Boost question 1998 t5

[andrewc1267]

Hi a friend of mine has a 1998 v70 t5 manual he's not on here so has asked me to post for him the car has an under boost issue he's replaced the tcv and borrowed my smoke Pro to check vacuum and boost pipes for leaks and all good the car is ex police and has covered nearly 325k I suggested that the wastegate unit could have a weak spring he is borrowing my mitivac tomorrow to test does anyone know what pressure it should start to open and what pressure should it be fully open the car has the ME7 engine management system

[JohnM 855 T5R]

Originally Posted by andrewc1267

Hi a friend of mine has a 1998 v70 t5 manual he's not on here so has asked me to post for him the car has an under boost issue he's replaced the tcv and borrowed my smoke Pro to check vacuum and boost pipes for leaks and all good the car is ex police and has covered nearly 325k I suggested that the wastegate unit could have a weak spring he is borrowing my mitivac tomorrow to test does anyone know what pressure it should start to open and what pressure should it be fully open the car has the ME7 engine management system

Although the wastegate spring could be the cause, they don't often give trouble. More likely is either a split diaphragm or weak spring in the TRV (turbo recirculating valve). Rebuild kits are freely available.

Regards
John

[sdg1970]

When this happened to me (similar car) it turned out to be the throttle body hose had a 2inch crack in it. I also replaced several vac hoses, the TCV and the TRV with a Forge Motorsports uprated version. I also replaced all the boost hoses with scilicone ones and the main intake (black plastic one) pipe. It now boosts to 16psi max with the remap I have on it.

[andrewc1267]

Originally Posted by JohnM 855 T5R

Although the wastegate spring could be the cause, they don't often give trouble. More likely is either a split diaphragm or weak spring in the TRV (turbo recirculating valve). Rebuild kits are freely available.

Regards
John

The TRV was blanked with an aluminium blank as it failed ages ago he has smoked and the intake and vac system and has no leaks he has a boost gauge fitted what should it read at full boost

[JohnM 855 T5R]

Originally Posted by andrewc1267

The TRV was blanked with an aluminium blank as it failed ages ago he has smoked and the intake and vac system and has no leaks he has a boost gauge fitted what should it read at full boost

Generally not a good idea to run with a blanked off TRV unless you are relieving the excess boost pressure upon throttle lift off via a dump valve of some sort. The excess pressure flows back into the turbo causing turbine flutter which can damage the turbo bearings and blades over time (some turbos are tolerant of this but TD-04's don't have the strongest of bearings compared to others) and also increases lag when reapplying throttle as the back pressure slows down the turbo.

Full boost should be around 9 to 9.5 psi - don't expect to achieve this over the entire rev range, i.e. at lower revs, and it can slacken off a little at very high revs on the standard ECU mapping. Also note, that some boost gauges can be notoriously inaccurate.

If you are sure that all pipes are leak tight (even tiny leaks can make a significant difference) then that only leaves the wastegate from what you have said. As a previous poster has said, replacing everything with silicone hoses (vac pipes, turbo hoses, etc.) is good practice and closely inspect all of the "hard piping" for cracks. I had the main turbo pipe from turbo outlet to intercooler develop a small split on my C70 T5 many years ago. Also, check all the blanking caps on the vacuum tree are in place and tight.

Regards
John

[sdg1970]

I must also add that the smoke test isn't neccessarily a reliable indicator imo. I was ripping my hair out trying to find the problem on mine (around 3 years back) and resorted to having a local garage smoke test it. They did so and apparently found nothing, so I continued on with the car and it's inability to boost over 7psi and a chronic 'wooshing' noise coming off boost.

A few days later I disassembled the throttle body (at that point I'd only replaced about half of what I said in my previous post) and found the hose had a near 2 inch burst in it that the garage and their oh so good smoke testing hadn't detected. Just be aware is all I'm saying...

[andrewc1267]

Originally Posted by sdg1970

I must also add that the smoke test isn't neccessarily a reliable indicator imo. I was ripping my hair out trying to find the problem on mine (around 3 years back) and resorted to having a local garage smoke test it. They did so and apparently found nothing, so I continued on with the car and it's inability to boost over 7psi and a chronic 'wooshing' noise coming off boost.

A few days later I disassembled the throttle body (at that point I'd only replaced about half of what I said in my previous post) and found the hose had a near 2 inch burst in it that the garage and their oh so good smoke testing hadn't detected. Just be aware is all I'm saying...

I'll have a look with him over the weekend. Maybe run some live data while driving to see what boost the Ecu thinks it is running and compare that to the gauge. I did think that the ME7 would put the MIL on and store a code for under boost or intake system leak or maybe lambda system to lean but nothing
The intercooler has been replaced a while ago with a billet replacement and all is hard piped with silicone bends and joints and all so hard piped from MAF to turbo charger I think the only original pipe is the plastic one going uder and up to the throttle body because at the time no one made an aftermarket pipe I think it wS because of the sensors that clipped into it think from memory theres 2 one temperature and one pressure it does have a recirculating dump valve fitted and he blanked that off at the beginning of the saga

[sdg1970]

I'm assuming it's a very late 98 car if it's ME7? Mine never threw the MIL either, but it's obviously Mojo 4.4.

Keep us updated anyway, would be good to know what the problem is.

[andrewc1267]

Originally Posted by sdg1970

I'm assuming it's a very late 98 car if it's ME7? Mine never threw the MIL either, but it's obviously Mojo 4.4.

Keep us updated anyway, would be good to know what the problem is.

It's definitely ME7 I had the throttle valve rebuilt for him

[andrewc1267]

There's definitely no vacuum or boost leaks does anyone have a vacuum system diagram so I can check that it is plumb in correctly