F96 Altitude sensor problems

[gmac78]

Hello all,

I've been having issues recently achieving full boost (1.4bar) on my homefried 3B.

System airtight with new hoses all round.

In 3,4,5 gear on WOT the boost gauge climbs up to around 1.1- 1.2 bar where the needle will bounce around and only in 5th gear if you hold it long enough it will slowly creep round to 1.3 to 1.4 bar, again with the needle bouncing around.

Having scanned through the forum i came across the F96 altitude sensor thread and decided to test mine.

When tested for resistance using a multimeter i got the following readings-

1-2 - 1402 ohms
1-3 - Unable to get a proper reading as when the probes are connected to the pins i get an initail reading briefly then goes straight to 1 (short) i tried several times and the initial reading was sometimes really high then really low. i.e 2500 then 500
2-3 Same again across these pins, eratic initial readings then the meter reading 1.

I take it i should be able to get an accurate reading across pins 1-3 and 2-3 like i can across 1-2.

I googled the local atmospheric pressure and was coming in at 759mmHg

Would this explain my WOT boost problems.

Also where would be the cheapest place to buy one of these sensors?
Audi just quoted £109, eeek!!

Look forward to your reply guys.

Thanks

[Jamo]

TPS will be the best bet, pm s2avant

[gmac78]

TPS you reckon. What makes you think that then?

I'll PM s2avant to see what he reckons.

Cheers

[Jamo]

TPS is the name of the company!!

[gmac78]

Ah i see, i thought you meant the throttle position sensor. He he.
Cheers

[UrS4boy]

Not saying you don't have an F96 issue but you seem to be mixing up 759 mm Hg with Paul N's 1020 mBar and thinking you have a problem.

Barometric pressure at sea level (without the influence of weather) is:

29.9 inches of Hg (mercury), 760 mm of Hg, 14.7 pounds per square inch gauge, 1.013 Bar (where 1 Bar = 14.5 psig), 1013 milliBar (mBar) or 101.325 kPa.

So your 759 mm Hg and Paul's 1020 mBar are correct, just different unit systems.

[Error404]

Get the Bosch part number off it and try your local Bosch dealer, bet its half the price

[gmac78]

What i was most concerned about today was when i took resistance readings across pins 1-3 and 2-3 the multimeter only registered a reading for a second then read 1 on the display. Is the reading not meant to stay on the display until the probes are removed? From what i've read on the forum so far no one else has reported this behaviour when taking readings so was thinking my sensor was at fault.

Can anyone confirm if this is normal when taking readings?

Cheers

[gmac78]

Also, i forgot to mention that i'm roughly 132m above sea level and got a reading of 3.84v across pins 1-3.

[Rusty]

A flickering boost gauge needle would indicate a boost leak to me. How have you tested the system, which parts of the system have you tested and to what pressure?

[UrS4boy]

A flickering boost gauge needle would indicate a boost leak to me. How have you tested the system, which parts of the system have you tested and to what pressure?

IME, a flickering analogue boost gauge is more the result of an undampened gauge and the response of the gauge to the WGFV which modulates the boost a some frequency = flickering.

Dave F.

[gmac78]

I blocked off the maf to turbo hose and intercooler exit to intake hose. This was tested to around 1.5 bar with a only a slight leak which was nipped up. I then pressurised the intake side up to 1.5 bar which showed a couple of slight leaks on the vacuum hoses at the rear of the head but again were nipped up. Obviously the pressure drops off through intake side but any major leaks would have shown up when the initial pressure was applied.

The gauge is dampened also so that is not the problem. My question is should i get steady readings when i measure the resistance on the F96 sensor, surely the eratic readings on the mulitmeter aren't normal?

Has anyone who has tested the F96 experienced this behaviour?
Thanks

[newsh]

You should get a steady reading, as long as the unit is disconnected from the loom.. The unit is a simple potentiometer operated by a barometer mechanism. The track of the potentiometer probably needs cleaning. See if you can pop the top off the device and get some switch cleaner on the track. There's a product called Cailube which is perfect for cleaning and lubing faders and pots.
When my unit was reading wrong I took it apart and tweeked it till it gave the correct readings, I've had no problems since and that's a few years back now.

[twoqu]

Try increasing the range of your MM!

I have got the following:
1-2 1.05K
1-3 2.54K
2-3 2.40K

That is from off the car. According to the data, 72m above sea level here!

[gmac78]

Newsh- That is interesting now, i did suspect that these eratic readings weren't normal but couldn't find a definitive answer anywhere. That's helped clear up my query now so hopefully like you say it simply needs a clean inside. That will be my first job tomorrow morning so will report back then on my findings.
Thanks for all the input guys, much appreciated.