Advice for hesitation at 6k rpm

[Ben]

Hi guys,
I recently picked my sw20 rev 1 turbo up from the mechanic after getting my distributor rebuilt. I was pretty happy because after the fix (it was leaking oil) my idling issues went away. Between this and getting my injectors cleaned some time ago my car felt like it was brand new with how it came onto power. However just tonight I put in half a tank of Mobil 98 after the car's boost gauge seemed to be playing up a little. (It was creeping up when on very mild throttle in fifth gear, say going from 75 up to 80kph on the motorway and then the gauge saying 50% boost while the turbo made no noise.) I found that after the BPV is a weird cylinder, with small - 50 cent piece size - paper filters that connects by hose to the intake manifold, had come apart. I cable tied it together as a temporary fix and the issue above went away, although when i floored it in second gear it felt like i was hitting a fuel cut at 5600 to 6500 rpms intermittently. It did this when my injectors were bad but hasnt since i had them rebuilt. Is the BPV (boost bypass valve) the likely culprit for this hesitation or should i be looking elsewhere? Knock sensor? Fuel quality? Fuel filter (replaced 10 thousand km ago)? New spark plugs? Any help would be greatly appreciated,
Thanks
Ben

[Benckj]

The small filter by BOV is called a VTV which stands for Vacuum Transfer Valve, I believe. It controls the amount of air bleeding through for BOV operation. Most likely this is your issue as the BOV will not hold boost correctly if the VTV leaks. These little control valves are no longer available from Toyota but there is a procedure in BGB on how to test.

As a trial you could simply pinch off the vacuum line which will disable BOV from opening. Many of us run with it completely blanked off so it’s fine to test.

[Jabeo]

Could be a multitude of things to check. If using the stock boost gauge, my advice is to basically ignore it, it doesnt offer any useful info at all. Based what you have described and personal experience you could clean all the engine bay grounding points (this fixed a bogging hesitation issue i chased for a long time). This could also be related to a faulty ecu coolant temp sensor, which is known make the ecu think the engine is colder than it actually is, causing it to run a bit rich and bog and break up at around 4500 - 5000+ rpm.

Old leads can cause a misfire, as well as plugs that have gone bad. If your dizzy has been rebuilt, could be that ignition timing was not set correctly when the dizzy was installed so it is not firing when it should, this is also quite common

[Ben]

I haven't had a chance to look at it again since last night. Thanks for the advice. Is there a way I can block off the VTV but keep the BOV? What size plug or fitting would I use? And which is the coolant temp sensor? Is it the 'switch' that screws into the radiator halfway up on the driver's hand side?

[GDII]

The purpose of the VTV like Jim said is to limit air movement through the valve. It goes fast one way and slow the other. I think I made a post on Instagram about how it worked when I did a write up on the GEN4 3SGTE.

Here it is!
https://www.instagram.com/p/CEfxAG1nf6c/

Coolant temp sensor is the green sensor on the coolant tree on back of the head. Should be facing forwards.

[Ben]

I tried to repair the valve with super glue and no success there. However the problem seemed a little less severe. I've ordered a new one as well as that coolant sensor; so I'll see how I get on after they get here early February.

[GDII]

That broken valve can be bypassed. All it does is slow the air movement out of the bottom of the BOV. Run a vacuum hose from the T to the bottom of the BOV to test if this is really the problem.

[Ben]

I have gotten a bit stuck.
I replaced the vacuum transfer valve with a new unit, took it out for a drive, car seems a little happier. However the boost gauge in the dash is misbehaving just as much as before so I don't want to thrash the car too much to work out if that has fixed the problem. Today I went around trying to find some suitable vacuum line from repco, thinking that the tired lines around the valve must be leaking, as I only had an issue after finding my old valve broken in half. So fitted those and plumbed it up to the car and still having issue with the boost gauge. Had a brief look in the engine bay to see if there is some hose (from the parts diagram for vacuum lines on the motor) and nothing immediately jumps out to me as being wrong. Not saying that there isn't an issue with the lines; I am just not confident finding it.

So the symptoms I am having are:
-key on, without starting, boost gauge two thirds full.
-car idling shows no boost, all good there
-boost gauge climbs early and disproportionately to how it used to when it functioned properly
- at 2500 rpm in fifth gear I can get it to go the the 12 o'clock position with half throttle.

I want to get my gauge working again as it was before my vacuum transfer valve broke. Any help is appreciated.

[GDII]

My advice is to bin or ignore the factory boost gauge and get a real one. I have watched the factory gauge vs a good gauge as the car comes on and off boost and at 5psi it still shows full vacuum and it's increadably slow to respond to what is really happening plus is has no numbers. I would not rely on that for any testing to find this problem.

I'm not sure what your problem is exactly but I can assure you it's not the gauge. It takes its electrical signal from the MAP sensor of which is only there for boost cut and the gauge. It does not control fueling.

[4CylinderSpecial]

If you want a stock looking solution then you can get small 45mm boost gauges that go in place of the stock one. You can see my one in this section (halfway down). https://mr2.org.nz/forum/viewtopic.php? ... 4&start=30

The stock gauge is useless and is at best a way to indicate that you are hitting some sort of boost