Hesitation / judder (electrical)
Thread Starter
Rennlist Member
Joined: Oct 2008
Posts: 225
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From: Surrey, UK.
Hesitation / judder (electrical)
Hi all
I've got an issue whereby the car stutters for no apparent reason at cruising speed.
It has to be electrical because all of the power (even dash lights, stereo etc)
goes off for a fraction of a second each time it stutters.
The pain in the butt is that it's intermittent (normally only happening on a long run)
and I can't recreate the fault.
I've fumbled around the ignition key wires, but nothing seems to affect it.
I've also cleaned and polished the front earth points and ensured that the battery
is really well connected.
I notice that lots of people have trouble with the ignition coils, but that
wouldn't explain the dashboard lights going out would it.
An obvious weak points I should check?
Cheers
Rich
I've got an issue whereby the car stutters for no apparent reason at cruising speed.
It has to be electrical because all of the power (even dash lights, stereo etc)
goes off for a fraction of a second each time it stutters.
The pain in the butt is that it's intermittent (normally only happening on a long run)
and I can't recreate the fault.
I've fumbled around the ignition key wires, but nothing seems to affect it.
I've also cleaned and polished the front earth points and ensured that the battery
is really well connected.
I notice that lots of people have trouble with the ignition coils, but that
wouldn't explain the dashboard lights going out would it.
An obvious weak points I should check?
Cheers
Rich
Last edited by RichieRoo; Mar 25, 2009 at 10:25 AM.
Pro
Joined: Oct 2007
Posts: 504
Likes: 0
From: PA
I had the same problems and found that replacing the main ground from the battery solved it. I replaced the original braided line with exposed copper with a newer style one with insulation from Pelican. It was only around $10, my cheapest fix yet.
Thread Starter
Rennlist Member
Joined: Oct 2008
Posts: 225
Likes: 3
From: Surrey, UK.
Yeah. I did remove the old braided cable and really cleaned it up (soaked in a corrosion
remover over night) and refitted. I guess it wouldn't do any harm to replace it altogether.
I'll get one tomorrow.
The reason I didn't before was that I figured the car should run fine even without the
battery connected at all as the alternator should provide enough power. So to my mind
the battery earth is pretty much redundant.
But what the hell... I'll try anything.
Thanks
Rich
remover over night) and refitted. I guess it wouldn't do any harm to replace it altogether.
I'll get one tomorrow.
The reason I didn't before was that I figured the car should run fine even without the
battery connected at all as the alternator should provide enough power. So to my mind
the battery earth is pretty much redundant.
But what the hell... I'll try anything.
Thanks
Rich
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Joined: Aug 2007
Posts: 903
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From: Cape Cod, Ma
Our cars are very sensitive to electrical problems, so it could be allot of things.Check other ground points, like transmission ground. You could unplug and then re-plug the computer under the drivers seat to make sure there is no corrosion. And then there is always the coils. If they never have been replaced, might be worth a try.
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Andreas
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From: Virginia Beach, Va.
Check connection at starter where the battery cable (positive) is attached after travelling through your 964 on the passenger side. 
Also, there is a ground strap from one of the nuts that holds your starter in the transmission bellhousing, the one (bottom) that can be reached from just under the car...this bolts to the "hoop" support for your rear shocks...this can be a MAJOR culprit.
Also, there is a ground strap from one of the nuts that holds your starter in the transmission bellhousing, the one (bottom) that can be reached from just under the car...this bolts to the "hoop" support for your rear shocks...this can be a MAJOR culprit.
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Thread Starter
Rennlist Member
Joined: Oct 2008
Posts: 225
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From: Surrey, UK.
Belt and braces
Ok. I'm liking all the suggestions and plan to address them all.
My check list looks something like this:
Air flow meter wiring - my car is a '91 so I didn't have to remove
the protective wire covering, but I did the wire tie and also found
that the breather pipe bracket was floating around as it had not
been reattached by the last owner when the shock absorbers were
replaced. That has been bolted back down and bend as per the
PDF instructions.
Battery earth cable - I've ordered a custom made earth cable which
is really chunky.
Starter to chassis earth cable - I did the starter motor recently and
went to extreme lengths to ensure that it made a really good connection.
You can see what I did here.
In addition, I have also ordered a thick custom cable to connect from the
engine bay chassis earth point to a large bolt on the aircon compressor.
So this should ensure a good ground to the engine/transmission.
Connection to engine management under seat - I'll disconnect and
reconnect as suggested.
Will let you know how I get on.
Thanks for all the suggestions so far. Really appreciate your help.
My check list looks something like this:
Air flow meter wiring - my car is a '91 so I didn't have to remove
the protective wire covering, but I did the wire tie and also found
that the breather pipe bracket was floating around as it had not
been reattached by the last owner when the shock absorbers were
replaced. That has been bolted back down and bend as per the
PDF instructions.
Battery earth cable - I've ordered a custom made earth cable which
is really chunky.
Starter to chassis earth cable - I did the starter motor recently and
went to extreme lengths to ensure that it made a really good connection.
You can see what I did here.
In addition, I have also ordered a thick custom cable to connect from the
engine bay chassis earth point to a large bolt on the aircon compressor.
So this should ensure a good ground to the engine/transmission.
Connection to engine management under seat - I'll disconnect and
reconnect as suggested.
Will let you know how I get on.
Thanks for all the suggestions so far. Really appreciate your help.
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Thread Starter
Rennlist Member
Joined: Oct 2008
Posts: 225
Likes: 3
From: Surrey, UK.
Slight update
Just took the car for a test run. Looks like it wasn't anything to do with the
air flow meter wiring because the problem is still there.
The hesitation was accompanied by the infamous "Christmas tree" illuminated
dash board (see picture).
Let's hope the new earth leads fix it. They should arrive tomorrow.
air flow meter wiring because the problem is still there.
The hesitation was accompanied by the infamous "Christmas tree" illuminated
dash board (see picture).
Let's hope the new earth leads fix it. They should arrive tomorrow.
Thread Starter
Rennlist Member
Joined: Oct 2008
Posts: 225
Likes: 3
From: Surrey, UK.
New battery lead fitted
Afternoon all.
Leads arrived today. Very impressed with the service of the company making
them up (Kojaycat in the UK).
Sent them all the details yesterday afternoon. Had an email to say they had
been made up and posted the same afternoon. Arrived this morning.
Lovely quality too (check out the pic). Nice rubber boots on every terminal.
So I've replaced the old braided battery earth and added a cable from the
chassis to a big mounting bolt on top of the aircon compressor.
Has it worked? Well I took it for a short test drive and it seems ok. I'll report
back either way after a proper run. If this fails I guess it'll be Jonny's plan
of replacing the coils.
Leads arrived today. Very impressed with the service of the company making
them up (Kojaycat in the UK).
Sent them all the details yesterday afternoon. Had an email to say they had
been made up and posted the same afternoon. Arrived this morning.
Lovely quality too (check out the pic). Nice rubber boots on every terminal.
So I've replaced the old braided battery earth and added a cable from the
chassis to a big mounting bolt on top of the aircon compressor.
Has it worked? Well I took it for a short test drive and it seems ok. I'll report
back either way after a proper run. If this fails I guess it'll be Jonny's plan
of replacing the coils.
Thread Starter
Rennlist Member
Joined: Oct 2008
Posts: 225
Likes: 3
From: Surrey, UK.
Hi Boxsey
Here are the specs for the cable. The diagram here shows the braided battery
cable replacement at approx the same length as the original (I did mine a bit
shorter because I have a battery disconnect switch attached).
The longer engine/chassis ground cable connects to my aircon compressor bolt.
If you don't have aircon, obviously the length to a suitable bolt will vary.
As you can see from the photo I allowed plenty of slack in the longer lead
to allow for engine movement. Don't know if it hampers air filter removal -
haven't tried. Obviously the cable is pretty chunky and space to get to the
chassis ground is a bit limited, but it's doable.
Here are the specs for the cable. The diagram here shows the braided battery
cable replacement at approx the same length as the original (I did mine a bit
shorter because I have a battery disconnect switch attached).
The longer engine/chassis ground cable connects to my aircon compressor bolt.
If you don't have aircon, obviously the length to a suitable bolt will vary.
As you can see from the photo I allowed plenty of slack in the longer lead
to allow for engine movement. Don't know if it hampers air filter removal -
haven't tried. Obviously the cable is pretty chunky and space to get to the
chassis ground is a bit limited, but it's doable.
Nordschleife Master
Joined: Feb 2007
Posts: 5,095
Likes: 3
From: Cheshire, UK
Where does the engine compartment strap attach to on the chassis? I've got a braided strap that links the air con compressor bracket to the nearest engine mount bolt. Not being particularly knowledgeable in car electrics I'd never really worked out what it was there for. I'd assumed it was to earth the compressor for safety? But now I'm guessing it's more for grounding the engine? 
I think I've got a pic of it somewhere and will post it up if I can find it.
I think I've got a pic of it somewhere and will post it up if I can find it.
Thread Starter
Rennlist Member
Joined: Oct 2008
Posts: 225
Likes: 3
From: Surrey, UK.
There is a brass earth point in the rear wing, adjacent to the dipstick pipe.
It uses one M8 bolt to secure two earth cables.
My choice of the aircon bolt was very arbitrary. I was just looking for a good,
solid connection to the engine which was easily accessible.
This extra cable is simply an addition to the earthing loop under the car which
Jeff mentions earlier in this thread.
I believe the small braided cable you mention simply ensures a good earth with
the outer (pulley side) components of the compressor.
It uses one M8 bolt to secure two earth cables.
My choice of the aircon bolt was very arbitrary. I was just looking for a good,
solid connection to the engine which was easily accessible.
This extra cable is simply an addition to the earthing loop under the car which
Jeff mentions earlier in this thread.
I believe the small braided cable you mention simply ensures a good earth with
the outer (pulley side) components of the compressor.
Last edited by RichieRoo; Mar 27, 2009 at 12:57 PM.