Jaguar Daimler 1989 - 3.6.

Hi,

I have the following problem that is puzzling me. My engine has a very uneven "ride"/ignition timing. It almost feels like it is running on 5 cylinders instead of 6, but still maintain most of its power. It is worse on cold engine, but also noticeable when hot. It must fire on all cylinders, I wouldn't have the power and the accelleration I have if not. It must be said that it is slightly less power and a bit hesitation when flooring the accelerator, but not enough to indicate that only 5 cylinders fired.

Otherwise the drive is "normal" with no misfire or puffs, it just the uneven timing all over the rev scale. (To illustrate, it sounds mor like tacka-tacka-tacka, than a smooth vrrrrrrr over all revs :-)

Then we have the vibration. It is quite noticable from idle 7-800 rpms (at standstill) and when driving, vaguely noticable through the whole scale up till approx 3000 rpms at 3rd gear where vibrations are heavy until gear change to 4th gear, where the vibrations stop entirely. This when engine is under load. The heavy vibrations only occur over about 50 miles (80 Kmph) and not at different revs below that speed. It also feels that the gear shifts are a bit more harsh than normal as well.

Idle Control Valve (ICV), steppermotor, 02 sensor, Distr. cap, rotor and leads are only 6 months old. Tried to change to an old set of cables I had, but no result.

I have a suspicion towards the Crankshaft Position sensor (CPS), and ordered a new sensor. (Always have one available, right?)

Any other suggestions for what is causing this, or where to start search for trouble areas?

Thank you very much in advance.

 

Hi Harald,

It really does sound as though you have one cylinder that isn't firing. These Jaguar straight six engines are so smooth that losing a cylinder doesn't produce as much roughness as you might expect. If one of your spark plugs isn't firing, the unburned fuel in the exhaust sensed by the O2 sensor may be prompting the ECM to enlean your fuel mixture.

You might check all six spark plug cables at both ends to be sure they're fully-seated, and if that doesn't improve things, it might be worth pulling the spark plugs to see if you have one that looks different than the others (wet with fuel, for example). It wouldn't hurt to check the inside of the distributor cap for any signs of trouble with one or two of the terminals.

Another possibility is a clogged or inoperative fuel injector - it might be worth checking the wiring to all the injectors since both the wires and electrical connectors harden over time and become very brittle. Two of our connectors crumbled in my hand as I removed them from the injectors.

Rough running like this isn't normally associated with the CPS, but it is definitely a good idea to have a known-working spare in the glove box or trunk at all times!

Cheers,

Don

 

Thanks a lot, Don.

I have gone through leads and distributor cap and all looks fine. I have not checked plugs for unburned fuel, but I will as soon as possible.

When you mention fuel injectors, I had an issue with water in fuel, if you remember. That may have caused a faulty injector and I will have a look at the wiring. I found your excellent cleaning procedure on Jag-Lovers. But if it is a non working ignitor, is it any way to identify which one that does not work - If it is only clogged it still will "tick" as normal? You have to get all out and clean?

 

Hi Harald,

You can probably identify a non-operating fuel injector by disconnecting each injector while the engine is running. If you disconnect an injector and nothing changes about the way the engine is running, you've found your suspect. You can test that injector's power supply with an inexpensive noid light available from most auto parts stores.

Please keep us informed!

Cheers,

Don

 

Thanks again, Don.

Started by listening to each injector with a screwdriver. Each one ticks as they should.

My attention is back to the ignition. Tried all six HT leads once more with a old set of spares. No change.

As you instructed I removed all plugs and hey, cylinder #3 is wet of fuel. Cleaned plug, checked spark gap, all fine. With no Jaguar dealer near, I called a friend with a XJ40 and asked if I could borrow his distributor cap. Did so, but no change. I am really out of ideas, after changed three cables. As a last resort I tried cyl #3 cable from my friend, and glory - immediate change. All is well and good.

This means that the original lead has been dodgy from new, it is only 6 months old. What is the chance of three cables being faulty???

Well problem solved, and thanks to Don for the wet plug tip...

But I must say, Jaguar have made the smoothest engine ever to run on five cylinders! :-)

 

Hi Harald,

Congratulations on tracking down the problem!

I am curious to know if the spark plug wires you had trouble with are made by Rists (Lucas)? See the photo album at the link below for a problem I had with two different brand-new sets of Rists wires. I'm wondering if you've had two #3 wires with this same problem:

Welcome to Jag-lovers - Members Photo Viewing Page


I try to resist ever saying, "I told you so," but... "I told you so!"

Cheers,

Don