Mazda 323 BJ (1.3, B3 Engine) Flat Spot

[Duncan]

Long Story, took the wife’s Mazda 323 down to visit the inlaws – a long trip. On the way there it felt a bit low on power, but otherwise OK. Took a break for half an hour, restarted and the vehicle was missing, flatspotting and jerking.
When I got it home checked the ignition as this has caused problems in the past.
The genuine parts distributor cap was well worn, and missing the centre brush (Less than 2 years old), so I replaced that, the rotor arm, and leads and plugs for good measure.
I also changed the air filter at the same time, as the old one was mucky, I had a spare, and you need to open and shift the filter housing to get at the distributor

This has perked it up, so it’s not violently missing and jerking, but the engine now just feels “Constipated” for want of a better word
It starts fine, and when cold revs and pulls well. When hot, it feels like it wants to miss a bit when at full throttle. On light throttle it seems ok. When you depress the throttle it seems reasonably smooth with no position causing a particular problem.

This is a UK spec, ex motability 1.3, register in 2000. Pre-OBD, but there are no check engine lights on.
Mitsubishi distributor, 75K on the clock, but otherwise in good nick.
NGK plugs fitted

Any thoughts on this, as I think I must be missing something obvious, but can’t for the life of me think what

Thanks

Topic

[college man]

See if the car has a fuel filter. If so change it. More in this link for performance issues.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

[Duncan]

Thanks for the reply.
As I understand it it has the glorified plastic strainer over the in tank fuel pump. The only replaceable item in the engine bay is a vapour canister that draws fumes out of the tank, and sucks them into the manifold for burning when the engine is running.
I’ve dumped a bunch of injector cleaner into the fuel to see if that helps perk things up a bit

cheers

[Duncan]

Update on this.
As mentioned, a top end service of the ignition parts did perk it up, but it was a bit flat. I thought it felt a bit like an old car with a manual choke, that wasn’t quite pulled out far enough when cold.
I changed out the coolant temperature sensor for a new one and it seems to have done the trick. The temperature guage doesn’t rise as quickly as it did, even though when the car is fully warmed up the end position is the same.
So it seems that the CTS had gone non-linear, ensuring that enrichment during warm up cut out faster than it should.

A good blat down the motorway proves that fuel delivery is sufficient, however, I did get a spare fuel filter, which apparently is built into the in tank fuel pump, which has to be dismantled to change it (Whoever thought that one up needs a few things explaining to them with a half inch breaker bar).
That can wait until the weather is better, and the Daily Driver discovery is deemed worthy of an MOT, as I want to have a back-up car fully working in case I have to break out the welding equipment on Solihull’s finest.

[Author]

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