so, my 1985 xj6 still studders all the time. it doesn't matter if it's hot or cold, wet or dry, high speed or low speed, my car loses power, it never dies, but it does it frequently. There are some days where it doesn't do it at all, and then there are some days that it does it constantly. we have ruled out a fuel issue, now what else can it be?

 

How have you ruled out a fuel issue? replaced everything?

its a 6 cylinder?

 

Yes, its a six, and I have taken apart everything and cleaned it or replaced it and it still does it

 

Tried the fiddle and wiggle technique?


A few decades ago, I bought a very nice used 85 Ford F150 4x4. It ran great, most of the time. But, at times it did "stutter". Was that why it's PO sold it??? I'll never know.


So, I fired it up. It was idling nicely in my drive. I commenced the wiggle wires "technique". First off a harness in the left front of the engine bay.
wiggled, engine stuttered !!!!


It was a two wire black harness and a connector. Sure enough, one side went directly to battery -! The other to a ground!!!


I did a multi fix. Part not needed, perhaps.


1. Cleaned both ends of that harness.
2. Cut and removed the connector, it seemed "puny". With solder and shrink tubing I reconnected the wire.
3. I created a parallel black wire ground circuit.


Yahoo, no more stutter for the rest of it's life in our fleet.


Lesson. Good grounds cure a lot of issues.


Carl

 

Definitely. A common issue on these cars!

A good place to start is the ground from engine block to chassis (braided cable, rear of engine where trans connects). I've added a parallel cable to a different chassis point just in case! Then work progressively through all remaining grounds.

 

try this:

find a medium thick wire, about 12" inches long, wrap it very tightly around the oxygen sensor, where the sensor meets the manifold iron. (engine must be cold).

wrap the other end of the wire to a nearby bolt, for example loosen one of the cruise control bracket bolts, wrap the wire, and tighten the bolt.

if that doesn't fix it, and you have checked the other grounds suggested, then you need to wiggle the Air Flow Meter serial connector, if any change, remove the connector and clean it.

 

Jose:


Interesting. Your fix is designed to make a ground that substitutes for the intended ground that may have failed. Through the threads that join the sensor to the manifold?


I've read of that. But, in applications to other critters. I'm a bit confused as to just what the sensor does in this application. Merely count an
interval and light a lamp on the fascia ? Or a trim to the mixture.
In each case, a non functioning sensor would not create a noticeable stutter?


My thinkin also goes back to my removal of my DOHC. The sensor was quite loose. Not good. They are usually much tighter. Hard to remove in both cases.


Not a criticism, merely an observation.


Carl

 

Normally and ideally the threaded attachment provides a decent ground: The sensor grounds to the manifold, the manifold grounds to the engine....and the engine is grounded to the body via the heavy ground strap. But with age and corrosion these grounds can degrade.



On these older application the oxygen sensors really just trim the mixture; the major player in fueling/mixture is still the Air Flow Meter. A flat-out inoperative O2 sensor would likely be preferable to a functional-but-not-quite-right O2 sensor. If the sensor is flat inoperative the system will default to a prescribed fueling map....probably just a bit on the rich side. Personally I doubt the O2 sensor is the culprit here. I've run with the sensor disconnected with no engine roughness. But, in chasing faults you have to cover all the bases and a redundant ground for the O2 sensor is never a bad idea.

Until USA model year 1987 the Series IIIs had an interval counter (early models mechanical; later, electric) which triggered the "Oxygen Sensor" warning light every 30k miles. This was eliminated for the 1987 model year with the advent of the heated oxygen sensor. As an aside I'll add that you can find earlier cars with the heated sensor. It was a recommended modification (there's a Jaguar TSB covering it) and some cars (registered in California, as I recall) were retrofitted with the heated sensor as part of a recall to comply with emissions standards.

Cheers
DD

 

Please describe "everything"!

cheers
DD

 

Carl & Doug,

this fix was recommended back in the late 1990's by a mechanic that worked for Motorcars Ltd. and who frequented the Jag lovers forum.

In my 1984, which has a single wire O2 sensor, it cured an unstable idling whether the engine was cold or warmed up. He also mentioned that the 1986 & 1987 Jaguar engines came with 3-wire O2 sensors and that one of the wires was a Ground, asking me, why do you think they added a separate ground??

so the logic is that the rusting of the iron manifold and exhaust parts due to aging causes a loss of grounding, causing a number of symptoms as the engine ages.

 

Firstly:
Have you checked your spark plugs for a good decent spark?
No good spark? Replace spark plugs
Still no good spark? see below.

Secondly:
Have you checked the spark plug leads for any cracks, loose fitting etc?
If they look old or dried out: replace!

Thirdly:
Is you distributor in sane condition and doesn't the rotor show signs of arching? Any signs? Replace!

Fourthly:
You can measure the resistance of your coils.
The right values should be listed in a Haynes or Jaguar workshop manual.
Resistance out of spec? Replace coil...

If fuel is getting to the cylinders in the right way, the only other possibility for your stuttering is in the electrical department.

 

yes, my second guess is one bad spark plug.

remove the spark plug closest to the firewall and inspect it; Is it wet with crud? clean it good with gasoline and reinstall it.