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Discussion Starter · #1 ·
So, whilst I am waiting for the fuel in my tank to run low enough to remove the tank to fix its leak (hopefully this weekend), I thought I'd see if anyone knows what may be the problem with my cars strange boosting tendencies.

I thought I had solved the issues with my boost when I fixed my ignition timing that was quite badly out, but it still doesn't seem normal to me and I believe some issues still persist.

I have found that if I am at low rpm in 3rd, 4th gears (I assume 5th, haven't tried) and put my foot flat to the floor, even as revs build higher and higher, boost will sit at a bit past half way through the yellow zone and stay there. A sort of "fluttering" noise can be heard in the exhaust note also.

However, if I have the engine sitting at higher rpm (not revving it's head off, just mid-range sort of speeds) and give it full throttle, boost goes right to the start of the red zone as it should and seems to stay there fairly well, without the flutter sound really being noticeable.

I am sure it isn't just a case of turbo lag as when I have trialled it up longer hills for example, the boost still won't reach what I think are normal levels.

It is a bit annoying because it's not like it just prevents me from driving the car hard, but also driving up hill the car requires more throttle, doesn't pull very well and sounds a bit unusual.

Any ideas what could be causing this?
 

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I have found that if I am at low rpm in 3rd, 4th gears (I assume 5th, haven't tried) and put my foot flat to the floor, even as revs build higher and higher, boost will sit at a bit past half way through the yellow zone and stay there. A sort of "fluttering" noise can be heard in the exhaust note also.

However, if I have the engine sitting at higher rpm (not revving it's head off, just mid-range sort of speeds) and give it full throttle, boost goes right to the start of the red zone as it should and seems to stay there fairly well, without the flutter sound really being noticeable.
Can you put some RPM figures to them?
 

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Sounds like this may be normal behavior, particularly if you have a Garret turbo. But as James has asked, can you be more specific and put some rpm figures on this?
 

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Install a knock light is my first piece of advice.

The only thing I can think of at this stage is that your car is knocking under heavy load at lower RPM and reverting at base boost (the exhaust fluttering note as I have explained before is due to the wastegate oscillating open and shut due to the APC)

I would suggest the usual possibilities but you've dealt with those.

A car will knock in high load conditions but not necessarily high RPM conditions (low load)

A knock light would prove/disprove my theory.
 

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Discussion Starter · #5 ·
I will try to get a bit better of an idea about the rpm tomorrow. I will also get a knock LED wired up as soon as I have time.

I think I will use these instructions:

"Pin 19 on the APC is grounded when the apc senses knock. Basicaly we want to wire an LED to this pin. In later cars, the APC receives 12v from the brake pedal switch, to cut boost during braking. Since you probably wanted to remove this feature anyway, we can kill two birds with one stone by using this wire and connector. First identify which wire goes to the APC at the brake switch, cut it free. Now at the APC end, remove the big plug from the apc, and unscrew the one screw that holds the cover on the plug. Locate the pin that the brake pedal light goes to (20 I think). I used an x-acto to free the pin from the connector, replace it in pin 19. You now have a wire from the knock pin of the apc into the cabin. Find a good 12v power source, and wire a lamp to it and the wire you cut from the brake switch. If your using a LED that's not 12v ready, wire a resistor in one side of it to keep it from blowing. 300 ohm should be sufficient. Now you know when the APC thinks you're pinging. With the car on (not running) you can get the led to blink, and the solenoid to go crazy, by tapping the knock sensor with something hard. "

Although I am not sure why the author says I would probably want to remove the boost dump upon braking feature?
 

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One more thing; have you got the vacuum hose from the inlet manifold to dizzy capsule connected correctly?
 

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If your using a LED that's not 12v ready, wire a resistor in one side of it to keep it from blowing. 300 ohm should be sufficient.
On later APC boxes, which your's is, you don't need the resistor for the LED. It won't blow.

Although I am not sure why the author says I would probably want to remove the boost dump upon braking feature?
You don't need to do this unless you're left foot braking during rallying.
 

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On later APC boxes, which your's is, you don't need the resistor for the LED. It won't blow.


You don't need to do this unless you're left foot braking during rallying.
OR trying to get on the newcastle motorway ....:lol:

For whats its worth , I have very similar in my aero I get full boost around 2700 to 3000 In lower gears .. but it will only pull base when under heavy load ..in say 4th up a hill... or pulling a trailer ..

I have no doubt it my case its the APC reacting to Knock .
 

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For whats its worth , I have very similar in my aero I get full boost around 2700 to 3000 In lower gears .. but it will only pull base when under heavy load ..in say 4th up a hill... or pulling a trailer ..

I have no doubt it my case its the APC reacting to Knock .
All very good, indicating the APC is working as it should....
 

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For whats its worth , I have very similar in my aero I get full boost around 2700 to 3000 In lower gears .. but it will only pull base when under heavy load ..in say 4th up a hill... or pulling a trailer ..

I have no doubt it my case its the APC reacting to Knock .
I'm inclined to agree Aussie. I suspect that Julian's boost performance is normal, but let's wait 'till he gives us more info.

What's special about the Newcastle motorway? Is it really bad?
 

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Discussion Starter · #13 ·
Right, so I have finally gotten back round to dealing with what may either be an issue, or just normal performance.

I have taken a couple of videos of me accelerating in 3rd gear up a quite steep hill near my house. One shows the results of me being at low speed/rpm and putting my foot to the floor in 3rd, and the other shows what happens if I am at higher rpm and do the same.

Not sure if this is normal or not, but it's just that the car didn't do this when I first got it. That being said, I have fixed some things since I first got it, and they may have returned the car to normal performance from what was dangerous to the engine.

Hopefully these videos upload, because they were taken with a new fangled phone and I forgot to turn the quality down.
 

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Discussion Starter · #16 ·
Hmmmm. So I thought I'd take the Swedish Dynamics APC out and replace it with the original just to see what would happen.

Even from lower rpm, the boost climbs (pretty slowly) up to just before the start of the red zone, which is what I would think is normal for the original APC. I think something might be amiss with the SD APC.

Might open it up tonight and have a look inside just in case there is obviously a resistor burnt out, or a capacitor has decided to share its insides with the components around it or something.
 

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in this country it is against the law to drive with no shoes on:nono;
There is no specific law in the UK banning driving in bare feet. Unsuitable footwear may be a cause for prosecution. The legal requirement is simply that your footwear must allow you to distinguish between the pedals, and be firmly attached to your feet.
 

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yeah flip flops/ thongs are illegal because they can get caught etc, in Aus barefoot is not illegal - the charge is failure to maintain proper control of the vehicle and I have never personally heard of anyone being pinged for it.

Julian your high boost video looks normal to me, the boost held steady at the edge of the red (or it seemed to) what's the problem ,that it isn't going into the red?
 
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