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Topic: Intermittent jerk ! (Read 4438 times) |
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gozz
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Intermittent jerk !
« on: Jan 18th, 2014, 10:58am » |
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I wonder if any of you stout Scorpists have experienced an occasional jerk whilst driving,not other motorists but about a second as though the ignition is switched rapidly off and on again,the tacho drops by a couple of thousand revs and immediately returns to normal,the engine has not yet completely stopped but as this is a funeral car it is rather daunting waiting for it to do so 
It is a 2.3 running on propane,but the fault occurs when either fuel is used thus it does point to ignition,there is nothing on the scanner, making for a tricky diagnosis.
In the past I have repaired the baked engine loom which caused the engine to cut out completely,but to start again immediately,the crank and cam sensors have also been replaced.
Doubtless if we ever trace the fault it will be the usual insignificant broken wire or something of that ilk.
Your thoughts and experiences would be much appreciated gents,before all my hair falls out 
GOZZ.
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Scorpio_Mike
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Jeep Grand Cherokee 3.0 V6 & 2.8 Sierra XR4i 4x4
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Re: Intermittent jerk !
« Reply #1 on: Jan 18th, 2014, 12:21pm » |
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Sounds like either a coil pack failing or the dreaded wiring on the fuel shut-off loom 
Loom fault could cause bad reading from any of the sensors it connects to...maybe time for a new one ?
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Sierra XR4i's are great...especially when fitted with 4WD 
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Tompion
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1997 2.3 Ultima estate.
Posts: 2918
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Re: Intermittent jerk !
« Reply #2 on: Jan 18th, 2014, 1:06pm » |
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Is this at any speed or just low speed? I had an intermittent problem with the MAF causing the engine to almost die when pulling away but recover when I took my foot off, but I did have a code. You could try unplugging it & see if it still happens. Since the MAF isn’t part of the shut off loom you may not have looked at those wires, but once again you’d expect a code, although if the reading is within acceptable limits but fluctuating you may not get a code.
You could try unplugging the cam sensor – mine runs fine without it but I don’t know if that applies to LPG.
You could also try disconnecting the EGR vacuum pipe just in case that’s cutting in when it shouldn’t.
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fieldashley
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V plate facelift scorpio 2.3 Ultima.
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Re: Intermittent jerk !
« Reply #3 on: Jan 18th, 2014, 7:40pm » |
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Hi if it only happens when your using it on petrol it could be the fuel filter, I had this happen with a couple of fords, changed the fuel filter and it's cured the problem, very cheap part so worth a try.
Ashley...
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gozz
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Re: Intermittent jerk !
« Reply #4 on: Jan 18th, 2014, 7:48pm » |
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Thanks for your replies chaps,Mike it has been my experience over many Scorpy years that a coil pack failure causes a horrible misfire as the other one still works causing two cylinder running,a bad wire somewhere that I have missed is always a distinct possibility though.
Dave,this problem is most apparent when cruising on an even throttle,it may be,and most likely is my imagination that it occurs after a roundabout or sharp bend as if there is a'pendulum 'affect involved.If I unplug the cam sensor the engine misses a couple of beats and the code comes up,I have a spare MAF, though I'm not suspicious of it being the culprit,the malfunction of the EGR valve had not occurred to me though.In my desperate grappling I did change the EDIS unit and gave the wiring a good yanking,but alas to no avail.
My mechanic pal at the local friendly garage says that a failing sensor may indeed never produce a code,and he has frequently needed
to experiment to find the problem,faulty cam and crank sensors being the usual culprits.So much for modern technology
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gozz
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Re: Intermittent jerk !
« Reply #5 on: Jan 18th, 2014, 7:55pm » |
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Ashley,the problem occurs on either fuel,I do tend to change the fuel filter occasionally though.Thanks for your thoughts.
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Glyn
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Now an OAP ! 95 cossie and another !and a 12v
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Re: Intermittent jerk !
« Reply #6 on: Jan 19th, 2014, 12:55am » |
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Had similar problem which eventually turned out to be a fine crack in a vacuum pipe at the back of the engine-but that was on a Cosworth.
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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: Intermittent jerk !
« Reply #7 on: Jan 19th, 2014, 8:53am » |
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Another thought. I had a problem that felt like the car had fuel shut-off to the engine, as if also the car had been put in neutral, then banged back in drive, all happening very quickly. Gearbox fault! Just a thought!
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I love 'Movvy'
1995 Jaguar XJ6 X300 3.2 (Henley)
1995 Jaguar XJ6 X330 4.0 (Dopey)
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Andycan
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I'm a YaBB newbie!
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Re: Intermittent jerk !
« Reply #8 on: Jan 19th, 2014, 10:46am » |
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@ PJ I had that same problem and I was lucky that it turned out to be low oil level in the gearbox.
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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: Intermittent jerk !
« Reply #9 on: Jan 19th, 2014, 12:24pm » |
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on Jan 19th, 2014, 10:46am, Andycan wrote:| @ PJ I had that same problem and I was lucky that it turned out to be low oil level in the gearbox. |
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Unfortunately, my problem resulted in a Auto-Box re-build. On the bright side though, having had the Auto-Box re-built by our good friend on this forum, it now works perfectly and well-worth the money knowing that the Auto-Box is now in fabulous condition.
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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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gozz
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Re: Intermittent jerk !
« Reply #10 on: Jan 19th, 2014, 4:53pm » |
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Thanks for your further thoughts lads,PJ I had ruled out the gearbox because the tacho drops when the jerk occurs then immediately recovers,it does appear that something is momentarily shutting the engine down,if it remained a momentary thing I could live with it,the not knowing is the worrying part
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PJDavis
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Re: Intermittent jerk !
« Reply #11 on: Jan 19th, 2014, 5:26pm » |
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on Jan 19th, 2014, 4:53pm, gozz wrote:| Thanks for your further thoughts lads,PJ I had ruled out the gearbox because the tacho drops when the jerk occurs then immediately recovers,it does appear that something is momentarily shutting the engine down,if it remained a momentary thing I could live with it,the not knowing is the worrying part |
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Hmmmm. I thought the tacho took it's message from the speed-sensor on the side of the gearbox, and therefore a flickering tacho was a sure sign? Or am I thinking of a flickering Speedo?
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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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Tompion
Administrator
1997 2.3 Ultima estate.
Posts: 2918
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Re: Intermittent jerk !
« Reply #12 on: Jan 19th, 2014, 8:55pm » |
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Yes, you’re thinking of flickering speedo, tacho is from the EDIS.
I don’t know much about LPG but presumably you could have a wiring problem to its controller/switchover or whatever that would affect both fuels.
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ABS multiplug wheel sensor pins MK IV or MK 20
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scorpio_man
Administrator
Ford Kuga awd
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Re: Intermittent jerk !
« Reply #13 on: Jan 19th, 2014, 10:19pm » |
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hi gozz
i'd go with the coil pack idea. do you have spare you could try?
hth
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gozz
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Re: Intermittent jerk !
« Reply #14 on: Jan 19th, 2014, 11:20pm » |
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on Jan 19th, 2014, 10:19pm, scorpio_man wrote:hi gozz
i'd go with the coil pack idea. do you have spare you could try?
hth |
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Thanks Andrew,I did change the coil packs when I repaired the fried engine loom last year.This fault is a complete but very brief total switch off.
Dave there is always a chance that joints in the wiring loom for the gas system where they join the main loom may have a fault but they all look OK
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scorpio_man
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Ford Kuga awd
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Re: Intermittent jerk !
« Reply #15 on: Jan 20th, 2014, 7:57pm » |
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hi there
mind that 'gas' takes a much larger spark to ignite. that could put more stain on the packs.
also it used to be recommended to close the spark plug gap a little.
hth
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gozz
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Re: Intermittent jerk !
« Reply #16 on: Jan 21st, 2014, 8:53am » |
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Yes Andrew,when the bloke fitted the system he said that there was no point in fitting platinum plugs,just ordinary ones with a 25thou gap.The 'jerk' happens on either fuel though
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pedropedro
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Re: Intermittent jerk !
« Reply #17 on: Jan 21st, 2014, 12:59pm » |
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I had similar issue..was the wiring from the edis unit which of course feeds the ecu signal to the coil packs under the washer bottle......wires had coroded and shorted...its not difficult to examine..I ran wires direct to ecu and solved..symptoms were would run fine then instantly die for a few secs
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gozz
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Re: Intermittent jerk !
« Reply #18 on: Jan 21st, 2014, 7:41pm » |
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That is the sort of thing I get,but I previously changed the EDIS unit and examined the wires,all seemed well there.
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Tompion
Administrator
1997 2.3 Ultima estate.
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Re: Intermittent jerk !
« Reply #19 on: Jan 22nd, 2014, 11:46am » |
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I think I've seen people had similar issues caused by problems at the PCM end of the EDIS harness, mainly trouble with the 3 shielded wires, might be worth checking there if you haven't already.
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ABS multiplug wheel sensor pins MK IV or MK 20
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