Having had to change the ECU on the car approx 6months ago, it's showing the same symptoms once again. On attempting to start the car from cold, it is turning over a number of times before eventually struggling to start. Then once started, it will struggle once or twice before running as normal, ticking over fine. This has only happened twice in the last week and is usually when the car has been standing for 12hours or so and the weather has been wet..
After the last time, when it took ages to start as it is starting to once again but struggled to not cut out and was loosing power etc. After that, i made sure that the ECU itself was 100% protected from any water that could have splashed from draining down from the windscreen. However, it seems to be happening again..
Any ideas?
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Hi,
While you may already have done this, it may be worthwhile checking over the basics before condemning the ECU.
This problem happens in the damp - are you happy that the high tension ignition circuit is in good order?
Are there any leaks in the fuel system - pressure should be maintained in the system, ready for the next start-up.
When you are cranking the car over, do you get a spark?, do you have a running fuel pump?, do you get an injection pulse? If you find any of these are not present, then you have a start in diagnosing the problem.
I hope that helps, and the problem turns out to be cheaper than an ECU.
number_cruncher
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get a new blue temp sender..£10 job done
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Are you talking about an injection or a carburettor model? If it's carburettor, suspect the pull-down unit on the back of the carb.
Andy
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A new set of ignition leads cured similar symtoms on my Golf 2 GTI with the Digifant engine. The replacement temperature sender as advised above is a good suggestion. If the ECU detects thinks the sender is not working, it adopts a 'limp home strategy' and assumes the engine is hot. This makes it difficult to start a cold engine. The temperature sender can be checked by 'backprobing' it where the cables enter the rubber boot and measuring the voltage across the sender with the ignition turned on. If the voltage is 5 then the sender is open circuit. On a cold engine the voltage should be 1 to 1.5 volts. Hot engine 0.2 to 0.4 volts.
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Thanks for the replies. I didnt get chance to check the temperature sender etc as yet. The car packed in totally this morning and had to be towed home. I have had it suggested that the voltage amplifier on top of the ECU itself may be faulty and when the breakdown chap came out, he said that the spark got progressively weaker and then failed altogether.. so i shall try a new one of those tomorrow (have a spare from the last time this happened) but my money\'s on it being the ECU itself that has somehow burned out again..
how the hell can it keep burning out, when it has more waterproofing than a ducks pink fluffy dice??! watch this space..
Thanks again.
JH
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Hi JH,
If the ECU is being damaged, and it isn't getting wet, then it might be being damaged by electrical interference.
If any component in the car's electrical system is putting voltage spikes into the system, any delicate ECU components may be damaged.
It may be worth checking;
a) the ignition HT system is in tip-top condition, and that the HT leads are not clipped closely to the vehicle wiring loom
b) the ignition LT system is all in order
c) using a fast oscilloscope, check the alternator output - some ripple is normal, and indicates correct rectification. Anything other than ripple may indicate a problem.
d) using a fast ascilloscope, check the voltage supply at the ECU. Checking at the battery may give misleading results - the battery smooths out any transients, or spikes.
I hope you find the cause before another ECU becomes damaged,
number_cruncher
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I have very frustrating experience of this.
The earth strap that goes from the -ve battery terminal, to the bodyshell, to the gearbox housing: Disconnect the battery, and clean up the earth connection to the gearbox very, very thoroughly (and put some copper grease on there too).
If this earth fails, the current from the starter goes through the ECU. This blows the fuel control circuits, and leaves the injectors wide open. When you put the ignition on, the injectors spew fuel down the bores and the engine hydraulically locks very rapidly. I drained 9 litres of fuel & oil from the sump.
Failure of this earth will cause all sorts of strange behaviour (my instrument panel kept rebooting for one) before eventually leaving you stranded, needing a new ECU. If you replace the ECU without repairing the earth, pop goes the new one when you turn the starter over again.
Ignition amps are the same on all Polos, Golfs etc. from that era, and eminently pocketable on a scrapyard trip, and they're quite easy to test following Haynes with a multimeter. Slow hall sender death in the distributor is quite common too, it's well worth buying a brand new replacement.
For gawd's sake don't put a new ECU on without cleaning the gearbox earth.
RF
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Thanks for all your advice number cruncher and Robert Flemming, its all much appreciated. You probably know yourselves how frustrating it is when a problem keeps rearing its ugly head once you think that you have fixed it!
The latest is that I changed the voltage amp (or hall sender) on top of the ECU and the problem "seems" to have gone away for now. I already had one from my previous problems and so it cost me nothing. It was good advice from the top man Simon from Central VW Audi in Ellesmere Port.
As far as the earthing strap is concerned, this may as you thought be the source of the problems. Some timne ago i had spates of the car making a loud clicking noise when i tryed to start it and wasent turning over at all. A car spark came out and put a new earth lead from the -ve of the battery to the gearbox housing as you quite rightly mentioned. This did seem to solve the problems and i had no idea that this could all be linked...
I will follow your advice and clean up the connection with some copper grease and some emmery.
Thanks again for taking the time to help..
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Thank you also for taking the time to report back on your experience.
number_cruncher
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I havent yet applied the copper grease, got some from work tonight.. And as I started the car to drive to work, the thing struggled again. Ive got a spare hall sender in the car and ive got a feeling that i'll be putting the grease and new hall sender on the car this morning, which is nice when you've just done a 12hr night shift!!
Fingers crossed..
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JH
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