Stock S4 boost levels?

[nrowensby]

I have searched and searched and can't seem to find what a stock S4 should be boosting... I'm spiking at about 7psi and tapering down to 4-5psi. I have a feeling stock boost pressure should be a little higher than this.

[Mooseimage]

Should be 7-9 psi stock. I'm not sure if this is peak and hold, or it tapers down to it. I assumed it hits it and holds.

[nrowensby]

That's what I was thinking but couldn't verify it anywhere... I guess I will be trying to find someone to pressure test the car and find my leak.

[S4_NE]

I have searched and searched and can't seem to find what a stock S4 should be boosting... I'm spiking at about 7psi and tapering down to 4-5psi. I have a feeling stock boost pressure should be a little higher than this.

what gage did you buy? I belive 8-9 psi spike stock

[nrowensby]

I got a VEI Systems digital boost/vac gauge.

http://www.veisystems.com/bhm-m.html

[AudiSportB5S4]

Why guess when I can show you what the ECU asks for!



OP. Seems you may have a boost leak... Time to pressure test that sucker. What do you hold in HG @ idle?

[nrowensby]

Vac holds at 19-20mmHG@idle w/o AC

How was that log taken? Vag-Com?

[AudiSportB5S4]

Vac holds at 19-20mmHG@idle w/o AC

How was that log taken? Vag-Com?

That is ECUx... The vacuum is OK for you, but it could be considered low as well... People will generally say 19-21 is acceptable. But 21 is solid. Know what I mean?

Do you have access to VAG? Log block 118 and see requested versus actual. It wont look pretty like my graph, but you could work something out. Just really have to compare the two numbers and hope they are similar.

[Strange Design]

That's crap, there goes my delusion of having the only Silver S4 in Columbia.

PM me if you need access to a VAG-COM.

[nrowensby]

LOL, I had the same delusion... Jake was the only other one I knew of and he moved away.

Check out ColaDubs.net

Some pretty cool guys over there :D

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Back on topic... What would cause my boost leak to mysteriously fix itself, completely? I have been driving her all day, the most boost I have seen was 7.1psi at WOT in 3rd gear... so I went over to my uncle's to see when I could meet up with him to do a pressure test and we talked for about 30 minutes or so. I get back in the car and head home, I go to pass some fool and give her some gas, the gauge reads out 9.3 (that was the stored peak psi after I let out of the throttle). I was like, "WTF?!? Must've been a fluke" ...so I get on it WOT in 3rd and peak 11.9psi, held ~10psi before tapering down at high RPM.

What could cause this? DV going bad? N75 going bad?

[AudiSportB5S4]

Could be a million things unfortunatley..

It could be your diverter valves.

It could be a boost leak from your F hose, TBB, etc, (you are a 2000 so you have the lovely F hose as well)

It could be N75

As you can see, the list is long and exciting. I would still pressure test. If you rule that out, then you can move onto logging 003 and 118 in VAG com and seeing if you are hitting the req. boost levels. Pressure test though, it's a fun. Cap the PCV connection on Y pipe and remove oil cap. Crank it to 15 PSI no more, you don't need to since you're not surpassing those levels yet.

[nrowensby]

I checked the F-hose visually, didn't notice any oil anywhere around it... Also, if it were the F-hose or TBB, what would cause it to no longer leak?

[nrowensby]

Well... spoke too soon, back to 6-7psi :(

[nrowensby]

No boost leak... Had one bad DV (710A), replaced it with a 710N, the other DV is a 710B and holds quite nicely.

New symptom, unhooked MAF and nothing changed... Car didn't stumble, car didn't hesitate, but no CEL... Is this normal?

[Karl]

Does the light come on when you first start the car? Could it be burned out? That really doesn't make sense. Otherwise maybe you were disconnecting a headlight or something...

[nrowensby]

After about 25miles of driving, the CEL finally came on... Going to replace the N75 today and see if that's the culprit...

[AudiSportB5S4]

After about 25miles of driving, the CEL finally came on... Going to replace the N75 today and see if that's the culprit...

Did I read it right? You only replaced on DV with a 710N?

While you do your N75, once its off take the right hose and blow into it. You shouldn't be able to at all it should be air tight. The bottom one should be like a straw. Just figure while you're back there might as well check torn wastegate line issue.

[nrowensby]

Yes, I only replaced one DV with the 710N, the other DV appears to have been recenly replaced with a 710B and held quite nicely under vaccuum.

I will definately check the hoses coming off the N75. Could you clear up which hose goes where for me?

[AudiSportB5S4]

Here ya go... The N75 picture applies to you here.. Looking at it, the bottom should blow through and line on the right is the wastegate line and shouldnt be able to blow into.

[nrowensby]

Testing that theory tonight... We put a new N75 on the car, also blew into the hose on the right to be sure that no air passed (confirming it going to the wastegate). Still on hitting ~7psi