VVT fault diagnosis
20 April 2013, 04:31 PM
#1
VVT fault diagnosis
It's a known fact that a possible fault with the vvt on certain models of STi can exist. I'm having suspicions that there could be a problem on my 03 STi.
After a turbo swap and re-map there was a definate 'kick' when the turbo spooled (MDX321T) Often the 'kick' is not there and acceleration, whilst 'brisk', lacks the punch I remember when test driving the car directly after mapping. Today, I exited a roundabout and squeezed the throttle and the 'kick' returned in 3rd and 4th before I settled at cruising speed. Later, it seemed not to be there again.
What tests can be done to determine if the vvt is working and if there's a problem what is the fix?
JohnD
After a turbo swap and re-map there was a definate 'kick' when the turbo spooled (MDX321T) Often the 'kick' is not there and acceleration, whilst 'brisk', lacks the punch I remember when test driving the car directly after mapping. Today, I exited a roundabout and squeezed the throttle and the 'kick' returned in 3rd and 4th before I settled at cruising speed. Later, it seemed not to be there again.
What tests can be done to determine if the vvt is working and if there's a problem what is the fix?
JohnD
20 April 2013, 04:47 PM
#2
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Sounds like a neutral position switch problem. Its common for them to cut in and out when accerating hard causing the avs to switch off. Need a laptop and cable to check it though.
20 April 2013, 06:58 PM
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Vvt was all working when mapped as everytime you program the ecu you have to wait for it to function. It was also working on road test as I always check.
It is of course possible the neutral position sensor has started to fail since december.
Easy to check on the laptop if you want to meet up John or not an expensive part to change etc. does sound like it could be the issue. When in neutral it switches the vvt off, if the sensor is faulty it will flick from neutral to not in neutral randomly as the box moves about when driving as the sensor is right on the limit as the end wears away over time.
Simon
It is of course possible the neutral position sensor has started to fail since december.
Easy to check on the laptop if you want to meet up John or not an expensive part to change etc. does sound like it could be the issue. When in neutral it switches the vvt off, if the sensor is faulty it will flick from neutral to not in neutral randomly as the box moves about when driving as the sensor is right on the limit as the end wears away over time.
Simon
20 April 2013, 07:18 PM
#6
Blimey! that was a quick reply, Simon. It's Saturday night - you really must get away from the computer!
I'm about to depart for the watering hole
I'm having a clutch change (ACT HD organic as recommended) in a couple of weeks so it would seem sensible to replace the NPS at the same time while the gearbox is out.
If I may, I'll let you know if it provides a cure or not. If not, I'll give you a shout?
JohnD
I'm about to depart for the watering holeI'm having a clutch change (ACT HD organic as recommended) in a couple of weeks so it would seem sensible to replace the NPS at the same time while the gearbox is out.
If I may, I'll let you know if it provides a cure or not. If not, I'll give you a shout?
JohnD
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21 April 2013, 10:29 AM
#8
Big thanks to Simon for prompt reply and great service. It comes as a pleasant surprise after previous experiences of poor communication with the mapper I used to use! Thanks also to Turbotits for suggesting a possible culprit.
I believe Subaru sorted the problem on later models? Was the cure a re-designed switch or different location? If re-design, I assume a replacement would be that?
Am I correct in thinking that the system is switched 'off' then 'on' again at every gearchange? Once 'on' what are the conditions for advancing the valve timing eg RPM, load, throttle opening?
I've never needed to delve into the NPS function so now it's become a (possible) issue, I want to know all about it!(Even at my age
)
JohnD
I believe Subaru sorted the problem on later models? Was the cure a re-designed switch or different location? If re-design, I assume a replacement would be that?
Am I correct in thinking that the system is switched 'off' then 'on' again at every gearchange? Once 'on' what are the conditions for advancing the valve timing eg RPM, load, throttle opening?
I've never needed to delve into the NPS function so now it's become a (possible) issue, I want to know all about it!(Even at my age
)JohnD
21 April 2013, 10:46 AM
#9
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they changed the polarity on the later nps but not sure if the design is different also..
if you get a newer one the polarity can be reversed via the map so is no issue other than you will have to visit me to reverse it.
yes the vvt reacts fairly quick and goes off on the gearchange or rather has a different vvt target, the main advantage on the subaru is earlier spool and more torque which would coincide with the missing kick you are describing.
Simon
if you get a newer one the polarity can be reversed via the map so is no issue other than you will have to visit me to reverse it.
yes the vvt reacts fairly quick and goes off on the gearchange or rather has a different vvt target, the main advantage on the subaru is earlier spool and more torque which would coincide with the missing kick you are describing.
Simon
21 April 2013, 05:05 PM
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An STI with a NPS fault is smooth just as you described. Just not powerful !
When mine was first mapped back in the dark ages, I tried to show off just how fast my car was, and it simply wasn't ! LOL.
I asked Richard Bulmer what was up and he said NPS has failed, he was right to !
Later on I fitted a Hawkeye DCCD gearbox and Simon swapped the polarity of the NPS detection to suit.
dunx
P.S. He's a good lad, with great customer service
When mine was first mapped back in the dark ages, I tried to show off just how fast my car was, and it simply wasn't ! LOL.
I asked Richard Bulmer what was up and he said NPS has failed, he was right to !
Later on I fitted a Hawkeye DCCD gearbox and Simon swapped the polarity of the NPS detection to suit.
dunx
P.S. He's a good lad, with great customer service
11 May 2013, 01:23 PM
#11
An update.
On inspecting the original NPS there is a small flat worn on the tip although I have no way of knowing if this would be significant. I tested the switch on an ohm meter and found that it was open circuit with the plunger out changing to closed after depressing the plunger a small amount BUT changing to open circuit again with the plunger fully depressed. Can't remember the new switch going open circuit on full depression!
JohnD
On inspecting the original NPS there is a small flat worn on the tip although I have no way of knowing if this would be significant. I tested the switch on an ohm meter and found that it was open circuit with the plunger out changing to closed after depressing the plunger a small amount BUT changing to open circuit again with the plunger fully depressed. Can't remember the new switch going open circuit on full depression!
JohnD
11 May 2013, 02:38 PM
#13
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John Could you take a picture of the chassis to transmission harness and where the NPS connects to?
I have a non DCCD and found 2 4 pin connectors to the chassis near the transmission
I have a non DCCD and found 2 4 pin connectors to the chassis near the transmission
11 May 2013, 04:18 PM
#14
https://www.scoobynet.com/general-te...on-bugeye.html
JohnD
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