406oc.co.uk

I have some questions/problems that maybe somebody here can help with.

Standard boost pressure on this engine I believe is 0.5bar (7.5psi approx). The engine reaches this boost level at around 3000rpm and I presume it should be able to hold this all the way to the red line. At 4000rpm its already dropped about 5 psi and at 5000rpm nearly down to 3psi, redline is probably about 2psi (these figures are all approx).

What could cause this or is it supposed to run this low at high rpm? If I disconnect the hose from the solonid to the actuator and drive very carefully its well capable of holding boost all the way past 4000rpm. I've also done a boost leak check and couldn't find anything. I have noticed that the car had an occasional miss on WOT and when boosting over 8-10psi that time (briefly) it was very much apparent, also I'd to change the battery and the first time after I did it the boost in first gear went slightly higher than usual, probably 8psi and then would miss slightly, the boost hasn't went as high since though so could the ECU be cutting the boost because of this. I've since changed the plugs and ignition leads as they were a bit dodgy.

My knowledge of turbos is fairly limited at the moment so any help is appreciated.

helps if you state what vehicle it is , year , reg, model etc

It's a 1996 406, 2L 8v turbo (petrol)

Archangel wrote:helps if you state what vehicle it is , year , reg, model etc

If the car's got an XU10J2TE under the bonnet there's very little it could be, and the differences are irrelevant in this context.

JK1 wrote:Standard boost pressure on this engine I believe is 0.5bar (7.5psi approx). The engine reaches this boost level at around 3000rpm and I presume it should be able to hold this all the way to the red line. At 4000rpm its already dropped about 5 psi and at 5000rpm nearly down to 3psi, redline is probably about 2psi (these figures are all approx).

What could cause this or is it supposed to run this low at high rpm?

That's the way it's supposed to be - it's a VERY relaxed engine...

also I'd to change the battery and the first time after I did it the boost in first gear went slightly higher than usual, probably 8psi and then would miss slightly, the boost hasn't went as high since though so could the ECU be cutting the boost because of this.

The ECU learns the best timing/fuelling/boost levels over time and tweaks itself to compensate for minor differences between engines (manufacturing discrepancies, wear, etc). Disconnecting power reverts it to a stock mapping before it re-learns.

I got around to reseting the ECU today after changing the plugs leads and filling it up with 99RON and its running better and boosting a little more and holding it better. ECU must have been cutting the boost back a little before.