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        General >> Problems >> Intermittent jerk !
        
(Message started by: gozz on Jan 18^th, 2014, 10:58am)

Title: Intermittent jerk !
Post by gozz on Jan 18^th, 2014, 10:58am

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 :o
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.

Title: Re: Intermittent jerk !
Post by Scorpio_Mike on Jan 18^th, 2014, 12:21pm

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 ?

Title: Re: Intermittent jerk !
Post by Tompion on Jan 18^th, 2014, 1:06pm

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.

Title: Re: Intermittent jerk !
Post by fieldashley on Jan 18^th, 2014, 7:40pm

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...

Title: Re: Intermittent jerk !
Post by gozz on Jan 18^th, 2014, 7:48pm

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 ::)

Title: Re: Intermittent jerk !
Post by gozz on Jan 18^th, 2014, 7:55pm

Ashley,the problem occurs on either fuel,I do tend to change the fuel filter occasionally though.Thanks for your thoughts.

Title: Re: Intermittent jerk !
Post by Glyn on Jan 19^th, 2014, 12:55am

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.

Title: Re: Intermittent jerk !
Post by PJDavis on Jan 19^th, 2014, 8:53am

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!

Title: Re: Intermittent jerk !
Post by Andycan on Jan 19^th, 2014, 10:46am

@ PJ I had that same problem and I was lucky that it turned out to be low oil level in the gearbox.

Title: Re: Intermittent jerk !
Post by PJDavis on Jan 19^th, 2014, 12:24pm

on 01/19/14 at 10:46:45, Andycan wrote:

@ PJ I had that same problem and I was lucky that it turned out to be low oil level in the gearbox.

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.

Title: Re: Intermittent jerk !
Post by gozz on Jan 19^th, 2014, 4:53pm

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 :o

Title: Re: Intermittent jerk !
Post by PJDavis on Jan 19^th, 2014, 5:26pm

on 01/19/14 at 16:53:14, gozz wrote:

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?

Title: Re: Intermittent jerk !
Post by Tompion on Jan 19^th, 2014, 8:55pm

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.

Title: Re: Intermittent jerk !
Post by scorpio_man on Jan 19^th, 2014, 10:19pm

hi gozz

i'd go with the coil pack idea. do you have spare you could try?

hth

Title: Re: Intermittent jerk !
Post by gozz on Jan 19^th, 2014, 11:20pm

on 01/19/14 at 22:19:48, scorpio_man wrote:

hi gozz

i'd go with the coil pack idea. do you have spare you could try?

hth

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

Title: Re: Intermittent jerk !
Post by scorpio_man on Jan 20^th, 2014, 7:57pm

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

Title: Re: Intermittent jerk !
Post by gozz on Jan 21^st, 2014, 8:53am

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

Title: Re: Intermittent jerk !
Post by pedropedro on Jan 21^st, 2014, 12:59pm

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

Title: Re: Intermittent jerk !
Post by gozz on Jan 21^st, 2014, 7:41pm

That is the sort of thing I get,but I previously changed the EDIS unit and examined the wires,all seemed well there.

Title: Re: Intermittent jerk !
Post by Tompion on Jan 22^nd, 2014, 11:46am

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.

Title: Re: Intermittent jerk !
Post by gozz on Jan 22^nd, 2014, 4:58pm

Thanks for that Dave,I didn't realise the four cylinder engines had that shielded cable,I had to rewire several 12 valve sixes whose three shielded signal wires from the distributor to the PCM had dissolved into one causing amazing happenings.I will have the glove box out and have a nosy in there.These Coleman Milne vehicles are devoid of those security clamps all riveted up,so the job is much easier.

Title: Re: Intermittent jerk !
Post by gozz on Feb 8^th, 2014, 9:32pm

Further to this ongoing problem,I sent the ECU away for testing,the man rang me to say that he had good news,"there is nothing wrong with it",I said that was not what I had hoped,in the interim another 2.3 unit was tried resulting in a mad flashing of the PATS light and a no start,thus it appeared that mine,being 1999 registered has the PATS inside the unit.
I decided to go round again and fitted yet another used EDIS module,so far the car has performed impeccably,thus it would appear that this was the problem all along,no fault codes ever came up on the scanner making for a trial and error diagnosis only.
The temptation now dare I say,is to replace it with the last of the line OMEGA :o When the Scorpio production finished,Coleman Milne (the coach builders) had to resort to stretching the Australian Ford Fairlane which,whilst being a good robust product,is devoid of agents in the UK,and with increasing age could prove difficult to keep running reliably.My Dorchester funeral limousine (Scorpio) although having covered only 52000 miles and in pristine order,is becoming increasingly unreliable due to Ford's inbuilt self destruction systems,having run many of these cars in my business,they have all tried my patience at one time or another due mainly to poor wiring which has always been overcome by sheer determination and a lot of teeth gritting,which as one advances in age becomes increasingly undesirable ::)

Title: Re: Intermittent jerk !
Post by Mike H on Feb 8^th, 2014, 11:25pm

Have you tried it with the MAF unplugged ~ when I had similar, it was duff MAF.

Title: Re: Intermittent jerk !
Post by gozz on Feb 9^th, 2014, 2:04pm

Yes Mike,I paid attention to the MAF earlier on in the proceedings as that is one of the most common problems and the easiest to get at.It appears to have been the EDIS module this time,thanks for your input.
GOZZ.