Does anyone know how to test an XJ8 ignition coil with a Multimeter?

 

You can Ohm them out, but what are your symptoms leading to the need to test coils? Year of XJ8 also, please.

 

2000 Vanden Plas, 85k miles. Has a rough idle and stumbles when applying throttle. While trying to fix, I recently installed new secondary tensioners, plugs, fuel filter, downstream O2 sensors. Cleaned throttle body and MAF. Fuel pressure is 41+/-psi at the rail. No OBD II codes, except a pesky P1646 I can't get rid of even after the new O2 sensors. After all this, nothing has changed. Still a rough idle and stumbles during acceleration. Coils are next on the list. Feels like it's running on 7 cylinders, part of the time.

 

1646 - Is the front O2 Sensor Bank #1. This is the one on the right sitting in the car. I just replaced my left one -- code 1647. These codes are for the heater circuit for the upstream sensor. Its a 4 wire sensor. My car was running fine but needed to pass inspection.

The right sensor is much easier to replace -- it is sitting out in the open right on top. Mine was a pain since its covered by a few components. New sensor fixed the problem.

I bought a Bosch sensor from Amazon for less that $75.00 -- as well as couple of different O2 tools since I was not sure what I would need. The original sensor out of the car was made by Denso. I read where some had problems using a universal sensor - The correct one is an exact replacement.

You have replaced a lot of stuff -- before I replaced any coils I would have the engine scoped -- Its silly to just replace parts.

 

Thanks for the insight yeldogt, but my thread is about testing parts, not replacing them. Is there a part listed in my post that you would not have replaced? The tensioners were cracked, the fuel filter and spark plugs were original on an 85k mile car. You spent most of your post explaining how to replace O2 sensors after I already stated that I replaced them. The O2 sensor was throwing a code, and I was always tought to replace both if you're going to replace one. If you don't know how to test an ignition coil, please move on to the next thread. Giving me info on something I've already done is just SILLY.

 

Well I hate being silly.

You mentioned that you replaced the "downstream" O2 sensors -- maybe you really wanted to say you replaced all four of the O2 sensors. But, P1646 is for the "upstream" sensor. I was trying to explain the difference and help you out and to also point out that people have had running problems with the generic sensors - not knowing what type of "downstream" sensors you installed or why you had to replace them. The sensors can last a long time --certainly more than 85k -- and they do not need to be replaced in pairs.

As to replacing parts - I most likely would not have replaced the plugs or the fuel filter. I have rarely found them to be the main cause of your idle problem on a modern car - but they can't hurt as long as the correct ones are installed and you are certainly allowed to fix whatever you want. Plugs at 100k are often in almost perfect shape if nothing else has failed. Did you look at the plugs when you took them out -- a fouled plug could have pointed to a failing coil. I can't tell you the last time I changed a fuel filter - or had any luck cleaning a failing MAF sensor. Did you get a code for the MAF?

What you are describing could be a typical coil failing -- and it is often very hard to diagnose without a scope or replacing them -- that is what I thought you meant by the "coils are next on the list". My experience -- and this is only mine -- testing for a weak coil out of the car is problematic. Also, since these cars are now getting quite old I try to refrain from removing parts unless I have a good reason to be believe they are the problem - I have found that it can cause other problems down the line.

So .......... I was just trying to help ........Good Luck

 

The normal intermittent failure mode for a coil is "high voltage leakage". Since we are being sorta nit picky here, it is actually "high voltage arc over through failed insulation" Anyway, you cannot measure it with a multimeter. So, usually there is a code generated if it is a specific cylinder misfiring, and you swap coils to see if the problem follows the coil. Since you have no code, then the scope suggestion seems to be the valid test procedure. My experience with the X308 is that the OBD misfire detector catches a specific cylinder, so the stumble may not be specific cylinder related. It would be interesting to see the charts of the O2 sensors.

The "pesky" code sure implies a wiring or connector proble since yiou have changed the sensors. I would look into that. I did notcheck, but if the code is for the heater circuit, that can be tested with the multimeter to see if the heater is on, and drawing current when the engine is started cold.

Good luck and keep us updated.

 

for someone wanting advise that right there is REALLY HARSH
and IMO he's correct. you said "BOTH" there are 4, 2 upstream and 2 downstream. your code is for the passenger side upstream 02 sensor heater. And if you replaced all 4, or at least the 2 upstream, then you need to "TEST" the heater circuit from the 02 sensor connector to the ECU for short to ground/power, or open circuit. But then you can also have a bad N.E.W. (NEVER EVER WORKED) part.
And sparkenzap is correct too. youll never find the high voltage leak till it(the coil) goes dead, or becomes more severe. Best suggestion is to call the dealer close to you and talk to a tech and ask if they still/ever had Jaguars Genrad handheld scanner. Not all dealers bought them and theyre no longer made or avail. With this perticular scanner you can pull up misfire counter in "non continous" testing and see which coil/coils are guilty. It shows anything from 1 to 1000's of misfires on a single/multiple cylinders and youll never have know which one if the check engine light isnt on.
Of course then "stumbles" can also on your car be a bad mass air flow sensor that gives incorrect airflow readings to the ecu so you end up with stumbling. If I suspect that I have "TEST" parts to swap in and see what happens. Much faster than running "tests and checks"
Dang and people say IM BRUTAL...

 

I believe he was trying to tell you that the code related to UPSTREAM, not downstream sensors... we certainly can't be aware of what you were taught, but failed to mention.

I sure hope you were just having a bad day, because if this is the way a noob normally comes asking for help from people that are willing to assist, when it is YOU who is in error, then I don't think you're going to do a very good job of making friends or influencing people here in the forum, not to mention getting any more substantive help.

 

Thanks Quadmaniac, I meant downstream when I said upstream. And yes, I was having a bad day. I guess I got defensive when yeldogt called me silly. For that I apologize to yeldogt. Closest Jag dealer is 200+ miles away, so I'm stuck trying to figure this out on my own. I ordered a new coil, should arrive in the next couple of days. I've cleaned the MAF with CRC MAFS cleaner, nothing changed. Then soaked it in alcohol, nothing. Ohm tested the fuel injectors, all good. Getting ready flow test them.

 

Well then now you atleast know why you still get the 02 code, you got the wrong 02's replaced. What coil are you replacing and why. An ohm test will show an open or short, but these coils most often misfire from voltage leaking or going to ground through the head instead of firing the plug. If you really want to replace something with out alot of testing and the right equipment to do so at hand. Buy all new coil boots and replace them all. Just like plug wires in days long ago, when then get old the crossfire and arc giving misfires. Someone may jump in and tell you where and what is avail outthere that works for boots without having to buy a set of coils

 

Not to belabor a point -- but I did not call you "silly". It was a reference to future parts replacement that I called "silly".

Finding rough idle issues can be annoying - the fact that it continues into acceleration issues changes some of the things to look for. As others have said the computers in the car are normally quite good at finding a cylinder coil misfire especially if it is arcing out - but a dying one can be difficult because it can be working enough to not trip anything but still not strong enough to allow the engine to run smooth. I have found that if you allow the engine to sit and idle for a while -- sometimes (if you are lucky) the plug will foul enough to trip the sensor and the CEL -- then you can read the codes. I did this last week on one of the older high mile fleet cars we have. Now I'm talking about 15min -- not 2hours -- and I stay around the car.

You could have a bad injector - But its less likely than the coil - and I try not to play with them. Same with the MAF -- they can be destroyed easily .... Not sure they like alcohol? .......... Did you get a code for the MAF?

Now .. one more ......... You said "downstream" again.
I don't see you saying "upstream". The code you list is for the upstream 4 wire sensor not the downstream two wire sensor.

Keep the faith

 

And... As yeldogt was trying to point out about changing parts, you will bankrupt yourself doing diagnosis by parts changing on a Jaguar. For instance, swapping the suspect coil with another and seeing what happens with the code is a bunch cheaper than buying another coil.
As a case in point, I was getting codes on my F150 truck. Since the O2s had 250,000 miles on them, and it is a gas hog, I admit that I decided to change the sensors without bothering to do diagnositics. BTW, it did not fix the code (I scanned it and found it was the EGR!) nor did it improve the mileage enough to measure. HOWEVER, my point is that the sensors were $33.58 each, not $149.00 each. And they are much easier to get to on the truck.

 

Sorry Brutal, I said downstream again when I meant upstream. Let's simplify things a bit, I replaced the two O2 sensors with 4 wires that are closest to the engine. I checked and they are getting voltage to the heaters and from the heaters. As far as the coil goes, my plan was to swap out the new coil with each one of the existing coils until I found the bad coil. I ordered one from advance auto for $98, I had a coupon and free shipping. It should be here Monday. I checked the fuel injectors and they appear to be working properly. I pulled them all, reAttached them to the rail, put a tray underneath and had my wife crank the engine. All had what appeared to be good flow. At this point I'm pretty confident it's not a fuel problem. As far as the MAF goes, after cleaning, the car ran the same as before. So it's either broke and I didn't break it any worse, or it's not broke, and I didn't break it cleaning it. Any way to test one?

 

One more thing about the O2 sensors. While I was making sure the connections were good on the passenger side, I cleared the codes, started and stopped the engine, checked the codes again, and the 1647 code appeared and no 1646 code. I cleared the codes again and after starting and stopping the engine once more, the 1647 was gone, and the 1646 was back. After several more attempts, no more 1647, but always the 1646. Go figure.

 

I use my scanner and pull up MAFS and monitor reading at idle and increasing rpm. but like I said earlier(wont work for you) I have test parts that I know are good and much faster if I suspect the MAFS. Otherwise without scanner it would have to be put on a scop to look at the wave form. or useing a fluke and set the scale really fast and again watch for blips in readings. seldom do you get a code for mafs problems.

 

[QUOTE=JDSIMPSON55;234005]"I checked and they are getting voltage to the heaters and from the heaters. "

Hmmm- What do you mean by voltage to and from the heaters?- That would indicate no voltage drop accross the heaters. That would indicate the controller circuit is not turning the heaters on since it APPARENTLY works on the ground side of the circuit. BTW The 2000 NA North America diagram shows 4 wire sensors at both locations. Since you now have codes from more than one sensor, I might suspect the lambda heater relay (EM75) or it's power supply. Or, possibly, the ground circuit on the ecu. As I remember, there have been reports of a paint/ corrosion problem on the ecu ground stud, although none of mine have ever had that (yet).

 

Skip

 

Where is the ground stud for the ECU?

 

The voltage running to and from the heater side of the O2 sensors on A and B bank is around 14 volts. The signal wires are around 3.8 volts and the ground wire is 3.8 volts. I used Bosch's wiring instructions to determine which wires are which. I realize I might be comparing apples to oranges, but I went ahead and tested the voltage on the lower o2 sensor A bank. If the wiring is the same, I got 14 volts on one side of the heater, a fluctuating voltage of 7-12 volts on the other side, 0 volts ground, and 0 volts signal. Any insight?