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erratic idle and black smoke

jagrob
Posts: 60
Joined: Thu Jan 19, 2012 5:44 am

erratic idle and black smoke

Postby jagrob » Sat Mar 02, 2019 12:48 am

hi all, my 95 xjr 4.0 has started to sometimes run rough. when slowing down and coming to a stop the revs drop right down and sometimes stalls. on starting again will run rough and black smoke comes out of exhaust. have to keep the revs right up and take off quick before it dies again. this started to happen now and again but now more often. any ideas on what to check first?
1995 xjr 4.0 supercharged.

naki_k
Super Moderator
Posts: 28097
Joined: Sun Feb 21, 2010 9:25 pm
Location: Kirton, nr Boston, Lincolnshire

Re: erratic idle and black smoke

Postby naki_k » Sat Mar 02, 2019 2:31 am

I would think it’s overfuellimg.
It’s usual means there are faulty sensors, giving incorrect fuelling information to the ECU.
Most likely Lambda sensors, or coolant to sensor.
You need to put it on a code reader, or start checking resistance values with the multimeter.
88 3.6 XJ6 PDH/CEM
90 Range Rover Vogue SE 3.9 V8 LPG
91 4.0 XJ6 Manual
92 4.0 XJR Manual
92 4.0 XJR
93 3.2s - 4.0 Manual conv
93 4.0 Sovereign
93 6.0 XJ81 DD6 x2
93 6.0 XJ81 XJ12
94 4.0 XJR
94 4.0 Daimler
96 4.0 X306 XJR
96 4.0 X300 D6
97 4.0 X300 Sport Manual
2000 LR Discovery ES TD5 A
Breaking 40/ 300

jagrob
Posts: 60
Joined: Thu Jan 19, 2012 5:44 am

Re: erratic idle and black smoke

Postby jagrob » Sat Mar 02, 2019 3:19 am

hi, thanks for the reply. overfueling is what i was thinking too. i dont have a code reader but i do have a multimeter somewhere. would not know what readings to look for though.
1995 xjr 4.0 supercharged.

naki_k
Super Moderator
Posts: 28097
Joined: Sun Feb 21, 2010 9:25 pm
Location: Kirton, nr Boston, Lincolnshire

Re: erratic idle and black smoke

Postby naki_k » Sat Mar 02, 2019 1:53 pm

jagrob wrote:hi, thanks for the reply. overfueling is what i was thinking too. i dont have a code reader but i do have a multimeter somewhere. would not know what readings to look for though.


I don’t know the values off the tip of my head. You will need to look them up.
It’s common for the Lambda sensors to go out of range at this age.
I would think your Mpg figures will be low too currently? Or have you only just bought the car and fixing the inevitable raft of issues?
88 3.6 XJ6 PDH/CEM
90 Range Rover Vogue SE 3.9 V8 LPG
91 4.0 XJ6 Manual
92 4.0 XJR Manual
92 4.0 XJR
93 3.2s - 4.0 Manual conv
93 4.0 Sovereign
93 6.0 XJ81 DD6 x2
93 6.0 XJ81 XJ12
94 4.0 XJR
94 4.0 Daimler
96 4.0 X306 XJR
96 4.0 X300 D6
97 4.0 X300 Sport Manual
2000 LR Discovery ES TD5 A
Breaking 40/ 300

NMV 1E
Snr Member
Posts: 824
Joined: Fri Apr 17, 2009 9:26 pm
Location: Lydiate, Merseyside.

Re: erratic idle and black smoke

Postby NMV 1E » Sat Mar 02, 2019 8:05 pm

............. I've got a feeling this might possibly have something to do with the fuel pressure regulator. Worth checking the vacuum pipes to it. Apart from that intermittent overfueling can only be caused by a sensor issue :?:
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jagrob
Posts: 60
Joined: Thu Jan 19, 2012 5:44 am

Re: erratic idle and black smoke

Postby jagrob » Sat Mar 02, 2019 8:59 pm

naki_k wrote:
jagrob wrote:hi, thanks for the reply. overfueling is what i was thinking too. i dont have a code reader but i do have a multimeter somewhere. would not know what readings to look for though.


I don’t know the values off the tip of my head. You will need to look them up.
It’s common for the Lambda sensors to go out of range at this age.
I would think your Mpg figures will be low too currently? Or have you only just bought the car and fixing the inevitable raft of issues?

hi, yes mpg is down, about 13.8
1995 xjr 4.0 supercharged.

naki_k
Super Moderator
Posts: 28097
Joined: Sun Feb 21, 2010 9:25 pm
Location: Kirton, nr Boston, Lincolnshire

Re: erratic idle and black smoke

Postby naki_k » Wed Mar 20, 2019 11:08 am

Reduced mpg figures can often be a good indicator of running rich.
Did you get it sorted?
88 3.6 XJ6 PDH/CEM
90 Range Rover Vogue SE 3.9 V8 LPG
91 4.0 XJ6 Manual
92 4.0 XJR Manual
92 4.0 XJR
93 3.2s - 4.0 Manual conv
93 4.0 Sovereign
93 6.0 XJ81 DD6 x2
93 6.0 XJ81 XJ12
94 4.0 XJR
94 4.0 Daimler
96 4.0 X306 XJR
96 4.0 X300 D6
97 4.0 X300 Sport Manual
2000 LR Discovery ES TD5 A
Breaking 40/ 300

jagrob
Posts: 60
Joined: Thu Jan 19, 2012 5:44 am

Re: erratic idle and black smoke

Postby jagrob » Thu Mar 21, 2019 11:07 pm

hi all, all running great, problem was a blocked up air filter. looked to be in good nik but must have been full of dust etc.
1995 xjr 4.0 supercharged.

naki_k
Super Moderator
Posts: 28097
Joined: Sun Feb 21, 2010 9:25 pm
Location: Kirton, nr Boston, Lincolnshire

Re: erratic idle and black smoke

Postby naki_k » Fri Mar 22, 2019 12:00 am

jagrob wrote:hi all, all running great, problem was a blocked up air filter. looked to be in good nik but must have been full of dust etc.


Ok, a nice easy fix. Just lack of basic servicing then.
88 3.6 XJ6 PDH/CEM
90 Range Rover Vogue SE 3.9 V8 LPG
91 4.0 XJ6 Manual
92 4.0 XJR Manual
92 4.0 XJR
93 3.2s - 4.0 Manual conv
93 4.0 Sovereign
93 6.0 XJ81 DD6 x2
93 6.0 XJ81 XJ12
94 4.0 XJR
94 4.0 Daimler
96 4.0 X306 XJR
96 4.0 X300 D6
97 4.0 X300 Sport Manual
2000 LR Discovery ES TD5 A
Breaking 40/ 300


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