Discussion
Eventually got the 996 Turbo back on the road today after a nightmare with the brakes over the winter. The car seems to run fine but has no turbo boost at all, zero, zilch, nil.
The bar gauge shows zero irrespective of revs /welly or surprise and the car is definately not as quick.
There is also a PSM/ABS fault (lights on) which only comes on over 30MPH and goes off when the car ignition is switched off.
Has anyone any ideas of either fault. I had the same PSM fault last summer and it showed a front offside wheel sensor which I have replaced... Could it be MAF related????
Any thoughts on either problem much appreciated
The bar gauge shows zero irrespective of revs /welly or surprise and the car is definately not as quick.
There is also a PSM/ABS fault (lights on) which only comes on over 30MPH and goes off when the car ignition is switched off.
Has anyone any ideas of either fault. I had the same PSM fault last summer and it showed a front offside wheel sensor which I have replaced... Could it be MAF related????
Any thoughts on either problem much appreciated
You need to borrow a mityvac and connect it to the actuator on the turbo, you'll see a small hose going to the actuator, remove this and connect the mityvac, apply 0.5bar of pressure and the wastegate should move 4mm, it'll be obvious if one is stuck.
It would be a good idea to check for error codes in the ECU as you clearly have other faults, it could also be a dodgy N75 valve, or a knackered MAF, but you would usually get 0.5bar of boost if it was an issue with these as that is the default boost setting determined by the mechanical nature of the wastegates. No boost AT ALL would point at either a stuck open wastegate, a split boost pipe from the turbo to the intercooler (or other major boost leak), or even a torn diverter valve diaphragm? It's been known for the stock diverter valve diaphragm to make its way into the turbo and cause some major damage. These can be checked with the same mityvac that you will use to check the wastegate actuators
It would be a good idea to check for error codes in the ECU as you clearly have other faults, it could also be a dodgy N75 valve, or a knackered MAF, but you would usually get 0.5bar of boost if it was an issue with these as that is the default boost setting determined by the mechanical nature of the wastegates. No boost AT ALL would point at either a stuck open wastegate, a split boost pipe from the turbo to the intercooler (or other major boost leak), or even a torn diverter valve diaphragm? It's been known for the stock diverter valve diaphragm to make its way into the turbo and cause some major damage. These can be checked with the same mityvac that you will use to check the wastegate actuators
...way above my ability. I've booked it in to Tom Ferguson for tomorrow to see whats going on. The last time I used it it was overboosting slightly but I thought it might just be the map as Id just bought it. The PSM/ABS fault clears when you switch the ignition off and doesnt come back on until you hit 30mph. I have already replaced one wheel sensor.
I hope the turbos arent screwed..
I hope the turbos arent screwed..
Car still in at Tom Fergusons. Their kit shows the fault as the front offside speed sensor, but no matter how many new ones they try the fault reappears. One thought is its the wiring to the sensor.
Turbo boost still shows as zero, albeit the turbos seem to be working (not seized). They think the car has some boost but it isnt registering on the dash gauge.
The car is definately down on power from what I remember.
They are now exploring if the two faults are linked - maybe a faulty boost pressure switch? or if there is a leak somewhere.
Turbo boost still shows as zero, albeit the turbos seem to be working (not seized). They think the car has some boost but it isnt registering on the dash gauge.
The car is definately down on power from what I remember.
They are now exploring if the two faults are linked - maybe a faulty boost pressure switch? or if there is a leak somewhere.
John mate, Sorry to hear about the grief your having and not too sure about your recurring speed sensor fault but if your experiencing no boost at all then the usual suspects would be a badly leaking/holed or disconnected intercooler hose, a failed N75 boost control valve (would have expected this to show a code on tester though), or as mentioned above a wastegate/actuator stuck fully open.
Pretty sick at the moment Andy. Spent all winter sorting the brakes, which in itself was a pain as new discs turned into new calipers as the nipples were shot and had to be drillled out... eventually got it back out of hibernation to find the same pigging fault code as the Malton boys found at Raby Castle...
I put a new FOS wheel sensor on and Tom has tried 3 others which show the same fault.
It resets when you turn it off, then clears and is fine until you hit 30 or so then it comes back on.
It was overboosting when I took it off the road at the end of Sept and now the bar gauge doesnt register anything. The car isnt lumpy but just feels slower. That launch into next week feeling has gone, and bearing in mind Ive spent all winter in a 1.5 DCI Meganne it should feel fast.
Even though of getting shot of it for 355, very pi%%ed off at the moment.
I put a new FOS wheel sensor on and Tom has tried 3 others which show the same fault.
It resets when you turn it off, then clears and is fine until you hit 30 or so then it comes back on.
It was overboosting when I took it off the road at the end of Sept and now the bar gauge doesnt register anything. The car isnt lumpy but just feels slower. That launch into next week feeling has gone, and bearing in mind Ive spent all winter in a 1.5 DCI Meganne it should feel fast.
Even though of getting shot of it for 355, very pi%%ed off at the moment.
SIIX TT said:
Pretty sick at the moment Andy. Spent all winter sorting the brakes, which in itself was a pain as new discs turned into new calipers as the nipples were shot and had to be drillled out... eventually got it back out of hibernation to find the same pigging fault code as the Malton boys found at Raby Castle...
I put a new FOS wheel sensor on and Tom has tried 3 others which show the same fault.
It resets when you turn it off, then clears and is fine until you hit 30 or so then it comes back on.
It was overboosting when I took it off the road at the end of Sept and now the bar gauge doesnt register anything. The car isnt lumpy but just feels slower. That launch into next week feeling has gone, and bearing in mind Ive spent all winter in a 1.5 DCI Meganne it should feel fast.
Even though of getting shot of it for 355, very pi%%ed off at the moment.
Let us know the outcome, good luckI put a new FOS wheel sensor on and Tom has tried 3 others which show the same fault.
It resets when you turn it off, then clears and is fine until you hit 30 or so then it comes back on.
It was overboosting when I took it off the road at the end of Sept and now the bar gauge doesnt register anything. The car isnt lumpy but just feels slower. That launch into next week feeling has gone, and bearing in mind Ive spent all winter in a 1.5 DCI Meganne it should feel fast.
Even though of getting shot of it for 355, very pi%%ed off at the moment.
Any news yet? It can't be the N75 valve as the worst it can do is only allow 0.5bar of boost, if you were to bypass it all together and connect the actuators directly to manifold pressure, the wastegates only open 4mm at 0.5bar, basically the lowest boost possible is 0.5bar. To have less than 0.5bar it has to be something else...
Your ABS issue could be the same as here http://forums.rennlist.com/rennforums/showthread.p... long shot i know, but it's worth a check!
Your ABS issue could be the same as here http://forums.rennlist.com/rennforums/showthread.p... long shot i know, but it's worth a check!
LATEST..
turbos checked - all ok
MAF 3 different ones fitted all ok, same fault appears and no boost
Wheel sensor- 3 fitted same fault reappears.
Wiring to wheels sensors checked ok
Fault is only triggered if you apply boost, IE If you drive round at almost zero revs with no load the light stays off. As soon as you give it any beans the fault trips in. The garage seem to think the fault lies in the boost solenoid, which is triggering the ABS/PSM fault in much the same way as a knackered MAF would.
Wil find out today or tomorrow.
turbos checked - all ok
MAF 3 different ones fitted all ok, same fault appears and no boost
Wheel sensor- 3 fitted same fault reappears.
Wiring to wheels sensors checked ok
Fault is only triggered if you apply boost, IE If you drive round at almost zero revs with no load the light stays off. As soon as you give it any beans the fault trips in. The garage seem to think the fault lies in the boost solenoid, which is triggering the ABS/PSM fault in much the same way as a knackered MAF would.
Wil find out today or tomorrow.
SIIX TT said:
LATEST..
turbos checked - all ok
MAF 3 different ones fitted all ok, same fault appears and no boost
Wheel sensor- 3 fitted same fault reappears.
Wiring to wheels sensors checked ok
Fault is only triggered if you apply boost, IE If you drive round at almost zero revs with no load the light stays off. As soon as you give it any beans the fault trips in. The garage seem to think the fault lies in the boost solenoid, which is triggering the ABS/PSM fault in much the same way as a knackered MAF would.
Wil find out today or tomorrow.
The 'boost solenoid' is the N75 valve, and even if that is broken and fully open you will still get 0.5bar of boost. The wastegates on the turbos hold 0.5bar by default. The only way you can get absolutely ZERO boost is with a huge boost leak somewhere, like a boost hose split or disconnected, or fully stuck open wastegate.... They need to pressure test the intake, not difficult to do, there must be a huge leak somewhereturbos checked - all ok
MAF 3 different ones fitted all ok, same fault appears and no boost
Wheel sensor- 3 fitted same fault reappears.
Wiring to wheels sensors checked ok
Fault is only triggered if you apply boost, IE If you drive round at almost zero revs with no load the light stays off. As soon as you give it any beans the fault trips in. The garage seem to think the fault lies in the boost solenoid, which is triggering the ABS/PSM fault in much the same way as a knackered MAF would.
Wil find out today or tomorrow.
Sorry, on a 993 turbo it's called an N75, it may be called lots of different names, but it's the same thing which is a electronically controlled solenoid valve, it basically controls the boost by opening the wastegates.
It'll have a hose connected to the manifold, one to the airbox to sense intake temps, and one going down to a 'T' connection which branches off to each wastegate actuator. And of course the electrical connection.
If they said the words boost and solenoid in the same sentence it can only be the one thing.
I hope they get to the bottom of it for you
It'll have a hose connected to the manifold, one to the airbox to sense intake temps, and one going down to a 'T' connection which branches off to each wastegate actuator. And of course the electrical connection.
If they said the words boost and solenoid in the same sentence it can only be the one thing.
I hope they get to the bottom of it for you
I had a similar problem where i was under power and the PSM and ABS lights came on after a very short time. The turbos were also making a hairdryer sound when i booted it. Nick at Auto 2000 in Bedford fixed it eaily as one of the turbo pipes had come loose, this was causing the MAF to get confused and sent the PSM/ABS warning lights off. The car kept stalling as well even though its a boring old auto box. Cheap fix after diagnosis and now back to full on mental 996 TT power and sound. hope this helps.
John, details of boost control valve here mate... http://www.pistonheads.com:80/gassing/topic.asp?h=...
Andy... the bit he pointed to when I spoke yesterday was the pressure transmitter ref no 99660618000, which is just to the left of the boost valve on your attached photo. Im sure he said the boost solenoid was the probable cause of the problem, but the fault code he would have expected didnt show. He definately said the bit was 180 quid, which is about the price of the transmitter rather than the valve.. Unless I misheard...its may as well be in French most of the time.
As Ive said I havent a clue, I put my faith in greater minds. I should know tomorrow.
PS What does the transmitter do and would it throw the PSM/ABS fault and stop the boost?
As Ive said I havent a clue, I put my faith in greater minds. I should know tomorrow.
PS What does the transmitter do and would it throw the PSM/ABS fault and stop the boost?
Nothing can 'stop' the boost other than a boost leak, i know i keep repeating myself here, but it's GOT to be a leak. I'm not sure whether blown diaphragmns in the diverter valves would cause a total boost loss? They need to pressurise the intake and listen for leaks, because there is nothing electrical that can stop boost building to 0.5bar, the wastegate actuators are set that way!
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