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Running problems, advice needed.


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timmypolo1.3

Hi Everyone,

               I would like some help with a problem i have with my Polo. Its a 1995 1.3, 6n1 ADX engine. I got the car for my partner some months ago. We picked it up and it drove home fine, some 25 miles. I then set about changing out the timing belt as it was due at 59k miles. Whilst at it, i did these other jobs too.

Water pump change, timing belt tensioner and coolant change, auxiliary belt change, thermostat, spark plug change (NGK BUR6ET), coil and HT lead change, air filter, oil and filter, distributer check (for clean terminals in lid and rotor arm clean), new vacuum pipes to back of throttle body and under air filter housing and a dose of wynns fuel cleaner on a longer run. I have also done work on the brakes and changed gear oil, but that is of no consequence here! 

And so it ran perfectly for 6 weeks (some 560 miles), starting well and running fine at any point in its temperature range.

Then we got a sudden problem, not with cold starting, but with the 'return run' of the day. If you try starting anywhere between 15 mins and a few hours after switching off, from fully warmed up.

It has problems starting, and runs lumpy, kangarooing when the throttle is pressed a lot. If you feather the throttle and keep changing down it just about gets you back home, but will struggle and cut out on idle. I looked at the spark plugs and they showed to be running quite lean. So i checked the fuel filter only to find it was the original VW one date stamped 12/3/1994  !!!. Thinking i had found the issue I changed out the filter immediately. It didn't make any difference whatsoever. 

I then took off the inlet fuel pipe to the throttle body and turned on the ignition to check the fuel pump. It comes out for a moment (clean) and then stops. I assume this is because the ECU or the fuel pump senses that the line is open because there is no back pressure?

I then changed out the Lambda sensor (upstream). I carefully removed the fuel pressure regulator valve and it was clean, spring was intact and the diaphragm without holes or tears.

The throttle body looks spotlessly clean inside. Alas! It still behaves the same.

As i say, it will start and run fine until you go to start and drive on the return journey.

I have a classic car guy up the road from me who had a quick look and said that sometimes the block/gasket that the throttle body is connected to the inlet manifold with can perish and start to let air in, post fueling. But he removed the air filter box and wiggled the throttle body to find it felt very firm and had a good look around it, so dismissed that idea.

 

Any HELP GREATLY appreciated. I don't want to scrap the car just for this!

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Just got home and found the VW invoice for the new temp sensor VW supplied. Part No. 6U0-919-501-B (Sensor) & N-903-168-01 (O-Ring). Cost £39.05+VAT directly from the parts department at the local

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nige8021

First Welcome to the forum.

 

Normally the first thing would be to check for any stored fault codes, but the symptoms sound like the coolant temp sensor is giving out false info, so causing the ECU to miss adjust the fueling schedule, if you have a code reader that gives live data you should be able to confirm this, the sensor is a dual element device with one section for the dash display the other for the ECU it's mounted in the thermostat housing and held in place with a simple clip, so if you're quick you should be able to replace it without loosing too much coolant, make sure you don't forget the "O" ring on the new sensor or it will leak ! also do not buy a cheap pattern part from the likes of ECP/GSF/eBay as the quality is suspect at best, better to buy a genuine one

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Just as a reference, I bought a new temperature sensor directly from my VW dealership just a few months ago. It set me back about £45 - £50. It's definitely worth making sure they include the new O-Ring as Nige said. When I ordered mine it only took a day or two for the dealership to get the part. When I get home this evening I can take a photograph of the new-type sensor in position so that you can tell if yours has been replaced (the old and new type are visibly different), although given what you've said about the car in the above post I think its unlikely that it has been changed.

 

 

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timmypolo1.3

Hi Thanks for that nige8021. Maybe i ought to have mentioned that when it is 'playing up' the temp gauge in the car is reading only 70 deg when on a run and fully warmed up. When it is behaving properly it reads a normal 90deg.

So that kind of supports the idea that the sensor is playing up. Also thanks for the tip about buying bad quality pattern parts.

 

Jbrown, also thanks for the heads up. 

 

I just got the sensor out of the housing and it is date stamped (like most VW factory parts) 03/95. So thats the original part, 25 years old. It is made by ELTH in Luxembourg. Also has the usual Audi/Vw marks on it too.

Part number is 357 919 501A. 

Just going to source one now. 

I will keep you posted...

 

 

 

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nige8021
25 minutes ago, timmypolo1.3 said:

Hi Thanks for that nige8021. Maybe i ought to have mentioned that when it is 'playing up' the temp gauge in the car is reading only 70 deg when on a run and fully warmed up. When it is behaving properly it reads a normal 90deg.

So that kind of supports the idea that the sensor is playing up.

 

 

 

 

As I said the sensor is a dual element device, so the reading in the dash doesn't necessarily mean the same temperature is being sent to the ECU but as it looks like it is an original factory fitted item it's probably due a replacement.

 

With the temp sitting at 70c that would tend to indicate a thermostat sticking, but I see you have already replaced this, was it a genuine one or from ECP/GSF ? as the same applies to the thermostats as the sensors, the stuff they sell is very poor quality, the other thing, the cover over the thermostat has a bridging piece across the outlet that the thermostat needs to push against to work properly and these bridging pieces are a very common failure item, and as it looks like a few items you've already found were factory fitted original items it's probably worth a look and see if the bridging piece is still intact and the bit where the pin on the thermostat sits is still solid

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timmypolo1.3

Hi there. 

Yes i remember that bridging piece when i replaced the thermostat. I used a quality thermostat at the time, but will bare that in mind if the problem does not rectify after the sensor change.

Thanks.

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Just got home and found the VW invoice for the new temp sensor VW supplied. Part No. 6U0-919-501-B (Sensor) & N-903-168-01 (O-Ring). Cost £39.05+VAT directly from the parts department at the local VW main dealer.

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timmypolo1.3

Hi, 

 I just put in the new coolant temperature sensor and guess what? 

It started well, as it always does from cold, and then i ran it up to temperature and shut it off. 

Two hours later, I go to start and .. Yup! Its doing it just the same. Not wanting to start and struggling to tick over when it finally does. However the temperature gauge seems to behaving in a smoother fashion now so was worth while doing it i think, even to just tick that off the list of possible causes.

So I took the air filter housing off and pulled the plugs to find they don't look to be lean or rich, just right shade.

While i was there I took off the engine vent chamber below the the throttle body to find it had some yellow and white gunk in it (see photo). Looked like water and oil mix?. I cleaned it all out, dried it off and put it back on. I thought this chamber ought to have a gauze or mesh packed in it??

Any way, I am now wondering if this was just a bit of engine condensation or possibly a breech in the head gasket between a coolant gallery and one or more of the cylinders?

Coolant is all clean though and oil on the dipstick is spotless to.

Any Ideas anyone?

 

20201017_152006.jpg

Edited by timmypolo1.3
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I've done a bit of digging and come up with an old post on the forum that seems similar to the problem you're having. Might be worth a look.

 

 

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