850 t5 96' Can Too Much Wastegate Travel Cause Low Boost?

splifdrift · Post by **splifdrift** » 01 Jul 2026, 07:53

I've been running a billet wastegate actuator on my TD04HL-16T for a few months and can't get boost past 9 psi, no matter what spring or preload I use. It always fixed from mid to high RPM.
When I compared it to the stock actuator, I noticed the stock one only has about 10 mm of travel, while the billet one has around 15–20 mm. Could the extra travel be causing the wastegate to open too far and bleed off boost?
I've tried different springs, different preload settings, and even stock preload specs with no change.
My thought was to use a lighter spring and shorten the rod as much as possible so the wastegate can't open as far, while still keeping the correct preload. Does that make sense, or am I looking at this the wrong way?
Or is the ECU simply commanding the TCV to open the wastegate more for some other reason?
Car: 1996 Volvo 850 T5, almost Stage 0.
Only codes are for bad ABS sensor readings.
radiator is leaking (idk if it pulls timing for this)
Turbo was rebuilt (not sure what was replaced, maybe just the CHRA).
Fuel pressure set at 3.5–3.8 bar.

Post by **scot850** » 01 Jul 2026, 10:29

How old is your TCV and hoses? If they are original they may not be helping your cause. Can't comment on the aftermarket travel on the wastegate, but it could be your turbo cannot boost enough to open the wastegate. As you are running an 850, I don't know the spes for the original TCV on those, but the later P80's are only reliable to 12 or so psi of boost. Beyond that you need to look for a different TCV that can allow higher boosts. I have one on my 00 R as it boosts to around 20 psi. I have an IPD unit, but I have had issues with the unit, not because it is bad, but because you have to be careful when adding the plastic 'leg's for the pipes to not crush the filter which prevents the valve sliding. This is only an issue on the 'middle' leg. Turn the leg no more than 4 turns in. It may feel loose, but more than that it may damage the unit. I have advised IPD on this issue a couple of times, but they still have not updated the instructions with a warning.

Neil.

splifdrift · Post by **splifdrift** » 01 Jul 2026, 12:28

hi nail, my car is almost stage 0.
tcv is a pierburg from ipd (also tried the stock one , seems to boost different, stock one tries to go beyond 10 , peak a little past 10psi and backs off where the pierburg one is firm in building boost but stays fixed at 9 psi).

all air and vaccum hoses are replaced and clamped thight. triple checked everything so i guess no problem from there . i know the turbo can boost more since in one test the WG actuactor hose got disconnected and the car was pushing 18 psi on 3rd gear.

im trying to run 12psi nothing crazy

splifdrift · Post by **splifdrift** » 01 Jul 2026, 12:31

when i say stage 0 , almost every sensor replaced, all hoses replaced, front and rear headgaskets , injectors , sparks, coil , cables.. etc|

Post by **Clemens** » 08 Jul 2026, 00:31

Is the 16T new as well or just the actuator? I once git a replacement 15G with too short of a lever that wouldn't go into full boost.
But the actuator needs to be quite exactly the correct length, I feel.

Post by **scot850** » 08 Jul 2026, 08:31

I am thinking that Clemens and you may both have a good point on the rod length of the actuator. If the aftermarket one has twice the rod travel, it could be it is only opening 50%. You would have to find a way to see if the actuator is opening fully on full boost. I'm no turbo expert but there must be a way to find this out. Peirburg I believe was the OE on the later P80's, I seem to recall the 850's having a different shaped one. I think it was round.

Is there a reason you changed to the billet actuator? Was it specified for your car and turbo?

Neil.