Looking at a 1996 XJ6 to buy that hasa misfire. Water got in the gas due to one of the drain holes near the fuel tanks was clogged (so he says?). Ran the tank through and changed one of the injectors but it still runs rough at idle. I'm thinking it's the ignition coils. Is there a way to testthe coils? Car has 160K on it and it's rather cheap to buy.

 

If the engine has adead missfire, or close to it, you can just do a power balance test by disconnecting each coil in turn until you find the dead cylinder. Then trade coils and see if the problem moves with the coil.

Normally a missfire that has been occurring for any length of time will illuminate the check engine light, and a code will be stored. An intermittant or failed coil will generate a code which tells you which one it is.

You can also remove a coil, reconnect the lead, stuff a spark plug in it and watch the plug fire while the engine is running. None of this will harm the converter or anything else, unless you try driving to Chicago that way.

Injector failures occur but are not common, and you can usually hear the difference if you listen with a stethoscope. Regarless, I wouldn't buy it with the missfire unless I ran a compression test so I knew that, regardless of what the resolution turned out to be, the cost would be relatively minor.

Get in touch if you need a coil, I have new and good used OEM coils on hand. Happy shopping!

 

tr_car_nut,

It sounds like a bad ignition coil. Replacing one is easy, but they are rather pricey at around $300 or so. I would try another car in your area. Try autotrader.com or cars.com to find one in your area.

 

Coil problems are rather common on these cars. I'd look there first, using advice already given.

That said, all three of my Jags have had idle problems of one sort or antoher and all three have been improved by professional injector cleaning.

IF you have a pronounced mis-fire type roughness that is actaully worse in "Park" than it is in "Drive" then it is probably an injector problem. Fuel demand is lowest at idle in "P" and apparently ananomoly can develop where an injector is unable to electrically respond at "minimum pulse width".

Cheers
DD