Wifes runabout (mk3 1.6 abu)has been faultless for the last 18 months.The mot is due this week,but as of last weekend the car refuses to start when hot.It will start second time in the morning,but as soon as its up to temp it plays up.It has fuel and spark,but the only way to get it to start when hot,is to turn engine over on key,then turn on to starter and let the key flick back,then repeat this procedure till it starts.Once started it stinks of fuel at first ,but then runs and drives perfectly.Any ideas guys,as it needs to go for an mot in the morning,and i don't want it playing up at the mot garage.We work miles apart,and really need both cars,so lending her mine is a no no.HELP!!
That'll be the coolant temperature sensor. There's a double sensor that gives the ECU a signal and the temperature gauge on the dash. IIRC it's under the dizzy. Unplugging it will help a lot, although may give emmisions probs on the MOT, as will the broken one. 5 mins to change, you'll prob loose a bit of coolant tho, get a new O ring with the new sensor. Get to it
Oh well,i disconnected the plug on the sensor,and expected it to fire up,but sadly its much the same.Don't want to sound like a tight a**e,but i'd rather be sure its going to help before i spend 9.00 on a new one.Yes i know its only 9.00,but if it doesn't cure the starting prob,its money i could of spent replacing the offending item (whatever it is).Really need to try and sort it by Monday,so i can get it in for the mot.Any other idea's guys? I have access to diagnostic equipment if going down that route might help.
If you've got a digital meter you can measure the resistance of the sensor, between the pins and the battery -ve on the highest ohms range. If you get a reading from any pin, prob Meg Ohms, it's knackered.
It's well worth changing that sensor anyways as they under-read with age, you'll save the 9 in fuel over a year or so...
Okay,i think i might be getting somewhere.Today i changed the temp sensor for a new one.The starting problem is cured,but now there is a massive flat spot and stutter from tick over untill the engine reaches about 16/1700 rpm,and the temp guage that used to read between 80/90 degree's once the stat opened,is now reading 110/120.So i'm guessing the first temp sensor was reading too cool,so over fuelling,and the new temp sensor is reading too hot and under fuelling.I disconnected the sensor,and the engine revved perfectly,but the starting prob reappeared.Silly i know,but i bought the sensor from GSF,as it was 8.50+vat,and the vag one from the main dealer was 22.80+vat and out of stock.Any idea's what i should do?GSF won't refund on the sensor.So thats a tenner wasted,and the vw one is going to sting me to the tune of 27.00,is there an alternative?
Anybody help? I have now swapped the sender back to the original,as the gsf sender just makes the car undriveable.I'm guessing it must be something to do with the temp sender,as swapping them makes so much difference.Are the GSF senders crap,or am i just unlucky?has anyone had similar probs with aftermarket senders?Come on guys someone must know a cure? please.
Buy one from VW, the GSF ones are rubbish! If you disconnect the sender the car will only start when warm, when cold its virtually impossible to get them going without a temp sender connected! Edit: If the temp sender is at fault this would be why it didnt show on the diagnostics, its possible for them to be broken but still return temp values in a range the ECU expects!
This type of fault can be measured tho. If you measure the resistance from the pins to the engine block and get < 20 MEG Ohms, on any pin, it's faulty.
only if the temp sensor has failed in a way to give <20 ohms on any pin Sometimes they just read too hot, or too cold, as you can see the GSF one works enough to get the car running, but not enough to get it running right. This is why I just replace them rather than mess about testing them, as they are a right sod for failing in odd ways. For example sometimes my GTI would never start on the 1st turn of the key, no matter how long you held it on the starter. But if this happened it would always without fail fire on the 2nd turn of the key and run perfectly. Replaced the ECU sender, and hey presto problem solved. I'd like to see you diagnose that one with a multimeter
Easy to say, just like my first post (the first reply) in this thread! But a lot of people won't believe anything you say, and don't want to take a chance on 6 quid If there is a way of measuring the knackered sensor to indicate a fault, this will help a lot of people!
Thats the thing, normally you cant diagnose a faulty sender with a multimeter. Sometimes they die totally or give wildy inaccurate readings though but if the sender is reading out enough for you to measure it, then VAG-COM will register a fault. (I say this because I found this page from a link from another thread, where the guy said it was put on VAG-COM and had no faults) Mostly however they just under or over read slightly or fail intermittantly. The type he needs costs considerably more than 6 quid unfortunatly The 2 pin MK2 type is like 13, but the 4 pin one that also runs the dash gauge is more like 35! Never ever buy GSF ones either, total rubbish
Diagnosed my mk3 4-pin one with a DVM. ~6 Meg to earth (the head), where the case had gone pourous. GSF one did the trick, since July anyway.
The senders have resistances calibrated to run from -48 deg C to 130 deg C. An open circuit would indicated -48 and a short will give full scale reading of 120 degrees C. If the circuit is open then your engine will flood and the car will be a non starter.In the same way if the sensor is reading hot ot short circuit to earth and the engine is cold and the ecu would compute that you should have a lean mixture for cold start. mark25s method is the right way to inspect a sensor if you do not have a vag compatible tool to scan. GSF/EuroCarParts one work fine if you need replacements.
this assumes the sender has failed open or closed circuit, wont help if its just under/over reading slightly
I cannot see why large companies will deliberately sell the wrong sensor to match the application. I have bought these as well as other components from both suppliers includung lloyds and have had no problem.
