As per my thread on supercharger crank pulley, I got my car back from my mechanic 5 days ago with the new Powerhouse crank supercharger drive pulley fitted, which is 10% bigger than the factory pulley. The car was going beautifully for 2 days , definitely more noticable power . Hard to quantify, but feels like 5-10% which makes sense.
However on the 3rd day the engine started missing and losing power when properly hot (summer here). I replaced all 6 NGK plugs with Champion RC12YC’s on Boxing Day, went for a 30 mile drive, no missing but feeling of slight air/fuel mixture mismatch. Got home, started running rough again. Tried removing each connector to the coils in turn, but it had smoothed out again before I could do so. It was raining so in frustration I dropped the hood/bonnet and the car immediately stalled.

On the XJR the air flow meter sits higher up than the N/A cars, and is (I think) a poor packaging design in that the wire connector to the AFM sticks up on an angle and hits the sound deadening material under the bonnet. So I jiggled the connector and it slipped right off. I think my ancient afm has a loose connection which may be part of my problem (also possibly an intermittently faulty coil, hard to pin down which one).
So this morning I used a pair of long nose pliers to gently twist each of the 3 blade connectors on the AFM about 5’ so the plug would be a firmer fit, which , touch wood, seems to have worked today with two trips totaling 60 miles with no problems.

About 3 years ago I bought a Worldcarparts XJR AFM part number LNA1620AA, not available as a genuine part anymore. It has been a good flow meter but has gone AWOL at the moment as the car has an old genuine AFM on it. So I have got on the net and ordered a new AFM from worldcarparts, direct from them, cheaper than ebay as no VAT tax to send it to NZ.

I have 4 ‘made in Japan’ new coils and may have to resort to putting all 4 on the car, and if still intermittent trouble, swap the old 2 ones around until I hopefully work out which one is faulty. But my troubles may just be coming from the seemingly loose electrical connection on the AFM.
I will also look into modifying the AFM where it attaches to the filter box to let it rotate the plug away from the underside of the bonnet..

Tonight I dropped in on the auto electrician to see if he thinks it’s feasible to wire a second Bosch intercooler water pump into the other side of the intercooler circuit to hopefully improve water flow through the intercooler. I think he thought I was bit mad! But he thought it would be ok to do so, maybe increase the size of the relay..
Last year I replaced the 20 year old Hella pump with a Bosch one, which has largely eliminated heat sink on repeated bursts of full power on hot days

 

Sorry to read of your problems with your XJR. I agree that the orientation of the AFM plug leaves it exposed and liable to rubbing on the sound deadening material attached to the underside of the bonnet. However, the metal clip on the harness side of the connector should keep it firmly attached to the AFM plug without the need to twist the terminals to increase the tension.


However, this is not the reason for my reply. I was very concerned to read that you have fitted Champion RC12YCC spark plugs. I think this plug was only specified on the XJR for the US market. I think the Champion RC9YCC plug was specified for all other markets. This 9 grade plug plug will run colder than a 12 heat range in the Champion range. As you have fitted a bigger crank pulley, I would very strongly recommend that you fit a colder running plug such as a RC9YCC. In fact I run Champion RC6YCC plugs in my XJR to which I have fitted the larger Eaton M112 supercharger. I've had no problems running this even colder plug, but I don't drive my car in winter or in heavy traffic. Given the choice I would rather live with spark plug fouling than pre-ignition induced engine failure caused by using a spark plug that runs too hot.

 

 

Andy, would you recommend the RC9YCC for anyone running the larger lower pulley?

I've got my pulley on the shelf, and planned to install it sometime this spring.

I'll be fitting the larger volume Bosch intercooler pump, and using the V12 oil cooler as a second intercooler radiator to help keep temperatures down. If I can lay hands on an X308 intercooler radiator cheap I may fit that too as I think it is slightly larger than the X300 intercooler radiator.

BTW, does anyone know the correct torque specification for the four bolts that hold the SC lower pulley on?

.

 

22-28 N-m.

Belt tension is 993-1033N for a new belt; drive for 10 min and allow to cool for an hour. Reset tension to 835-875N. In service reset tension to 835-875N every 16,000 km. Replace belt every 48,000 km

 

Hi Al,
I've checked my hard copy of the AJ16 Engine Service Manual. According to this document RC12YCC spark plugs were only ever specified for North American specification naturally aspirated engines, so should NEVER BE FITTED TO ANY SUPERCHARGED JAGUAR AJ16 ENGINES.


One word of caution about using an oil cooler as a second intercooler. It is possible that the oil cooler may not be compatible with engine coolant, and may result in corrosion inside the oil cooler. I don't know for sure.

 

Andy, is there a mismatch between Jaguar AJ16 Engine Service Manual and Jaguar Technical Service Bulletin? Here is an extract from TSB 05-1-07 entitled Spark Plug AJ16 - Change in Specifications "The spark plug specification is updated on all AJ16 4.0L Sedan Range Vehicles to include supercharger engines.... Hotter spark plugs (Part Number EBC8143) were installed for supercharger engines in production from 1997 MY. ACTION: Use EBC8143 as service replacement for all AJ16 engines." My understanding is that the hotter plug, later identified as Champion RC12YCC, should be used on ALL 4.0 AJ16 Engines including supercharger engines, but NOT on other X300 models such as 3.2 and AJ12 which should stick with RC9YCC.

 

Well spotted Marcus. I wasn't familiar with this TSB as it came out after I left Jaguar. Personally, if the performance of an engine has been increased (eg bigger crank pulley) then I would still fit the coldest plug that I can get away with.

 

That TSB was the basis for my purchase of the 12YC’s a week ago. However I am about to fit the 9YCs this morning. I’d go 6YC as per your advice, Andy, as it is hitting 30’C here over summer, but I can’t get any locally.
By the way, slightly twisting the 3 flat blade connectors on my tired AFM seems to have resolved the intermittent trouble I was having . When the new WorldCarParts AFM arrives, I’ll fit that.