Boost drops to 0 psi @ 5K RPM in 3rd (4EAT)

[wtdash]

EDIT:

Issue resolved by replacing a collapsing hose between the coffee cup mod and turbo, w/a 90° silicone coupler and piece of metal pipe. The hose got Warm>>Soft>>Collapsed...esp. above 14psi.

Another option:

Back when I first used a TD04 I used a 90 degree coupler to make the air intake work, this worked fine while I was running 12psi.

Later down the road I got an intercooler and a fuel cut defender and raised boost up to 16psi. When I mashed the throttle more than 50% the motor would bog and boost would fall way off. I found that the 90 degree coupler was actually sucking flat at high boost/load (this took 4ever to find BTW). I ended up cutting a 2.5'' piece of pipe at an angle so I could jam it further down the 90 coupler, short side of the angle facing the turbo and the long side facing the intake runner. After I did this I had no more problems and actually ran 17psi a couple times. The best fix is to have a metal 90 welded to the turbo. Remember that a turbo blows and SUCKS!!!

I'm not saying this is your problem but I figure it might help someone

When WOT in 3rd gear (auto) @ approx. 5K RPM boost suddenly drops to 0 and the car stops accelerating - but continues to run fine.

It doesn't sputter or miss, and no CEL.

If I let off the gas and then floor it again, it repeats the process.

If I left off the gas, but only go to 3/4 throttle it'll continue to accelerate and boost stays solid, and pulls to 6K before shifting to 4th.

It doesn't do it in 2nd gear - floor it and boost holds steady and RPMS rise until it shifts to 3rd.

Initially it appeared to be due to the Select Monitor being connected as I'm doing some final testing for the Revtronix chip, but yesterday it did it regardless of whether it was connected or not.


Input appreciated.
Thanks

[Legacy777]

You may need to reset the ECU.

[wtdash]

The ECU was reset about 50 miles ago when I put in the latest Revtronix chip so it could 'learn', but certainly willing to try it again.

[Legacy777]

You said it started happening when you plugged in the select monitor?

[wtdash]

You said it started happening when you plugged in the select monitor?

I can't say for sure it started then, only that I noticed it when it was connected, as that's when I was doing the full throttle runs. And, inititally, when I disconnected the select monitor it worked fine...now it's doing whether it's connected or not.

[tturnpaw]

This first occurred to me when i had the 4eat. After checking nearly everything, (except finding that i was missing the black diag. connectors) i found that both my bypass valve was leaking and recirculating at atmospheric pressure, but also that my boost control solenoid was failing. I disconnected it, and replaced my bypass valve with a supra unit, and voila, no more problems.

mind you, i never used a select monitor or chip initially, and would happen at 2nd gear and above.

[wtdash]

How did you test the BPV?

I suspect the BCS, as well. I have a GM BCS on the way and I'll see if it helps.

Thanks

[skid542]

Todd, I have an extra BPV. It's not from a Legacy but it's a DSM I believe, metal housing. I picked it up from Phil (I think) last year when I thought mine was going out. Where I'm headed, you're welcome to borrow it and see if it makes a difference.

To answer your question on how you test it, I don't really know. Seems that if it holds the pressure at a lower gear it should hold it at the higher gear as well.

[Legacy777]

You can test your BPV by removing it and blowing through it. It should be completely air tight. If you have a vacuum pump you can hook it up to the nipple and as you put vacuum on the valve, it should start to open. It should open smoothly as more vacuum is applied.

[wtdash]

We're finally due for some nice weather this weekend (although skiing was epic today!).

I'll hook up the MBC to see if it's BCS related and test the BPV, too.

I also heard from Mike @ Revtronix that if I didn't properly disconnect the Select Monitor AND restart the car the SM could still affect the ECU, so I'll double-check that as well.

Lee, I'll let you know about the BPV..I've got an extra one, too.

Thanks for the info guys.

[wtdash]

Update:
It didn't occur on the 1st full throttle run, but it did occur on subsequent runs....so it's temperature related?

What does a bad/going bad turbo act like?


The MBC made no difference, so it doesn't appear to be a BCS issue.

The Select Monitor connection isn't the issue - happens regardless of whether it's connected or not.

I took off the BPV and could not blow thru it (either way), but could open/close the valve w/the little bit of vacuum my lungs could apply. (no vac gauge)

If the BPV was bad, wouldn't I still get some boost?

I need to review how a turbo system works, as I don't understand how it could drop to 0.

Thanks

[beatersubi]

It could be something other than the turbo or BPV. But being intermittent, it sounds like it could be the turbo. Check whether it spins freely or has any shaft play.

[Adam West]

Watching.

[wtdash]

It could be something other than the turbo or BPV. But being intermittent, it sounds like it could be the turbo. Check whether it spins freely or has any shaft play.

As this is a major PITA to do, I'll exhaust all other options 1st. (pun intended.)

If it was the turbo why would would it still accelerate @ 3/4 throttle/12-14 psi vs. full throttle 16-17 psi? Would that 4 psi make that much difference?

It does run the full 16-17psi in 2nd gear, just not 3rd gear. EDIT: Does it in 2nd and 3rd gear.

What if the WG is getting stuck open? Would that cause the boost to fall to 0?

[beatersubi]

I'm not fully understanding the symptoms.
It'll reach full boost (16-17psi) @ >3/4 throttle in 2nd gear consistently. And it'll only make up to 12-14psi regardless of throttle postion in 3rd gear and higher.
That, to me, sounds like a boost control promblem. If those are, in fact, the symptoms. You have aftermarket EM?

[wtdash]

I'm not fully understanding the symptoms.

The main issue is that @ full throttle in 3rd gear Boost drops to 0 psi @ about 5,000 RPM. The car continues to run fine, just no boost. If I let off the throttle, the boost comes back, and if I go full throttle again, it repeats.
However, if I only give it 3/4 throttle the car stays on boost (albeit less than @ full throttle) and RPM's continue to climb 'til it gets to about 6200 RPM and shifts into 4th gear.

Thanks

[beatersubi]

How fast are you going when you do this, and where do you do it?

The only thing I can think of is a problem w/ the wastegate or actuator. That doesn't really add up if you're making full boost in lower gears, though.
Have you tried running the stock EM to see if it still happens?

[wtdash]

How fast are you going when you do this, and where do you do it?

5K rpm in 3rd is about 80 mph. I do the testing on a stretch of freeway near me...usually up a hill that's a couple of miles long.

Have you tried running the stock EM to see if it still happens?

No, this would be almost as much a PITA as checking the turbo....replace the MAF/Injectors/etc.

I do have another WG actuator I could try.

I've got 2 BPV's on order (used). I'll see if they help.

Thanks

[Legacy777]

Well.....I think beatersubi may be onto something.

You can try changing all the parts, and if it still doesn't help anything, I'd highly suggest trying a MBC to eliminate the ECU from the picture.

[wtdash]

I tried an MBC a couple of days ago (see above), which made no difference.

I also installed a GM BCS last nite, which also made no difference (I was trying to fix another issue w/the different BCS).


Changing the WG actuator and BPV are easy.

Should have another update this weekend.
Thanks

[skid542]

I wonder if it's a function of the RPM or how long the turbo is under load?

Say you get it up to speed in 4th gear, say 75mph, and then dump the gas and throw the TCU into power mode and get it to downshift. At that point you should be able to pretty much make instant full boost at close to 5k. Will it still drop the boost then?

I'm still just confused why being in 3rd gear would make a difference. The ECU doesn't care what gear the TCU says it's in does it?

Basically I'm thinking that if you're running it up through the gears, 2nd and 3rd, at WOT and then in 3rd it drops the boost then maybe it is the WG sticking.

[wtdash]

Lee,
I think I've read on here that the turbo TCU and ECU don't talk, but I wonder since mine was an NA if there's a connector? I'm using a turbo TCU, too.

I know Josh C. mentioned something back during my EJ22T swap, but since the car ran fine, I never worried about it.

And this issue just started, so I don't think it's TCU/ECU related.

The 1st Revtronix chip I tested didn't have an issue and it started about 1/2 way thru testing the 2nd chip.

It appears to be possibly heat-related (doesn't do it on the 1st full throttle run when car's just warmed up), load-related (heaviest load is in 3rd gear WOT), and/or mechanical - BPV, WG act., turbo (!), etc.

[Bdub]

FWIW, I was having a very similar problem (4eat, vf11, no EM). I plumbed in an MBC and a larger BPV meant for a VW/Audi, and the symptoms have pretty much disappeared.

It felt as if the car wasn't recirculating correctly, because when I hit 3rd the car would just totally stumble, yet it would build boost no problem in 1st and 2nd.

I say pretty much because the 4eat does not ever seem like it is in synch with rev's at WOT.

[wtdash]

Swapped WG actuator....No Luck.

BPV up next.

[Adam West]

I plumbed in an MBC and a larger BPV meant for a VW/Audi, and the symptoms have pretty much disappeared.

I've hear about upgrading BPV and that there's a VW one out there. I've seen it but never found the specs on how much different it is from stock. It is made of metal but features X lbs spring? Did you ever find this out before you went with it? Do share please. Thanks!