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Discussion Starter · #1 · (Edited)
I have been doing a few bits of work on my Dec 2001 XJ8 4.0. last job before a 300 mile round tri[p to Norfolk, was to replace leaking cam cover gaskets. All went OK and no more leaks. After getting back I parked the car outside to unload the luggage. an hour later I went pout to put it in the garage and on starting, it sounded to be running a bit lumpy. Blipping the throttle didn't clear things. It could be plugs, ign coil, injector, or the MAF sensor, which I will check tomorrow. Does anyone in the Hull area have an OBD scanner they could plug into my car to determine the cause of the problem. A lot easier than the substitution with a known good item. If anyone can help I would appreciate it. Thanks Bill W
 

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You can buy one from eBay for just £15, which would be a lot easier? Have you broken the part load breather pipe which you would have to have moved on doing the cam covers?
 

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Discussion Starter · #3 ·
The reason I asked if anyone local had one was I would like to get it sorted before the weekend.. The problem seems to be the initial acceleration. I cleaned the MAF sensor this morning and that made no difference. On my trip to Norwich It seemed to run OK except for selling off from a roundabout, when it hesitated before picking up, or accelerating to overtake without using the "kickdown" Part load breather pipe is OK, unclipped and clipped back on after doing the cam cover gaskets
 

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Is it possible you lost one of the springs out of the coilpacks when you took them off ? I'd of expected that to result in a permanent misfire though.

Did you do anything like clean the plugs up or regap them ? You haven't pinched one of the wires in the coilpack loom putting the covers back on ?
 

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Plughole full of water/oil/crap? Also look carefully at the induction duct - especially the seal onto the Throttle Body an the joints between sections.
 

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Discussion Starter · #6 ·
Ordered OBD scanner. Changing out the calipers on my wife's MR2 MK 2 this weekend. I will run over the induction system with a fine tooth comb once that's finished. If I slowly accelerate it is fine, but a blip of the throttle when stationary, or hard acceleration whilst on the move, causes the engine to hesitate before it picks up. When I did the cam covers I checked and cleaned out the plug wells. I have a new set of NGK IFR5N10 plugs which I will replace first.
 

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Mine used to be a bit like that and a replacement MAF made it feel supercharged by comparison!
 

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Discussion Starter · #8 ·
Hi, Got a code reader which has brought up P1646 and P1647, which seems to indicate the O2 sensors on both sides. The lumpy running I originally described, would have probably been better described as hesitation on acceleration when cold, and only a bit better when warm. Also a noticeable drop in mpg, from 29/30 on a long motorway journey, down to 24/25 on same journey.
 

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Can I ask where did you get your OBD scanner, what model and how much ?

Think I need to check some things :roll:

Ta.
 

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I changed my top HO2 sensor, nearside bank, a few years ago. Easy with the right LAMBDA socket and a length of wood to hit it with - murder trying without. My average fuel consumption on a run had fallen to 21-22 and I now get 27-28 on the same run,
 

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My yr 2000 XK8 4.0L has pretty appalling fuel consumption. I can actually watch the fuel gauge dropping on 'in town' runs. I also have a sluggish performance issue. Could my Lambda(s) be responsible? How can I find out and are they easy/expensive to replace?
 

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I bought my XJR in 2011 and it stalled twice on the way home. I thought that it might be because the car hadn't been used for a couple of months and that it would sort itself out. I had the intermittent lumpy running and stalling. I thought it was the MAF sensor so bought some MAF cleaner. Problem came back. Bought a cheap code reader - which was the best thing that I ever bought. Had the same codes as Bill W in his posts ie. 1646 and 1647 (O2 sensors). Garage were reluctant to change them as they thought that it was unlikely that both sensors would go at the same time. So I lived with the problem even though it really put me off the car. Had problems getting car through MOT's. Fuel consumption was bad. In 2013 the car stalled at high speed in lane 3 on the motorway. Car failed MOT on emissions this time last year. So garage replaced both downstream lambda/O2 sensors as I didn't fancy doing the job myself. No problems since and mpg increased by between 25% to 30%.

I keep my cheap code-reader (U480) in the car and check (and if necessary) clear the codes at least once every couple of months. As I said previously, it's the best thing that I ever got for the car. It cost less than £10.

The car still throws up the occasional odd code - usually the ECM or MAF sensor, but nothing permanent and no stalling.
 

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I bought my XJR in 2011 and it stalled twice on the way home. I thought that it might be because the car hadn't been used for a couple of months and that it would sort itself out. I had the intermittent lumpy running and stalling. I thought it was the MAF sensor so bought some MAF cleaner. Problem came back. Bought a cheap code reader - which was the best thing that I ever bought. Had the same codes as Bill W in his posts ie. 1646 and 1647 (O2 sensors). Garage were reluctant to change them as they thought that it was unlikely that both sensors would go at the same time. So I lived with the problem even though it really put me off the car. Had problems getting car through MOT's. Fuel consumption was bad. In 2013 the car stalled at high speed in lane 3 on the motorway. Car failed MOT on emissions this time last year. So garage replaced both downstream lambda/O2 sensors as I didn't fancy doing the job myself. No problems since and mpg increased by between 25% to 30%.
I think you might have got slightly confused here: The downstream sensors are post-cat and have nothing to do with fuel consumption - they simply provide confirmation to the ECU that the cats are functioning correctly.
It is the upstream sensors which affect consumption, and to which the DTCs P1646/7 refer. I suggest it is probably these that your garage replaced.

My yr 2000 XK8 4.0L has pretty appalling fuel consumption. I can actually watch the fuel gauge dropping on 'in town' runs. I also have a sluggish performance issue. Could my Lambda(s) be responsible? How can I find out and are they easy/expensive to replace?
Lambda probes only affect steady state behaviour i.e. when the throttle has been at a constant position for more than a fixed amount of time, typically 20 seconds.
You can see that happen on a diagnostic machine, when the reported ECU state toggles from open loop to closed loop.
Closed loop is when the lambda values are used to back off the fuelling and increase advance as much as possible whilst keeping the lambda within an acceptable zone for engine longevity.
Dynamic performance is open loop, i.e. it is governed by the fuel and ignition maps in the ECU, and protected by knock detection. Lambda is ignored.

For lots of useful information on engine management I find Dave Walker's articles both readable and helpful: http://www.emeraldm3d.com/articles/cat/knowledge-zone/
 

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Discussion Starter · #17 ·
Just to revive this old thread. I got a couple of O2 sensors and put them in and cleared codes, but the problem still exists.

Whilst I was checking under the bonnet, I was manually operating the accelerator, I found that if I accelerated slowly all was OK. If I tried to blip the throttle, the engine hesitated before picking up. If I continued with the throttle blipping I could hear what sounded like a backfire in the exhaust.
Also, on a couple of occasions, whilst blipping the throttle I have found that if I blip the throttle fully open, the engine will stall.

This produces no codes on my scanner ???????

Any ideas? Bill W
 

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Just to revive this old thread. I got a couple of O2 sensors and put them in and cleared codes, but the problem still exists.

Whilst I was checking under the bonnet, I was manually operating the accelerator, I found that if I accelerated slowly all was OK. If I tried to blip the throttle, the engine hesitated before picking up. If I continued with the throttle blipping I could hear what sounded like a backfire in the exhaust.
Also, on a couple of occasions, whilst blipping the throttle I have found that if I blip the throttle fully open, the engine will stall.

This produces no codes on my scanner ???????

Any ideas? Bill W
If I understand you correctly, you're saying that no fault codes are showing up on a generic OBD code reader? In which case you'll need to use a dedicated Jaguar OBDII device, such as SDD/IDS or AutoEnginuity or Autel.

The fact that your problem relates only to transient fuelling indicates that it can't be related to the lambda probes for the reasons described above i.e. lambda values are only relied upon when in closed loop mode, and that only occurs after at least 15 seconds of constant throttle, and the moment that you blip the throttle the ECU will revert to open loop.

On that basis, I'd be looking at either the MAF or the throttle.

You could probably confirm this by watching the real time lambda values which are likely to go massively lean everytime you blip the throttle. (By which I mean that the lambda values are present, but that the ECU is not actually using them to determine fuelling or ignition timing)
 

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Discussion Starter · #19 ·
I totally agree Zulu 10. I was deceived by the fact that it was only the O2 sensor codes that showed up. With faulty O2 sensors I would have only expected a decrease in MPG, mine were down at 21/22mpg. I have cleaned the MAF sensor but I suspect the throttle body needs a good cleaning as well?? Bill W.
 

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Apologies about resurrecting an old post but I have symptoms exactly like those described below. Fine with 'normal' gentle driving but definite hesitation with firmer throttle inputs from idle and sometimes a sound like backfire in the exhaust manifold. I have recently, changed the plugs (new NGK Iridium) and while I had the ducting off spray cleaned the MAF and gently wiped the inside of the throttle body around the butterfly (held open with fingers while I did so). Not much muck in there but 'while it was accessible'...
Car is 2000 XJ8 3.2 with 62,000 miles (just run in). I don't have a scanner (yet). It was running sweet as a nut before I touched it (regrets).
I'll check the intake duct for leaks (it looked in good condition) but where else should I check?
If you're still on here Bill W what was the resolution?
Thanks in anticipation of help,
Eric aka Oily Mist

Just to revive this old thread. I got a couple of O2 sensors and put them in and cleared codes, but the problem still exists.

Whilst I was checking under the bonnet, I was manually operating the accelerator, I found that if I accelerated slowly all was OK. If I tried to blip the throttle, the engine hesitated before picking up. If I continued with the throttle blipping I could hear what sounded like a backfire in the exhaust.
Also, on a couple of occasions, whilst blipping the throttle I have found that if I blip the throttle fully open, the engine will stall.

This produces no codes on my scanner ???????

Any ideas? Bill W
 
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