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jockthedog
Experienced


Car: S4-B5.3
Power: C5-RS6Plus
Torque: in' hell!
Engine code: 0xFA

Joined: 14 Mar 2011
Posts: 3132

Location: Moonbase Alpha

PostPosted: Wed Mar 16, 2016 12:34 am  Reply with quoteBack to top

I reckon I must have dislodged something in the IC circuit which has jammed the thing.
I'll check it on an ohm-meter and see if I can get it to open with a 12v supply, but I'm assuming it's goosed.

I'm a little disappointed that what seemed to have been an equivalent boost with the FMIC as the SMICs, vs what turns out to be a loss, once I'd fixed the n75 issue.

These N75s are tuned by that wee screw, but that is done in the factory so I'd hope they should all be the same.
I think MRC fitted that last one, and I didn't check the code on it but I'm assuming they fitted a stock one and not a race-spec one.

Thinking now about an MBC.

Good info on N75 here...
http://forums.fourtitude.com/showthread.php?5934686-Stock-n75-225-amu

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Doug
MRC Tuning



Joined: 21 Apr 2008
Posts: 3447


PostPosted: Wed Mar 16, 2016 8:09 am Reply with quoteBack to top

have you pressure tested it? unless you have a really bad setup to really good setup the boost should not change that much
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jockthedog
Experienced


Car: S4-B5.3
Power: C5-RS6Plus
Torque: in' hell!
Engine code: 0xFA

Joined: 14 Mar 2011
Posts: 3132

Location: Moonbase Alpha

PostPosted: Wed Mar 16, 2016 1:33 pm Reply with quoteBack to top

I haven't Doug. I need to get hold of a compressor. I have the rest of a pressure-test setup.
I'll see how the car runs this weekend and then think about the next step.

Cheers for the response tho. Always nice to hear from the horse's mouth

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Doug
MRC Tuning



Joined: 21 Apr 2008
Posts: 3447


PostPosted: Wed Mar 16, 2016 3:17 pm Reply with quoteBack to top

drive to Tesco and use their compressor - pressure test before thrashing it please!
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jockthedog
Experienced


Car: S4-B5.3
Power: C5-RS6Plus
Torque: in' hell!
Engine code: 0xFA

Joined: 14 Mar 2011
Posts: 3132

Location: Moonbase Alpha

PostPosted: Sat Mar 19, 2016 7:16 pm Reply with quoteBack to top

hehe missed this and duly thrashed the car to within an inch of its life, as always.

Perfect day for it, cool and dry and bright. Car was pulling a steady 15psi peaking at 17ish, and despite a wee tweek to the N75 it made no difference.

No sign of any leaks, boost or otherwise, car was purring happy. Well, ok, wailing

Thing is, I went out while it was still quiet and was immediately doing the faster times I've ever done. 60 point somethings lap after lap. Not quite fastest, but I wasn't trying too hard.
Ok I have monster stupid big brakes now that I really trust and was eeking 10m out of every corner, but if I had those extra 5 psi back up the straight, I reckon 60 secs will quickly fall.

So, how do I get them back? Where in the map is the code?

I took an ohmeter to the 'borked' N75 and it read 25 ohms, which sounds about right.
Thing is, these things should fail safe, electrically, so the plunger inside must be jammed slightly open perhaps? Maybe a broken spring?

I'll take it to bits tomorrow

Doug, do you guys keep records of your maps? Know what boost was mine mapped to?

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jockthedog
Experienced


Car: S4-B5.3
Power: C5-RS6Plus
Torque: in' hell!
Engine code: 0xFA

Joined: 14 Mar 2011
Posts: 3132

Location: Moonbase Alpha

PostPosted: Fri Mar 25, 2016 12:42 am Reply with quoteBack to top

compressor got

leak fixed at fmic

Fun times ahead

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jockthedog
Experienced


Car: S4-B5.3
Power: C5-RS6Plus
Torque: in' hell!
Engine code: 0xFA

Joined: 14 Mar 2011
Posts: 3132

Location: Moonbase Alpha

PostPosted: Wed Mar 30, 2016 1:19 pm Reply with quoteBack to top

Ah well, so much for that.

The leak I found was very small/slight and fixing it has not given me back the missing 5psi.
Was battering round the track again on Saturday and had the same boost as I had last week - 15-17psi.
Car's running perfectly.

So where could my boost have gone and how do I get it back?
Is my only option a remap?

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ScottR
Veteran


Car: B5 S4

Joined: 22 Apr 2008
Posts: 8539


PostPosted: Wed Mar 30, 2016 2:13 pm Reply with quoteBack to top

Are you pressure testing upwards of 17psi?

Years ago I had a boost leak which only reared its head above 19psi.
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pjbRs
Veteran


Car: Noggy blue b5 Rs4

Joined: 20 Jul 2010
Posts: 7495

Location: west london

PostPosted: Wed Mar 30, 2016 2:34 pm Reply with quoteBack to top

Still sounds like a boost leak, your car certainly shouldnt need remapping, unless you've changed something else.

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mikey-s
Veteran



Joined: 11 Jun 2008
Posts: 7466

Location: Mars

PostPosted: Wed Mar 30, 2016 2:51 pm Reply with quoteBack to top

Whatever the fault is,  you  need to stop kicking it's ass until the fault is found.   Boost leaks aren't good for turbos!

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jockthedog
Experienced


Car: S4-B5.3
Power: C5-RS6Plus
Torque: in' hell!
Engine code: 0xFA

Joined: 14 Mar 2011
Posts: 3132

Location: Moonbase Alpha

PostPosted: Wed Mar 30, 2016 2:57 pm Reply with quoteBack to top

Well I'll fire up the compressor again and have another check.
Car isn't due on track again till May so there's plenty of time.

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jockthedog
Experienced


Car: S4-B5.3
Power: C5-RS6Plus
Torque: in' hell!
Engine code: 0xFA

Joined: 14 Mar 2011
Posts: 3132

Location: Moonbase Alpha

PostPosted: Tue Apr 12, 2016 10:47 am Reply with quoteBack to top

So, I may actually have found the issue, which is not so much a boost leak as a boost gauge leak!

Wee bit of soapy water highlighted a small leak where the boost gauge takes its feed off the hose, which I am hoping means that the boost gauge is simply reporting the boost too low. I didn't have any spare hose or clips to fix it, yet.
Everything else (car performance) points to the boost being still at historical levels.

When I tried to get some pressure into the system, I found that it seemed to leak very fast past the pistons. I can hear the oil bubbling away in the sump. I couldn't get more than 10psi in there, despite having plenty of oomph in the compressor. Maybe I'm just not brave enough with the pressure I'm adding.
Again, no performance loss is noticable so unlikely to have an issue inside the engine.

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ScottR
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Car: B5 S4

Joined: 22 Apr 2008
Posts: 8539


PostPosted: Tue Apr 12, 2016 2:03 pm Reply with quoteBack to top

Have you pressure tested it when the engine is hot? That should minimise loss passed the rings. Struggling to reach 10psi does sound like an issue. I guess you at least tried to cap the leak (ie: put a big fat finger over where you found it) whilst you were testing?
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jockthedog
Experienced


Car: S4-B5.3
Power: C5-RS6Plus
Torque: in' hell!
Engine code: 0xFA

Joined: 14 Mar 2011
Posts: 3132

Location: Moonbase Alpha

PostPosted: Tue Apr 12, 2016 2:27 pm Reply with quoteBack to top

sound idea Scott, to get it all hot first.

When it is running, there's no problem holding more than 10psi boost, according to the boost gauge. I see a stable reading while my foot is on the gas.
I didn't have a way to cap that leak without destroying the existing hose, and it certainly wasn't a big enough leak to account for the lack of pressure in the system.

I'll get the wee tiny leak fixed and then we'll see what the gauge reads. I'm hoping it will magically start telling me what I expect to hear.

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