Clio hesitation when cold

[elthorne]

My 1992 Clio 1.4 automatic recently started hesitating when accelerating from cold - a sort of 'blind spot'. If I accelerate very slowly I can avoid this. When fully warmed up the problem disappears. It is a bit scary when this happens when joining traffic flow on a busy road. Can anyone help this poor OAP? Many Thanks.

[boss]

your car doesnt seem to be running a correct air/fuel ratio for the conditions needed,

I would suggest checking for an air leak and renewing the water temp sensor for the ecu not the one for the temp gauge,

what speed does your car idle at first start????

I do take that your car is fuel injected (single point)

can you recall this problem steming from something, think hard and carefull, sometimes you might have had a small job done and this has happened from the sssame or next day..

[elthorne]

Thanks for your kind response boss.

It revs at 1100 at first start.
I recently changed the air filter.
Yes - fuel injected.

What is 'ecu' boss?
Do you mean 'check for air leaks' in hoses?

Many Thanks,
Steve (elthorne)

[larsen_huw]

Sorry I'm not Boss ... but i can answer these questions:

ECU - Engine Control Unit (or Electronic Control Unit ... I've heard both be used). This is a small computer that takes inputs from various sensors and sends an output to the fuel inejctors telling them when to inject fuel into the engine. The timing and amount of fuel depends on what the sensors are telling the ECU.

An air leak in this case would be between the engine and where the air enters the car's airbox. In the piping is an sensor that tells the ECU how much air is entering the engine. If there is an air leak after this sensor, then the amount of air entering the engine isn't what the ECU is expecting, and so it tells the injectors to inject the wrong amount of fuel at the wrong time.

A good way to check for an air leak in this case would be to spray WD40 (or any flamable aerosol) round the air pipes while the engine is running. If there is an air leak, the aerosol spray will enter the engine and be burned in the cylinders along with the petrol. The result will be the engine revs harder ... as if you'd pressed the accelerator. So if this happens, you have an air leak somewhere. By spraying more precise areas, you should be able to narrow it down it a particular location.

I hope this is of some help to you.

[boss]

Dont want upset huw but, in theory wd-40 sounds good to be spraying around the carburettor but it does not work because its flashpoint is too high because it has lubricant in it and it cannot atomise so if you could get it to burn in the cylinder then it would be uncontrolled and would not have enough expansion rate in the explosiveness of it to have any effect on engine speed, even using something like carb cleaner or easy start would be too rich for the engine, VW spares dept stock an aerosol called a leak detector around £10, This is the good one, Also if you had an air leak it would be more apt to stall when hot, because the ecu richens the mixture up to 20degrees and air leak wouldnt bother it too much, but when hot and ecu tries to fuel the engine at 14.7to1 ratio air would make the mixture weaker and hence slow the engine down and maybe stall.

Theres a good chance that your oxygen sensor is at fault ( lambda probe )

This device measures how much oxygen is left in the exhaust after combustion has taken place, if too much oxygen then lambda probe tells engine controll unit (ecu) and ecu ajusts accordingly dependent on the signal from lambda probe. Also if not enough oxygen a different signal is sent to the ecu and vice versa,

If the lambda probe does not work then the ecu does not get any feedback from engine efficiency, there are three ways to test the probe,

Disconnect the lambda probe connector when engine hot.

method 1 = connect oscilliscope to the small black wire on probe and measure the wave pattern, the output should be between 250 milli volts and 750 mv, ideally you want 450-500mv, to check that it switches fast enough remove a vacum pipe to allow air to enter the engine, there should be a significance difference, also try richening it by clamping the fuel return pipie to increase rail pressure and mixture, see what the reading is,

mathod 2 = can be done with a voltmeter but not as good.

method 3 = remove the lambda probe from exhaust and take to test bench, connect voltmeter to black wire and touch thread on lambda probe with other and light a blowtorch to simulate real heat, and notice if readings change with heat?

If tests are poor than renew oxygen sensor, available in the uk as universeal for about 29+vat.

Hope this helps.

[larsen_huw]

Dont want upset huw but, ...

Don't worry about upsetting me! :)

I'm still a young dog (21) and so am quite willing to learn new tricks.

I tend to work at the more "budget" end of the market (for example, i know Tesco's Value Deoderant works just as well as Cold Start, but is much cheaper and makes your car smell nice!!! :D ).

[boss]

i am a tad older (30), i know how to make hydrogen gas ffrom using glow plugs, water and baking powder, very interesting....

Also nail varnish is just as effective as locktite, just watch the mrs!!!!! it might not be worth it.

I know fords quitte well i have had a capri and escort 1 +2, transit etc,

I am an enthusiast which sits back now and helps others keep their pennies in their pockets.

:freak:

[larsen_huw]

... Also nail varnish is just as effective as locktite, just watch the mrs!!!!! it might not be worth it.

Now that's well worth knowing ... cheapo nail varnish is very cheap indeed. Might look a little odd with it at the counter though! :D ... might be one for the missus to pick up! :)


... I know fords quitte well i have had a capri and escort 1 +2, transit etc,

I am an enthusiast which sits back now and helps others keep their pennies in their pockets.

Ford's are just about the only thing i do know ... had 2 Sierras and now a Capri. RWD Escorts are too expensive for me at the moment ... but maybe one day! :)

I too am an enthusiast with no formal training whatsoever ... i know two types of information ... things people have told me, or things that have previously gone wrong with the car and I've had to fix! :) Hopefully when i get the alternator running properly again I'll know a little about those too! :)

[elthorne]

Dear Friends,

Thanks for all the help. Most of which is way over my head. Oh for the days of my Morris Minor and Oxford. Both quiet and smooth. Open the bonnet and there is everything wide open and accessible. Four plugs, oil and air filters. No electronics or miles of tubes, hoses and wiring. Even this nerd could do his own servicing. Have we really moved forward?

I think I'll just part exchange the ruddy thing (while the engine is hot and fault not apparent) for another used banger. You all do a very good and kind service in this forum. Keep it up (the service I mean).

Steve.