Corrado VR6 warm starting issue + pic :)
Discussion
Hi all,
I've got a 95 Corrado VR6 with a warm starting issue and although I usually use the corrado forum I thought I'd open up the analysis to a wider community. Warm starting issues seem common on the VR but no concrete cause. No fault codes registered, although it's a pretty basic OBD1 diagnostic system.
When cold the car starts perfectly, but once warmed up - even after a 15 min test spin - it will take 10 or so cranks to fire into life. I don't use the throttle to get it going for fear of flooding the engine. If I turn it off after it's warmed up and restart immediately it starts straight away.
If I disconnect the MAF sensor it starts straight away when warm (2 cranks) and will idle, however when I rev it will miss or generally not behave smoothly. Would I be right in thinking by disconnecting the MAF the ECU will use a default value so the MAF might not be at fault?
I've read generally warm starts could also be coolant temp sensor or crank sensor but not sure how to test these. I do have a multimeter but I must confess I don't know how to measure stuff with it yet; any guidance much appreciated.
Fuelling could be another issue but I was thinking as it fires straight away with the MAF disconnected and it starts perfectly from cold it's probably ok - i.e the fuel pressure reg is retaining pressure in the system and if disconnecting MAF resorts to default fuelling/values it's probably working OK. Could be the wrong assumption of course.
Other things that might be related or of note:
- Fuel economy is fine - 37mpg on a gentle run and generally 30mpg driven normally with a few full throttle sprints etc.
- On idle and when warm it's a tiny bit rough - you can feel a slight pulse but the tacho doesn't show it. It's very subtle.
- It's done 150k and uses no oil and serviced yearly / generally well looked after.
- My wife followed me for 40 miles yesterday and I asked her to watch for blue, black or grey smoke from the exhaust and she reported nothing at all.
- Drives fine but sometimes feels a bit flat lower in the revs, but that could just be me as my other car is a tdi.
- Recently the coolant gauge has started to get stuck at 70 degrees rather than the normal 85. I realise the sensor for this is different to the sensor used to send the temp value to ECU so is only a guide. Thermostat was likely changed in 2011 from it's history.
- I've bought an OBDelevan and am awaiting for it to be delivered to start reading codes. Previous fault codes were read and cleared (and re-read a couple of weeks later) by my mechanic.
- Sparks were changed 2 months ago but HT leads I don't know when they were last replaced,.
- The car does get used - 1000 miles over the last few months and no short trips.
A picture just because! I have a set of Bilstein B12 20/25mm drop to go on but that's all I have planned apart for maintenance, a bit of surface rust curing and an alloy wheel refurb.
Thanks for any help.
I've got a 95 Corrado VR6 with a warm starting issue and although I usually use the corrado forum I thought I'd open up the analysis to a wider community. Warm starting issues seem common on the VR but no concrete cause. No fault codes registered, although it's a pretty basic OBD1 diagnostic system.
When cold the car starts perfectly, but once warmed up - even after a 15 min test spin - it will take 10 or so cranks to fire into life. I don't use the throttle to get it going for fear of flooding the engine. If I turn it off after it's warmed up and restart immediately it starts straight away.
If I disconnect the MAF sensor it starts straight away when warm (2 cranks) and will idle, however when I rev it will miss or generally not behave smoothly. Would I be right in thinking by disconnecting the MAF the ECU will use a default value so the MAF might not be at fault?
I've read generally warm starts could also be coolant temp sensor or crank sensor but not sure how to test these. I do have a multimeter but I must confess I don't know how to measure stuff with it yet; any guidance much appreciated.
Fuelling could be another issue but I was thinking as it fires straight away with the MAF disconnected and it starts perfectly from cold it's probably ok - i.e the fuel pressure reg is retaining pressure in the system and if disconnecting MAF resorts to default fuelling/values it's probably working OK. Could be the wrong assumption of course.
Other things that might be related or of note:
- Fuel economy is fine - 37mpg on a gentle run and generally 30mpg driven normally with a few full throttle sprints etc.
- On idle and when warm it's a tiny bit rough - you can feel a slight pulse but the tacho doesn't show it. It's very subtle.
- It's done 150k and uses no oil and serviced yearly / generally well looked after.
- My wife followed me for 40 miles yesterday and I asked her to watch for blue, black or grey smoke from the exhaust and she reported nothing at all.
- Drives fine but sometimes feels a bit flat lower in the revs, but that could just be me as my other car is a tdi.
- Recently the coolant gauge has started to get stuck at 70 degrees rather than the normal 85. I realise the sensor for this is different to the sensor used to send the temp value to ECU so is only a guide. Thermostat was likely changed in 2011 from it's history.
- I've bought an OBDelevan and am awaiting for it to be delivered to start reading codes. Previous fault codes were read and cleared (and re-read a couple of weeks later) by my mechanic.
- Sparks were changed 2 months ago but HT leads I don't know when they were last replaced,.
- The car does get used - 1000 miles over the last few months and no short trips.
A picture just because! I have a set of Bilstein B12 20/25mm drop to go on but that's all I have planned apart for maintenance, a bit of surface rust curing and an alloy wheel refurb.
Thanks for any help.
Chimune said:
Saw your bio. Similar taste in cars!
Loved the raddo L, replaced after 9 years with Alfa 156 Gta, and had Tiv Chim 500 at same time!
Yes we do! I haven’t had an interesting car in ages (married, having kids, buying a house etc. etc). The raddo was a long time waiting. 14 years to be precise! It’s off to the bodyshop tomorrow to get a few minor rust patches seen to in readiness for summer. Loved the raddo L, replaced after 9 years with Alfa 156 Gta, and had Tiv Chim 500 at same time!
I’d love a GTA for the noise alone and almost any TVR would suit (noise factor too) except the wedge. VW ownership is hopefully cheaper for now however that said although this is a sound base car it stills needs £1k in bodywork, an ABS pump (£100 quid) and whatever this hot start issue is.
annodomini2 said:
Start with coolant temp sensor.
Could be in range but under reading
Cheers, seems a cheap way to get started (~£25). The MAF is around £200! Could be in range but under reading
Edited by annodomini2 on Tuesday 17th April 16:37
Does anyone know what the blue sensor under the MAF might be, seems to be connected to vacuum pipes - would it be air temp? I thought the MAF did this?
pfnsht said:
annodomini2 said:
Start with coolant temp sensor.
Could be in range but under reading
Cheers, seems a cheap way to get started (~£25). The MAF is around £200! Could be in range but under reading
Edited by annodomini2 on Tuesday 17th April 16:37
Does anyone know what the blue sensor under the MAF might be, seems to be connected to vacuum pipes - would it be air temp? I thought the MAF did this?
More info here: http://the-corrado.net/showthread.php?51640-VR6-ho...
Lovely VR6, i've got a picture of a white Corrado VR6 on my hallway wall!
The FAMOUS BLUE temperature sensor on the front of thermostat housing can indeed causing issues with hot starts. This is because typically when it fails the ECU thinks it's cold all the time. Fine for cold starts, but too much fuel for a hot start.
it is worth doing ALL thermostat/housing seals/sender seals in one go with a coolant swap as it is essential to mount VR6 thermostat housings to a dry block. Check the conditions of the wiring on the thermostat housing to as they are notorious for going brittle and snapping off right at the connector which means you need to put a new JuniorPin in - there is VW specific tool but any auto electrician will do it. The critical wire is the blue/white on the blue sensor as that is the one that goes to the ECU.
Another possibility are the ECU (109) an fuel pump relays (167) which can cause issues when they get hot the contacts start failing. Go for a drive and when you park up whip the fuse box cover off an feel how warm the relays are.
The crank position sensor is also a candidate, it is located at the front of the engine and has a multiplug connector which is mounted just to the side of the starter motor. The sensor can be swapped with the car on axle stands but it is lot easier on a ramp where you can see the allen key bolt that holds the sensor in the block rather than doing it blind.
It may also be the CAM position sensor on the top of the head, this should create a fault code though.
IMPORTANT note, if you are using VCDS LITE aka vag com basic when you put the key in the 2nd position and read the
codes you will ALWAYS get a crank position sensor fault as the engine is not turning over. If you clear the fault codes then start the car and shut it off you will see if the crank IS a problem.
My wild card suggestion is the starter motor/solenoid and it's wiring including the live lead from the battery failing under load when hot. It only takes a relatively small drop in voltage for a non start event to occur.
The FAMOUS BLUE temperature sensor on the front of thermostat housing can indeed causing issues with hot starts. This is because typically when it fails the ECU thinks it's cold all the time. Fine for cold starts, but too much fuel for a hot start.
it is worth doing ALL thermostat/housing seals/sender seals in one go with a coolant swap as it is essential to mount VR6 thermostat housings to a dry block. Check the conditions of the wiring on the thermostat housing to as they are notorious for going brittle and snapping off right at the connector which means you need to put a new JuniorPin in - there is VW specific tool but any auto electrician will do it. The critical wire is the blue/white on the blue sensor as that is the one that goes to the ECU.
Another possibility are the ECU (109) an fuel pump relays (167) which can cause issues when they get hot the contacts start failing. Go for a drive and when you park up whip the fuse box cover off an feel how warm the relays are.
The crank position sensor is also a candidate, it is located at the front of the engine and has a multiplug connector which is mounted just to the side of the starter motor. The sensor can be swapped with the car on axle stands but it is lot easier on a ramp where you can see the allen key bolt that holds the sensor in the block rather than doing it blind.
It may also be the CAM position sensor on the top of the head, this should create a fault code though.
IMPORTANT note, if you are using VCDS LITE aka vag com basic when you put the key in the 2nd position and read the
codes you will ALWAYS get a crank position sensor fault as the engine is not turning over. If you clear the fault codes then start the car and shut it off you will see if the crank IS a problem.
My wild card suggestion is the starter motor/solenoid and it's wiring including the live lead from the battery failing under load when hot. It only takes a relatively small drop in voltage for a non start event to occur.
aka_kerrly said:
Lovely VR6, i've got a picture of a white Corrado VR6 on my hallway wall!
The FAMOUS BLUE temperature sensor on the front of thermostat housing can indeed causing issues with hot starts. This is because typically when it fails the ECU thinks it's cold all the time. Fine for cold starts, but too much fuel for a hot start.
it is worth doing ALL thermostat/housing seals/sender seals in one go with a coolant swap as it is essential to mount VR6 thermostat housings to a dry block. Check the conditions of the wiring on the thermostat housing to as they are notorious for going brittle and snapping off right at the connector which means you need to put a new JuniorPin in - there is VW specific tool but any auto electrician will do it. The critical wire is the blue/white on the blue sensor as that is the one that goes to the ECU.
Another possibility are the ECU (109) an fuel pump relays (167) which can cause issues when they get hot the contacts start failing. Go for a drive and when you park up whip the fuse box cover off an feel how warm the relays are.
The crank position sensor is also a candidate, it is located at the front of the engine and has a multiplug connector which is mounted just to the side of the starter motor. The sensor can be swapped with the car on axle stands but it is lot easier on a ramp where you can see the allen key bolt that holds the sensor in the block rather than doing it blind.
It may also be the CAM position sensor on the top of the head, this should create a fault code though.
IMPORTANT note, if you are using VCDS LITE aka vag com basic when you put the key in the 2nd position and read the
codes you will ALWAYS get a crank position sensor fault as the engine is not turning over. If you clear the fault codes then start the car and shut it off you will see if the crank IS a problem.
My wild card suggestion is the starter motor/solenoid and it's wiring including the live lead from the battery failing under load when hot. It only takes a relatively small drop in voltage for a non start event to occur.
Thank you aka_kerrly you've given me a great guide and heads up on the various bits! The FAMOUS BLUE temperature sensor on the front of thermostat housing can indeed causing issues with hot starts. This is because typically when it fails the ECU thinks it's cold all the time. Fine for cold starts, but too much fuel for a hot start.
it is worth doing ALL thermostat/housing seals/sender seals in one go with a coolant swap as it is essential to mount VR6 thermostat housings to a dry block. Check the conditions of the wiring on the thermostat housing to as they are notorious for going brittle and snapping off right at the connector which means you need to put a new JuniorPin in - there is VW specific tool but any auto electrician will do it. The critical wire is the blue/white on the blue sensor as that is the one that goes to the ECU.
Another possibility are the ECU (109) an fuel pump relays (167) which can cause issues when they get hot the contacts start failing. Go for a drive and when you park up whip the fuse box cover off an feel how warm the relays are.
The crank position sensor is also a candidate, it is located at the front of the engine and has a multiplug connector which is mounted just to the side of the starter motor. The sensor can be swapped with the car on axle stands but it is lot easier on a ramp where you can see the allen key bolt that holds the sensor in the block rather than doing it blind.
It may also be the CAM position sensor on the top of the head, this should create a fault code though.
IMPORTANT note, if you are using VCDS LITE aka vag com basic when you put the key in the 2nd position and read the
codes you will ALWAYS get a crank position sensor fault as the engine is not turning over. If you clear the fault codes then start the car and shut it off you will see if the crank IS a problem.
My wild card suggestion is the starter motor/solenoid and it's wiring including the live lead from the battery failing under load when hot. It only takes a relatively small drop in voltage for a non start event to occur.
For now I've managed to get the car in the bodyshop early (today) and it's going to be there for a couple of weeks at least so further testing will have the wait.
In the meantime I'll work out how my new OBDelevan fault device reader works and prepare for measure temp readings on the ECU when I get the car back. Will probably buy the sensor anyway (plus o-ring and clip) as it sounds like it's prime suspect for failing either now or at some point!
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