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Petrolhead Q&A thread

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Petrolhead Q&A thread

Old 27th Dec 2010, 19:54
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Petrolhead Q&A thread

Merry Christmas all!

Feel a bit guilty coming on here this time of year and posing this kind of question, but here we go...

I have an '05 Mazda 6 petrol with 90k (Miles) on the clock, and recently noticed a problem which is gradually worsening - during the first 5-10 minutes of driving (never happened during Summer, only when cold), the engine will lose power intermittently, giving the same mild 'choppy' feeling you get when you're about to run out of fuel (a friend explained how this feels, it's never happened to me personally... ).

Power always smooth and continuous within ten minutes once warmed up.

I should get it down the garage, but unfortunately my schedule's full for the next two weeks!

Somebody mentioned moisture (what with the snow recently) messing up with the injectors? So that's the popular amateur opinion.

Any ideas peeps?

p.s. I use the car to get to aerodromes, so this is aviation related!
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Old 27th Dec 2010, 19:56
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If there's a coolant temperature sensor and it's failed in the "engine warmed up" sense, the injection will not enrich the fuel mixture as it should do for a cold engine condition.
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Old 27th Dec 2010, 20:21
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with 90k (Miles) on the clock,
There's one of yer problems, the miles should be on the odometer.


You seem to be describing a possible over fueling. You could I suppose pull one of the plugs at say, 7 minutes, and see if it's too black. This is an easy first step to diagnosing the fault.
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Old 27th Dec 2010, 20:58
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May be worth checking and/or replacing your plug & coil leads, had something similar on my much missed old '88 Sunny Turned out that the HT leads were susceptible to moisture ingress, which wasn't a problem when the engine was warm, as the moisture evaporated. Let it get cold again and the moisture condensed causing an occasional short & giving the rough running.

If you're still using the original leads, they might well be suspect and although they could last for many years, it might be worth changing the leads anyway, as they shouldn't be very expensive & they're dead easy to change, as you can do one at a time & they generally come numbered nowadays.
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Old 27th Dec 2010, 21:10
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Turned out that the HT leads were susceptible to moisture ingress, which wasn't a problem when the engine was warm, as the moisture evaporated. Let it get cold again and the moisture condensed causing an occasional short & giving the rough running.
Old Jaguar problem - frequently had to remove the set and dry them out in a warm oven to avoid severe misfiring. Mind you the leads were 'rubber' rather than plastic. The set was 'sized' in length so that it was impossible to connect them up wrongly (unless you unplugged them from the distributor cap).
I don't suppose current cars have distributor caps (or rotor arms) . . .
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Old 27th Dec 2010, 21:24
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I don't suppose current cars have distributor caps (or rotor arms) . . .
Dunno....... I've been 100% diesel for a few years now.
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Old 28th Dec 2010, 01:00
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It'll be a sensor problem of some description, of that I have no doubt. Which sensor has gone no-one can really tell from just the symptoms with 100% certainty, but a diagnostics machine/Code reader should be able to pinpoint it immediately.
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Old 28th Dec 2010, 01:34
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Many thanks to all for their precious time invested in my problem

Loose Rivets - funny you should mention over-filling; for the first time in yonks I 'brimmed' the tank (because I could), and the car was then sat for two days during Xmas before driving again. Maybe it exacerbates matters, but the problem existed well before this, in my days of 20-30 'fill-ups'!

SAS - That was my personal instinct, although I didn't think it was possible for a diagnostics machine to register any codes unless the computer had thrown a check engine light (which mine hasn't)? This is based on an experience I had before with my old Mondeo, the engine of which started juddering for a few seconds after startup before running smooth. The CEL was illuminated for those few seconds but apparently even that wasn't enough to get anything off the 'machine' - it needed to be on or flashing at the time of test...

I'll get it into the local garage when I find the time, but I like these ideas people can come up with - most sound simple enough to have a look at myself = less .

Why didn't I post this on Mazdaownersanonymousproudofmycarbutwantsomewherefreetogetmec hanicaladviceclub?

Pilots can be trusted...


...
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Old 28th Dec 2010, 01:59
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`` If this is a problem that happens solely on cold-starting , then presumably linked to one of the inlet-air sensors which are trying to balance air temperature( vs cylnder tempeature )


My solution is to live with it as it has limited inpact on the car, but you may wish to intervene before it becomes a failure. Likely cost GBP 100 -500 depending how rapacious Mazda GB is and if you buy genuine or "parallel" parts.

So my answer similar to Shy Torque

Vis-a-vis the(implied) guilt, that keeps the Pope in a job.

Last edited by AlpineSkier; 28th Dec 2010 at 02:12.
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Old 28th Dec 2010, 05:50
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I had a car that suffered from carb icing when it was damp and cold.
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Old 28th Dec 2010, 06:36
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Pilots can be trusted...
There's your first mistake.
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Old 28th Dec 2010, 07:33
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Oooooh! *sucks in breath through clenched teeth and shakes head*

A can sort it, mate, but it's gonna cost yer. Big job an no way can yer get bits fur dem Mazda six no more.

Fer a favour, can do a crakin deal on this ere Trabant we just gorrin terday.....
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Old 28th Dec 2010, 10:33
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There are certain sensors that aren't always plumbed into the check engine system. Lambda sensors can often fail for example and you won't know anything about it other than that the car runs like crap.

The check engine light doesn't always show up and a sensor might simply be faulty rather than completely duff. The magic box will often store falt codes that can only be read by a diagnostics machine.
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Old 28th Dec 2010, 10:40
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I have a Mazda 6 2.0 litre petrol. A good car but it has bugger all power to start with.

By the way your title says 'engine specific' - but you don't specify the engine.
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Old 28th Dec 2010, 11:53
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Yes he does....he definitely mentioned that it was an engine problem.

I remember because he said "the engine will..." ...see!

You should pay more @ttention!
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Old 28th Dec 2010, 18:33
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Originally Posted by EW73 View Post
You should pay more @ttention!
Actually you should pay @tention:

http://www.pprune.org/jet-blast/4378...gn-pprune.html
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Old 28th Dec 2010, 20:38
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When the engine is cold/damp in this weather,go out at night ,open bonnet,minimise all lighting,use an old blanket,and start it up. If you are shorting any leads/plugs,you should be able to see it`sparking..
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Old 28th Dec 2010, 20:51
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I had a car that suffered from carb icing when it was damp and cold.
I did, too. But it had a carburettor
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Old 28th Dec 2010, 21:23
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funny you should mention over-filling; for the first time in yonks I 'brimmed' the tank
In the mid to late 1980s I had an X-reg (August 1980 to July 1981) Austin Maxi.

When the fuel level in the tank was 'low' (I eventually worked out) the engine would die during 'flat-out' motoring (on motorways). I would coast onto the hard shoulder then it would restart and run as normal until again called-upon to deliver high speed.

When I removed the fuel tank and tipped out the contents there was a sliver of paint (don't know where it came from) that was getting sucked over the fuel outlet (delivery) pipe - until the suction ceased when it would float again. With a full tank it never got close enough to the outlet pipe to become 'attracted' by the suction of the fuel pump.

It took me quite a while to analyse the circumstances that provoked the fault such that I suspected something floating in the fuel tank.
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Old 28th Dec 2010, 22:48
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I would have diagnosed an air vent blockage in the filler cap leading to vacuum induced fuel starvation there.
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