Porsche Enthusiasts Club Forum

Hi, I have an issue with my 944 T not giving any boost after the pipes where changed. I replaced all under inlet manifold piping with OEM parts, from new inlet gaskets to all air lines, hoses and clips. I made sure all pipes were fully re-tightened before reassembly. Now I have no boost. I'm not sure if the inline hose restrictor was put back in, in the correct orientation. Could this be the issue?

Any help would be grateful.

Sounds like the cycling valve is stuck open, allowing constant boost pressure to the wastegate meaning it opens at the first sign of boost (the stock spring is very weak). Either that or you've accidentally bypassed the cycling valve.

Either way the wastegate is seeing boost too early, or you have a monster boost leak but you probably would have noticed that as it would run like cr4p!!..

That's probably right as I noticed the wastegate connection pipe was disconnected, thinking that was the cause of my rough running. I now have better idle and smoother running but no boost. What would you recommend as a replace or an uprated cycle valve?

The cycling valve cannot be upgraded. It is part of the factory boost control. Some however do bypass it when going to a dual port wastegate; basically going beyond a 'Level 1' tune (i.e chips, and a boost enhancer) where the valve will become a stopping point when increasing boost.

If it were me I would test the cycling the valve as per Clark's guide and also double check that the vacuum pipes are correct.

Could the cycling valve be tested in situ. Clamping the wastegate connecting pipe or disconnecting it as it was?

If you had boost before, I don't think it would be something failing or braking without running or using the car.

Have you checked all your vaccum lines and boost hoses. Is it zero boost? Where's the boost needle sit on tickover

I think you may need to do a thorough check of everything under the manifold, assuming that you had removed it to change hoses etc. The problem is that everything under there will be very brittle due to heat and age so moving things about could have broken something. As has been suggested I would start with the cycling valve, being plastic it will be very brittle, you could have broken hose connections or wiring....my own many moons ago more or less fell apart with the plastic unions that the hoses attached too falling off. Start here and then work your way through what's been changed...hope you find the problem quickly

regards

Pete

My boost needle has never worked correctly, It would raise a little on cold mornings and stay still whilst driving. All vacuum lines are now new and pretty sure they were all connected correctly on re-assembly.

Yes Pete, the manifold was off on the weekend and all new vacuum hoses, clips and lines were replaced. I don't think I have damaged any wire and I'm pretty sure I've reconnected all hoses correctly as I took photos along the way of dis-assembly and re-assembly.

Just to state when I removed the manifold the wastegate hose was disconnected from the cycling valve.

The car runs much smoother and feels a better drive, however, without any boost

ok well best go back to basics and check what you have with a diagram for a non modified turbo...this may help...


Pete

Clamping the wastegate connecting pipe has fixed the problem. Does this mean it's the cycling valve which would need replacing?

Looking at your last thread, it would strike me you've connected the Cycling valve up wrongly and rather than boost building up then the wastegate opening up to reduce the boost, the cycling valve (or connections) are keeping the w/gate open permanently rather than at 15psi/ 1bar.

C

Hi chris, this is how the cycling valve is connected. These not any other way to connect the hoses.

Well in fairness from the photo the CV certainly looks plumbed in correctly - I can only go on your symptoms = No boost. In one of your posts you had blanked off/ shut down the pressure feed to the wastegate and found that gave you boost.

So, by default if this worked, the wastegate is clearly being opened all the time. So, my diagnosis (difficult without seeing in person) would be:

1. Plumbing of the system is incorrect - thing we've established it isnt this.
2. The cycling valve is broken/ non functional and open permanently - simply acting as a connector.

ISTR that cycling valves are massively expensive, so my advice would be order a new one from your local OPC and see if that cures the problem !

Yours

Chris

so are you saying there was NO boost control before? if thats the case (assuming no aftermarket parts fitted) you potentially have a serious problem. the car should have overboosted and blown itself to bits, but couldnt produce enough boost with no wastegate??