Hi just bought this car and new to this forum so firstly hello and hope someone could shed some light I am a mechanic by trade.but this is my first jag normally I ride in an Impreza turbo.car is a 96 xjr x300 lazy starting suspect the battery.but the main problem is from cold runs fine when hot get a intermitant misfire like a coil pack.spark plugs done changed all coil packs from a xjs that I have access too with starts on the button no misfire.still I have this misfire.when driving cannot fault.apart from the high fuel usage 14miles to the gallon and less driving like Arthur Dailey. Just rectified the exhaust downpipe blow.faylt code in ecm p1178 sensor 1 bank 1 checked no leaks on intake and throttle body cleaned.would you just bite the bullet put new 02 sensor.unless anything else and would the price reg xjs 4.0 normally aspirated o2 sensor fit on mine thanks Steve

 

So you have eliminated coils and plugs. The high fuel usage indicates something. Maybe just loss of power due to the misfire. Maybe an injector gets stuck and is wasting fuel plus causing that one not to fire properly.

If it's an injector then injector cleaner in the tank (redex?) might clear it without you having to do any work.

PS mine does 20mpg (according to the trip computer) if I do a bit of A roads a bit of dual carriage way and a bit of going flat out.
If I go careful it does 22mpg.
If i did flat out everywhere then probably 12mpg.
When I first got it there were 6000 miles on the trip computer and the average MPG was 19mpg and average speed was 32mph. I feel the last owner never went on dual carriageways since my average speed is 42mph.
So 14mpg is wrong.

 

That sounds like high fuel usage unless there is a lot of stop and go and congestion. I would be looking at the coolant temp sensor, as well as O2 sensors. NTK are the OEM O2 sensors, they are good and can be bought aftermarket for much less than Jaguar wants for the same thing.

I should also mention that these cars seem particularly sensitive to the type of plugs. May misfires have been cured by new Champion plugs.

 

Well up fate fitted a good used o2 sensor in bank 1 nut still have this misfire like a plug or coil shorting I have new bosh plugs fitted air gap as per auto data manual 0.6mm all coil packs changed with good confirmed used ones as I have another complete xjs 4.0 jag for spares..

 

You may find that fitting the proper Champion plugs will solve the problem. It's also possible that a coil is shorting through a defective or damp boot to the head or valve cover.

 

Well after a long 6 months in body shop.it developed a flooding issue.
After fitting another set of plugs it ran but had misfire?
Had to replace two coils with 2 good used ones and rectify bad injector wiring on cyl one.also changed both 02 sensors as failed mot on high c02.
I've used insulation tape on all coils to prevent arching.but this misfire remains I'm starting to think injectors.whats the best way to check them ie spray pattern or does anyone know someone who can check I'm local to Heathrow..I think an injector is sticking....

 

Hi Steve,

Did you install the correct Champion RC12YC plugs that RJ recommended, gapped to 0.035 in. / 0.9 mm or 0.038in/0.96mm? Many members have experienced problems with other plugs, even expensive Platinums and Iridiums and 2- and 4-electrode types.

Do you have any stored diagnostic trouble codes related to a misfire, such as P0300 and a cylinder-specific code such as P0301-P0306?

One check you can do is to disconnect the fuel injectors, one at a time, while the engine is running, to see if disconnecting one causes no change in how the engine runs. You can do the same with the coils.

One potential contributor to flooding is failure of the fuel pressure regulator (FPR) diaphragm. You can test this by detaching the vacuum hose from the FPR, cranking the engine, then checking for signs of wet fuel in the vacuum hose fitting on the FPR, which indicates failure of the diaphragm, which allows raw unmetered fuel to be inhaled into the intake manifold.

One other thought is that a failing crankshaft position sensor (CKPS) can cause hard-to-diagnose issues. If the CKPS from the XJS will fit your X300, it might be worth swapping it in to see if the engine behaves better.

Cheers,

Don

 

Hi Don thanks for reply.regarding the plugs into have always since owning had this misfire.i serviced the car removed old plugs champion.and replaced with bosh.still has misfire only sometimes intermitant.

When the body shop flooded the car I replaced the plugs again with ngk bkr7e.but still had a constant miss which turned out to be two coils packs and a dodgy wire to number 1 injector.
Since back changed 02 sensors as was only getting codes for them.
On road test other night the misfire is still there but tandem like a poofing sound.ive taped up the coils with insulating tape no joy.and even remove coil pack plugs one at a time to see if the random miss goes.
I thought no4 made it go changed coil but still there.so I'm suspecting injectors but need someone local to clean and balance.and regarding the crank sensor I fitted Andy bracket but crank sensors normally either work or don't work..

 

Yes, theoretically, crank sensors either work or don't work. But the longer you study Jaguars, the more you'll understand that plenty of difficult-to-diagnose symptoms have been resolved with a new CKPS. Whether the failure mode is thermal- or vibration-related or due to some other factor I do not know, but Jag crank sensors don't always either work or not: sometimes they mostly work except when they intermittently don't.

Cheers,

Don

 

I had an XJR/6 for many years. Great car but I discovered that its failure modes often didn't follow [what we've come to expect as] traditional patterns.

Cheers
DD

 

I've ordered the correct plugs and try that.
Then I will try a good known used one of my donar car see if that helps..wwill let you know thanks guys..

 

I chased a misfire that only misfired after car was completely warmed up. I tried swapping out coils with known good ones but only fixed misfire after I changed out all 6 together. Used cheap aftermarket coils so may not last, but so far so good.

 

Well swapped the crank sensor today of a good running car still the same misfire.but since changing the 02 sensors engine running rougher than normal at the moment and still has that annoying intermitant misfire.so swapped the 02 sensor plugs around runs smoothly now like it used to but still has the misfire.
I think it's either complete coil change but that would be expensive or injectors.but gonna change the plugs to champion first but not holding my breath.

 

When you change the plugs, pay close attention to each Bosch plug as you remove it. If the same cylinder is misfiring repeatedly, you may see evidence on the plug from that cylinder such as wet fuel or oil fouling. Also inspect the insides of the plug wells for signs of arcing through the coil boots.

Earlier you mentioned finding someone to clean your fuel injectors. I considered sending mine off to a professional ultrasonic cleaning service but after doing some online research and finding an inexpensive filter and O-ring kit on eBay, I opted to clean my own, and it was very effective. See the photos at the links below for the setup I used:

Fuel Injector Cleaning, Filters & O-rings Part 1 of 2
Fuel Injector Cleaning, Filters & O-rings Part 2 of 2

Cheers,

Don

 

Hi Don I connected the solus up again and I have the code p1178.
Run engine till hot and the fuel trims are not even on bank one to bank two.!
Banks 2 soft is hovering + - 6 or less but bank 1 sits always in the negative band - 6/7 on idle.
Even when at 2000 rpm they both go into the - but bank 1 sits at -9.0 while bank 2 sits at - 4.0.
average and air flow meter gas rate at 0.12....I still need to pull plugs but my theory is if massive flow sensor playing up with fuel ratios it would effect both Banks not bank1...also readings above can be a little different from every time I reconnect after key off on .
I still think an injector on bank1.but I have the code above come up the other day with a low rev range misfire cleaned maf and it went away.this morning before checking the above that misfire was back t uk ll it got hot it went away again and that p1178 code is back..

 

Update...due to the fuel trims on bank one reading - which I believe means the 02 sensor on bank 1 is telling ecm to lower fuel into bank 1 as it believes to be rich.
I removed all injectors and swapped bank 1 to bank2 and vice verses check data.

Results are now bank two acting the way bank one was in - most of time.
Bank 1 is on 0 to + - 0.6 0.7....

So I have a bad injector on there somewhere before doing this fitted champion rc12yc plugs gapped at 0.96 mm made no difference..

Anyone know where to get injecrors cleaned or replacement near to Heathrow London..thanks steve

 

Hi Steve,

Trying to make sense of all the data you posted - you can help the rest of us read your posts more easily by adding some line breaks every so often.

Here is a snip from the page of the DTC Summaries Guide that gives Jaguar's definition of P1178 and gives possible causes:



You can download the entire guide at this link:

Jaguar X300 AJ16 DTC Summaries 1996/1997

The first thing that jumps out at me is your reading from the Mass Air Flow Sensor, which seems low at 0.12 if the units are pounds per minute. Are you sure that it wasn't 1.2 lbs./min.?

When you cleaned the MAFS, did you also clean its electrical connector and harness connector? Another thing worth doing would be to clean the grounds associated with the engine management system.

Another question that comes to mind is regarding the high fuel usage, are you measuring the usage the conventional way (fill up tank, drive known mileage, fill tank again and divide mileage by miles driven), or are you just checking the fuel economy reported by the car's trip computer? In my experience the computers can be regularly off by 2 or 3 mph.

Also, I can't remember if you've changed the fuel filter and checked the fuel pressure.

Cheers,

Don

 

Hi Don. As for checking fuel milage it is for a known milage then do the calculation.have not do e recently.

As for the maf reading 0.12 is what solus is saying.i have back probed and do get voltages changing with rpm 1.25v and upwards.

Update on injectors just had phone call from testers saying they have checked spray pattern and back flow and there spot on so wouldn't recommend cleaning.

So I will refit them and check clean earth's a I can do really.

Also could someone confirm on the maf three wires one is battery voltage, other is voltage depending on rpm.but the signal ground is approx 30 ohms!!!! Is is cause the ecm ground is o a resistor circuit..thanks steve

 

What are the units of that measurement? Pounds-per-minute or some other unit?


I don't know how much if any resistance should be on the ground. Are you measuring from the MAFS electrical connector to a chassis ground point? You might have a look at the AJ16 Engine Management System manual for an explanation of how the MAFS is controlled, and if it isn't clear, I'm sure there are lots of explanations of 3-wire MAFS operation online.

Looking at the schematic, the MAFS receives power from the ECM on the same Black/Light Green wire circuit that feeds all the fuel injectors.

The Green/Pink (GK) wire appears to be the signal input to the ECM, which leaves the Pink/Slate (KS) as the ground or control wire.

It is always worth cleaning the ground points associated with the ECM and the rest of the engine management system (EMS), which are all identified on the schematics, and their locations are given on the page before the schematic.

Cheers,

Don

 

Hi air flow measured grams per second. G/s 0.5 idle.
Refitted injectors removed ecm pinned out both 02 sensors on loom all OK 0.8 ohms.

Pinned out the ecm signal ground to maf 0.8 ohms ok.
Cleaned up earth's.
Symptoms are changing I'm getting a misfire when I give the throttle a blip to full revs stationary. My fuel trims when I blip throttle are the same go into - readings..but when comes to idle the bank 1 goes -25 and bank 2 goes plus 25.which is different from. Other day nothing making sense.intermitant misfire seems to have gone.but know misfires through lower rev range..