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Running rough when cold
https://www.ausmini.com/forums/viewtopic.php?f=2&t=63184		 Page 1 of 2
Author:  ryan [ Thu May 20, 2010 6:47 pm ]
Post subject:  Running rough when cold
Hi all,

A couple of weeks ago there was a post on here about running rough when the engine was cold. I replied to the post that the car should be able to be set up to run rough without much warming up.

Now my car has started doing exactly the same thing and it with the cooler weather it is taking about 10mins to get to a nice warm running temp.

Whats the problem?
How do I fix it?
Author:  GT mowog [ Thu May 20, 2010 7:01 pm ]
Post subject: 
In rounning rough, is it a 'regular' roughness or ir-regular?

If regular, look at the ignition system, particularly plugs and leads. If ir-regular, could be fuel system. Maybe over-fueling.

Taking 10 minutes to warm up seems a bit long. I'd suggest testing the thermostat. An 82 or maybe even an 88 degree one should be fitted.
Author:  ryan [ Thu May 20, 2010 7:08 pm ]
Post subject: 
I'll expand on that.

It runs fine when idling when cold, but needs the choke. As soon as its under load it starts to stutter etc.

Leads and plugs etc I have checked. Points are fine, so is the condenser.

It seems slightly rich, but nothing over the top.
Author:  ryan [ Thu May 20, 2010 7:10 pm ]
Post subject: 
Thanks morris....never thought of that :lol:

But seriously, the choke helps to some degree, but still very rough.

it also feels as though it struggles more when the revs are low.

EDIT: Morris1100 had a post there about using the choke.
Author:  simon k [ Thu May 20, 2010 8:47 pm ]
Post subject: 
I reckon the coil is on it's way out...
Author:  1275LS [ Fri May 21, 2010 2:39 pm ]
Post subject: 
I would check the dashpot is topped up and also the piston body for dirt.
Particularly if it is a bit inconsistent when warm and perhaps misbehaves on decelleration when warm.

Hope this helps
Author:  ryan [ Fri May 21, 2010 4:10 pm ]
Post subject: 
Dashpot is fine. It runs great when warm.

Why do you think the coil simon? it is pretty old. Maybe I'll try and find another one and check it.

Ryan
Author:  simon k [ Fri May 21, 2010 4:35 pm ]
Post subject: 
ryan wrote:
Dashpot is fine. It runs great when warm.

Why do you think the coil simon? it is pretty old. Maybe I'll try and find another one and check it.

Ryan


I guess the only way to reply is "coils ain't coils" - I had one die over a period of a few weeks, the car just started getting grumpy, then one morning after a rain storm I got around the corner the ignition started cutting in and out and the car just died.... I ran home, found another coil and off it went. I don't remember how I diagnosed the the coil over simply a wet distributor, but the coil was definitely dead when I tested it later

Dad used to tell a story about his old dodge ute, it was running badly and no-one could figure out why, someone suggested it needed a rebuild, so the engine was rebuilt, but it still ran badly. By chance he changed the coil and problem solved. When he told his dad, who was a radio engineer, his dad said "a spark isn't enough, it has to be a good quality spark" or something along those lines

just sounds to me like you've got a bad spark - sparks come from the coil.... besides, it's a 1 minute job to bung another coil on and see - if you've got a suitable one laying around that you know is good. Go and visit a mate "hey, while I'm here, mind if I borrow your coil for a minute?" :wink:
Author:  Fiji [ Fri May 21, 2010 5:25 pm ]
Post subject: 
how did you test the coil ??

i get some missing that comes and goes. i was think due to cold but wasn't convinced. havent yet diagnosed it. seemed to run great today .mmmm
Author:  GT mowog [ Fri May 21, 2010 6:39 pm ]
Post subject: 
simon k wrote:

............. When he told his dad, who was a radio engineer, his dad said "a spark isn't enough, it has to be a good quality spark" or something along those lines



It is the colapsing magnetic field in the coil that produces the HV to make the spark. This field begins to colapse when the points open. The magnet circuit does store some energy, a little bit like a capacitor.

If there is not enough resistance in the HT circuit the spark will literally be over in an instant as it will be seen as a short circuit so draining the stored energy very rapidly. With the right amount of resistance in the circuit (typically 2k ohms to 10 k ohms) the spark will spark for longer. This will allow for better, cleaner and more complete burning of the mixture.

A poor magnetc circuit will have a similar effect.

If there is too much resistance in the circuit, it will have trouble making a spark (jumping across the spark gap of the plug) when in the cylinder, under pressure (more load) and like wise under vacuum (over-run).
Author:  drmini in aust [ Fri May 21, 2010 7:13 pm ]
Post subject: 
Put a meter on your plug leads and check resistance. I toss them away when they get to 4K ohm.
If they read ~ they have well and truly had it.

Bosch leads ($5.95 ea @ Supercrap) are around 2K resistance, and the core is not just carbonized string like Top Guns etc are.
My Bosch are 5 years old now and still reading 2K. 8)
Author:  ryan [ Fri May 21, 2010 8:36 pm ]
Post subject: 
Ok, so I took it for a drive round to my mates this arvo to help him with his car. It got progressively worse. When I got there he wasn't home yet, so I popped the bonnet to investigate. Took the dissy cap off and it looks as though the points have closed up and are burnt. It was getting dark and didn't have a spare set in the car. So I will do it in the morning and see how it goes.

:lol: :lol:
Author:  simon k [ Fri May 21, 2010 8:51 pm ]
Post subject: 
ryan wrote:
Ok, so I took it for a drive round to my mates this arvo to help him with his car. It got progressively worse. When I got there he wasn't home yet, so I popped the bonnet to investigate. Took the dissy cap off and it looks as though the points have closed up and are burnt. It was getting dark and didn't have a spare set in the car. So I will do it in the morning and see how it goes.

:lol: :lol:


but.... :?

ryan wrote:
Points are fine, so is the condenser


I know hiw to fix it!

throw the coil, condenser, distributor etc. away and do a megajolt - my local ford wrecker has the required mondeo bits. There was a local guy keen so I chased organised the bits with the wrecker, then he changed his mind :roll:
Author:  ryan [ Fri May 21, 2010 8:56 pm ]
Post subject: 
Simon, points did look ok. but after driving it for a week or more and the problem worsening I thought I would check them again.

I will fix them up and see how it goes. If it fixes the running cold, then great.

If it just makes it run smoother, than that is great too. And, I'll just be back to square one.
Author:  drmini in aust [ Fri May 21, 2010 8:57 pm ]
Post subject: 
When points close up, weird things happen...
Thank God there are now electronic dizzys about (eg Nissan Pulsar, Honda Civic, Subaru 1600) that fit an A series.:mrgreen:
Saves me buying a laptop to make a Megajolt work.
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