I have a 96 XJS 4.0 AJ engine. When I start the vehicle The engine visibly shakes and I get an intermittent puffing sound from the exhaust. I replaced the ignition coils and the spark plugs. Last month I attempted to move the vehicle and the vehicle stalled just as I drove it from my driveway. I left it parked in front of my house for two days and attempted to start it again. It started but just as I backing the vehicle in my driveway, it stalled again. I waited a few minutes and tried starting it again, it started but it runs poorly. Once I got it into my driveway, I let it run. The engine visibly shakes with the intermittent "puff" from the exhaust. I then noticed the Bank 2 catalytic convertor was glowing red hot and the Bank 2 downstream O2 sensor was also glowing red hot.


Fast forward to today: I removed the ignition coils and the spark plugs and noticed the two closest spark plugs to the windshield (I'll say that is coils 1 and 2) were clean. the others were carbon fouled. I cleaned the others, reinstalled the plugs and the coils started the vehicle. Results:


Engine visibly shaking along with the intermittent "puff"from the exhaust.
Disconnected ignition coils one at a time:
Coil 1: engine did not change exhaust puffs
Coil 2: engine did not change exhaust puffs
Coil 3: engine idle changed
Coil 4: engine idle changed
Coil 5: engine idle changed
Coil 6: engine idle changed


the engine does not shake as bad when coils 3-6 were disconnected but resumed when reconnected along with the puffing exhaust.
The Bank 2 catalytic convertor again glows red hot along with the Bank 2 down stream O2 sensor.


Where should I begin? when this problem started, I went to an auto parts store to see if the car had any codes, none were present. I am certain I will need new cats and O2 sensors. Suggestions are welome

 

Where did you get the coils from?

 

Car Parts.com. Vehicle was displaying the same symptoms with Lucas (OEM) coils. Used cheapies to see if the same issue would occur instead of purchasing OEM or the next best expensive coils just to have the same issue. I do not believe at throwing parts at a car w/o finding out the cause of the failure.

 

Hello Lonejag, welcome.

FYI, cylinders are numbered from the front of the car.

Please check that your ignition coils are plugged in to the correct connectors at the rear of the engine, namely, coils 5 and 6 (that you referred to as 1 and 2). It is easy to confuse those two leads when changing coils and plugs. A glowing red-hot rear cat will happen if they got swapped. The spark plugs are not firing at the right time and fuel is "pouring" into the exhaust manifolds and burning there. Not good!!! Not to mention there will be no work done by those cylinders, leading to really terrible running, if running at all.

The coil wire for coil #6 (closest to the windshield) should have a small piece of tape on it, to identify it as #6.

If this is what has happened, you wouldn't be the first! It would also be a super easy fix. That is probably why those two plugs were still clean when you checked them. They haven't seen any combustion! Let's hope no harm was done to the cats. I'd suggest another new set of spark plugs too. Get the Champion RC12YC or the platinum version. This engine is very sensitive to spark plugs.

New aftermarket coils should work for a while, but are short-lived. They create all sorts of havoc when they start to fail. You might still have the originals. They might still be good.

Keep us posted!

 

I suspect the ECU could be suspect. I had an issue on my 96 where the O2 sensors would not swing back and forth. I changed all of the 02 sensors, but ultimately it was when I swapped out the ECU with one I had as a spare, that my problem went away.


I had no moisture issues at the connection point...which has been a concern for others.


I suspect it could have been caused by a crappy attempt at a jump start. My battery was old and died. It could not be jumpstarted and someone plugged one of those lithium battery jump starters into the cigar lighter. That could have created the problem.

 

Took your advice car cranks but will not start.

 

Is it plausible that the O2 sensors need to be reoriented?

You have four O2 sensors. Perhaps the car is confusing which sensor is upstream and which is downstream. There's a procedure under IDS/WDS that researches the car which is which. I wonder if you switched the plugs on the O2 sensors? They are all plugged to a harness between the engine and firewall, if I remember correctly.

 

What is the compression like? Mileage and last time the valves were adjusted? Have you listened to the injectors or pulled them to see what they are doing? Test the o2 sensors if you get the chance. Idk much about the 4.0 and the rest of it's systems. Maybe check out the crank sensor, but it really sounds like it is just dumping fuel.
If you are really wondering about the ECU since you have had an issue with it before, grab another on ebay. I only did a quick glance and it seems that year 4.0 is between $50-150. I would try to check out other stuff before resorting to that though. Hopefully you have other means of transportation, have your daily down always sucks.

 

I have a 79 corvette also. I removed the engine last month and 'Im rebuilding it. I bet I will have my Vette on the road before the XJS.

 

Well that just depends on how much time you spend working on one compared to the others, so that doesn't mean much. You just have one problem to diagnose and one thing to fix. As far as time that shouldn't take long.

But if you spend all of your time rebuilding the engine in the corvette, trouble shooting possible starting or running issues, etc then of course it would be done first.

Is it easier for you because it has a carb? If you can't work on fuel injected cars or don't want to figure them out, then sell the jag and get something you enjoy working on more. Don't keep it if you don't like it, but also don't **** on it just because you can't diagnose it and don't want to spend the time doing so.

What is the compression? What are the injectors doing? Are the O2s in spec? Your car sounds like it is dumping fuel or not completely burning it.

It doesn't need to be frustrating, just do the tests and checks to gather the data needed to diagnose the problem and ask for help here if you aren't sure where to check or what to do next. We are asking for more data so we can help you diagnose the issue

 

The corvette will be ready before the corvette before the xjs


The XJS Timeline:
Nov 2014
Vehicle suddenly develops crappy, engine shaking idle.
Replaced Spark Plugs: still crappy, engine shaking idle.
Drove vehicle in said condition until June 2014


June 2015
Suspected vehicle was running on 5 cylinders. Stopped driving vehicle
July 2015
Drove vehicle to repair facility that works on Jaguars (there were any there including a few facelift xjs's.
Found out through shop that coils were firing intermittently, two were good need to replace coils to investigate further. ( was on invoice) Price of coils $750.00. Went to pick up car and vehicle would not start. $65 tow on top of $100.00 diagnosis charge.


August 2015
Purchased aftermarket coils. Vehicle did start had same crappy, engine shaking idle.
(glad I did not spend $750 on coils to have the same problem) Did not do anything else to vehicle until Feb 2016.


Feb 2016
Started Vehicle, still crappy idle but farting from exhaust this time around. Moved vehicle from drive way (to have space to remove the engine from the corvette) to the street and vehicle stalled on me twice. Tried to start vehicle to straighten it so it would be parallel to the curb. Left it there for 3 days. Attempted to start vehicle and it did start but stalled when I just barely got it on the apron of my driveway. Waited 20min and started the vehicle. It started I let run crappy engine shaking farting exhaust.


March 2016
replaced spark plugs with Champion rc12yc plugs (no cc in US)
Attempted so start vehicle, same symptoms.
Mar 29: replaced battery b/c last battery was at it's last quarter of it's life
Attempted to start vehicle and I only get one crank does not start.

 

1. Sounds like the shop misdiagnosed the car.
2. You have eliminated the spark plugs and coils from the list as possible culprits.

I would either find a shop better suited to diagnose this car, or diagnose it myself. Throwing parts at the car will probably not work out.

There are posts above that have made suggestions and recommendations to diagnose. Keep us posted as you make some progress. Based on your narrative, you've made no attempt since the shop gave you a crummy prognosis.

 

Again, my opinion on the next step in diagnosis is checking out what the injectors are doing, checking whether the O2s are in spec, inspecting for possible wiring faults, and checking compression (since it is easy and will tell you if the exhaust valves are too tight). But that is just based on the info given.

Before you said the cats were cherry red, but now the car won't start at all. The car should still run on 4-5 cylinders so that may be an indication whatever was failing completely failed, but then again you also just elaborated and told us that this car has had a problem for 2 years and you put some plugs and coils in it and can't figure out the problem. It may not be starting due to other problems now. Has it had the same gas in it this whole time?

After it running poorly and having cat problems, I would also look into removing and inspecting the cats themselves. Perhaps they collapsed from the problem, or perhaps they collapsed and exhaust restriction is the problem.

Also, maybe the shop was partially right, maybe those coils were intermittently firing, but maybe it was further in the circuit than the coils themselves, but a simple test would have determined that. I don't have a diagram for the later AJ16 so I could only assume that, being distributor-less, its ignition system is based on coils, O2s, engine and cam position sensors, as well as a few other sensors. If it was an ignition issue and fuel dumping issue was due to unburned fuel igniting in the cats, some of these sensors, the wiring, or the ECM itself could be at fault.

Part of diagnostics is gathering more info to determine the problem. It doesn't mean you can test 2 things, find nothing, and so it is all a wash, it means you can eliminate those things and keep moving on.

Obviously it sounds like a lot to just say "check the entire fuel and ignition system" but it is more systemic than that. You start at the end point and work your way out until the fault no longer exists, the same you do with an electrical fault. So at the base, is there good spark, is their compression, and is their good fuel pressure in the proper ratio? Maybe spark is intermittent, maybe injector is stuck open. Is this the injector or the signal to it? Swap with another injector, etc.

I can't really sit here and tell you exactly how to diagnose, it is a puzzle-solving process that varies everytime. But if you had had the car for 2 years in this condition and all you did was put coils and plugs in it, you either lack the motivation or know-how to diagnose it. Ask about whatever it is. I don't know the spec for 96' O2s, but if you looked it up and couldn't find it, maybe a general spec can be used or we can dig it up. If you don't know how to test the O2s and couldn't find a tutorial, then ask.

It is just a process of elimination.