The Daimler Century has been running perfect until we discovered a spark plug lead that was damaged. It only ran on 11 and the exhaust was sooty and black. We ordered new ngk bcpr6ef plugs and new set of leads and replaced all the ngk bcpr7ef and all leads. Now idle is still a bit uneven and the fuel consumption is extreme. almost double what it used to.

Have connected the obd reader and found some codes. I am also not sure bit looks like only two O2 sensors work?

any ideas?

 

I know this sounds a little crazy but have you considered putting the old spark plugs and leads back on to compare? I always think of what I changed before things went south, maybe you have bad leads or wrongly gapped/bad/plugs? New stuff is sometimes faulty.
Also what obd reader are you using? That looks useful output

 

old plugs and leads are scrapped already..
i boughta cheap 5$ obd reader on ebay and i operate it with the Torque app on my phone. very handy!

 

Unable to help on this one but I can tell you when the wolf drives ours she gets twice the gas mileage I do? Not sure why.

 

get another set of plug leads and a pair of EDIS-6 modules.

colder plugs generally affect idle a little bit

 

Here's a few little ideas. Gotta keep that sapphire beauty in top shape.

1. P0106 MAP Sensor Bank A (right side): Check integrity of the air tube to the MAP. Check the throttle linkage to be sure it is secure and operating in absolute unison with the left side. Both throttles must start to open at the same time or the MAP readings will not match and it will throw the code.

When I got the P1106 (left side MAP) on occasion, I swapped the MAPs. I still got the P1106, not the P0106 like I expected. Then I discovered the bushing on the left side was gone and the left side throttle was late to open. The MAPs were fine. But their outputs must match to within a close tolerance.

2. P0112 Intake Air Temp: On the right side air intake. Use your fancy new OBDII reader to read the live temperature from the IAT. Check connections. It is a reverse ranging thermistor you can test out of the vehicle if necessary. 20 degrees C = 2.45 kOhms, resistance going lower as temp increases.

3. P0300 Random misfire: Not too worried about this one. Too vague.

4. P1507 Idle Speed Control monitor, RPM high, left bank: Check throttle linkages again, Check connections and air hoses going to the ISCV. This could affect idle quality, but not sure exactly how. It is only a monitor test the ECU runs during a hot idle. This also assumes your reader is accurately giving you a legitimate Jaguar specific code.

Are you sure the Double Six has 4 O2 sensors? Hard to tell but I think the two listed are the upstream ones. Codes would probably show up if downstreams were not working.

If you were getting 28mpg before and now you are only getting 14mpg, don't worry. That is not a defect. It is a design!

 

we used a rather cheap set of leads from Britishparts. Could there actually be such a quality difference on leads in general? Is it worth the attempt to get a different set?

 

thank you for the very good input! Not sure about the amount of sensors actually. just tgought there were 2 on each side.
we will go over everything again and check

 

Looks like the new set of leads are shorter.. making the plug more exposed. Is it of any relevance?

 

**solved**!!
a wire to one of the MAP's had disconnected!
couldnt see it but realised it when we started to measure everything

its running smooth again and now uses about 12l/100km

thanks for your help everyone