hesitation when cold

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bozthesax
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hesitation when cold

Postby bozthesax » Thu Aug 18, 2016 1:48 pm

My 3.5 XJ is very slightly hesitant/jerky when cold, fine once warmed up. I've had it serviced, all filters changed, plugs checked (they were ok) gearbox oil changed (it's just gone over 100,000 miles) cleaned the air sensor thingy as recommended in the latest magazine. I've also put some injector cleaner in on the last fill - up which helped a little bit. No fault codes are showing on the dash, but it's not as silky smooth as it ought to be. Anyone got any suggestions? :?

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J44EAG
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Re: hesitation when cold

Postby J44EAG » Thu Aug 18, 2016 2:27 pm

Try some Cataclean to help burn off carbon deposits in the catalytic converters. They can get very blocked up over time and mileage. Two cans in half a tank of fuel, then drive reasonably gently until the fuel is consumed. The product is very effective and within a short space of time you should start to feel the engine smoothing out and producing more torque at slow speeds. Gear change speed will also improve. Available on the internet or at Halfords.

Injectors also need regular de-gunking. Nozzles can begin to block up and spray pattern deteriorate. Add a can of injector cleaner once a year as preventative maintenance.

On my X350R, I found the Inlet Air Temperature sensor on the back of the throttle elbow when I had the car in pieces recently. I wonder if a similar sensor is to be found on naturally aspirated cars. One Torx screw held it in place, after which it just pulled out of the mounting. Under a load of crank case breather sludge, I found the sensor bulb. I washed that bulb with spray carb cleaner to restore decent condition. It is very similar in function to the MAF sensor and the clean up is similar to the one you have just carried out to the MAF sensor.

An often neglected item is the throat and throttle plate found on the throttle body. Taking the air trunking off above the throttle body will probably reveal a gunked up throttle plate and a throttle throat covered in sticky black crank case breather sludge. Again spray carb cleaner is used to dissolve deposits. Removing sludge with a very soft rag can work wonders to engine running. I would expect you to find four long Torx bolts holding the TB to its inlet mount. Removing the throttle allows fuller and deeper cleaning. Masses of sludge accumulates below the throttle plate and on the plate itself. Removing the sludge will certainly help slow speed running and allow a decent quantity of airflow into the engine. Buy a new throttle body crush gasket before you remove the TB for a good clean up.

Even though your car is naturally aspirated, it will have similar vac pipes to the ones found on the XJR that I detailed in my "19 day glitch" article. These pipes get in a dreadful state after a few years and just disintegrate. The part number is mentioned in my article and there is enough pipe supplied to replace most, of not all vac pipes on a typical V8. Leaking pipes can cause huge issues on these cars. Once replaced, many of the issues we experience with these aging cars, disappear.

Once you have given the TB and associated area a good look over and tackled some of these prime causes, make sure to fully tighten all clips on the induction system.

Try some of these ideas and see how you get on.

Mike
X350 Co-ordinator

2004 XJR

bozthesax
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Re: hesitation when cold

Postby bozthesax » Thu Aug 18, 2016 4:15 pm

I'll give your suggestions a try. The MAF sensor wasn't at all dirty, the bulb section at the end, although brown, was semi transparent and the metalwork was nice and bright - the service history with the car indicates its been Jag serviced all its life so I live in hope! Thanks for the tips!

bozthesax
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Re: hesitation when cold

Postby bozthesax » Wed Sep 07, 2016 9:18 am

Latest developments - I've narrowed the problem down to a slight misfire - when I rev the engine up to 4000 RPM or thereabouts, it sounds like a boy racer revving at the lights! the engine rises and falls in RPM at an alarming rate - fuel delivery problem perhaps?

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robv12
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Re: hesitation when cold

Postby robv12 » Wed Sep 07, 2016 10:59 am

coil pack or plug breaking down under load, a quick scan will give you which one is at fault
88 3.6 XJ40 EX JDHT
88 3.6 XJ40 SOV
93 XJ40 XJ12
94 XJ40 3.2 Majestic Gold
94 XJ40 Daimler Majestic Insignia
93 XJ40 XJ6 3.2 paint test car
97 XJR 300 Manual
97 XJR 300 Manual EXJDHT
55 XTYPE EST 3.0 SP PREM
62 351 LWB PREM LUX

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BrianG
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Re: hesitation when cold

Postby BrianG » Thu Sep 08, 2016 11:35 am

I've had it serviced.... plugs checked (they were ok) ....(it's just gone over 100,000 miles)
I would have insisted that they changed the plugs: the recommended service interval is 100K. As the plug electrodes wear away at some point you risk a coil failure due to internal breakdown (instead of the spark going across the plug spark gap). I know this from my old X308 where the plug change interval is only rated for 70K - extend it at your peril!
Brian
X350 3.5 V8 Sport Premium in Midnight / Ivory
Previous XJs:
X350 2.7 TDVi in Westminster Blue / Barley
X308 4.0 V8 in Meteorite / Warm Charcoal
X300 3.2 in Spruce / Barley
XJ40 3.2 Sport in Gunmetal / Saville Grey

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J44EAG
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Re: hesitation when cold

Postby J44EAG » Thu Sep 08, 2016 11:53 am

I agree with Brian. Looking at a plug does not show what its internal insulation properties are like. Insulation does break down and cause the issues Brian describes.

Installing a new set of plugs gives a known base line from which to work. Bearing in mind the time it can take to extract the rear-most four plugs for examination, it is in my opinion a false economy not to take the opportunity to fit new plugs. New plugs will almost invariably make an engine perform better. The normal change interval is either 60k or 100k miles dependent on the quality of plugs installed at the last plug change.

Mike
X350 Co-ordinator

2004 XJR

bozthesax
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Re: hesitation when cold

Postby bozthesax » Fri Sep 30, 2016 12:15 pm

OK - new plugs installed, no difference. Took the car over to Jagtechnic who said it was misfiring on all 8 cylinders. They cleared the fault codes, did a software patch update. It's a little better, but still has a slight hesitation at around 1600 RPM on a light load which is worse once the engine is up to temperature. No fault codes logged at present. I'm wondering if it might be a fuel pressure issue?

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J44EAG
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Re: hesitation when cold

Postby J44EAG » Fri Sep 30, 2016 4:55 pm

Fuel filters can harbour an awful lot of muck and filth which can block a fuel line. Indeed I`ve today changed my own fuel filter. It is located just aft of the near side front jacking point. The front end of the near side under-tray needs to be lowered to get at the filter and its mounting plate. if you are unsure whether the filter has been changed, then this is the next place to visit. The filter only costs around a fiver.

I`ve owned my X350 for a year now and have been persistently chasing sluggishness from a standing start. If you have read my recent posts on this site and also my magazine articles, you will see that I`ve been through my car like a dose of salts. No stone has been left un-turned in my attempts to get this car back to original performance. I`ve had everything in pieces! Finally I had the car Terracleaned which is far more searching when it comes to getting injectors sorted out. In addition the combustion chambers also received the chemical clean. I was astonished that my car performed so much better after the clean. Just 83k miles are on the clock and this shows what a difference a Terraclean can do to even a car with only moderate mileage recorded. Hesitation cleared completely and I surmise that the injectors were more than just a bit gummed up. This despite me pouring loads of off the shelf injector cleaner through them via the fuel tank. You might try that line of rectification.

Knowing these engines as well as I do, (eleven years on the V8) I can`t help thinking that you may well have one or indeed all coil packs on their last legs. Coils will fail if persistent mis-firing spark plugs have been on the car for a while. Mis-firing is death to a coil and they do become damaged. Perhaps you could get the garage to data log a trip and induce the mis-fires which would then be recorded and then later analysed. You need to look for spark plug wells that fill up with engine oil if the cam cover spectacle seals have failed. Similarly water can also collect in the wells. Again this type of contamination can cause mis-fires and also wreck coil packs. I`ve seen some engines where the wells have been full of oil right up to the coil packs themselves. The rubber boots should also be inspected for degradation and contamination.

You might also try cleaning the MAP (mass air pressure) sensor which is probably located up-stream of the throttle body. Like the MAF sensor, these can get very dirty. It is also worth looking around the throttle body and examining each and every small bore VAC pipe that might be present. I know the XJR 350 well in this regard but am not that familiar with the naturally aspirated version. The small rubber pipes can leak rot or split especially at the ends and at any plastic joiner part. These can cause mis-fires, coughs and splutters.

Check also that all inlet trunking Jubillee clips are tight and that rubber collars are in place and securely fastened. Tighten inlet manifold bolts as an insurance against inlet air leaks.

Hope that helps.

Mike K
X350 Co-ordinator

2004 XJR

bozthesax
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Re: hesitation when cold

Postby bozthesax » Fri Feb 10, 2017 5:56 pm

Latest update - did all the things listed above, had the car Terracleaned - fantastic improvement in power and response, I'd recommend it to anyone, but the hesitation was still there. I then read about low gearbox oil levels and the symptoms sounded exactly the same as mine. Got the box topped up (not an easy job) and the problem has almost disappeared. There's a very slight 'surging' when under light load and the box is cold, maybe they didn't put quite enough fluid in?

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J44EAG
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Re: hesitation when cold

Postby J44EAG » Fri Feb 10, 2017 7:07 pm

The topping is done at a prescribed temperature and filled until the fluid starts to dribble out of the gearbox side plug.

I`d now look to de-gunking the throttle body throat with lint free rag, a very soft tooth brush and carb cleaner. Also ensure that the throttle plate is cleaned. Any gunk present can upset the idle.

Many unimformed people decry Terraclean. I`ve had one stupid mail following my article. The person was incredibly misinformed......I`d suggest you now run your car for a couple of hundred miles, then check the colour of the oil. You might be surprised how black it has become after the Terraclean. My oil was clean before I had the treatment done, then it blackened rapidly. Bravo Terraclean for loosening up carbonised deposits which were then grabbed by the oil. I also used a can of engine flush when I dropped the oil after 2,300 miles of post Terraclean treatment. My water/methanol injection system also seems to have been beneficial. 500 miles now on the new oil and it is still mild yellow instead of black. Result!

See how you get on cleaning the throttle body.

Mike
X350 Co-ordinator

2004 XJR

vernon
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Re: hesitation when cold

Postby vernon » Thu Feb 16, 2017 3:59 pm

Hi, not sure what age, engine etc. Your car is, but if it before 1990 then the problem is ignition interference upsetting the fuel injection enrichment, that happens until the coolant reaches 78deg c.
There is a mod for this that does work, I had the same trouble.
Go to Jag lovers web site, look for cold starting EFI Overfuelling, or XJ6 Series III.
Simple mod, just have to fit a 100uf 25volt capacitor across pin 6 and 8 of the airflow meter plug.
Good luck and happy cold running.
Vernon
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PaulGover
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Re: hesitation when cold

Postby PaulGover » Tue Feb 21, 2017 11:57 am

...
Go to Jag lovers web site, look for cold starting EFI Overfuelling, or XJ6 Series III.
Simple mod, just have to fit a 100uf 25volt capacitor across pin 6 and 8 of the airflow meter plug.
...
Wrong sort of XJ - that's fix is for the "XJ Series" cars, not the X308/X350/etc.
1981 XJ6 Series III basket case
1991 XJS V12 "facelift"
2008 XJ TDVi


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