Fuel Pressure Up VSV

[Silver MK3]

Hopefully someone can answer some questions I have about the fuel pressure up vsv on my 87 7M-GE Supra. I have been having a hot start/heat soak issue, and I think I have finally found out what is causing it. I think it is the fuel pressure up vsv, because when you start it when it is hot, and pull the vacuum line from the vsv off of the fuel pressure regulator the idle instantly rises and smoothes out, and when you put it back on the idle drops to below 500 and it gets really rough. When the line was pulled off of the regulator there was vacuum in the line. I was able to repeat this test about ten times with the same results every time.

Now here are some questions that I have:

1. I noticed that there is nothing about the fuel pressure up vsv in the online 1990 TSRM for the 7MGE, but in the 87 TSRM there is information. I looked in the Electronic Parts Catalog, and saw that the 89 plus N/A Supras don't have the vsv, and it looks there is nothing attached to the vacuum line coming off of the fuel pressure regulator. So does this mean that the regulator just recieves constant atmospheric pressure, and has no vacuum applied to it?

2. This question goes along with my first question. Would there be any harmful side effects of disconnecting the vacuum line off of the fuel pressure regulator and let it go to the atmosphere, and leave the vsv down there with nothing attached to it's vacuum lines?

3. Instead of needing a replacement ($80 from Toyota), is it possible that the vsv is just clogged and stuck in the vacuum position, and therefore needs a cleaning so that it can switch back and forth between vacuum and atmospheric pressure?

Thanks in advance for any answers,

Gavyn

 

[jetjock]

I doubt your problem is FPU related. It's possible but unlikely. Many people run without it. You should check rest pressure to be sure it's holding. I was under the assumption the GE didn't have FPU but apparently I'm wrong. That said:

Idle will increase when vacuum is removed from the FPR due to enrichment of the mixture.

There's supposed to be vacuum on the line at all times except for about 90 seconds after the engine is started hot.

The FPR must have vacuum for the system to meter fuel properly. It's purpose is to keep the pressure differential across the injectors from changing as manifold pressure changes.

You can test the valve. It's nothing more than a three-way solenoid. However, the valve is plumbed so as to be fail safe ie; to apply vacuum to the regulator when off (or busted) because that represents normal operation.

Does that help?

 

[Nick M]

JJ unfroze a VSV once. There was a post when he mentioned it. It also seems like the VSV is the same for multiple uses. You might try a different unit. Mine died on my 91, causing the problems you have. You could just have too low of fuel pressure.

 

[jetjock]

Yea, that was a coolant valve VSV. In my experience the molded coils on these things tend to fail rather than the valve itself. The filters need to be kept on them though. After going through two I finally gave up on OEM and stuck a $16 sub-miniature industrial grade three-way in there. Never a problem after that.

 

[Nick M]

The other VSV I had fail over 18 years was the for the vacuum reservoir on the 7MGE manifold.

 

[Silver MK3]

Thanks for the reply jetjock. The reason I think it is my FPU VSV is because there is vacuum on the line at all times, including during the initial 90 seconds after a hot start, and that is when I have the problem(during the intial 90 seconds). Also, when I disconnect it during the intial 90 second start up, it starts to idle smoothly. I guess I will try to test it this weekend. I assume I can get to it by just removing the alternator?

 

[mk3mark]

any updates? i have the exact same problem

 

[Silver MK3]

Here's an update. I got the vsv off, and did the TSRM tests on it and it passed all of them. I also checked the connector on the wire harness to make sure it was getting a signal, and it was. The only thing that I did notice about the FPU VSV was that mine had a crack going right down the middle of it.

Is there any chance that this crack would effect the operation of the switch, even though it passed all of the tests in the TSRM?

Jetjock, you said that I should check rest pressure, and Nick, you said that I may just have low fuel pressure. What exactly is rest pressure, and what controls it?

 

[jetjock]

If it passed the tests it's good but that crack means it likely won't for long. One reason I dislike molded coils.

Residual fuel pressure (rest pressure in Bosch parlance) is pressure that remains in the supply side of the fuel system after the engine and fuel pump are shut off. By keeping the fuel under pressure it's boiling point is raised and vapor formation is prevented. Same physics as in the cooling system. It's done to prevent vapor formation from effecting restarts between 15-45 minutes or so after shutdown.

A fuel pressure gage is needed. Jumper the fuel pump on to build pressure then remove the jumper. The minimum spec is 21 psi after 5 minutes. Sans gage one way to see if pressure is bleeding off quickly is to look at the screw on top of the fuel dampener. It stands proud of the dampener body when pressure is present.

Even quicker is to jumper the pump on and build pressure before attempting to hot start the car. If it fires right up when it didn't before then Bob's your uncle.

Which reminds me: To verify if FPU was the problem all you had to do was pop the hose off the fuel regulator.

 

[CyFi6]

If it passed the tests it's good but that crack means it likely won't for long. One reason I dislike molded coils.

Residual fuel pressure (rest pressure in Bosch parlance) is pressure that remains in the supply side of the fuel system after the engine and fuel pump are shut off. By keeping the fuel under pressure it's boiling point is raised and vapor formation is prevented. Same physics as in the cooling system. It's done to prevent vapor formation from effecting restarts between 15-45 minutes or so after shutdown.

A fuel pressure gage is needed. Jumper the fuel pump on to build pressure then remove the jumper. The minimum spec is 21 psi after 5 minutes. Sans gage one way to see if pressure is bleeding off quickly is to look at the screw on top of the fuel dampener. It stands proud of the dampener body when pressure is present.

Even quicker is to jumper the pump on and build pressure before attempting to hot start the car. If it fires right up when it didn't before then Bob's your uncle.

Which reminds me: To verify if FPU was the problem all you had to do was pop the hose off the fuel regulator.

Apparently that idea is completely ludicrous :aigo:

If it doesn't hold pressure it could be causing your fuel to boil in the rail.

You are kidding ...right?
The TSRM calls for rest pressure to be 21 psi or above for at least 5 minutes. Does the fuel "boil" after this time once pressure bleeds off?...what happens to residual heat after 5 minutes? Does it just go away? Come on...get a grip.

This statement is so far out in left field it would be hilarious...the problem is this is the tech section. Keep this kind of speculative crap out.

 

[jetjock]

Hmmm. Dunno what that's about. Not like him. Regardless, we're all wrong on occasion.

 

[mk3mark]

If the rail is not holding pressure... Does the damper or the regulator control it holding pressure?

 

[jetjock]

The regulator at one end and the fuel pump check valve at the other.

Simplified photo: http://www.aa1car.com/library/fuel_pump_diagnose.htm

 

[Nick M]

Jetjock, you said that I should check rest pressure, and Nick, you said that I may just have low fuel pressure. What exactly is rest pressure, and what controls it?

Already answered. Rest pressure is fuel pressure when not running.

 

[mk3mark]

sooo is the check valve what holds pressure in the rail after its shut off to relieve it of hot vapor? is it incorporated into the pump? i have literally the same problem. Ive tested everything from coolant sensor, fuel stuff, did the regulator test and tried a new vsv with no positive results. So its something before the vsv or what tells the vsv to do its job.

 

[jdub]

Hmmm. Dunno what that's about. Not like him. Regardless, we're all wrong on occasion.

JJ - you posted in the thread he's referring to...

Apparently that idea is completely ludicrous :aigo:

Completely different issue in that thread...lets put it in context:
http://www.supramania.com/forums/showthread.php?85039-poor-idle-after-warm-restart

In addition, this is the "complete" post I made:

You are kidding ...right?
The TSRM calls for rest pressure to be 21 psi or above for at least 5 minutes. Does the fuel "boil" after this time once pressure bleeds off?...what happens to residual heat after 5 minutes? Does it just go away? Come on...get a grip.

This statement is so far out in left field it would be hilarious...the problem is this is the tech section. Keep this kind of speculative crap out.

He may be having a fuel problem, but it's not this and it's not vapor lock. Did you notice how cold outside Grim said it was?
I agree, it wouldn't hurt to test fuel pressure, but not for these reasons.

If you're going to take a shot at me, be a man and post complete info. Editing out part of what I really said in a post and completely out of context is simply unsat...and, a cheap shot.

 

[jetjock]

Ok, I see now. That was an interesting thread. Btw nice to see you're still around. Thought maybe you went to the lav and couldn't come back :icon_razz

mk3mark:

1) When the pumps stops the check valve built into it closes and so does the FPR. Those actions trap pressure in the supply side of the system (between the pump and FPR).

2) The ECU controls the VSV depending on coolant temp. It vents the FPR to atmosphere (it turns on the VSV for that) during appx the first 90 seconds after a hot start. Pulling the hose off the regulator does exactly the same thing.

Again if doing that, or even better, jumpering the fuel pump on for a minute or two before a hot start doesn't help you're not dealing with a vapor problem.

 

[jdub]

Ok, I see now. That was an interesting thread. Btw nice to see you're still around. Thought maybe you went to the lav and couldn't come back :icon_razz

mk3mark:

1) When the pumps stops the check valve built into it closes and so does the FPR. Those actions trap pressure in the supply side of the system (between the pump and FPR).

2) The ECU controls the VSV depending on coolant temp. It vents the FPR to atmosphere (it turns on the VSV for that) during appx the first 90 seconds after a hot start. Pulling the hose off the regulator does exactly the same thing.

Again if doing that, or even better, jumpering the fuel pump on for a minute or two before a hot start doesn't help you're not dealing with a vapor problem.

Anything CyFi6 says about me should be immediately suspect - it's not the 1st time he's done this crap.

Yeah, lav breaks seem to be a hazard now! LOL!
I'm still around, just had a bunch of personal stuff requiring my attention lately - thankfully, those are starting to abate

 

[3p141592654]

JetBlue 191 may have an opening for one of you two. :icon_razz

I am confused about this whole thread. Didn't he state in post #1 that pulling the vac line off the FPR caused it to run better? Seems like it could be the FPU, but then all his tests say its working okay??

Here is all I know about FPU

; THA > 60C & THW > 100C or
; THA > 75C & THW < 95C
; command FPU on

So its only coming on if underhood temps are through the roof.

 

[jetjock]

He does say that but doesn't say if the idle later clears up. Even when everything is working right the idle will increase with the line off because it enriches the mixture. I've lost track of the people who pointed to that and exclaimed "See, vacuum leaks do cause idle up on a Type L!"

I shouldn't joke about 191. It's a sad affair and there but for the grace of God. I'll say one thing though...if I was locked out I'd become pretty steamed too.