beensoldaduffscooby

Please help.
I have searched all the threads on here and found many with similar problems to me but I have checked everything mentioned, and more, and not found the solution yet.

Car : MY00 PPP.

I recently changed the downpipe back to a cat for the MOT. I noticed a slight drop in boost pressure of about 1 or 2 psi for both peak and held pressure but thought nothing of it as I would expect a slight drop when re inserting the cat.
I then put the de-cat down pipe back on and boost now peaked at about 10 psi and dropped down to about 8 at higher revs. I have tweaked the actuator a little so would expect about that psi if the boost control solenoid was not working.

I immediately thought I had a boost leak and removed and checked all the pipes I had to remove to change the exhaust. Icould not find anything wrong and the boost was the same.

I then removed the battery for about one hour to reset the ecu. This made no difference.

All the threads on here seemed to point towards the boost control solenoid, the MAF sensor or the lamda sensor. My MAF is quite new and I have tried two lamda sensors and the air fuel ratio guage displays exactly the same as it did before the problem started so I thought it was the boost solenoid or pipes to it. I removed, cleaned and checked this solenoid and all was OK. Pipes were free flowing and solenoid operated when connected to a 12v supply.
At this point I removed all the boost pipes and re-checked to see if I could find a leak. No leaks were found.

I then connected the two green conectors under the steering column to check the solenoid actually pulsed. It did, you can quite clearly feel it.

I then connected the two black connectors under the steering column to check if there was an ecu fault. No faults were reported.

I then decided to reduce the size of the restrictor in the small pipe from the turbo to T piece to see if this changed the pressure and would indicate if the solenoid was working under normal driving conditions. I reduced it from 1.15mm to 0.95mm (I have a complete range in 0.05mm steps). This did change boost pressure - boost now peaked at 15 psi again but dropped back to 10 psi at higher revs. This indicated to me that the boost solenoid may not be working when driving normally.

If I hold the solenoid and move the thottle off idle I can not feel the solenoid pulsing. From reading threads on here it would appear it should.

So while reducing the restrictor did give a boost spike increase I think it is masking the problem and not the cause.

My asumption is that the ECU has stopped controlling the solenoid under normal driving conditions - but why?

Any suggestions from the boost gurus would be most welcome.
I am leaning towards getting a separate boost controller - any thoughts.

Thanks in advance,

Steve.

Bob Rawle

The solenoid only gets pulsed once the boost passes zero, so moving the throttle will not cause it to react, also changing actuator and restrictor settings from std is indeed confusing the issue as the ecu boost control dynamic maps are set to work correctly with the std settings. Since the ecu pulses the solenoid according to map settings and a closed loop algorythm then it must be seeing either a false input from the maf, excessive knock sensor output or the mapped max duty is now inadequate. Adjusting the actuator will not help, since actuator boost is normally 8 psi then it would appear the ecu has dropped into limp home. You need to establish why.

Lambda sensor has nothing to do with boost control and does not affect anything above zero boost level, maf could be showing the ecu a low output running the car lean triggering limp home from high knock sensor output.

If you disconnected the battery in all this its probably a maf problem, you do need to restore your tweaking to std though else once resolved you could get very oscillating boost control.

bob

beensoldaduffscooby

Thanks.

The actuator had been tighted way before this problem started (about a year ago) and I have not moved it during my fiddling this time.
I have now gone back to the original restrictor size.

I was not sure that the solenoid should start pulsing when just off idle (some posters on here say it does) so I have now connected a fluke scope accross the solenoid and driven the car. The solenoid stays completely closed - no pulses were seen on the fluke.

I did not disconect the battery at all when the problem started - It was disconected after the problem became evident to reset the ecu.

Another check of the ecu fault codes still gives no fault.

I have a air fuel ratio guage fitted and the reading is exactly the same as it was before the problem started. Do you still think it could be the MAF sensor, it is less than 6 months old?

TIA
Steve

beensoldaduffscooby

Please somebody help.....

kev1

iTrader: (2)

Alright Steve, have you fixed the problem yet?