Intake R&R progress
01-24-2008, 07:34 PM
#76
Nordschleife Master
My airbox studs were also not straight.. complete with slanted rubber between the two threaded parts.
I had one of the ones under my airbox shear in two when I was unbolting it a few months back, so I ordered a few replacements (there's more of the same part under the intake).
I was suprised when the replacements were all straight, but they fit correctly and I can only assume that 20 years of heat and hydrocarbons has caused the originals to plasticise and flow slightly.
I had one of the ones under my airbox shear in two when I was unbolting it a few months back, so I ordered a few replacements (there's more of the same part under the intake).
I was suprised when the replacements were all straight, but they fit correctly and I can only assume that 20 years of heat and hydrocarbons has caused the originals to plasticise and flow slightly.
01-24-2008, 09:51 PM
#77
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The air box bumpers deform with age. New ones are straight.
01-24-2008, 11:01 PM
#78
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Interesting- my airbox is a major PITA to line up on the (old) studs. I'll have to see if they're bent/off-kilter.
01-25-2008, 04:04 AM
#79
Drifting
Thread Starter
No cat on mine Malcolm, so I could just plug this at the throttle and have one less vac line to re-attach/route. Unless I will need it as a test point some time in the future?
01-25-2008, 07:32 PM
#80
Drifting
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Couldn't get much done today, so just stripped the old flaking black paint from the cross brace (used a wire brush attachment on drill). Got hold of some primer and satin black to repaint it.
Also posting photos of the two rubber bonded studs on the airbox brackets - both have distorted alarmingly! Will get replacements for these and get an extra one for the ISV mount.
I'm playing with the old ISV with a 9V battery and watching it rotate. Does anyone know what the ISV actually does and how?
Family haven't seem much of me while I've been in the garage this week so will probably leave it over the weekend.
Also posting photos of the two rubber bonded studs on the airbox brackets - both have distorted alarmingly! Will get replacements for these and get an extra one for the ISV mount.
I'm playing with the old ISV with a 9V battery and watching it rotate. Does anyone know what the ISV actually does and how?
Family haven't seem much of me while I've been in the garage this week so will probably leave it over the weekend.
01-25-2008, 08:35 PM
#81
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The ISV receives a pulsed signal (AFAIK) from the LH. The frequency of the pulses determines the effective angle of rotation of its innards. When you test the ISV you see the inside rotate so as to make an opening? That opening allows manifold vacuum to draw air from the long hose that goes up to the Y connector in the rubber air guide that connects the MAS to the throttle body. Air thus drawn into the ISV bypasses the throttle plate and goes into the throttle body.
So, the LH can vary the amount of air bypassing the throttle plate and consequently control idle speed. More air means a higher idle. Less air means a lower idle.
Once the car is warmed up the 02 sensor is used to trim the fuel mixture to keep combustion stoichiometric. The system is adaptive - it learns - and will compensate for mild degradation of various components.
So, the LH can vary the amount of air bypassing the throttle plate and consequently control idle speed. More air means a higher idle. Less air means a lower idle.
Once the car is warmed up the 02 sensor is used to trim the fuel mixture to keep combustion stoichiometric. The system is adaptive - it learns - and will compensate for mild degradation of various components.
01-25-2008, 08:40 PM
#82
Nordschleife Master
The same part is also used to support the fuel rails.. PET shows 4 of them mounted on the intake. I haven't started my intake job yet, so don't know what condition mine are in but you might have an idea?
01-25-2008, 08:41 PM
#83
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One more thing: when you get all this done - new hoses, ISV, gaskets, etc., reconnect the battery and fire up the car it should idle rock-steady at very close to the correct idle. You have, in effect, returned the car to a state where the 'factory defaults' should be correct. The correct idle will be a few hundred RPM higher when the car is cold. Within a few minutes the idle should settle to the warm value in the spec book. (IIRC 675 for S4s and 775 for GTs +/- 25 rpm.)
If you do not get behavior close to the above then you have more work to do (or work to re-check.)
If you do not get behavior close to the above then you have more work to do (or work to re-check.)
01-25-2008, 08:52 PM
#84
Drifting
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Yep, thats what mine were like. The more distorted of mine sheared in two when I was tightening it.. so it got replaced.
The same part is also used to support the fuel rails.. PET shows 4 of them mounted on the intake. I haven't started my intake job yet, so don't know what condition mine are in but you might have an idea?
The same part is also used to support the fuel rails.. PET shows 4 of them mounted on the intake. I haven't started my intake job yet, so don't know what condition mine are in but you might have an idea?
Will have a quick look tomorrow (trying to make it a 928-free weekend!) and report back.
01-25-2008, 08:55 PM
#85
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That is what PET says. But, I'm not sure I believe it. Below is a picture zoomed-in on that part of the intake. I've looked at all my pictures of intakes and I haven't yet found anything that looks like the rubber buffers. Yet, I vaguely recall having seen them on some S4 intake. If anyone finds them I'd be very interested in knowing the model-year. My vague recollection is that I found them on an early-VIN '87. The picture below is from a high-VIN '87.
01-25-2008, 08:56 PM
#86
Drifting
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The ISV receives a pulsed signal (AFAIK) from the LH. The frequency of the pulses determines the effective angle of rotation of its innards. When you test the ISV you see the inside rotate so as to make an opening? That opening allows manifold vacuum to draw air from the long hose that goes up to the Y connector in the rubber air guide that connects the MAS to the throttle body. Air thus drawn into the ISV bypasses the throttle plate and goes into the throttle body.
So, the LH can vary the amount of air bypassing the throttle plate and consequently control idle speed. More air means a higher idle. Less air means a lower idle.
Once the car is warmed up the 02 sensor is used to trim the fuel mixture to keep combustion stoichiometric. The system is adaptive - it learns - and will compensate for mild degradation of various components.
So, the LH can vary the amount of air bypassing the throttle plate and consequently control idle speed. More air means a higher idle. Less air means a lower idle.
Once the car is warmed up the 02 sensor is used to trim the fuel mixture to keep combustion stoichiometric. The system is adaptive - it learns - and will compensate for mild degradation of various components.
01-25-2008, 09:04 PM
#87
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That is what PET says. But, I'm not sure I believe it. Below is a picture zoomed-in on that part of the intake. I've looked at all my pictures of intakes and I haven't yet found anything that looks like the rubber buffers. Yet, I vaguely recall having seen them on some S4 intake. If anyone finds them I'd be very interested in knowing the model-year. My vague recollection is that I found them on an early-VIN '87. The picture below is from a high-VIN '87.
I have the same as Dave's pic where the fuel rail mounts to the intake by means of a stud, spring washer and nut.
01-25-2008, 09:07 PM
#88
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Adrian............for someone who said you were taking the weekend off your not starting well; have a wee dram for Burns and off to bed now
01-25-2008, 11:37 PM
#89
Nordschleife Master
That is what PET says. But, I'm not sure I believe it. Below is a picture zoomed-in on that part of the intake. I've looked at all my pictures of intakes and I haven't yet found anything that looks like the rubber buffers. Yet, I vaguely recall having seen them on some S4 intake. If anyone finds them I'd be very interested in knowing the model-year. My vague recollection is that I found them on an early-VIN '87. The picture below is from a high-VIN '87.
The rubber bit looks white for some reason (flash reflection?), but its in the right place and I think I can see the two metal plates either side of the rubber. As far as I can tell from the parts catalogue, they're in all 87-95 MY's.
01-25-2008, 11:49 PM
#90
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Nope. Not a flash reflection. That "white" part is the intake casting. Trust me. Or not - I can post a dozen or more pictures of that area from different intakes from different angles. There ain't no rubber there.