Two weeks ago my 1996 Jaguar XJ6 was running beautifully. I drove home 30 miles without problem. After sitting for 1 day the car would turn over but not start. I pulled the plugs, cleaned them and swapped in a set of working coils that I had on hand. The car started and ran fine. Until I drove it down the street. It stumbled and barely got me home, stalling and smoking terribly. I have since tried any number of fixes to get it running:

• Replace crank positions sensor.
• Replace with known working coils
• Verify throttle position sensor resistance.
• Clean MAF sensor (with appropriate cleaner)
• Disassemble intake manifold and injector rail and clean throttle plate
• Drain fuel tank and replace with new fuel
• replaced fuel pressure regulator
• Charged battery.
• Checked ECU no corroded pins found.
• Two trouble codes referring to intermittent misfire are shown

The car will usually start, and sometimes it will idle beautifully and then cut out. When the engine stumbles it is like the ignition switch has been turned off. Then when the engine kicks on again I can hear the air injection pump kick on as if the engine is newly started. I will upload a video of the operation for you to see. I am holding the throttle at about 2000 RPM, the dropping is due to the engine's. . . misbehaviour. The biggest thing are the quick dips in RPM, just like if I had shut off the ignition. When it dies it isn't a stumble but rather a power off.
Any ideas?
Erma

 

Hi,

I had similar idle issues caused by a failed Coolant Temperature Sensor. It looks like you already checked everything I did, although a failed MAF Sensor on my 97 XJ6 4.0 also gave erratic idling until it was replaced.
I suggest checking the Coolant Temperature sensor first. It's simple enough to check the resistance on the sensor and confirm with the expected Ohms on page 78 of the EMS Study Guide below.

Hope this helps.
EMS Self Study - 801S - 2000.pdf

 

With the air pump coming on as in a restarting of the start sequence look for interruption of power to the ECU

Swap the Right engine fuse box corner of the box relay ( referred to as a ignition positive relay ) with the one on the left ( left is only the horn )

Swap the large ECU controlled relay with the fog or headlight relay ( this is the second source of power going into the ECU )

see page 17 and 19 for relay location in the file below :

You have to put your finger on the relays and not just listen for them as others close by in starting sequence

http://www.mediafire.com/file/45wwgj...0+1996+LWB.pdf

 

Thanks for the suggestions,
Parker, I swapped the two relays that you mentioned. I am still getting the same behaviour. I will need to get a friend to help me with the relay click. Car starts and keeps cutting out then back in. Nobeel, It is raining pretty hard, so I will wait to check the thermostat resistence if the sun ever comes out again. Thanks for the involvement - misery loves company.
Erma

 

Have you replaced your fuel filter? I saw that you replaced your crank position sensor, is the connector on the wiring harness clean? these do get gunked up. Its too bad that these cars don't have an easy way to check fuel pressure.

 

The 2 wire coolant temp sensor above the thermostat will read the same as the 2 wire inlet air temp sensor just behind the mass air flow sensor on the top of the 90 degree turn in

This sensor will cause the ECU to jump back and forth on the mixture or short term fuel trim

The CEL code for the coolant temp is P0140

Connector clean ?

One other relay you can swap is the fuel pump relay with the Acc located inboard in the trunk relay row

The fuel pressure at the rail at idle is 43 psi

May be a floating relay or burnt contacts on the edge of enough current to the pump

 

Thanks to all those who helped. I have fiddled with the car for some weeks. What may be the solution cost about $8500. I bought a Fiat to drive, and I think that the effect of a Fiat being more reliable shamed the Jaguar into complying. More probably, I spent the day probing all of the contacts in the ECU. None of them came back bad. I probed the sensors and all were reading as to be expected. Finally, in wrath I reved the engine up to 6000 rpm and let it buck against the limiter. After about 10 seconds of that it stopped cutting out. I am gingerly expanding the range that I am willing to risk driving the Jaguar to see just how 'fixed' the XJ6 truly is.
I absolutely do not recommend doing this, it was foolish of me and frankly done in desperation and frustratoin. I will check back if anything develops.

 

Well, that was quick. I tried driving the car today and it returned to its past behavior - smooth idle with periodic cutting out. Cutting out while driving and flashing the check engine lamp. I pulled the panel cover and checked the ECU behaviour. There is not loss of voltage to the ECU or any out of specification reading on either of the thirty six pin connectors. I will pull the alternator and have it checked and then maybe check the fuel pump.

 

If you do a search on my posts, I encountered a strange issue where I noted a dip in the voltmeter every 32 seconds. Sometimes it would stall out the engine. No issues while driving, just at red lights, and when the car was at idle.

It turned out to be a failing intake exhaust manifold. Took a few shops to finally identify it. I wonder if you're experiencing a similar issue. Not sure why the voltmeter dipped consistently at 32 seconds.....

 

Thanks Vee,
I'll check into it. My next step is to start stripping the wiring harness to find any potential shorts.
Good Luck!
Erma

 

Which manifold was it, Vee? I thought my brain was tired!

Cheers,

Don

 

Intake.

Part # EBC11081

 

So an update. After swapping ECM, BCM spark plugs, ignitors and ripping into the intake manifold several times I think I have found the problem. There are two connectors just aft of the passenger side headlights and below the relay sets. The upper is black and the lower white. The ECM power relay passes through this connector. Another owner mentioned a TSB about unclipping the white connector and relocating it higher as it suffers from water ingress at the original location. The TSB was 05.1-14 and can be found at http://jimbutterworth.co.uk/8connector.pdf.

 

Thanks for the update, Erma!

Did one or both of your connectors (PI1 or PI61) exhibit signs of water ingress or arcing/melting? Photos would be of great help to other members in the future.

Cheers,

Don

 

Hi All,

I was looking into an intermittent problem with the front right head light just this weekend I noticed the wires connect to these connectors.
After reading Erma's update I decided to separate both connectors and check for any corrosion. Luckily both connectors pretty clean so I reconnected them.
This seems to have fixed the intermittent light problem, so far so good anyway.
After a few local drives, I decided to look at the obd2 readings and noticed that the Evap. readiness test had completed. This was the only test which hadn't for some time now.
After a few days the test still reads as complete.
I'm not sure if these connectors are related to the Evap system, but I will take a look at the schematics and see if they are.

 

After going over what I could find on wiring diagrams and schematics, I haven't found any direct link from these two connectors to the Evap system. They do lead back to the ECU though.
I am wondering if a short on these connectors could have a knock on effect on the Evap system via the ECU. Although it seems unlikely.

For the moment, reconnecting these 2 connections has resolved an intermittent flickering of the right headlamp and allowed the Evap Readiness test to complete, which are both still working after a week.