Mazda 626 GLX

[madken]

I'm having problems with the auto choke. When cold starting is not imeadiate then when started the revs are high on tickover, black smoke from exhuast, petrol consumption's high. Any ideas folks?
Regards. Ken

 

[jonnyfishing]

Ken

Sounds like you have cylinder trouble,worn or broken piston rings. The black smoke is oil burning in the combustion chamber(s)also you probably have pressure going down to the sump,remove filler cap,and if you have excessive pressure,it is a sign of rings passing.The best thing to do is have a compression test done and work from there.

Jonny

 

[madken]

Hi Jonny, I've had a pressure test done last week and also new spark leads, plugs etc. The black smoke is definitely petrol soaked by the smell. and when the engine eventually gets warm the problem eases off and there's no sign of black smoke. Also if I take off the airfilter I can see the choke's half closed. There's a diaphram control leading to the choke but I'm not sure if it can be a fault with that or is there some kind of solenoid controling that. Thanks for the reply Jonny.
Regards.Ken

 

[PowerTool]

Burning oil causes blue smoke - black smoke is fuel (unburnt carbon) as you have discovered.

Is your choke controlled by solenoid (electric) or water (heater pipes) ?
Sounds like the mechanism is sticking - if fuel consumption is bad when warmed up as well,it's probably permantly sticking and still running rich when warm (but not enough to produce noticeable smoke)

 

[madken]

Hi Powertool. The choke's controlled by a solenoid but this in turn seems to be some way controled by the water heater becuse when the engine gets hot the choke is no longer a problem. Any more ideas will be very much appreciated.
Regards Ken

 

[keyplayer]

. Also if I take off the airfilter I can see the choke's half closed

When hot or cold? Should be fully closed when cold and engine not running, and fully open when engine hot. I'm with Powertool in that you should ensure all your carb linkages are nice and free, remember when choke is on, it opens the main throttle butterfly a touch as well as the choke butterfly so is quite an intricate mechanism.

Also check condition of all vacuum hoses and renew as necessary. And possibly your float chamber needle valve is sticking open when cold.

 

[madken]

Here's the situation up to date folks The hoses seem to be ok. the linkages have been checked and sprayed with WD40 and all are free. when the engine is hot there's no sign of petrol vapour from the exhaust even when I put my hand over the outlet and smell my palm after. What do you think about this next question? gear five seems to be controled by the engine heating up in that it won't go in this gear untill the engine is quite hot, so on short `town` runs I'm never able to use it. To me this is not right some how. Now my question is is it possible that the choke is also relying on the thermostat? If so is there only one stat (The main engine stat) or is there two. (One being hidden from view in the heating system?
Regards to all. Ken

Hi I've replaced the engine thermostat and the choke control seems to be working fine now.
But the 5th gear won't select untill the engine is quite hot. this being and automatic gearbox. It seems there's a narrow pipe coming out of the bottom of the radiator and into the gearbox. I do know that 5th gear is controlled by the water temp' or is it water pressure? I'm not quite sure how this setup has to work. Now I've sorted out the thermostat and the gear still doesn't behave as should. Is it possible that this `small bore` pipe could be `sludged up`? I'm reluctant to take it off before I get to know what this pipe is for. The confusing thing is that the end of this pipe nearest the ran base has got oil sludge on it. I was wondering if the bottom of the rad has a hidden oil cooler inbuilt. So maybe it isn't controlled by warm pressurized water, but warm oil?
So come on my friends what's the verdict?

_____________________________
moderator

plesae note 10a

 

[Quick Fit]

Yes it is an oil cooler, most Auto's have an oil cooler built into the rad.
Get it flushed with a good rad flush, or remove and have a steam clean.
One thing are you sure your Auto gearbox is 5 speed?
QF

Edit........
Not a bad idea to change the Automatic fluid as this can cause problems if it has not been changed for a long while.

 

[madken]

Thanks QF for your valued help with this problem. Yes it is an automatic box. The 5th gear is supposed to engage at a certain water temp, but failed to do it unless the car has been running for some miles.
There is a seperate oil cooler at the lower front of the radiator.
There are two pipes, Flow and return? form the cooler to the gearbox. But the pipe that's my concern is a small bore pipe that comes out of the lower bottom rear of the water radiator to the gearbox, as if it's some kind of water pressure gadget. Which when I think of it, it makes sense that if this is so, then the gear will only engage when the main water control stat opens fully. This will obviously let the main stat let the engine get up to running temp' before it lets the top gear engage as the rad pressure builds up. So this small pipe could then be under water pressure which in turn activates some kind of gadget in the gearbox control, but only gear 5. The transmission fluid was changed a couple of years ago.
The water seems clean, and when I changed the thermostat, I was surprised to find the housing was spotless. But I'm taking your advice on flushing the system. Because I think this small pipe could have sediment in it that's stopping the necessary pressure that activates the gear.
Any further advice on exactly what this small pipe is will be very much appreciated mate. Kind regards. Ken