Hi,

Yesterday afternoon my stock 1.8 started really hesitating when I give it more than 10% throttle. It was so bad that I stalled it three times before finally being able to pull out into the traffic.

When cold, the problem isn't apparent, but steadily gets worse as the engine warms up. You can stall the engine in neutral just by giving it 50% throttle in the right rev range (2000 - 2500 rpm). One of the engine tuners at work thinks that it's going really lean at that throttle position. This hesitation happens in all cylinders, and sometimes backfires. The spark is certainly still there, and looks to be happening at the right spot (I checked it with a timing light). Distributor cap and rotor look fine.

That morning I was running REALLY low on fuel, so put half a tank in, perhaps it's the crap that floats on top of the fuel that got sucked into the fuel system?

Initially I thought it was the throttle position sensor, but I checked that and it appears fine.
I've filled up the rest of the tank with Optimax (high octane unleaded), put in Wynns spitfire injector cleaner, taken the battery cable off and hit the brake pedal for 30 seconds, and changed the coolant just for kicks. None of this helped.

When I disconnect the engine temperature sensor the engine goes into some form of 'limp home' mode, idles at 1600 rpm, the mixture gets richer, and the problem is much diminished, allowing me to drive around reasonably normally. But the idle is very high, not really all that good.
I checked the temperature sensor and it looks OK to me (350 ohms).

Any ideas?? I'm really scratching my head here.

Someone at work suggested making the computer flash some codes at me, does anyone know which pins to bridge to make the computer tell me what it thinks is happening?

Thanks for any ideas,
Ben

Air flow sensor? Dirty or duff Lambda Sensor?

My car has done something similar after I've cleaned the engine (before I knew better) and water has got done the sparkplug 'cavities', making the spark short out to the head. Doesn't sound like this is your problem though.

Mark

Having spoken to my cousin recently who is a toyota mechanic (used to be mazda) he said that the ignition leads that mazda uses are very prone to causing all sorts of ignition troubles, he has recommended changing to one of the many available low impedence one that the 'motor sports' type companies supply, i got some from [url]http://www.motorsportworld.co.uk/[/url]

They do the trick and i've had no problems at all.

Might be worth a try

Nick

I'm sure that the ignition leads aren't the problem, as when I disconnect the engine temperature sensor the engine works a lot better (as in the problem almost completely disappears). The problem also happened fully at one time, rather than a gradual decline in performance as you might expect.

It's also happening to all cylinders, and there's no central spark plug lead like on some other cars.

But I guess it could be the ignition coil or something? Not having enough oomph to make a proper spark at high compression (like when at low revs and high throttle). Hmmm... food for thought, thanks for the post.

This sounds a bit simplistic, but as you mention removing the temp sensor and the engine running fine i thought of a similar problem i had on a saab. If any of the main sensors (temp, lambda, crank position etc) started to go wrong, the ecu would revert to 'standard' factory settings, e.g. it would 'invent' a reading for the damaged or bust sensor to enable the engine to run. (albeit at reduced economy!)
Might the temp sensor be at fault, and by removing it and allowing the ECU to 'invent' a figure it is providing a temp solution?
Have you tried a replacement? Apologies if you have already and i missed it in the post.

Just re-read and see the bit where you tested the sensor, have you tried sourcing a replacement to test it. This does sound like a temp sensor problem, the sensor will give a stock impedence when cold, and will only start to change the signal when the water temp reaches the required figure (this changes from car to car and i haven't see a figure for the 323), if the warm impedence is incorrect you will see all sorts of drivability problems.


Nick

Hi,

Thanks for all the replies, they've all been good food for thought.

Looks like it might have been dirty fuel as today when I started it up it ran fine, even when the engine was hot. Maybe it was the Wynns spitfire, maybe it was changing the coolant , but whatever the case it's all better now. I did leave it for 5 days because of work commitments, and wasn't looking forward to trying to fix the damn thing... but it looks like it fixed itself!

nickj633: that was pretty much what I was thinking, in the ECU software I've dealt with you can put in default values for all the sensors so that if a wire falls off then the value doesn't fall off the edge of the map. Eg. we normally run a default value of 80 degrees for water temp, 'cos that's what it normally runs at.

Phew, I wasn't liking the estimated repair bill for something like this!!

Hopefully this post stops someone else from taking it to a mechanic and getting a huge repair bill that says "Sorry mate we couldn't find the problem".

[quote="nebbian"]Hi,

Yesterday afternoon my stock 1.8 started really hesitating when I give it more than 10% throttle. It was so bad that I stalled it three times before finally being able to pull out into the traffic.

When cold, the problem isn't apparent, but steadily gets worse as the engine warms up. You can stall the engine in neutral just by giving it 50% throttle in the right rev range (2000 - 2500 rpm). One of the engine tuners at work thinks that it's going really lean at that throttle position. This hesitation happens in all cylinders, and sometimes backfires. The spark is certainly still there, and looks to be happening at the right spot (I checked it with a timing light). Distributor cap and rotor look fine.

That morning I was running REALLY low on fuel, so put half a tank in, perhaps it's the crap that floats on top of the fuel that got sucked into the fuel system?

Initially I thought it was the throttle position sensor, but I checked that and it appears fine.
I've filled up the rest of the tank with Optimax (high octane unleaded), put in Wynns spitfire injector cleaner, taken the battery cable off and hit the brake pedal for 30 seconds, and changed the coolant just for kicks. None of this helped.

When I disconnect the engine temperature sensor the engine goes into some form of 'limp home' mode, idles at 1600 rpm, the mixture gets richer, and the problem is much diminished, allowing me to drive around reasonably normally. But the idle is very high, not really all that good.
I checked the temperature sensor and it looks OK to me (350 ohms).

Any ideas?? I'm really scratching my head here.

Someone at work suggested making the computer flash some codes at me, does anyone know which pins to bridge to make the computer tell me what it thinks is happening?

Thanks for any ideas,
Ben[/quote]

You can check if the idle is correct by warming up the engine to operating temperature then bridging two contacts in the diagnostic box. Bridge GRD(ground) and TEN, then adjust the idle screw till ticking over at 700-750 rpm. This will re-map your mixture perfectly.