well, yet another rough idle . so, have this 1996 xj6 with a rough idle . it misses . car has 145k on it . power is fine once you get going . sometimes stalls for no reason .starts back up and she goes. I have swapped some coils before with used ones . not sure if problem remained or got better . in any event, this is driving me nuts. some codes would be nice . I did once get a p0400 code . egr temp ? I cleaned throttle body a little and nothing. do crank sensors really go out on these things? is it best to get new coils and call it a day ? perhaps dirty injector and or injectors ? you can feel the miss at a light .almost seems like it wants to stall . any help would be great . thankx

 

We are starting to get a fair amount of this type of complaint here on the X300.

Ignition coils seem to be a common issue, but mine has done 173k kms and still original coils and fine. Maybe being a "Big Block 3.2ltr" makes a difference, doubtful, but just could not resist.

The crank angle sensors do "just go out". Mine did, drove in the drive, got change for an outing with spousy, and NOTHING, cranking, NO fire in the belly, took her XJ-S V12 and heard about it ALL night, fair dinkum. Swapped the crank sensor all good, swapped the old one back, just for fun, dead as, so it was the culprit.

This was at 168k kms.

Word has it that anything over about 100k miles (160k kms) is borrowed time, and I have no idea why, as there are NO working/moving components in it ??.

The in tank fuel pumps also have an "average" life of 100k miles, and then begin to "go off".

We do not have air pumps, EGR valves, etc down here on this model, so we are not blessed with the faults that is caused by all that add ons. Had heaps of it on the earlier V12's, real PITA, until the pumps etc were removed, then all was sweet.

 

thankx for the info . I read somewhere here that there is a way to test the coils . perhaps Ill ohm them out and see what I get . I can swap crank sensor as its original along with the fuel pump . had my fuel pump in my 99 xjr go out . 100k no signs , just out .however,I dont feel the pump could cause this miss at idle but as I have experience with the 99 perhaps I should just replace it .another thing I should mention is sometimes I get some smoke out the tailpipes. looks like an over rich condition .in fact the tips have black residue on them . gas milage is poor but then again it was never great new .

 

You want .75 ohm primary resistance





It might be a good idea to get a scan tool so you can see what the oxy sensors, coolant sensor, etc are doing.

That said, I have a scan tool and can't find any abnormal reading that would account for a slightly rough idle, especially, as in my case, a come-n-go slightly rough idle.

A leaky injector could cause a rough idle and rich running. Just a thought.

Exhaust smoke is certainly an indicator of rich mixture but black tailpipes doesn't say much, really, unless it's caked-on soot.

A few years ago I had my injectors professionally cleaned and it definitely helped so I might have it done gain. In fact, all three of my Jags have had idle problems or one sort or another (grrrrr!) and injector cleaning has helped all of them.

Another issue on these cars....a bit more specific in nature...is a smooth idle that turns choppy when the gearshift is is "P". This is apparently caused by a faulty injector that essentially goes dead when the ECU commands a minimal pulse width...as it would at idle, in "P".

It's really frustrating to continuously battle these rough idle problems. I drive so many older, lesser cars that have a glass smooth idle at all times !

Cheers
DD

 

This engine/ecu suck for misifire codes. Mine can sit there and miss and miss and miss. Ive never gotten codes except when a coil goes totally dead and no fire on the cylinder. Then..it sets a cylinder code. I always have to resort to swapping out coils 1 at a time with a set of used ones ive saved. But ill tell you next time im changing them all since i found them for $58-75 each depending on manufacturer on partsgeeks.com
ive been plagued twice on stalls. First time yes the crank sensor and would stall driving down the road then restart, but got to the point that it had to sit a cool alittle so that was the give away on that. Couple weeks ago it starting just stalling leaving a stop occassionally but i felt it was more like the tps kinda lost track of my foot command. So i did a throttle and 02 sensor reorientation with ids and that cured that. My next repair needs to be a new cam cover since mine has deteriorated inside the plug wells to the point that the metal has corroded and expended to touching the sides of the coils which as the boots get old lets the spark go out the side to ground causing misses also. But for the most part i consider allt his normal time and mileage things that come up on a 15yr old car with 140k

 

thankx for this info . I checked some coils I have (spares) . they all get .90 ohm reading . I do recall seeing some oil in a couple plug wells before . cleaned out and re installed coils . is this what we can call the valve coner gasket ? I have thought of injector cleaning . I do this on my other line of cars I own (rotary powered ) . so at this point , I have learned that the crank sensor should be replaced at or near 100k . coils failing are normal and perhaps easiest to swap all six with new ones. I do have code scanners and I own a launch x431 system . o2's seem to read fine along with water temp . guess at this point Im going to swap crank sensor and see what happens and try to find some good priced coils . I might also mention the miss does happen in park and nuetral . worse in gear as you have more load on the motor . oh, while Im here, I read something about only using champion spark plugs ? I have ngk or bosch in there now ..any thoughts ? thankx again ..

 

When i used to service those alot more than now, i do remember them being tempramental about plug gap and plugs. I still only use champion on that engine

 

In my limited experince.....just my own car.... I've concluded that 1.0 ohm seems to be the top-over point








I bought Beck Arnley from Rock Auto, about $60 each. I don't know what actual brand they are. No markings except "PEC".

I've heard some say that only OEM coils should be used as the aftermarkets don't last. <shrug> I have my fingers crossed. $150-$175 each for genuine OEM Lucas coils just isn't in the cards for me right now.





I agree, although the peculiar injector fault I described is just the opposite....occuring with minimal load on the engine








Hard to say as there's so much anecdotal and contradictory evidence out there. It's just like tires and motor oil, IMHO.

I've gone back-n-forth with Champs and NGK iridium and felt no difference of any kind on MY car. I went with the NGKs purely because I heard that the iridium plugs are easier on the coils <shrug>. I dunno.

Cheers
DD

 

strange on the coil reading . mine will hit 1 ohm or so and settle down to .9 . could this be an indicator of coils going bad ? Im also tempted to try the champion plugs . like 2 bucks each . hmmm .

 

ok, well I played around with this thing for a bit . swapped crank sensor with a low mile used one . no change . swapped coils with some used ones I have . tried different locations and combinations and nothing . same issues . no check engine . I highly doubt that all my coils are bad . all check out at .9 ohm both hot and cold .didnt see any oil in the plug wells . so, Im thinking maybe an injector . maybe injectors are dirty ? 145k original injectors. I know fuel pumps go out on these but I cant see it on idle . the car pulls fine when on load . perhaps an injector is just leaking .I will be quite happy once I figure this thing out .

 

when reading a very low resistence, it is important to check the resistance of the test leads by shorting the probes together and remembering the reading. If it is not exactly zero, then subtract the lead resistance from the total measured.

 

Something else to check.

Wifey took my X300 to do what they do at the sales and I did an oil change etc on her V12. Did an oil change etc on the X300 yesterday. Anyway, she drives in a says "the car is idling rough as .....", is my V12 ready yet??.NO sense of humour.

Back to basics, concentrating on what I messed with yesterday doing the oil change, and eventually found a largish crack/split in the oil cap seal, and it was sucking air, which of course is detected by the system as "unmetered air", being "after" the air meter, mmmmm, and ANY unmetered air will give idle issues.

New (well s/h) cap fitted, sweet as any AJ16 you can find.

Maybe NOT relevent, but worth a simple look.

 

good point . Ill look into the cap today . wish it would be something as simple as that .maybe it is.going to swap injectors today and see what happens .good thing that I have many parts at my finger tips to play with.bad thing is I have to do the work .

 

well, I get .2 or .1 so that puts my coils at around the .75 or .85 ish range. all I can conclude is at this point we need fuel and spark to run . if there are no codes and there is spark, then perhaps something with the fuel is out . injectors do go out and or get dirty or leak .145k, well its possible . going to try swapping the injectors next .

 

well, today I swapped injectors with fuel rail and regulator . same issue .then I went and got champion oe plugs just for the sake of trying it . same thing .now Im really stumped . no codes, new plugs, working coils,good crank sensor,different injectors, whats next ?? Im tempted to try another throttle body . couple strange things . when I start it up at first it seems much better . this includes hot and cold starts .another strange thing . after the spark plug install, I noticed if I hit the brake a few times in park the idle keeps climbing and staying there . like around 1500 rpms .drop into park and it stays around 900-1000 rom but the miss is gone . as soon as the idle comes down the miss will be there again . Im determined to get this figured out asap . anyone got some ideas ?? thankx again

 

Do you have a scanner to read LTFT & STFT?

 

can the coils still ohm to spec but be shorting to the engine our anything like that?

Also, read in another thread a rough idle was caused by a crack in the oil cap... Something about unmetered air...

 

[quote=imagineaudio;366499]can the coils still ohm to spec but be shorting to the engine our anything like that?

quote]

Some members have discovered that by running the car in the dark with coil cover removed. I don't know whether or not those ohm'd properly or not though. Search on "instrument panel" or "ignition cuts out" or something like that. Most of those were having problems with cut-out and a flickering IP, I think. Still worth a check, given the relative ease of the procedure. Good catch.

 

yep, I will check that and post back the readings .

 

well, that is possible . however, when I did the coil swapping it was in the dark. on purpose to see if there was anything like that . saw nothing . did check the oil cap and it looks ok .