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Hi Guys,
Had a small ! miss fire for the last couple of months, nothing major but car didn't like lots of throttle it had to be treated nice and gentle (just like the wife ) and then it was ok. been doing a few bits of preventative work over last couple of weeks ie new water pump, thermostat tower full engine flush and coolant replaced and thought id change air filter, replace spark plugs & clean MAF sensor to cure small miss fire uhmm, now small miss fire is big miss fire and its all i can do to make it move, the harder accelerator is pressed the slower it wants to go ! there are no warning lights or messages on dash so i presume no good putting code reader on, read lots of old threads on all V8 engine posts on BB but cant pinpoint anything. although ive had miss fire for a couple of months cars only done about 200 miles in that time as its just used at weekends (sometimes !) and with lovely weather weve had and no garage i just didnt get round to checking it out, Any Ideas Please, Gary

it may be a coil pack on top of one of your spark plugs

when these fail there is no spark at all for that cylinder,

this usually manifests its self as ok when the engine is started , but a few miles down the road the engine can go lumpy , this is due to the heat breaking down the coil further ,

sometimes the coil is FUBAR to start and the miss-fire is always there,

these dont always throw the warning light on , but a code reader should tell you which one i playing up

if your car is before 1999 then it will have a 2 wire coil pack , if 99 or later it will have a 4 wire coil pack

take off the plastic cam cover-cover, and see how many wires to the individual coils ,

BB

Yip, that`s what happens.

Just done one on my S-type which was spluttering away like crazy on hills. Changed a coil on No 1 OS bank and instant result.
Mike

Thanks BB / Mike
car starts as soon as you turn key but missfire is there straight away wont rev cleanly and if you blip throttle theres a definate pause before anything happens, cleaned MAF sensor but made no difference looked clean but can you tell by looking ? no obvious faults on induction side but again with all sensors how can you tell ?, got a mate coming monday night with code reader to see if that will pinpoint anything ?, anyone know were plug is on car ? been told passenger footwell but cant see it (didnt have my glasses on though which may help ) also whilst stood staring at engine bay today i noticed a small coolant leak from top of thermostat tower ive just replaced, did notice there isnt a gasket in which seems strange for metal to metal cap tried to ring Neville but must be closed today or racing or something, anyone know if there should be a gasket / washer, help for any of these faults appreciated as im sick of the grief from wife about "that big red bag of shite blocking driveway must be really hard for her to get her massive PEUGEOT 107 in & out, oh for a peaceful life .

You appear to have exactly the same issues that I had. Suggest you go to the S-type BB and Club comment sections and see my posts on spark plug/ MAF / coolant temperature/ sensor issues.

Try this link to start with.
http://www.jec.org.uk/forums/viewtopic.php?f=193&t=5479


I suggest you go this way with the problem. Install a new set of plugs. Clean out the throttle body throat with carb cleaner, removing all traces of crank case breather oil residue to leave it spotless. The MAF sensor can be difficult in as much as an Autologic type interrogation does not always show a MAF that is on its last legs. I replaced mine even though it did not flag up when interrogated. Around £70 new but not much from a breaker as an experiment. Replacement did make a difference so I must assume that my MAF was past its best.

Start the car and let warm up. Go to the exhausts and listen to the engine note. The note should be even and you should hear bom, bom, bom, bom etc indefinitely if you do not have a misfire. Bom, bom, bom, POP, bom, bom, bom, bom, bom, bom, bom, POP, bom etc tells you that seven cylinders are firing ok in sequence, but the POP is the misfire. So you have one cylinder not firing. Two pops in a sequence of eight firings would suggest two cylinders at fault etc. If you listen intently to the exhaust note, it is possible to hear the pulses and count them.

If you remove the spark plug covers, this will access the plug on coils which are held in place individually with a 7mm headed x 25mm bolt. To disconnect a coil, depress the 12v DC plug tab on the connector and pull the connector off the coil. Remove the 7mm bolt and pull the coil off the spark plug. A new coil or number of coils can be changed in this way. A good way to find out which coil or plug is at fault is to individually remove each connector on each coil in turn. Switch off the engine on each occasion you disconnect a coil to avoid risk of a 20k volt belt from a coil. Insulation can break down allowing high voltage to squirt out of any cracks in a broken coil case. That voltage would take the shortest path to ground via your fingers! Check also that the spark plug well and rubber coil boot are not full of engine oil. If the are, that will also cause misfires. The only remedy is to change the cam cover "spectacle" oil seals to cure the leak. See Brake Busters V8 article in the July 2012 magazine for details.

If when you disconnect each coil in turn the engine note becomes even more uneven and even more pops are heard from the exhaust, you may reliably assume that that coil was ok. If there is no change in engine running and you still popping away without the engine note changing, then you may assume you have found a duff coil or spark plug. It sounds as if you have one or more coils gone, so perhaps buy at least one new coil which you could substitute in turn with each coil on the car, until you find the offending broken down unit. However your friends interrogation equipment is perhaps a quicker way of finding which coil or more might be defective.

Spark plugs misfire when worn. I have found on an S-type V8 which shares its engine with XJ8 and XK8 models, that worn plugs tend to misfire at around 1600 and 2300rpm. Duff coils begin to show early signs of failure when pulling up motorway inclines on light throttle and then coughs and splutters begin with a loss of torque. The car feels nasty to drive and as the coils continue to break down, pops can then generally be heard and felt at idle speeds when stationary. One also finds that the car is reluctant to accelerate cleanly and generally becomes irritable and drives like a bag of poo!

I`ve just replaced just one coil the other evening. Joy of joy! Instant fix with the car running like a sewing machine again with a nice even exhaust note again.

In addition to the above, a defective cylinder head coolant temperature sensor mounted within the front coolant manifold and the ambient air temperature sensor in the throttle body plastic trunking can also upset fuelling and ignition systems. I know this from recent experience. Both sensors are around £13 new. Mine began to fail at around 75k miles. Replacement of these and the other sensors listed above, even if found "ok" when interrogated, often produce improvements in engine running although still seen as ok by an interrogation programme. So a few hints here for you.

The ali thermostat tower cap seal is not good really. It is supplied with an o-ring which can get badly crushed and mis-shapen when the cap is tightened down. The top edge of the tower is very sharp and this is what can wreck that somewhat inappropriate seal ring. Not brilliant at all and the ali towers worst design feature. The remedy is simple. Replace the o-ring with a fibre washer and the leaks will stop.

Hope that helps. there is a cause and a reason for each issue. Just a question of finding it!

Mike

then there is also the part load breather pipe from the cam cover to the TB, they crack in the valley of the engine

that can cause rough running

BB

The OBD II port is on the drivers side under the knee pad on the left of the steering wheel.

I'm a great believer in diagnosing as much as you can before throwing money at new parts. For an elusive fault such as this, it's probably worth getting it put on an autologic or jaguar system so that you can see the performance of each coil + the readings of the MAF before you buy any plugs or coils etc.

Good luck

Paul

Thanks Mike, BB & Paul for all your advice, will try and sort this week and post any results, going to start with code reader and take it from there. already renewed plugs, air filter and cleaned MAF sensor but if anything made it worse, a tiny little bit of oil in spark plug wells (cleaned out before new plugs fitted) but not enough to cause miss fire i wouldnt have thought. Tried removing battery for a while and reconnecting as mentioned in other posts too. Gary

MAF sensors are very delicate instruments. No prod with a screw driver! Spray switch or carb cleaner only. You might find a cheap second hand one at a local breakers for direct substitution as an experiment or on the road spare.

The thing about diagnostics is that they can often only point you in the general direction of a fault. After that I find that unless the diagnostics point specifically at an out of limits item and the fault still persists after an analysis has been done, then it is down to eyeball and intuitive detective work to solve a problem an often to direct substitution of a suspected part to prove the point. Fault codes are not everything. Often only just the start.

I am now slowly building a "get you home spares" kit for my V8. MAF, temp sender, one spare coil and spark plug, header tank, serpentine belt, ambient air temp sender, thermostat, good metal bladed water pump, fuel pump etc. As I found out at Weston Park, it is not fun being miles from base with a car that is playing up.

Mike

Thanks Mike, boots not bigging enough on XJ to carry your get you home kit got breakdown cover and relay with insurance, cleaned MAF sensor with contact cleaner and then dried with hair drier and left in sun for an hour but as stated it didnt look dirty but can you tell, air filter was filthy so thought that might help when renewed, got my tempereture sensor but not sure were it goes . Just hoping that reader will show a coil pack down as that was my first thought. No doubt Neville will be a bit richer by end of week . Gary

Gary,

As Mike says, fault codes often don't get you very far. That's why I'd put a diag tool on it that can actually show you the readings on MAF, lambda sensors, temp sensor, individual coil packs etc.

My suggestion (for what very little it is worth) is don't change anything unless you have some form of evidence that it is not working properly. Our Bulletin Board is littered with examples of members randomly changing components in an attempt to resolve a problem.

Good luck

Paul

Paul
if i dont get no joy with codes il have to start thinking of a specialist but to be fair if car was running enough to drive safely i would have taken it to my local specialist, Bell Lane Garage South Elmsall or a new one at Armthorpe whose name escapes me at this moment because as you quite rightly hint at it could become quite expensive chasing an unknwn fault. Gary

Gary,
the new one is Chris Isle, " thejagspecialist " at Armthorpe.

Gordon

Gary,

Just a thought (and I'm sure you don't need any more random suggestions!) but I just noticed that you've done very few miles over a period of months. Modern petrol goes off much quicker than the old leaded stuff. How about syphoning it out and put a few gallons of nice fresh stuff and run it for a while? Might be all it needs!

Paul

Evening All
Found fault i think / hope, according to reader one fault only which is MANUFACTURERS SPECIFIC CODE P1647 which equates to LINEAR 02 SENSOR CONTROL CHIP (BANK 2) what i need to know now gents is What, Where How Hard and more importantly HOW MUCH, i await replys with baited breath Many Thanks Gary