Resolved - Lost boost and no second turbo

Following on from this technical thread, http://www.mkivsupra.net/vbb/showthread.php?354287-Failed-pressure-tank-and-or-hoses...

Spent a few hours testing pressure tank and associated system and actuators with a mityvac and I think that it’s holding pressure ok.

Looking at one of IanC’s posts on the sequential system faults I wonder if the IACV is stuck open hence not getting anything much on T1 and only getting something at high rpm when there is enough pressure in the system to operate the EGRV.

Anyone else experienced this? Also thought the HKS bov might have failed and just dumping the boost.

Thanks

Jon

Its worth stripping it off and having a look/giving it a clean for sure. BOVs do leak some times so maybe something else to look at, although you'd normally see oil coming out of it.

Looking at the old thread perhaps keeping it in TTC mode and then trying to get the boost solid first would help? You said it dropped off in that mode, so perhaps a boost leak.

You can run with no bov to rule that out and check over all pipework/connections. If you get it boosting well in TTC then you can move on to sequential trouble shooting?

Have a read of this thread, I think as your has been unused for a time, freeing up the valve by hand may help, it's surprisingly hard to move by hand...

http://www.mkivsupra.net/vbb/showthread.php?343594-sequential-issue-and-going-ttc-ideas-please/page4&highlight=exhaust

Thanks Scooter. Lots of good info on testing vsvs there and I’ll do some more testing in TTC.

I’ll be honest I can’t quite work out the operation of the EGBV from looking at the vacuum pipe work. I tried pressurising the pipe which I think goes from the vsv to the actuator and couldn’t get it to hold any pressure, although I’m not convinced I was able to get a good seal on it. Although if this wasn’t working I think I should still see decent boost from T1 under 3500rpm even if the sequential system wasn’t working properly.

As another thought, if the wastegate was stuck open I guess this would prevent T1 from spooling. Managed to test the wastegate actuator and can see the rod operating, but can’t see whether it’s connected to anything or not as it’s buried down in the engine bay

I think I’ll also check the big accordion link pipes

Cheers

Jon

Yes loads to check and I'm no expert at all, but there seems to be a few notable areas of degradation and whilst some might not be causing your specific issues they are probably not optimal so worth sorting as you go.

re the EGBV have you seen this thread?

http://www.mkivsupra.net/vbb/showthread.php?93712-Confusion-over-EGBV-function

Cheers. Just read that and also looked at the Wilbo666 website and saw the actuator on the egbv has 2 pipes on it, similar to the wastegate, hence why I couldn’t get it to hold pressure and operate the actuator and valve.

Am going to spend time next week doing the resistance checks on the vsvs and removing the 2 accordion link pipes and checking the operation of the IACV

Thanks. These posts and the links threads have really helped!

Jon

Something I don’t understand is how the pressure supplied to the pressure tank seems to get T’d off and feed the EBV. If the EBV VSV is normally open, then wouldn’t the pressure simply run through the EBV VSV and back into the air side of T2? Also, I can’t for the life of me find where this T is in the actual system. (Ie the T at the bottom of the diagram under the pressure tank)

Update. Since yesterday I have begun removing bits from the intake pipework and tested the following.

All vsv's show correct resistance and operate as they should with 12v applied.

Turbo link hoses have collapsed so ordered new ones

IACV observed. Closed with no pressure and then opens with pressure applied to the actuator.

HKS bov tested to 15psi and not leaking

Wastegate actuator tested and starts to open at about 15psi. Rod is connected to the external fitting on the exhaust housing (Can't really check whether the internal flap is working correctly, but I can hear 'something' slam shut when pressure is removed, so I assume it's that).

Next steps, once new link hoses arrived is to replace old vacuum pipes and try and get to the pressure tank hoses. The tank seems to hold 10psi and operate the IACV and

EGVC actuators but loses pressure after 10 minutes or so and the actuators withdraw. Have heard of people saying theirs holds pressure over night so could be a problem.

Also want to test the intercooler for leaks somehow.

Further update. Have removed the black metal Spaghetti pipes and removed the small bore hoses to / from the pressure tank and the return hose which feeds the IACV and EGCV has a hole in it. Awaiting some replacement silicon hose which I hope will work ok. Not an easy job to get to these hoses. Taken about 10 hours in total to remove everything (total novice, lol) and test the vsvs so I hope it’s worth it!

A few pictures

Those link pipes are pretty bad so I would imagine will make at least some of the difference, just be methodical with the new pipes so you don't introduce any new issues! I think silicon may not last well (so the hard to access hoses I'd try to use better stuff?), but also this work whilst slow will mean in the future you are undaunted and will be a lot faster.

Investigating anywhere boost can disappear and I’ve taken the reed valve on top of the IACV apart (which I guess allows the prespool from T2 to get to the Y pipe?) and here is a picture. There is a slight gap between the metal plates and the housing which I assume the boost from T1 keeps shut.

Cheers Scooter. I bought some thick sidewall silicon for the 2 pressure tank pipes. Absolute bastard to get back on. In the end I inserted a biro which was big enough to fit over the hard pipes on the car, cut it off and was able to push the pipes on. To be honest whilst silicon probably isn’t best, I don’t think I can get anything else on unless I remove the turbos...

.

Well it'll do the job for now at least, it only been the advice I've seen on here re silicon, but it'll probably last years on a limited use basis (which seems to be all we are doing with them now!)

The reed valve piece I have a couple in the garage I think I could open one up and see but I suspect you are right and that this should be fully closed in situ and looks to have just opened up with age/use/heat cycles.

All back together and tested and the difference is amazing. Replacing the collapsed link hoses means it can breathe so much better and with new pressure tank hoses (and I also replaced some of the 25 year old 6mm hoses) the transition from vacuum to positive boost on T1 is seamless. Am seeing 0.8 bar boost at 3k rpm on T1 and no more issues with T2 coming on line and am seeing 1bar boost rising to a max of 1.2 at high rpm.

Hopefully the silicon hoses will be ok, but well chuffed that for now at least it seems to have been worth the scraped knuckles and cuts and bruises...

Well done mate always nice to get a result first time and not have that one pipe off somewhere etc that leaves you chasing your tail a bit longer!

Those link pipe pics should be a nudge to anyone with an untouched original car to check them out.

Just to add to this incase it helps anybody else. When I bought my supra a couple of years ago off an old boy who didn’t really push it the second turbo wasn’t coming online. I replace as many vacuum pipes as I could at the time and still had the same issue and I think as mentioned above I gave the EBCV valve some lube and manual movement and it boosted perfectly from then on. I think if these valves aren’t actually activating for long periods of times they may begin to stick. And a weakened 20 odd year old diaphragm in the valves might to also add the issue. Sometimes the simple things are the easiest fix