Restricted perf after pushing 4.2 SC a bit harder than usual

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Davidqhog
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Restricted perf after pushing 4.2 SC a bit harder than usual

Postby Davidqhog » Sat Feb 23, 2019 2:30 pm

Morning All,

I was returning from the Gloucester area to Cirencester the other day, going up Birdlip Hill, a long 1 in 6 hill. Slow lorries on inside lane so put my boot down a bit. The SC started to howl and we whisked past everything with apparent ease. Turned onto the main Cirencester road (A419), still uphill and still pulling nicely.

Eased off for the 40 mph area near Nettleton and the Restricted Performance came up. Didn't feel any restriction and still happpy to go between 50 - 60 mph after the 40 zone. The eMIL light was on, normally denoting catalyst problems (I'd put Cataclean in the day before). After about 5 minutes, the restriction went off and so did the emil.

Checked the codes and there were none. I don't often boot it hard (local roads aren't up to it) so is this just the old girl complaining about not being pushed hard often enough or is there likely to be another cause lurking? Coolant level looks okay, BTW.

Any thoughts welcome.

Regards,

David Q

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J44EAG
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Re: Restricted perf after pushing 4.2 SC a bit harder than usual

Postby J44EAG » Sat Feb 23, 2019 4:13 pm

Take it easy when using Cataclean.

I had an incident with my old S-type V8 having put Cataclean in the tank then driving for about half an hour. As I drove gear changes improved as did the running. On the return journey, I forgot I had the cleaner in the fuel and floored the throttle hard to pass a bus. Bang! A big cloud of black stuff noted in the mirror and instant throttle wipe out. I coasted into a bus stop having failed to complete the over-take...Red Face!

The car re-started and ran badly for a few seconds before settling down and back to normal. I surmise the extra octane or other chemicals in the Cataclean had ignited in the cats, caused a detonation, threw out loads of semi-solid combustion by-product out the exhaust with the detonation/explosion completely confusing Lamda 02 sensors and shutting down engine control due to out of limit parameters. I drove the car rather more carefully until the car was back on plain un-dosed fuel.

I`ve never experienced the issue again but I`m always a little more careful if I have those high volatility products being pumped into an engine.

It strikes me you might have experienced a similar scenario to mine. That you have a SC pressurised engine with higher cylinder pressures will tend towards an increased propensity for detonation especially if you have just increased engine temperatures by thrashing it up Birdlip Hill! I know it well!!

Mike
X350 Co-ordinator

2004 XJR

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steve_m
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Re: Restricted perf after pushing 4.2 SC a bit harder than usual

Postby steve_m » Sat Feb 23, 2019 5:40 pm

Sounds like James Stewart using the Coffman starter in the original Flight of the Phoenix!

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J44EAG
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Re: Restricted perf after pushing 4.2 SC a bit harder than usual

Postby J44EAG » Sat Feb 23, 2019 7:57 pm

James just got a black face for his troubles. That`s what happens if you play with a Coffman cartridge. Essentially it is a shot gun cartridge without the lead shot!

I got a red race through the embarrassment of messing up the overtake due to throttle failure! Essentially, I blew out the fire that propelled me!! Yip, I had a dash full of lights and the EML. Switched off and then re-started, re-established acceptable parameters for the engine management system and off we went again...once again behind the bus out of Gosport which I had tried to get past.

I have an electronic throttle speed enhancer fitted to the XJR. This modifies the speed at which the throttle plate opens to give a more responsive feel to the car. If you were to take off all the inlet pipes down to the throttle body, turn on the ignition and have an assistant stamp on the throttle pedal, you would see the motorised throttle plate open in a very lackadaisical way. It is not particularly quick in opening. This can make a car feel lethargic to drive. The electronic gizmo fitted to my car has adjustable parameters which allow the driver to increase the throttle plate opening speed in a graduated fashion. If one adds too much advancement to that gizmo and that opens the throttle quickly for the ECU to comprehend, it is again possible to wipe out the throttle control system.

Young Mr Sinnott and I undertook some tests a couple of years ago to establish just what the gadget did to modify throttle speed response. Our test involved a block of wood under the throttle pedal and one of our ELM327 OBD chip sets bluetoothed to a Torque Pro App on an Android phone. We found that as we increased the throttle pedal to the block and also tried different settings on the gadget, it gave bigger throttle plate opening percentages the higher we set the gizmo. The XJR was booted hard at all settings to see the effect of raising the percentage of throttle opening with the eventual effect that we collapsed the ECU program due to forcing an excessively high "out of limits" situation. Phut, phut, phut...stop!

That achieved we then had to coax the ECU back into the game with the Torque Pro app on the phone. No doubt Jaguar would disapprove but Paul and I learned a bit about out of limits aspects of running S-type, XJ and XF power units. If they can be messed with, then I don`t mind pushing the boundaries to increase my knowledge! Had others in the after-market tuning business not had the will to experiment, we would never have seen the advent of an ECU reflash designed to unlock potential that manufacturers kept a secret.

So those are just two ways of upsetting the smooth running of any car. Cause an explosion in the exhaust which gives the Lambda sensors a coronary or do what Paul and I did and give the ECU a hernia. With the benefit of hindsight and the experience gained, I can think of several more ideas for causing the Power Train ECU to wish it had another less inquisitive owner.

Mike
X350 Co-ordinator

2004 XJR

Davidqhog
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Re: Restricted perf after pushing 4.2 SC a bit harder than usual

Postby Davidqhog » Sun Feb 24, 2019 7:03 pm

Thanks all, esp Mike.

Yes, I saw your Cataclean episode Mike some time ago so was careful on the first quarter tank. I'll top up tomorrow and see how we do.

Next service I'll get Paul at Wiltshire Jaguar to air-blast the radiators as I can see they are chocca with dead flies and other detritus. He has a 4.2 SC engine out of a S-type and we've discussed taking the SC off that, servicing it and fitting on my SV8 (valley pipes to be replaced, EGR cleaned or replaced).

If learn more on this, I'll post it here.

Regards,

David Q

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J44EAG
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Re: Restricted perf after pushing 4.2 SC a bit harder than usual

Postby J44EAG » Sun Feb 24, 2019 8:52 pm

Cataclean takes time and mileage to soften and remove converter deposits. If it has never been done before, I would leave the fuel/cleaner mix at full strength but keep off the loud pedal until you have fully used all the mix.

The problem with a standard car with standard diameter super-charger pulley is that the charger does not come into play fully until after about three quarters throttle. Then the power delivery comes in seemingly with a rush. The effect is rather all or nothing. So you suddenly hit full boost as a torrent of extra urge which can often upset the engine management system especially if the car has a bit of mileage under its belt and is a bit gummed up.

The after market ie Tom Lenthall in Finchhampsted or Lawson Smith at Powerhouse Automotive can supply to alternative reduced sizes of charger pulley which reduce the torrent effect and bring the charger into play usefully further down the RPM scale.The larger of the two gives a moderate power increase and more friendly grunt delivery from about 3,50RPM and needs no other modifications. The smallest pulley brings more power into play from about 2,000RPM and transforms a car. Grunt is much more linear and the car far easier to drive. However the modification requires rather more work to fit. Metal needs to be removed from the drive shaft snout to accommodate the smaller inside diameter of the pulley. Tom doesn`t like doing this job because of the amount of labour input required and the risk of making a mess of the job if using hand tools for the modification. The small pulley is best suited to an engineer who has time and patience available and has his eyes on a prize. Snout mods are best done placing the snout case in a four jaw lathe chuck and spinning down to reduced OD. With determination and tenacity, a mirror, files, a power file, a vernier and other engineering tools, this can be done by hand with the charger still fitted to the car. You need to have decent engineering skills and perception to tackle this mod at home. In addition, the up-rated and revised shouldered belt tensioner kit MUST be fitted due to the extra torque loading applied to the belt drive system. With a Viezu/Gerald Morten ECU reflash done, the XJR becomes a much more compliant and flexible car and given good Lambda condition, the propensity toward message centre errors and ELM illumination diminishes.

Oxycat and Cataclean are similar cat cleaning additives. In my experience, the Oxy-cat works faster but they are both very handy chemicals in the fight against blocked or partially blocked cats. The cats are 600 cell out of the factory which means only about 55% of the cross sectional diameter of the cat pipe is able to pass exhaust gas. Sports cats offer faster exhaust ejection but at the expense of cooling off on the MOT ramp and the need for a fast running engine run to enable the test to be passed. They are however far less likely to carbon and oil blockage because there is so little metal inside them when compared to a standard OE cat. One has to accept potential MOT difficulties with sports cats fitted. I enjoy the fitment on my XJR but at the expense of an easy MOT pass.

So use the Cataclean at full strength by keep off high boost pressures whilst it is in the tank. I treat my car to Oxycat treatment twice a year as preventative maintenance. Oxycat can be bulk purchased via eBay which makes it cost effective and gives a ready use garage shelf supply. I`d not be without it.

Mike
X350 Co-ordinator

2004 XJR

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jagecosse
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Re: Restricted perf after pushing 4.2 SC a bit harder than usual

Postby jagecosse » Sun Mar 24, 2019 12:46 pm

Have you checked the Trouble Codes? I had a similar problem and it turned out to be a faulty O2 sensor. I replaced both sides and have not had a problem since.
2007 XJR LHD, Frost Blue


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