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Topic: 24 valve Cossie backfire (Read 857 times) |
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Nunnspoet
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24 valve Cossie backfire
« on: Dec 31st, 2018, 9:41am » |
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My Cossie estate drives like a dream, has no fault codes, but when I ask for full power: she responds immediatly but then, within a split second she backfires and cuts back on the power. I ease off the throttle and all is lovely and peaceful...driving like a dream. She has plenty of power and will kick-down perfectly. it's just when I give her wellie when there is this problem.
So there you are folks. What is the problem and how do I fix it?
I look forward to all your advice;
Many thanks
Mike 
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a900one
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A scorpio is for life not just for christmas
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Re: 24 valve Cossie backfire
« Reply #1 on: Dec 31st, 2018, 9:53am » |
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Is the backfire through the exhaust or the inlet.
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Scorpio_Mike
Senior Member
Jeep Grand Cherokee 3.0 V6 & 2.8 Sierra XR4i 4x4
Posts: 2354
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Re: 24 valve Cossie backfire
« Reply #2 on: Dec 31st, 2018, 10:52am » |
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Sounds like a plug is not firing, unburnt fuel mixture igniting in the exhaust system, possibly giving the O2 sensors a bad reading and then altering the fuel mixture causing power loss.
Sudden demand on a failing coil pack springs to mind 
Is the loom to the injectors & coil packs in good order
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Star sign is Scorpio !
Sierra XR4i's are great...especially when fitted with 4WD
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Nunnspoet
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I love YaBB 1G - SP1!
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Re: 24 valve Cossie backfire
« Reply #3 on: Dec 31st, 2018, 12:35pm » |
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Please keep the advice coming. I have to deal with something, so I will be out of touch for a while.
Happy New Year everybody.
Mike
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PJDavis
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2 x 1995 Jag X300 3.2 / 4.0 (Henley) 1957 XK140
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Re: 24 valve Cossie backfire
« Reply #4 on: Jan 1st, 2019, 11:53pm » |
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Loom, or a coil pack. Dampness in one of the coil-packs, or a split in a coil body. If the car pulls well on gentle throttle, normally the fuel side is ok unless you have a 'weepy' fuel-seal to the main body. The loom I'd say is the main first line of attack.
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I love 'Movvy'
1995 Jaguar XJ6 X300 3.2 (Henley)
1995 Jaguar XJ6 X330 4.0 (Dopey)
1957 Jaguar XK140 USA (converted to RHD, and to have fitted Mk10 420G Engine with BW 65 Auto Trans)
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Nunnspoet
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Re: 24 valve Cossie backfire
« Reply #5 on: Jan 25th, 2019, 11:46am » |
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I'm back, so to speak.
Thank you you all for your excellent advice.
There is a development. Ahem: I Decided to rev the engine with the car on the drive and in 'P', She revved up as expected then she lost the revs, cutting right back, as though somebody had squeezed the fuel pipe to cut of the fuel. On releasing the throttle control the revs picked up and there she was idling perfectly as though nothing was wrong.
Driving sedately along she is okayish. Gearchanges both up and down are faultless. The throttle feels ever so slightly heavy.
I am confused . What do you think folks?
Mike
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Scorpio_Mike
Senior Member
Jeep Grand Cherokee 3.0 V6 & 2.8 Sierra XR4i 4x4
Posts: 2354
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Re: 24 valve Cossie backfire
« Reply #6 on: Jan 25th, 2019, 1:05pm » |
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"The throttle feels ever so slightly heavy."
Check the throttle cable is moving freely & that the butterflies are not sticking.
Might just need a drop or two of oil.
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Star sign is Scorpio !
Sierra XR4i's are great...especially when fitted with 4WD
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PJDavis
Senior Member
2 x 1995 Jag X300 3.2 / 4.0 (Henley) 1957 XK140
Posts: 1474
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Re: 24 valve Cossie backfire
« Reply #7 on: Jan 25th, 2019, 11:06pm » |
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on Jan 25th, 2019, 1:05pm, Scorpio_Mike wrote:"The throttle feels ever so slightly heavy."
Check the throttle cable is moving freely & that the butterflies are not sticking.
Might just need a drop or two of oil. |
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I concur. Give the throttle-body a clean with a good strong 'Carb-Cleaner' It's essentially thinners in a spray-can. It may need a few goes. Sticky butterflies..........that's the answer!
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I love 'Movvy'
1995 Jaguar XJ6 X300 3.2 (Henley)
1995 Jaguar XJ6 X330 4.0 (Dopey)
1957 Jaguar XK140 USA (converted to RHD, and to have fitted Mk10 420G Engine with BW 65 Auto Trans)
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Nunnspoet
Full Member
I love YaBB 1G - SP1!
Posts: 798
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Re: 24 valve Cossie backfire
« Reply #8 on: Jan 28th, 2019, 10:10am » |
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Thanks again folks.
I have checked things again and all seems okay.
Following advice from my mate Graham Toye, who suggests either a faulty Fuel Pump or faulty Fuel Pressure Regulator and having read the article, on this site, I have decided to fit the Fuel Pressure Regulator sourced from The Beast. If i can get it off without damaging it. Has anyone any hints on extracting the Regulator without damaging it? 
Mike
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Nunnspoet
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Re: 24 valve Cossie backfire
« Reply #9 on: Feb 15th, 2019, 10:27am » |
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Ookay, here goes:
I have changed the IAT, IAC, Fuel Pressure Regulator, TP Sensor and the MAF.
Yesterday when she was stone cold (covered in frost) I started her up. Perfect. I let her tick over, again perfect. When she was warming up I gave her some revs, at first all was well then she cut back, revs dropping, I gave her some 'gun' she backfired slightly and the revs dropped. I repeated this three times with the same result. I gave up. About three hours later, with the engine pretty cold I started her: Perfect and perfect idle. I let her warm up then I raised the revs up to 2500 and held her there. Well, for about a min and a half she was perfect Then the engine cut back and the revs fell, I kept my foot still, the revs and the engine picked up, maintaining 2500 hundred revs for about 20 secs. then the revs dropped as before. I repeated this action for about 3 times, then I released the pressure on the throttle, the revs dropped to idle where they remained rock steady.
Then I jabbed the throttle a few times, each time the revs rose as they should then very quickly there was a slight backfire and the revs dropped like a stone.
If I raise the revs slowly she behaves perfectly and then we are back to the above scenario's.
Well, there you go. What do you think? 
Mike 
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Tompion
Administrator
1997 2.3 Ultima estate.
Posts: 2918
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Re: 24 valve Cossie backfire
« Reply #10 on: Feb 15th, 2019, 12:21pm » |
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As mentioned earlier possible faulty coilpack.
As ever faulty wiring could be to blame.
Watching readings in diagnostics such as fuel trims, MAF, oxygen sensor, throttle position etc may give a clue to what's going on.
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Nunnspoet
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I love YaBB 1G - SP1!
Posts: 798
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Re: 24 valve Cossie backfire
« Reply #11 on: Feb 17th, 2019, 9:29am » |
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Thanks all.
I have written more in 'OBD Advice.'
Here is some more. Yesterday I took her for a drive, aprox 14 miles. Tickover beautiful, picking up speed steadilly, great.. up to about 75 then she cuts back, slacking off the throttle and all is peace and harmony.
She still feels slightly heavy on the throttle and needs more pressure on the pedal to attain the speed that I want.
i have had the Bty disconnected many times over the last couple of weeks, and not done very much mileage so I will use her for a couple of days and see whether things improve.
In the meantime please give me any advice that comes to mind
Mike
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a900one
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A scorpio is for life not just for christmas
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Re: 24 valve Cossie backfire
« Reply #12 on: Feb 17th, 2019, 9:35am » |
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When did you last change the fuel filter, could that be blocked.
Gerald.
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Nunnspoet
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I love YaBB 1G - SP1!
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Re: 24 valve Cossie backfire
« Reply #13 on: Feb 17th, 2019, 10:42am » |
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. Thanks Gerald. Graham changed it for me about 6 weeks ago. Freezing cold and in the dark on the Drive. What a friend!!
Mike 
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