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My boost level has been a bit poor for a while, so I thought that I'd try to eliminate some of the potential issues. Driving (briefly) with the wastegate vac. hose off showed that the turbo could boost fine :o well into the red...
A different wastegate actuator produced exactly the same levels of boost, so I dont think that is at fault either.
So then I thought that perhaps the APC was detecting knock, so reducing boost, but then this doesn't stack up, as the peak boost was never getting past about 0.6 bar. And tonight I very mildly tweaked the APC, and it now boosts solidly to around 0.75 bar stable.
There is a bit of noise that I'm thinking is the boost leaking, it seems to come from across to the left side of the car, but I can't really tell (difficult to focus on where the sound is coming from when you're on full boost and watching the road). I guess it could be the overboost switch leaking, anything else I should be looking out for?
TIA
Dave
check the functionality of your apc solenoid, disconnect the hose to the wastegate and that on the turbo inlet pipe
blow from the inlet to the waste gate (pull the plug on the apc up top) you shouldn't be able to blow through
then put 12V's on the apc plugs and make sur eyou can blow freely from the inlet to the wastegate
Yup, done all that. It's not that it doesn't boost at all, just that it doesn't boost very hard. The difference between base boost (i.e. solenoid disconnected) and full boost isn't huge, which makes me think that at higher levels of boost, something is opening up...
What do you think?
Thanks.
an excerpt from my site....
If the APC-system does not work according the "Normal Function" you can troubleshoot it fairly simple.
This guide assumes the following:
- Engine is free from any mechanical errors
- ALL vacuum hoses and ALL hoses between the air filter and intake manifold are controlled thoroughly for leaks
- The APC-box is not modified. If the box is modified the descriptions about how high the APC gauge shall rise at max.
Troubleshooting process if the APC gauge doesn't rise over the middle of the yellow field:
1. turn on the ignition (the headlights should now be activated), but do not start the engine. open the bonnet.
If the APC-valve is "chattering" all the time, it means that the APC believes one of the following:
- Turbo boost over 0.4 Bar
- Engine is "knocking"
- RPM is over 2300 RPM
none of these alternatives shall be present if the engine is off, so the APC must get wrong information.
Most probable cause is that the APC believes that the boost is high, even though that is not the case.
The pressure sensor, which gives info about the boost pressure, uses a resistance value that increases with increased boost pressure. If a breakage occurs in the
circuit the resistance becomes "infinite" which leads to that the APC believes the boost is "infinite" and thus trying to decrease the boost pressure.
De most probable cause is a faulty Pressure sensor.
Start by checking the pressure giver and the cables.
If the pressure sensor is ok, then the fault might reside within the APC box. Try to exchange to another APC-box.
2. Try to disconnect and reconnect the APC-valve electrical connector.
There shall be a "click" from APC-valve when the connector is removed and inserted.
If this procedure is repeted a few times the APC-valve might chatter a few seconds after the connector is inserted.
This depends on that the APC-box has became "unstable" and this is normal.
If the APC-valve does not "click", check the following:
- fuse to the APC-system is not broken
- The connector to the APC-box is fastened
- On cars with the new APC-box (25 pin), verify that the brake light does not shine
- The connector on the APC-valve is not corroded/oxidised
- Resistance through the APC-valve should be aprox 27 ohm
- That it is not possible to "blow" through the APC-valve "R" connector whilst the APC-valve is disconnected
If the fault remains, check and clean the electrical connectors attached to the ground point on the radiator beam.
Measure then following:
- +12 & ground to the APC-box
- ground to the APC-valve
- verify the cable from the APC-box to the APC-valve
If the fault can't be found try to exchange the APC-box.
If it's possible to "blow" through the APC-valves "R connector. Then the valve is broken and needs to be replaced.
3. Test-drive the car with the APC-valve disconnected (base-boost)
The APC-gauge shall rise to the middle of the yellow field.
If the APC-gauge stays in the beginning of the yellow field the base-boost must be increased.
Remember the APC-gauge is not a precision instrument. To ensure correct setting of the base boost you'll need a graded boost gauge of good quality.
4. Connect the APC-valve connector and test-drive the car.
Find a long road going uphill and start to drive upwards on the fifth gear and on max 1500 RPMs.
"Floor it" and watch the APC-gauge.
If the APC-gauge rises over the middle of the yellow field when the RPM is lower than 2300 and then at aprox 2300 suddenly "falls" back to the middle of the
yellow field, there's a bad connection to the knock sensor.
The function that checks that the signal from the knock sensor is strong enough, is activated above aprox 2300 RPM. If the signal is to weak the APC-valve is
disconnected above aprox 2300 RPM.
Check the connector to the knock sensor for corrosion/oxidation. Clean the connectors. If the connectors looks like they aren't connecting good to the pins in the
knock sensor, carefully mod the connectors with a fine screwdriver to ensure good connection.
If the fault remains check the cables between the Knock sensor and the APC-box.
Thanks Widde, I knew you'd be along before long :cheesy:
I'm pretty sure that I'll be back to checking all the vacuum lines and hoses from the intake *again* - problem is there's so damn many of them. The check for the knock sensor is good though, previously I was always using third gear to test where the max boost was going - I'll now try looking for a drop at 2300 rpm.
Cheers
Dave.