1.8t overboost (problem diagnosed....i think)

[Sheraton]

How'do folks

Almost 9 weeks into ownership now and making some headway with sorting out the minor issues the car had - she was just needing a wee bit LoVe

I was getting some serious overboost from the turbo - whining and dumping like a Subaru with huge boost spikes at 3000rpm (it would be interesting to know how much power was being made, too much to be useful anyway)

I changed the vac hoses to start - (note: someone else mentioned on another post, that they had experienced silicon hoses sucking themselves flat ??? from what i now understand, this would be unlikely given that the wastegate is actuated from a push and not a pull, or a blow and not a suck.....)
anyway i changed to 3mm i.d silicone hose - and i connected the hoses correctly (when i got the car they were switched around) but still had overboost

today i cleaned the solenoid with (mtb) brake cleaner.....and no difference
I wanted to rule out the wastegate actuator before i bought a replacement solenoid

I just unclipped the silicone hose that feeds the wastegate from the solenoid and it fit nicely into my mountain bike track pump with a push on the pump handle i could see the wastegate moving i pressurised and released a few times to make sure all was moving freely and it seems to be Good - so no need to replace the turbo - from what i understand you can't replace or service the wastegate actuator on this unit ? - also the wastegate seemed to be opening around 10psi - maybe 7-8psi - would this be correct ?

what i've done for now is bypass the solenoid - i've blocked the hose that returns the pressure after the airbox and connected a short hose from the compressor to the wastegate actuator (i'm assuming this to be less harmful to the car than running overboost ?) when i took a test run the car felt great
no overboost, no noisy turbo, no engine management cutting power and the car pulled evenly through the rev range all the way to 6500rpm under full throttle

now comes my decision - do i buy an original replacement solenoid, an aftermarket/upgraded one or..... do i fit a manual boost control

from what i can make of it - the original units have been giving this problem since the cars were new and replacements are prone to fail after a short period - upgraded units can be constructed better and less prone to failure (am i right in thinking maximum boost is set by the ECU so an upgraded unit will operate at the same boost pressure as the original ?)

I like the idea of having manual control - given that the electrical control is there to add a bit more boost pressure before the wastegate actuator is engaged - i'm not looking for more boost - also the electrical systems will all fail at some point - a manual boost control should be set and forget and less likely to fail.....maybe

or can the car be run indefinitely with the compressor and wastegate "hardwired" ?

Paul.....

[minimutly]

If you like how it drives you could leave it as it is - you're getting less mid range boost, and wont be doing any harm.
As for solenoids failing, really? Should be good for 50k at least, more if you're lucky, and you seem to have a handle on how the system works, so why not replace it?

[rich17865]

I had a solenoid fail in under 1000 miles

[Sheraton]

Originally Posted by minimutly

If you like how it drives you could leave it as it is - you're getting less mid range boost, and wont be doing any harm.
As for solenoids failing, really? Should be good for 50k at least, more if you're lucky, and you seem to have a handle on how the system works, so why not replace it?

50,000 miles lifespan for a solenoid would be more than acceptable (my car just passed 60,000 miles since i got her) however since i've been looking into the cause of my overboost, i get the impression this has been a common fault with 75s and ZTs and from new too - i found a copy of the Rover dealer Technical Tips Sheet - from 2004, i think - the year my car was registered. while i don't know that the solenoid has been the cause of the similar symptoms experienced by other owners, my research/ponderings have allowed me to come to the conclusion that the (original Pierburg) solenoid is the weak link in this particular chain (boost control)

Paul.......

[mrtngibs]

Originally Posted by Sheraton

50,000 miles lifespan for a solenoid would be more than acceptable (my car just passed 60,000 miles since i got her) however since i've been looking into the cause of my overboost, i get the impression this has been a common fault with 75s and ZTs and from new too - i found a copy of the Rover dealer Technical Tips Sheet - from 2004, i think - the year my car was registered. while i don't know that the solenoid has been the cause of the similar symptoms experienced by other owners, my research/ponderings have allowed me to come to the conclusion that the (original Pierburg) solenoid is the weak link in this particular chain (boost control)

Paul.......

My 75 has the opposite problem: if I floor the throttle the whole engine momentarily stops. Obviously I then slacken off and engine continues as normal. Could this be a solenoid problem?

[Gman2]

Common problem and had it c 7 years ago - replaced plugs, coil packs etc until someone on the forum suggested replacing all the small original hoses with slightly larger bore silicone hose. Once replaced I've never had the problem returning. Not sure on the fragility of the solenoid - mine has never been replaced in my 8 years of ownership and I'm on 95k

[Sheraton]

Originally Posted by mrtngibs

My 75 has the opposite problem: if I floor the throttle the whole engine momentarily stops. Obviously I then slacken off and engine continues as normal. Could this be a solenoid problem?

i'm no expert - but this sounds more like the ignition misfire i had - i'd say check plugs and re-gap to 0.80mm - the solenoid failing, to my understanding can't provide less boost only overboost(?) and if it fails you get too much power then a violent cut of all engine power, as the ECU senses overboost.... you'd also be able to hear the turbo overboosting. if the power cuts instantly when you hit full throttle - then i'd suggest ignition rather than turbo - the turbo would be unlikely to trigger the ECU cut-off instantly, as it would take a moment to build pressure and hit the cut-off limiter.

Paul..........

[Sheraton]

Originally Posted by Gman2

Common problem and had it c 7 years ago - replaced plugs, coil packs etc until someone on the forum suggested replacing all the small original hoses with slightly larger bore silicone hose. Once replaced I've never had the problem returning. Not sure on the fragility of the solenoid - mine has never been replaced in my 8 years of ownership and I'm on 95k

this helps me come to the decision that i'll replace with an original replacement (Pierburg ?) Solenoid
i want to keep the car as original as possible and i figure it to be worth trying for my own experience (i can get one for around £25 delivered) if it does the trick then all Good, if not i can explore the other options


Paul......

[Sheraton]

Originally Posted by minimutly

If you like how it drives you could leave it as it is - you're getting less mid range boost, and wont be doing any harm.
As for solenoids failing, really? Should be good for 50k at least, more if you're lucky, and you seem to have a handle on how the system works, so why not replace it?

I would like to have the car running to it's full potential - initially i'm just glad to have tamed the excessive power and sudden boost spikes - it's nice to have a smooth run through the rev range, however i'm aware of the car losing some of the pulling power gained from a bit more boost.

i've ordered a replacement Pierburg unit and will stick with this original set-up all going well

Paul..........

[arodriguez]

Let us know how you get on. I replaced my Pierburg unit but it didn't help. I've now replaced coil packs (one was faulty), leads, plugs (gapped to 0.6mm) and 3mm ID hoses but it still cuts out on overboost. It's a recon turbo too so I assume that's good.

Seems to be hit and miss when it cuts out (with flashing engine light) but I've no idea what's causing it. I was recommended to fit an upgraded MAC solenoid valve.. good luck.