS:
1) What would cause the scanner to fail to connect to the car intermittently if is not the connector plug or port? Could this be a symptoms of a faulty ECM?

2) Could the intermittent OBDII connectivity and intermittent "lumpy performance with those DTC codes be due to a single problem, perhaps a faulty ECM?

3) What would cause 4 ignition coils within the same cylinder group to suddenly and simultaneously fail? Is there a common wire or ground someplace for these 4 cylinders or could this also be due to a faulty ECM?

4) I opened the ECM and did not see any obvious problem capacitors. ECM connectors and wiring appear intact. Would it be worth sending the ECM for diagnosis?

5) Would it be worth replacing the ignition coils, either the four in question or all eight?

6) What other advice do you have?

Big Thanks,
DrDan

 

you can always swap coils between banks to see if the fault carries over to the other bank, but I would also do a thorough inspection on the cable harness to the coils. I was getting spurious misfires and swapping coils between banks ruled out coils but on inspection of the harness, multiple leads had flaking insulation exposing the wires and with engine vibration, they would rub and give spurious codes. Took some electrical tape and short term fix was wrap each individual lead until I can source a harness to replace. As for replacing a single coil or bank, that is a personal choice - me, I'd replace all as who's to say the others won't fail shortly

As for the scanner not connecting, I have had intermittent connection but usually shut everything down, disconnect obd, reconnect and restart the engine which usually resolves the issue

 

For the OBD2 connection part, you may be able to determine signal failures with an OBD2 breakout box. You don't need to spend much money on one. It will allow you to monitor each line for activity.The box plugs in between the connector and your scanner and each line has an LED indicator. If you have intermittent signals, this may help you to determine if there are any potential wiring issues. Can't add anything on engine performance I'm afraid.

 

On our early cars, each cylinder group (1A,2B,3B,4A and 1B,2A,3A,4B - i.e. 2 cylinders on each bank per module, as you note) is fed by an ignition module mounted on the bulkhead behind the throttle body. The P1368 also relates to a cylinder group 2 issue.
My first check would be to swop the connectors to these and look to see if the P codes change to the other group (P0351,P0354,P0356,P0357).

If the codes do follow the swop, then you have a faulty ignition module. If not, you could have a wiring loom issue, otherwise...

It's entirely possible for the ECM to fail without any visual symptoms. Given the '97 ECM track record, I would recommend having the electrolytic capacitors (for they are the usual cause of misbehaviour) replaced. You could send the ECM to somewhere such as ASI, but anyone competent with a soldering iron should be able to do this. The parts will cost around $10-15.
List here:
https://www.jaguarforums.com/forum/x...6/#post1806456

It's unlikely that 8 (or even 4) coils would fail simultaneously, so I wouldn't replace any at this stage

I'd treat the P0333 (knock sensor sense circuit out of range (high voltage) – B bank)

and P0405 (EGR drive circuits open circuit)

...with a pinch of salt until the ECM has been exonerated.

Curious - what are the last 6 characters of your VIN?

 

The last 6 numbers of VIN: 004596
Thanks,
DrDan

 

Ah, so an early car that really does have EGR.

I still suggest you ignore the P0405 code for the time being.

 

Prior to swapping coils, ignition modules, etc, I am trying to get my scanner to connect via the DLC (OBDII port) to the ECU. I have tested the DLC using a breakout box and multimeter for voltage and resitance and find normal function on pins 4 and 5 (grounds), pin 16 (battery voltage), pins 6 and 14 (CAN bus).

FOLLOW UP QUESTIONS re 1997 XK8 AJ26 engine & failure of scan tool to communicate with vehicle:
1. Is pin 7 the K-line? Is pin 7 used for communication between the scan tool, DLC, and ECM?
2. Can I check pin 7 with a multimeter? I do not have an oscilloscope. What pins or ground do I connect to pin 7? What multimeter readings should I get on pin 7? Voltage? Resistance? Key on or off?
3. For pin 7 connected to chassis ground & key off, I think I should get very high resistance or OL, correct? Low resistance would indicate a short to ground, correct?
4. For pin 7 connected to chassis ground & key on with no scanner attached, I should get 12V, correct?
5. Does the Jag use the L-line? If yes, might trouble with the L-line cause a failure of scanner to communicate with the vehicle? If yes, how do I test the L-line with a multimeter?
Thanks,
Dr. Dan

 

Going by the elec guide on JagRepair.com - Jaguar Repair Information Resource it's the K-line. Don't connect it to ground (probably would cope but why do it!). OBD is well-doc'ed on the net so answers are there. Again: I would not connect it to ground.
The same elec guide should show the L-line - looks unused at a quick glance.

 

There are several data networks on the car, the electrical guide shows which modules use which buses.

The CAN network is on pins 6 and 14 and should read 60 ohms on your mutimeter. There are 120 ohm terminating resistors at each end of the bus (IIRC one at the instrument cluster and the other at the ABS module), so if everything is connected ok, you should read half that with the ignition off, if not you have a short or a break in the bus. This bus has the extended PIDS that scanners can read and is the main data network in the car.

The Serial Data Link is that K line, pin 7, but I have read on the forum that on early cars pin 15 is used also as a wake up. This bus is for the standard PIDS. I'm not sure what useful information you can get from your multimeter, but a simple check for short to ground might reveal something. On voltage range with the ignition on, you should see some value between 0 and 12v, but you really need a scope to see if there is any data.