Overboosting/Fuel cut issue

Hi guys,

I’ve recently started having an issue with my twin turbo where at WOT it will stutter once the turbos hit high boost. If I accelerate moderately it’s fine. It’s only at WOT that I’m experiencing this problem. I have tried to diagnose the problem and it feels as if it’s overboosting. I think I have narrowed down the issue to the stock boost solenoid for the following reasons:

  1. It only happens at WOT. The boost comes in absolutely fine and the car feels a little faster than usual until it hits what feels like fuel cut.
  2. At first I thought it would be the spark plugs but the ECU doesn’t throw any CEL’s like it did in my Polo GTi before the sparks on that blew.
  3. The stock oil pressure gauge shoots up to above the half-way point under moderate acceleration and at WOT climbs even higher.
  4. The fuel gauge depletes very quickly (quicker than usual!!) although the problem might be fuel related.
  5. I’m getting a slight ticking noise when I let go of the accelerator which from what I’ve read; it may be coming from the boost solenoid.

Steps I’ve taken so far:

  1. Done an oil change just today. I put in some Castrol GTX 10w40 Semi-Synthetic and an OEM Filter. Lifter tick issue is temporarily gone and the car definitely feels smoother.
  2. Checked the Vac lines that go from the Y-pipe to the boost solenoid and the wastegate actuators.
  3. Checked the fuel filter for any leaks.

As I’ve said the car runs absolutely fine when driven normally. Its a 95’ with 111817 on the clock.

I’m ordering a manual boost controller tonight to see if that fixes the problem. I don’t have a boost gauge so I cant get an exact reading on the psi.

I would like to get some second opinions on the problem from all you experts out there just in-case I’ve overlooked something. I’m 99% sure it’s the stock solenoid though. Is there a way to test it? I have read that if I unhook the Vac lines from the actuators then it should only run 6 psi, is this true??

Any help is appreciated thanks!!

DO NOT FIT a manual boost controller to this car… More of these cars have been blown up from fitting Manual Boost controllers (Basically a coup[le of pieces of Plumbers hardware) than i care to remember…

The problem could be the Fuel Pump Relay or you have another fault that is making the injectors hit the cut point as the car is over fuelling and using all the available fuel

Do the fuel pump relay mod first and see if that help as its nice and cheap about 5p

Then I would check the vac lines and replace them with new and not the crap off ebay !!

Small steps and work through it not big stupid ones and you will fix it rather than have to fix the engine

Hope this helps

Cheers Rob

1 Like

Do you have any ability to datalog the car so you can see what the ecu is saying and what boost it thinks it is running etc. This can tell you a hell of a lot of what is going on without wasting your time changing bit willy nilly.

Cheers Rob, i remember you telling me on the phone not to cheap out on her!! I wasn’t going to increase the stock boost, I just wanted to use the mbc to bypass the stock solenoid to see if that was causing the issue. I’m leaving the car as stock as possible for now.

Do our cars have obd2 interfaces?? Because i do have a bluetooth elm device. Im going to go out and check the voltages on the fuel relay using a multimeter. I shall report back as soon as possible.


What year is your car? from around 94 on it switched from OBD1 to a Hybrid OBD2 so won’t work with the ELM bluetooth which is standard OBD2

I bought a bluetooth ELM just to check incase it did but it won’t connect or read anything.

HHH Hand Helo Halo data logger is probably the best and the one i use. Evoscan is also good but i could’t get it to work with my cars for sone reason. but many other get it to work ok.


I’ve fixed it I think!! The fuel pressure solenoid thing came unplugged. The clip is very loose and it looks as if the previous owner had tried to glue it back on!! I shall report back this evening after testing the car when I finish work. Thanks for all your help guys.

Btw I think the fuel relay bypass has been done by the looks of the harness. Non the less, I shall do it again just to be safe. God knows what the previous owner has done to this poor car :frowning:

Quick update - The problem may have been the stock boost solenoid. I bypassed it with the mbc and it seems a lot better, The oil pressure gauge doesn’t shoot up on boost anymore. Just to be safe I took the car to Garage-D and they reckon it may also be the spark plugs so I’ve ordered a new set of NGK Iridium bkr7eix plugs and a new gaskets for the throttle body and intake plenum

Why did you buy BKR7EIX ??

Buy a 2nd work solenoid and take the MBC out

And you say the OIl Pressure goes up with the Boost ??

Do you means goes up with Revs ??

I was originally going to buy bkr8eix plugs but i thought because of winter it may be better not to go for too cold of a plug. Should i return the 7’s and get 8’s instead??

I’ve taken the MBC off and shes running at wastegate pressure for the moment which is 6psi?

The oil pressure sits at halfway on the stock guage at high revs but on boost at WOT it goes to about 6/10 high. At the minuite with or without the mbc shes acting normal. I think my plugs need changing. Over the past few days its been cold and i dont think my current plugs can cope with the temp change. Today it was a bit warmer so i assume the plugs were managing to cope. Its a shame there are no garages close by that can check my car. Garage D said they wouldnt be able to work on my car :confused: