Real boost only above (exactly) 4000 rpm?

[OrMar]

What on Earth could mechanic do (or connect) wrong during complete engine rebuild, so car have no useful boost under 4000rpm, but exactly at 4000 rpm it starts boosting and goes like it should, except for minor cutting which I attribute to some small boost leak?
Car is A200 20v with 3b engine and RS2 components, but after rebuild I run it for few thousand km with standard turbo etc., and it behave the same, eg. no real boost under 4000 rpm.
Fact that change happends at exactly 4000 rpm leads me to theory that it's something electrical/electronical, what do you people think ?
Is there some component which starts beeing used at 4000 rpm ?

Thank you,
Mario

[david]

What on Earth could mechanic do (or connect) wrong during complete engine rebuild, so car have no useful boost under 4000rpm, but exactly at 4000 rpm it starts boosting and goes like it should, except for minor cutting which I attribute to some small boost leak?
Car is A200 20v with 3b engine and RS2 components, but after rebuild I run it for few thousand km with standard turbo etc., and it behave the same, eg. no real boost under 4000 rpm.
Fact that change happends at exactly 4000 rpm leads me to theory that it's something electrical/electronical, what do you people think ?
Is there some component which starts beeing used at 4000 rpm ?

Thank you,
Mario

did you have your ECU remap?
what rs2 components did you use on the engine?

[Jamo]

Cam timing is incorrect

[OrMar]

As I explained at other thread, my only oportunity here in Croatia was to buy software and then collect components as per software specification.
However - I was having same problem BEFORE i upgraded all components (including software) to RS2, so I believe it's something else.

Mario

[OrMar]

Cam timing is incorrect

You mean position of camshafts or something else ?
We checked distributor few days ago, and it's spot-on. Going to search on "cam timing" now ...

Mario

[GazzaG60]

jamo may have it there. its blowing straight out.

either that or you have a big manifold leak or cut back fins

[OrMar]

either that or you have a big manifold leak or cut back fins

Fins on turbine ? It behaved same with original turbo.
As for manifold, don't think so - I checked it before installing.

Mario

[Jamo]

You mean position of camshafts or something else ?
We checked distributor few days ago, and it's spot-on. Going to search on "cam timing" now ...

Mario

Yes it's common on the stock RS2 if the cam timing mark is not placed behind the marker it affects boost build up.

So what you need to do is set the car to TDC on the flywheel and check the cam timing in relation to this.

[david]

it's look's like you have too many mix match of component and that could be the problem.if you don't use exact spec on a car without modification your going to have issue's.

[OrMar]

it's look's like you have too many mix match of component and that could be the problem.if you don't use exact spec on a car without modification your going to have issue's.

As I said, car was behaving the same with stock components after rebuild. Before rebuild, it was ok.

Mario

[OrMar]

So what you need to do is set the car to TDC on the flywheel and check the cam timing in relation to this.

OK, that will be my next step. I hope this procedure is in details described in Bentley.

Mario

[OrMar]

OK, so we re-checked complete timing and it seems to be perfect.
But, we found another possible cause: throttle potetiometer which should have resistance of ~1000 ohms between pins 2 and 3 with the throttle closed, the ignition turned off and the connector removed from the throttle switch/potentiometer. Mine have around 8000. Tomorrow I will get another one and test, but could that be the source of my misery ?


Mario

[OrMar]

Tried another (known-to-be-good) throttle body with potentiometer, and it made no difference. All timing marks are spot on. Made a short run with MTFS disconnected, no change. Could knock sensors cause that ? Is the following scenario possible: one of knock sensors is bad, but software ignores it above 4000 rpm (thus it's running ok at high rpm) ?

Thanks,
Mario

[OrMar]

jamo may have it there. its blowing straight out.
either that or you have a big manifold leak or cut back fins

Could you guys please elaborate a bit more on this wrong cam setup; eg. is it possible that marks are spot on, but cams are still installed wrong ?

Thanks,
Mario

[istoo]

faulty knock sensors on the 7A make it feel flat until you hit EXACTLY 5000rpm then it goes like a scalded cat. So in that respect yes it could be knock sensors. You can run them disconnected but i would only do it to test for a short period to see. Assume you have vagcom'ed the car?