68jimmy

I recently picked up a very clean 1989 SR5 with the V6 and noticed that a couple of the VSV solenoids on the passenger fender well were missing what I would call a 'breather'? The other two had the breather, although it was pretty ratty looking, is this breather something that can be purchased from the dealer? Do I need them? Do I cap off the nipples where they were?

Thanks in Advance,

donovan

snobdds

They're not needed. I broke mine on the fuel pressure VSV and just ran with it for a while. Then I got sick of it looking broke and just ran vacuum directly off the manifold and did away with the VSV. No difference in driveability.

scope103

I don't know much about the 1989, but the '94 has four VSVs, plus two more for the ADD. The PAIR, EGR, and Fuel Pressure Up (that's the one snobdds is talking about) all have "breathers."

I doubt you'd be able to get them separately. You could probably get by without them, but they do keep dust out of the PAIR, EGR, and FPR. Consider fabricating a "breather" out of some foam.

The Fuel Pressure Up counter-acts vapor lock. Snobdds probably doesn't live where it gets hot enough (and he doesn't use the appropriate driving pattern) to suffer from that.

68jimmy

Thanks, I'll search the u-pull-it yard and see if I can find a couple...

d.

RAD4Runner

Snobdds,
Are you talking about the VSV for fue pressure regulator like I did
here?.

I did it in the process of troubleshooting my intermittent hard-starts (lots of cranking before combustion happens). Hard-starts consistently went away. Concerned about possibility of above (vaporlock, is the term, correct?), I put it back in stock configuration, and somehow the hard-starts stopped happening. Waiting for my fuel pressure gauge for more objective monitoring, to see what really fixed it.

I hope I'm understanding it correctly as follows:
(1) With engine cold, VSV connects FPR to manifold vacuum.
(2) With engine above certain temps, VSV disconnects Fuel Press Reg from vacuum and lets it breath atmospheric pressure.

My question is:
Doesn't connecting to vacuum when cold also mean lower fuel pressure? Why would we want lower pressure when starting a cold engine?

scope103

Specifically, I DON'T know those answers. Here's my best source (page 9) http://www.cygnusx1.net/Media/Supra/...taTech/h22.pdf

I suspect there is more to stopping vapor lock than just hot/cold. But other than that, yes, when the ECU calls for Fuel Pressure-Up it does it by connecting the FPR to atmospheric, which raises the pressure set-point.

Note that the ECU has several ways to enrichen the mixture. On (cold) cranking, the CSI just squirts extra fuel into the plenum. During open-loop warm up, the ECU can raise the mixture by increasing the injector open-time. During WOT, the ECU ignores the O2 sensor and uses the internal map, which is probably richer than the O2 sensor would indicate.

With the Fuel Pressure-up, it raises the pressure not just in the rail, but all the way back to the fuel pump. Vapor lock doesn't usually happen in the rail, but in some narrow passage (fuel line) near something hotter (the exhaust manifold). Presumably, a little extra pressure may exceed the partial pressure of gasoline vapor at that point and squash the vapor bubbles.

Last, I wouldn't be surprised if the ECU were smart enough to start Pressure-Up in the correct conditions, but then lean out the mixture back to normal by adjusting the injector open time. But I don't know.

Pretty fancy for a 25-yr old control system!

snobdds

The way I understand it, when the engine is warm, the fuel can go from a liquid to a vapor in the fuel rail, which makes it hard to start warm. The fuel pressure regulator raises the pressure in the fuel rail making it harder for the liquid fuel to vaporize. The VSV just gets a signal from the computer that opens the valve and sends manifold vacuum to the fuel pressure regulator to up the pressure. I just bypassed the VSV and ran a length of vacuum hose from the manifold directly to the FPR. I did leave the valve in place with the electrical connection hooked up so the computer can still send the signal. The breather, Toyota calls it a Filter, just relieves any extra pressure that may be left in the hoses.

I have actually bypassed my PAIR VSV as well and it doesn't change the way the motor runs either. If Toyota just kept making the part I would just buy new VSV's, but there discontinued now and I suspect most people will need to bypass them eventually.

RAD4Runner

Thanks a lot for the info, Snobdds and scope. And great pdf/link to help us understand the fuel system.
Merry Christmas to all our Yota bros and sis!

scope103

Other way around. "Usually," the FPR connects to manifold vacuum, so that the rail pressure is always a constant amount above the manifold pressure. (The manifold pressure changes with throttle position.) When the VSV opens, it connects the FPR to (higher pressure) atmosphere; that raises the FPR set point and raises the pressure in the rail. Bypassing the VSV just leaves it in the "usual" mode all the time.

The breather/filter is the connection to atmosphere, so air goes IN the filter when the VSV opens. The filter just keeps dust and dirt out of the FPR and its vacuum lines.
The PAIR is just for emissions, and it's one of the few emissions components that is strictly downstream. So I wouldn't expect it to affect the way the motor runs, but you're increasing emissions. It's a check-off item in California, so without it you shouldn't be able to pass smog (regardless of tailpipe numbers)

RAD4Runner

Understood.
4Crawler also did the "usual".
I wonder why putting it it the "usual" position (=lower fuel pressure) seemed to fix my hard-starts. Will have to monitor further.

Thanks again, Scope103; Really appreciate you sharing your knowledge and experience.

Snobdds,
Did you do yours to fix starting issue or just because you did not want to bother with the parts? Tnx for sharing your experience, too.

scope103

It's possible your FPU VSV was stuck open, so you were trying to start with it too rich (the ECU richen's the mixture at start anyway by fiddling with injector open time, but if it was done "twice" it's going to make it hard to start.)

But I'm only guessing. As you know, there are about 1,000,000 possible causes for hard starting. Stick with what works.

By the way, take pix of your fuel pressure gauge installation when done. Everyone is always advising "put a gauge on it," but I know it's not trivial.

snobdds

The VSV is not a mechanical switch, and does not get it's feedback by pressure. It is actually an electrically controlled switch that does get it's feedback from the PCM, albeit very simple feedback. Hence why there is an electrical connector on the VSV. The breather / filter does not suck in any air, it acts more like a release valve and blows off excess vacuum out the breather.

RAD4Runner

Understood that part. Thanks!
I still have a question:
Snobdds,
Did you do yours to fix starting issue or just because you did not want to bother with the parts? 4Crawler and others did same. Tnx for sharing your experience, too.

In order to release vacuum from FPR system, it needs to backfill with air, so it has to suck IN air, albeit little; Yeah, just a matter of terminology
Cheers!

snobdds

I bypassed the VSV on the Fuel pressure regulator just because I broke off the filter part of the VSV. So I bypassed the VSV with a direct run of vacuum hose from the intake to the FPR. I kept the electrical connection in tack so the PCM still sends the signal just to prevent any feedback issues.

I did not do it for any starting issues.

RAD4Runner

Thanks, Snobdds!

macmanboomer

How can I tell the difference in the different VSV's & where vacuum lines should run? The only schematics & vacuum line diagrams I've found are very vague & you can't tell which one is which. Can someone point me in the right direction?

Edit: 1994 pickup with V6.

scope103

http://web.archive.org/web/201403271...74layoutan.pdf

It helps if you tell us where you are starting from. Is everything in show-room condition, and you're just curious? Someone went nuts and pulled out all the vacuum lines and electrical? You're building a truck from scratch?

macmanboomer

I'm helping a buddy at work with it. Someone changed the engine & I believe haphazardly put vacuum lines just wherever. Some are missing, some are hanging loose, etc. I need to approach it like starting from scratch since I don't know if any of it is right or not.