Hi everyone,

I owned jags for years (best was a 97 xj6 and worst was a 98 xjr) but now my neighbor has a 96 xj6 that i've been helping her keep going and its been overall rock solid.

Here's my problem:

yesterday she tried to start it and got nothing, (dash lights up like normal, but no signal to starter) five minutes later she tried again and it started fine and ran fine the rest of the day.

This morning she starts it and goes to pull away then calls me to say it isn't running right.

I go out to the parking lot and can hear a dead misfire from fifty feet away. I tried running it at 3000 rpm to clear it out (used to help my 97 occasionally) but got nothing. Next I pulled the coil cover and started unplugging coils. I found a dead miss in cylinder four AND cylinder five. One two three and six are firing fine and you get the expected drop in rpm when disconnected. I can see one coil going bad but not two at once. I sent her on to work (she's only a couple miles up the road to work) and told her I'd ask around for ideas.

a few more things to help:

- the car has approx 180,000 miles on it and has only been maintained to a fairly low standard
- There are no vacuum leaks
- There is no check engine light set (odd for a dead miss)
-I haven't pulled codes but will tonight
-I did not switch coils around just to check but will tonight


Thanks for any ideas you may have!

 

"At once"?

How can you tell that both coils failed simultaneously?

Given the high failure of these coils it seems 100% plausible to have two of 'em giving trouble at the same time.....but that doesn't mean they both *began to fail* at the same time . One may have been giving trouble weeks or months ago.

Check the coil wiring as well, of course.

Lack of a check engine light is fairly common on these cars. The 'misfire detection' capabilty of the OBD II isn't very good.

Cheers
DD

 

+1 on bad coil(s).

See this thread:


https://www.jaguarforums.com/forum/x...0-coils-93966/

.

 

Check compression, sounds like head gasket between cylinders.

 

I say at once because it ran perfect yesterday afternoon and then this morning two cylinders are dead. I don't doubt the possibility of multiple weak coils but these are good.


after testing this evening: swapping the coils around with other cylinders the problem stays with cylinders 4 and 5.

I'm leaning toward an electrical issue as the problem literally started overnight but will do a compression check just to see.

Looking diagrams over it looks like there is no common wire for the two cylinders that are not shared with others as well.

could it be a computer?

 

Check for corrosion on the ECU pins


Cheers
DD

 

Hi al525i,

I like Doug's suggestion to check for corrosion on the ECM connector pins.

As you've seen in the schematics, all six coils are powered from the same source, the Ignition Positive Relay and Fuse #12 (10A) in the RH Engine Bay Fuse Box. The 12V power arrives via the White/Pink wires and you can test at each connector to confirm all the coils have power any time the ignition is switched on.

The coils are grounded individually by the ECM via the Light Green wires, each with a different color tracer line. The wire for coil 4 has a Red tracer line and connects to Pin 5 of the black (high power) connector at the ECM; the wire for coil 5 has an Orange tracer line and connects to Pin 9 of the same ECM connector. You can test for continuity and shorts to ground between the coil connectors and the ECM connector pins to rule out harness damage.

If you find even light corrosion on the ECM connector it might be worth opening the case to inspect for water ingress, which is not unheard of.

Cheers,

Don

 

I had a similar diagnosis on my car just recently! It was an intermittent failure at cylinder 4 then it became cylinders 4 and 5.

The solution ended up being (a) replacement of all original coils (b) replacement of all original oxygen sensors (c) replacement of EGR valve for good measure? and (d) resetting fuel adaptations using a PDU.

Ultimately the mechanic thought that it was a combination of weak coils and lazy oxygen sensors.

I originally brought it in for poor idling and intermittent stalls when stopping at stop lights/signs.

I had changed out the IACV just in case it was the idle control valve. It didn't improve anything.

Good luck and keep us posted.

 

Thanks for the report, Vee.

A combination of problems is not uncommon and can definitely complicate the diagnosis.

Just to add to your helpful info, a common cause of stalling at stop lights/signs or when turning is low transmission fluid. In some of the Jaguar service manual troubleshooting flow charts for engine stalling, checking the transmission fluid level is the first or second thing in the process. I haven't found an explanation as to why low transmission fluid can cause stalling, but my assumption is that the torque converter does not release properly, bogging down the engine at stops and when preparing to turn.

Cheers,

Don

 

Sorry for the delayed update. I've been working way to much and this damn cat has been fighting me.

The day after my last post my neighbor went out and the car ran perfectly again. drove fine for several more days then rain and suddenly back to misfiring. this time it was cylinder 6 ?!?

so I pulled the engine control unit and opened it up. nothing, dry as a bone. no water intrusion no corrosion on connectors, just nice looking stuff. At this point I started in on engine harness and still couldn't find anything. traced for several evenings to no avail. Finally i found that the cover on the ignition pickup (what used to be the distributor) had a little crack on it. Pulled it and opened it up to find lovely corrosion and a bit of moisture.


I'm still not 100% sure that was the problem but I replaced it and the car is running fine now. For the time being i'm going to say this one is closed.

 

Pardon my ignorance, but what is an ignition pick up and where do you find it?

 

I think the official name of the device in question is "the camshaft position sensor". It is only used by the ECM on startup, to determine the position of the camshaft. Once the engine is running the ECM knows the position of the cam without any silly sensors by counting the pulses from the crankshaft position sensor.

 

Hi al525i,

Thanks for the update!

Like others, I'm wondering which component you are describing as the ignition pickup that used to be the distributor. On an X300, the coils are fired by the ECM grounding them sequentially, so in effect, the ECM replaces the distributor. If it is the Cam Position Sensor (CMP) you are describing, then like juha, I wonder how it would cause the sort of misfires you were experiencing. Is it possible what you call the ignition pickup is the Crankshaft Position Sensor (CKPS)?

One other thing that occurred to me is the possibility of oil leaking down past perished cam cover gaskets into the spark plug wells and down the plug threads, where it can interfere with the electrical ground connections between the plugs and cylinder head. I'm not sure this would account for the misfires moving from 4 & 5 to 6, but it could account for the misfires staying with 4 & 5 when you moved the coils. It would be easy enough to rule out by pulling a couple of plugs and inspecting their threads and wells.

And as Vee mentioned earlier, sometimes it's a combination of multiple issues.

Please keep us informed!

Cheers,

Don

 

the part was definitely the camshaft position sensor (where the distributor was at on the xj40 cars) And while I don't know how it caused the problem, its run fine through two heavy rainstorms since. possibly an electrical noise feeding back was causing something to glitch out?

The cam cover gaskets are good, I pulled all the coils to check them out and swap them around just to see what happened, pulled and replaced the spark plugs as well and the bases were all oil free.

I've seen cars where the cam cover gasket goes bad and floods the spark plug well with oil causing weird problems before as well. This isn't the case here.

 

Could you post the part number of what you replaced?

Thank you!

 

just getting back to my issue and do not recall the name of the individual who responded with a solution. so here i go. no broken wires at the bend from the coils to the interior. Fact of the matter is I did not even go there. Rather I decided to check each oil connector back to the ECM pins by conducting a continuity test with my meter and low and behold each conductor was perfect. Tomorrow I will check each connector white power wire by turning the ignition to determine the health of each. I do however have a suspicion that i may need to replace my ECM.
Stay tuned.