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@The_Nuge did you ever get your boost pressures above 200mb?

Having installed my boost gauge I also see that mine is at stuck at 200mb at full throttle.

I have the metal solenoid so I'm not sure whether cleaning will do much. Did the new knock sensors fix it for you?
 

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Hi!
I haven't checked yet I must confess! I am still looking for a convenient place in the firewall to feed the pressure tube through.
I did replace both knock sensors and the plastic boost solenoid, and that did improve the performance subjectively. The change was already there with the knock sensors btw.

Cheers

Es
 

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Hi!
I haven't checked yet I must confess! I am still looking for a convenient place in the firewall to feed the pressure tube through.
I did replace both knock sensors and the plastic boost solenoid, and that did improve the performance subjectively. The change was already there with the knock sensors btw.

Cheers

Es
Which know sensors did you use? I see the originals are out of stock.

I'll get a picture for you of where we routed the tube into the glovebox.
 

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A picture would be great!

The knock sensors I got are Valeo 255400. They're for a Dacia Logan, so dirt cheap :)
You'll need a slightly bigger wrench / socket, but other than that they're the same as OEM.
 

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I recognised the boost solenoid when I saw it early on in this thread. Said to myself... that's off the Saab!

Here's a comprehensive guide for troubleshooting the Saab APC system. It's an old website which uses frames: 900aero.com APC tuning

If the boost controller on the Saab and the Bentley are really the same then it is possible on the Saab to fit a 'knock LED'. One of the wires from the boost controller will hit ground every time knock is detected.

With a knock LED you can not only diagnose knock problems but also see how much boost can be added to the engine before knock becomes unacceptable. Once a turbocharged engine starts knocking you can raise boost further but you must have control of the whole engine management. So ignition should be retarded and fuel increased depending what is lacking to cause the imbalance which produced the knock. If you don't have full control of the engine management then the best you can do is monitor for knock and turn down the boost if there is too much.
 

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Thread footnote - Zytec equipped engines only share the knock sensor(s) and plastic (Saab) boost control valves.

Zytec performs logic/analysis and boost valve actuation.
 

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someone said earlier in the thread that the whole thing was the same system. But maybe that's earlier cars?
 

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@ejenner The Saab website is really good - thanks for that!
Do you have any experience with the "Knock-LED" setup? What kind of LED do you use, and is it so that every time the LED lights up you have knock?

@detomaso have you found out where the OEM boost pressure sensors are in your car? I can't find them in mine...

Cheers

Es
 

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yes, each time knock is detected the LED will flicker. You can gauge from the intensity of the flickering how much knock you are getting. It's not uncommon to see a little bit. I actually welded the wastegate shut on my Saab and used my foot to control the boost keeping an eye on the knock LED. I had a modified turbo on it as well. It was very good. I've still got the engine in the garage, remained in one piece even after all that abuse, was running fine when I took it out. Had 200,000 miles on it.
 

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Hi!
It's been a while, but I think I've made some progress:

I fitted a relay in the wire to the solenoid, as described on the Australian forum, and that brought up the voltage to the solenoid by quite a bit. Also, and most importantly, the car seems subjectively somewhat quicker! It's a mechanical relay for the time being, but I'm in the process of sourcing a solid state one.

I've also found where the pressure transducer is hiding, and it is indeed inside the right front wing. You can spot it through a hole roughly where the ECU is.

Next up is fitting the boost gauge, but before that I "have" to go on holiday 😀

Cheers

Es
 

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Hi All
Does anyone know which pin the LED needs connecting to?
I've connected on to pin 18 (I think) but never seen it flicker.
Thanks
Mike
 

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Hi again,
I've just plumbed in a boost gauge in the line from the back of the manifold to the pressure sensor. I'm measuring vacuum when the throttle is closed, so it's definitely downstream of the throttle. However, I'm also getting maximum 0.2bar boost....:(

So far I've done the following:
  • Replaced the knock sensors
  • Replaced the boost solenoid (plastic one)
  • Wired in a relay in the supply to the solenoid to boost the voltage.
  • Replaced the TPS

What's next?

Could it be the wiring for the knock sensors? I suppose the ECU is expecting to "see" clean impulses. Will it reduce boost if the sensors are disconnected? How can it be checked?

Boost sensor? Can it be checked for output vs. pressure?

Any other ideas?

Es
 

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1999 Rolls-Royce Silver Spur, Mulsanne Green
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I have wondered if the turbo in my ‘99 Spur is giving the boost it should as well. Mine is a “light turbo,” though, so not sure if this info applies to my car?
 

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Hi again,
I've just plumbed in a boost gauge in the line from the back of the manifold to the pressure sensor. I'm measuring vacuum when the throttle is closed, so it's definitely downstream of the throttle. However, I'm also getting maximum 0.2bar boost....:(

So far I've done the following:
  • Replaced the knock sensors
  • Replaced the boost solenoid (plastic one)
  • Wired in a relay in the supply to the solenoid to boost the voltage.
  • Replaced the TPS

What's next?

Could it be the wiring for the knock sensors? I suppose the ECU is expecting to "see" clean impulses. Will it reduce boost if the sensors are disconnected? How can it be checked?

Boost sensor? Can it be checked for output vs. pressure?

Any other ideas?

Es
Could the wastegate be stuck open?
 
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