How does the timing belt tension sensor work electrically?
06-02-2004, 05:37 PM
#1
Deer Slayer
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Thread Starter
How does the timing belt tension sensor work electrically?
Hi,
I am examining all the things I will be reinstalling over the next several days and I have been considering how the belt tension sensor works.
A wire runs to the front of the cover. A wire runs from the cover internal side to the tensioning arm. That arm and wire are grounded by being bolted to the engine block (or, more accurately, the face plate of the water pump). That attachment point has a copper spring plate that rides between the tension shaft in the tensioner and the tension arm. There is a plastic tube/washer that isolates the contact from the body of the tensioner.
It SEEMS to me as though this thing is supposed to somplete a circuit whenever the tension assembly is under pressure, as supplied by a properly tensioned belt. And when the belt gets loose, the copper plate looses contact with the tensioner and/or arm, sending a signal to the computer, and a scary trouble light is the result.
I'm puzzled because, if the wire is carrying a positive charge, it would ground through the tensioner arm through the water pump. If the thing is supposed to act as a groud instead, there is no wire anywhere that supplies positive charge to the tensioner anywhere that would run the sensor.
What I'm asking is, is there supposed to be an insulating washer or something where the wire attaches to the tensioning arm? If so, this would make more sense to me, and I simply have a missing insulating washer. If not, I can't honestly understand how this thing senses a loose belt because the wire would be grounded all the time.
Please advise.
Thaddeus
I am examining all the things I will be reinstalling over the next several days and I have been considering how the belt tension sensor works.
A wire runs to the front of the cover. A wire runs from the cover internal side to the tensioning arm. That arm and wire are grounded by being bolted to the engine block (or, more accurately, the face plate of the water pump). That attachment point has a copper spring plate that rides between the tension shaft in the tensioner and the tension arm. There is a plastic tube/washer that isolates the contact from the body of the tensioner.
It SEEMS to me as though this thing is supposed to somplete a circuit whenever the tension assembly is under pressure, as supplied by a properly tensioned belt. And when the belt gets loose, the copper plate looses contact with the tensioner and/or arm, sending a signal to the computer, and a scary trouble light is the result.
I'm puzzled because, if the wire is carrying a positive charge, it would ground through the tensioner arm through the water pump. If the thing is supposed to act as a groud instead, there is no wire anywhere that supplies positive charge to the tensioner anywhere that would run the sensor.
What I'm asking is, is there supposed to be an insulating washer or something where the wire attaches to the tensioning arm? If so, this would make more sense to me, and I simply have a missing insulating washer. If not, I can't honestly understand how this thing senses a loose belt because the wire would be grounded all the time.
Please advise.
Thaddeus
06-02-2004, 08:00 PM
#4
Addict
Rennlist Member
Rennlist
Site Sponsor
Rennlist Member
Rennlist
Site Sponsor
IT simply looks for a ground after about 3 minutes of operation , no ground flashes the belt warning light . Some creative individuals simply attach the wire to the engine block to get rid of the annoying tension warning light !! after all it is not THEIR car ........
06-02-2004, 11:33 PM
#6
Deer Slayer
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Thread Starter
That's a great diagram, Tony, but from what I can tell the whole idler arm and the big pulley is "hot", not just the wire... they seem to be insulated from the block by the 2 bushings around the bolt that goes into the small pulley and water pump.
Thaddeus
Thaddeus
Trending Topics
06-03-2004, 09:56 AM
#8
Rennlist Member
The tensioner 'circuit' has to be the simplest - and most misunderstood electrical item on the entire car, at least regards the activation issue by the tensioner: it must be a symptom of "Timing Belt Angst".
Jim, Greg, and others have correctly commented on the initial 3 min activation delay of a loop which is normally grounded.
If the tensioned is correctly assembled, the ground path is insulated from the waterpump, and flows through the tensioner body. When TB tension becomes insufficient, the tensioner nose spring expands sufficiently to break the otherwise normal ground loop through the tensioner body.
The simple test of functionality is to pull the wire off the front cover, start up - and in ~3min, in comes the alarm.
If you respond to this in the normal 928 owner's fashion, change your shorts - and reconnect the wire.
Jim, Greg, and others have correctly commented on the initial 3 min activation delay of a loop which is normally grounded.
If the tensioned is correctly assembled, the ground path is insulated from the waterpump, and flows through the tensioner body. When TB tension becomes insufficient, the tensioner nose spring expands sufficiently to break the otherwise normal ground loop through the tensioner body.
The simple test of functionality is to pull the wire off the front cover, start up - and in ~3min, in comes the alarm.
If you respond to this in the normal 928 owner's fashion, change your shorts - and reconnect the wire.
