My 1996 with the AJ16 engine has developed a slight misfire and I will start troubleshooting with a change of spark plugs and oil seals. I don't know the maintenance history of the car, but I've read here on the forum that oil can pool around the plugs and cause a misfire. My question is can the cam cover be removed without removing the spark plugs first. I assume it can, but I don't want to mess things up.

 

Yes, it can. Make sure you have a new camcover gasket ready? The OEM is pricey, but the aftermarkets don't fit as well. (Eurospare) I would recommend spending on the OEM in this case...

Also, make sure you have six replacement gaskets for each of the spark plugs. You can go aftermarket here, I recommend URO.

Lastly, you'll want to replace each of the small rubber boots on the 13 camcover bolts. I also recommend URO here. I believe you'll find RockAuto has the best price for these pieces, but I could be wrong.

If you decide to swap out the spark plugs, I would recommend sticking with the inexpensive, but seemingly consistent performing Champion 71, or RC12YC. I have used the NGK BKR5E with success as well.

Lastly, you may want to replace your coils. Diamond brand,"Made In Japan" seemed to be the only manufacturer that knows how to make these that last more than 6-12 months, however many people have ordered QYL brand coils and have been happy with them as well. I would not recommend any other alternatives, even Lucas branded coils.

 

Thanks Vee. I've got everything you have suggested. The exception is that I have Chinese replacement coils. My plan is to replace the plugs and if the misfire still exists, then I will replace the coils one by one to see if that solves the problem. I may invest in better coils in the future. In the past with other cars I have used an inductive timing light to see if all of the plugs are firing. Is there anyway to test the coils to see if the plugs are firing?

 

Hi RickE

Here is a complete step by step guide to how I removed the Spark Plugs and Coils on my AJ16 Engine and cleaned them in an 'el cheapo' Ultrasonic Cleaner including replacing the Crank Position Sensor (which could be your problem)

As well as removing all the Injectors and doing a doing a pressure Test and almost every trick in the book to get the Engine Started when She wouldn't go (Link Below)

Carmen won't go! or How I got the Engine Running on my AJ16 Car

 

There are ways to check that the coils are firing, which they probably are, otherwise you would have CEL codes popping up. The OBD2 system okay at letting you know when catastrophic issues are afoot, when things are in a downward spiral, not so much.

So basically, you'll want to ask me, is there any way to check to see if coils are operating as they're supposed to. I believe there is, but you would need an oscilloscope to do it. If they're originals, their time has probably come. The QYL coils are quite affordable. Again, many people have had success with that particular budget brand. I wish you had come here before you purchased whatever knockoff coils you ended up buying, but please share the brand, and let us know how they worked out for you.

You can also read through this:
https://www.jaguarforums.com/forum/x...0-coils-93966/

Feel free to add your brand to the discussion!!!

 

Thanks Vee and OB, I'll let you know how things work out.

 

Why not figure out which cylinder is misfiring first?
Do you have one of those digital lazer temp finders? You point it at something pull the trigger and a red light shows what you’re taking the temp of?
they are cheap on E Bay or Amazon. $20 or so?
Point it at the exhaust manifold at each cylinder.
the misfiring cylinder will be the coldest.

 

I hadn't thought about that, but it probably would be a good idea to have one of those digital temperature readers in the toolbox. However with the misfire being intermittent, would it really show a temperature difference? It would be nice to know which cylinder was at fault or if it was something that was affecting all cylinders randomly. The car has 80,000 miles on it and I will be replacing the CPS just as a matter of course.

 

I don’t ever want to replace parts unless they are called for. I have an old SU fuel pump in my MGTD once I learned how to clean the points on them it’s been reliable for more than 25 years. I used to replace it at least once a year.
I have one of those temp sensors I use it all the time. When I bought mine 25 + free years ago it was state of the art and I paid $28 for it.
I cant tell you how much easier it’s made my life and not just on car stuff.

If it’s intermediate it will tell you as long as it’s miss-firing. Good cylinders will show a much higher temp than bad ones will.
it’s also good to use on radiators to detected if they are getting clogged. If the brakes or tires are running too hot. Check wheel bearings etc etc.
In your house detect which windows are leaking and where.
for cooking use it like a meat thermometer.
etc etc etc.

 

There are some parts on this car that defy any consistent way to bench test them.

1. The TPS
2. The coils
3. The crankshaft position sensor (not sure about the ability to bench test this one)

I have had a TPS that bench tested perfectly, with an analog multimeter no less! After hunting down an overfueling issue I was experiencing for years, as soon as I swapped it out with a new one, everything went to normal!

It is very common for the coils to be firing, but not firing enough, causing idle and driving issues. The coils check out as "firing", but apparently not well enough. The only sensible method is to move the coils around, but only if you're lucky enough to get the misfire in cylinder code, to see if the CEL moves with the coil. If they're old, or not made in Japan, the simplest thing is to replace it. They will degrade with age.

Not sure about the CKPS, but they fail, and when they do, the cause all sorts of havoc while driving or idling. I've only read about these issues, so I have no experience bench testing. I did replace mine, for no good reason, while trying to avoid buying a new TPS, chasing down the overfueling issue...

 

I do have a spare CPS that I bought after reading suggestions on this page. If changing plugs and replacing the coils one at a time doesn't work, then I will probably install the spare CPS.

 

...assuming you don't find oil in one, or more, of your cylinder wells. You'll add replacing camcover and spark plug gaskets to the list!

You may want to share a description of this slight misfire? I'm assuming it's an occasional vibration at idle,possibly affecting the RPM gauge? If this is the case, it could also be a small vacuum leak. I had an insane issue where I had the RPM needle dip every 32 seconds, when warm, at idle. It was the intake manifold gasket....

 

hit the easy button when checking coils.
what is the temp at the exhaust port? Use one of those cheap ($20) digital infrared temp sensors. Misfiring cylinders will be cooler than healthy ones. Want to check? Swap coils and if the temp in that cylinder comes back up to average, yep it’s that coil.
you can check injectors with a simple stethoscope. Put the tip right up to the injector steady tic-tic-tic it’s working silence or occasional tic it’s bad.
don’t buy new injectors, too cheap to have them cleaned.

 

Just as a follow up, I replaced the spark plugs with copper core plugs and fitted a NOS EGR valve that I already had. The original EGR valve was very sooty and I will clean it up and keep it as a spare. I also readjusted the throttle cable back to where it should be. I had previously used the throttle cable to keep the car from stalling out when I lifted my foot off the gas. Both that, and the intermittent misfire were recent occurrences that began around the same time. Voila, the car runs and idles perfectly! I took it out and did as much of an Italian tuneup that I could do in a city environment and am very pleased with the results. We'll see what tomorrow brings.