RASALIBRE

Well here’s more info on this subject only involving 80’s Toyota vans that apparently had a very similar TSB.
According to this source what I surmised is not the case. It’s indeed a boiling fuel/vapor lock situation and running higher fuel pressure with the VSV actuated shouldn’t cause any problems.

Super good read:
https://www.toyotavantech.com/forum/showthread.php?289-Is-it-the-infamous-hot-soak&highlight=hot+soak

“I will attempt to explain the issue as I understand it. Since the van is a mid-engine vehicle the engine compartment cannot be vented on top (smoke and noxious fumes in the passenger compartment isn't a good thing). So as a result the engine is sitting under a sealed metal dome. When you shut off the engine, since the cooling fan is run by the water pump, the coolant circulation and the air ventilation go away. Since heat rises it gets trapped there in the dome and cannot escape. If it's a hot day and/or if you've been driving it hard (like going up a steep hill or freeway driving) then there's even more heat getting trapped there. To complicate things, the fuel rail, injectors, pulsation damper, and FPR (Fuel Pressure Regulator) sit right above the exhaust manifold and are covered by the upper half of the intake manifold.

The extreme heat that's trapped there soaks into the fuel rail and depending on the quality of gasoline and the pressure in the rail, the gasoline may boil. The result is expansion and vaporization.......otherwise known as a vapor lock condition. Since there is still pressure in the fuel rail, the regulator will not allow more fuel into the rail until pressure is reduced. The only way vapor/pressure can escape is through the injectors (when you are trying to start). Of course vapor isn't dense like liquid, so there's not enough energy being delivered for your engine to start or run correctly. As the vapor/pressure escapes into the manifold new fuel trickles into the hot rail and immediately vaporizes. When vaporization occurs, volume increases exponentially (expansion) and that keeps the pressure up. This in turn prevents sufficient amounts of fuel from entering the rail. Once started, keeping the engine RPM's up helps because the injectors will vent vapor/pressure faster and allow more new gas to enter the rail. The faster the cool gas flows into the rail, the quicker the rail cools. Once the rail is cool enough to hold liquid gasoline the problem disappears and the van runs normal again.

Because this involves boiling and vaporization, there is a direct correlation between the quality of gasoline and this problem. Back in the 80s this wasn't such an issue because gasoline had a higher boiling temp. Todays gasoline has lots of additives (such as ethanol) and this can significantly lower the boiling point. You can minimize this problem by staying away from the gas that says it has a high percentage of alcohol/ethanol but this option may not be available. It's my belief that gasoline is becoming standardized and brand name doesn't matter much anymore.

So this leaves you 2 other options:

1. Increase fuel pressure in the fuel rail (higher pressure = higher boiling temp)

2. Provide ventilation to your engine compartment after shut-down

I'm not crazy about option #1 because increased pressure = more stress on injectors and other fuel system components (IMO this is more of a safety issue). If and when a fuel system leak occurs, more fuel will leak and your fire danger goes up. That being said, there is an easy way to automatically increase your fuel pressure for only a couple of minutes after start-up. IMO, the benefit of this is questionable because you will only be increasing pressure AFTER the fuel has been boiled. In other words this will minimize the effects of hot soak, but will not prevent it from happening.

There is also a way to permanently increase pressure in the fuel rail, and this makes more sense to me because it's more likely to prevent the problem from occurring. Of course this benefit is off-set by decreased safety.......and that's not to be taken lightly. Fuel leaks in the fuel rail area are not uncommon and several vans have gone up in smoke (sometimes taking other property with them).

Before changes are made, one should understand how the system works. Our FPRs (Fuel Pressure Regulators) have 2 output pressures. When vacuum is applied to the FPR diaphragm it will put out around 30 psi. When no vacuum is present, it will put out around 40 psi. There is a temperature switch on the engine coolant filler neck (vans that came with factory AC). This is a simple on/off switch that's triggered by coolant temp. The switch is normally open but when coolant temp hits 230 deg F it closes and grounds the wire going to it. That wire is attached to the ECU (Electronic Controlled Unit). Each time the van is started, the ECU monitors that circuit and if it detects a ground condition it activates the EFI VSV (Electronic Fuel Injection Vacuum Switching Valve) for a period of about 2 minutes. When the EFI VSV is activated, it shuts off vacuum to the FPR and vents the FPR diaphragm to atmosphere. With no vacuum, the FPR holds pressure at around 40 psi. After about 2 minutes, the ECU turns off the EFI VSV, vacuum returns to the FPR, and pressure returns to around 30 psi.

The existence of this system tells me that Toyota realized the potential for heat soak, but miscalculated the activation temp (of course the changing fuel market is partly to blame). Later on when heat soak became a bigger issue Toyota issued a service bulletin (TSB #E020). Part of that bulletin requires mechanics to replace the 230 deg F switch with a much much lower temp 140 deg F switch. The lower temp switches were only available for this service bulletin campaign (see PDF file attached to this post) and are now NLA (No Longer Available).

If you think about it, the normal operating temp of the engine is about 185° - 210° F so this means the new switch will activate the "pressure up" mode of the fuel injection system almost every time the van is started (unless the van has had over an hr to cool). Because of this, I think it's reasonable to assume it wouldn't hurt for the "pressure up" mode to be activated on every start (including cold ones). This can be easily achieved by simply cutting the wire off of this sensor and attaching it to ground.

To permanently increase pressure, there are several ways this can be done, but probably the simplest method would be to disconnect the vacuum line from the FPR and plug it to prevent a vacuum leak. I wouldn't put a cap on the FPR port because you'd want the diaphragm in there to breath. Again, I don't recommend this, but I'm providing the info to help create a better understanding of these issues.

Personally, the remedy I like best is the "ventilation after shut-down" method. I'm using this method (and this method only) on my van and I've been happy with it. A side benefit to this ventilation is increased life span of rubber seals, rubber hoses, and other sensitive parts (due to reduced temps in the engine compartment). I've heard other guys talk about opening their hoods each time they stop or using computer fans and ducts to ventilate small amounts of cool air into this area, and I don't disagree with the success of such methods, but who wants to have a super heated and/or smelly cabin on a hot day? As for the small fans and ducts, there's already limited space here and access to key areas is already tough enough. That's why I chose to install electric cooling fans on my radiator. I built a shroud and installed (2) 10" high output electric fans on the back-side (engine side) of my radiator. I rigged them up to be thermostatically controlled and wired direct to the battery (so they have power all the time). I got an adjustable t-stat with a submersible probe, put the probe into the extra 16mm port near the front of the head, and set the t-stat to come on at 200 deg F. Now whenever the coolant temp is 200 deg F or above, the fans will run (doesn't matter if the ignition is on or off). This has worked out great for me and completely solved the heat soak issue.

The fans do come on and run (on and off for about 20 - 30 min after shut down), but they eventually stop and I've always been able to restart the van easily.

I just realized this is a pretty long winded post so I'll stop here. If anybody is interested in pictures or more details, please ask and I'll be happy to answer questions and/or post pics/schematics. Tim

PS: Installing an 89 FPR will help, but only slightly. I probably wouldn't replace an earlier version just for this benefit, but if it needed replacement anyhow, I'd definitely go with the 89 FPR. FWIW, normal operating pressure of the earlier FPR's is 27-31 psi and the "pressure-up" mode is 33-38 psi. 89 FPR's normal operating pressure is 30-33 psi & "pressure-up" mode is 38-44 psi.”

jjswenn

I read this entire thread and still do not see a clear fix. People like to tell me that, “it runs, it has good power, lots of power, what’s the problem?“ Well, the problem is that I know damn well Toyota wasn’t selling these vehicles in the 1980s and 90s operating in this manner (yes, I’m aware of the TSB about the temp switch replacement, which is for older models). When you’ve spent the time and money I/we have, and you’ve done things right the correct way, you expect things to work correctly.

I’ve been dealing with the what seems is the exact same issue for over 8 years. I bought the truck nearly 10 years ago. A new cylinder head from Yota1 Perfomance, along with head gasket and timing kit we’re done around 4 years ago. Most recent work involved an entire long block, done two years ago. I’ve gone through all the same troubleshooting and replacement of parts that you list here, it’s nearly identical. However, in addition to the parts list and diagnostics you list, I’ve also done the fuel pump, fuel injectors cleaned, filter, fuel pressure regulator, have the LCE fuel pressure testing kit for CSI (pressure in spec in ALL conditions), Coldstart time switch, engine temp switch (for the ECU), big bore t body from LCE, new Idle air control valve, tested and swapped airflow meters, new tps, new O2 sensors (California emissions), egr is deleted correctly, and the only vsv I have is for the fuel pressure regulator, and I’m sure there’s more, but finally, yes, I did indeed swap ECU’s. Yet still I have a heat soak/hot start issue, with low rough idle, and a buttery smooth cold start idle. Ive also had experts (22re Perfomance) tell me I need to reinstall my emissions crap – EGR, vsv’s, etc.., but the truth is, that this problem presented well before I removed/deleted that equipment. Removal was done to attempt to fix this problem.

Now, all of these parts that were replaced our OEM/Denso/AisinToyota parts. Not to say that I did not used O’Reillys/AutoZone parts throughout this long voyage/period, but those have either been removed or returned and replaced with OEM Toyota parts. Still have issues..

Let me be clear, I’ve used this truck to commute, get groceries, drive halfway across the state of Washington etc for ~10 years., and the truck has never let me down. The motor starts and runs every time I hit the key. It just runs with the low rough idle on heat soaked conditions. It doesn’t matter what time of year it is how much rain there’s been snow etc. elevation blah blah blah.

Finally, I’ve been reading Yota tech posts for years (obviously given my dilemma), many years, but I’m very new to posting myself. I saw this thread, realized the similarities, and thought that I better comment. My 1986 22re 4Runner runs like a champ. I installed the head and timing kit on that one as well. Never a problem. So, short of driving the 1995 off into Puget Sound, I have no other ideas. I thought for some time that it’s possible the cold start injector is spraying, flooding the engine even in hot starts. But all the components test out OK (new time switch, temp sender, and swapped the injector itself), can’t win.. Like I said, it fires and runs every time, just idles like crap when hot.

PS- I have also replaced soft fuel lines underneath Including inline filter on return line- it’s there if you feel around enough..), have a resistor in the egr temp sender (no codes), replaced the pick up coil in the distributor, cap, rotor, plugs, wires (all denso, Toyota,or NGK), messed with various exhausts and cat converter (LCE header etc), air filter, messed with the airflow meter (both the wheel and screw), and have my pair valve removed. Swapped various igniters/coils (spark is good).

Thanks

JJ

scope103

You have a Fuel Pressure Up system (FPU), that is intended to address vapor lock. http://web.archive.org/web/201501160...ne/41fuelp.pdf When the engine is warm, it connects the FPR to atmospheric (instead of manifold vacuum). This raises the pressure in the rail, which I guess deals with vapor bubbles in the line. Could yours not be working? Could it be open too long (running rich when warm)?

This is sorta a long-shot, but testing it is trivial. Just get a 1/4" male-male vacuum adaptor, and "jumper" out the FPU VSV. If that clears it up, your FPU is open too long (or the wrong time). If that does nothing, when you have a hot start problem pull the adaptor apart (putting atmospheric into the FPR). If that clears it up, your FPU is not opening when it should. If neither of these do anything, you're out the price of a plastic adaptor.

Paul22RE

Co_94 brought up an interesting point in another thread. Anybody that is having rough hot starts running a higher octane fuel?

jjswenn

I’ve heard a lot about different fuel and octane, and over the course of 8 plus years have put every octane rating and ethanol free fuel you can find, never noticing a single difference other than ping tolerance while under high load.

Something else I hear a lot of is the removal of the EGR and air injection system, speaking in terms of the change/increase/decrease in heat/thermodynamics impacting behavior. I’ve done both of these, one and not together, and experimented off and on with it over the years, never seen a single difference improving low rough idle at hot starts.

jjswenn

So, this thread has died out a bit in the last few months, and I thought I’d provide an update during these unprecedented times (as it’s a good time to wrench).

I just installed LCE’s pro flow cat-back, replaced my dented csf 3 core rad (which is detailed in another thread), and put in Energy Suspension’s body mounts (an upgrade I highly recommend), wow, what an improvement those bushings made..

Something else I’ve messed with in regards to the low, rough hot start, is the fuel cap. I noticed a bit more pressure in the fuel tank at fill ups as compared to my 86 22re 4Runner (which never makes the “hiss” sound at full ups/removal of the gas cap). So, I swapped the caps around, eventually drilling a small hole in a cheap older moto rad one I had around. Ironically, there did seem to be a difference (keep in mind I have swapped and cleaned my charcoal canister several times over the years). Now, the problem didn’t fix or resolve, but there was different behavior..? It seems that with a good functioning cap, that on occasion my truck would not fire right away when very hot and soaked. I’d crank her excessively until she caught fire and sputtered into running.. a couple feathers of the pedal and she would run fine and off I’d go. I swap back to the over-vented cap I drilled, and she never has the hard start, but still has the rough hot start issue. In addition, I’ve noticed that when searching O’Reillys, Napa, Autozone, Rock Auto etc, that many list a non-venting has cap as a/the correct part given the year, make, and model, which I find irritating and confusing. So, which is it, venting or non-venting cap? When? Why??? I believe that the injected 22re is supposed to have a vented cap, and carbureted 22r should be non-vented, but I could be wrong. Finally, I’m currently running with my FPR vacuum line directly plumbed to the upper plenum (per 4 Crawler), no real difference observed there either (from experience, I could reinstall the switch and not see any difference). Lastly, I mentioned above that I had swapped in a “new” TPS, which is not true. I have swapped in numerous sensors pulled from the yards that tested 99% good (reading good on every test but the VTA-E2 which was ~ 0.45 kohms when >0.47 is good etc), and tried the Chinese crap from O’Reillys (computer threw a code for TPSa day later even though it was set and installed correctly, and so I removed and returned it). With that, I decided to buy a brand spankin new TPS that should be here June 15 (currently it’s June 12). I’ll set it to spec and we’ll see what that does. That is where I’m at. I don’t expect to see any fix with the new sensor (as not ALL 4 sensors I’ve popped in over the years from the yards can be bad), but it’s something I’ve always wondered about. Plus, it is one of the most important signals the ecu reads.

Lastly lastly, I noticed awhile back when replacing my IAC valve (as stated above first with an O’Reillys crap then with an Aisin oem) that some are stamped with different letters (an 1-A or 2-A or something like that). So I wondered if there could’ve been more than one version (set with different valve opening tolerances) of the late model IAC valve? Does one ecu get a certain IAC and so on.. based on emissions or model? I’ve searched and never found any evidence in the literature or forums. Let me know if I’m incorrect, please. Thanks

2ToyGuy

Given that the EFI fuel system is under a lot of pressure when running correctly, and my nearly 30 years experience with my two trucks, for what it's worth, the 22R has got a vented gas cap, and the 22RE is not vented.
I replace the gas caps every year, as the FSM recommends, with OEM caps from the dealership here in town, and my 4Runner hisses when I go to gas up, but the pickup, with a 22R, barely makes a sound, if any at all.

Just my experience with gas caps...
Pat☺

scope103

All gas caps are vented. They let air in, but nothing out. They let air in to keep the fuel pump from crushing the tank (figure that just 1 psi of vacuum translates into over 1,000 pounds of crushing force). The don't let fuel vapors out (a really big source of air pollution), and utilize the evap system to handle the vapors.

If you hear a "whoosh" when you take off the gas cap, that's because the fuel is low (which is why you're in the gas station in the first place) and the temperature is warm. Vapor has built up in the tank, and you're just getting ahead of the evap system when you remove the cap. The sound is fuel vapor escaping, not air sucking in.

jjswenn

Hey Pat, I appreciate the reply and information. I thought I had that EFI v. carb cap thing confused, and I suppose it really makes perfect sense given each system’s dynamics. My next question is what the “vacuum only” means on caps? I searched a tad online, but didn’t get a good parameter or answer.. The tps arrived early and I installed it tonight. I’ll pop my new-ish oem cap I have on and see how it acts the next few days without a massive vent in the cap.

2ToyGuy

I am not sure, but I think it might have to do with the way the two systems are designed. The 22RE system draws air in through the charcoal canister as the fuel, and of course the tank, cool off. Whether due to weather, driving and stopping, or whatever. I am not sure that the 22R does it that way, and the FSM isn't very specific about it.

It may also have to do with the 2 different fuel pump systems. Since the 22R fuel pump sucks fuel from the tank, and the 22RE pressurizes the whole fuel system, it may have to with the 22R's sucking. So to speak
May be to provide intake air if there's no enough coming in through the charcoal canister.

I'm likely wrong, though. This is certainly not my specialty...
Pat☺

scope103

Here's the ('93) FSM for the 22re EVAP system: http://web.archive.org/web/201109110...17evaporat.pdf As the tank cools off (and creates vacuum), air is pulled in through the check valve in the fuel tank cap (not the canister; the check valve there is closed). When the fuel tank warms, the vapors open the check valve in the canister, to enter the canister and get adsorbed. The check valve in the fuel tank cap is closed with pressure (vapor) in the fuel tank.

Apparently, some manufacturers (not Toyota) call for a high-pressure relief on the fuel cap. "This allows an escape path for pressure in the event of an impact situation where the fuel tank has collapsed."http://www.stant.com/index.php/engli...ent-fuel-caps/ Toyota doesn't call for such a cap, so apparently some after-market manufacturers label them "vacuum only." They vent in (when the fuel tank is at partial vacuum) only; they don't vent out.

2ToyGuy

Thanks Scope!
I knew someone smarter than me would have the answer(s).

Pat☺

jjswenn

Yes, it makes sense now.. Thanks. I’m also going to swap my fuel caps, putting the new oem cap I have on the 95’. We’ll see how it acts. When installing my new tps, I noticed that the resistance was virtually the same as my old sensor. I went ahead and installed. I only drove a short distance last night, but I did notice a slight difference at hot start, with the rpm’s popping right up into a smooth idle at ~800. Something else I should mention.. is that when I installed the new long block about 1.5 years ago, I did order the motor with an RV cam from Delta Camshaft here in Tacoma. A 272 cam with .431 intake and .431 exhaust valve lift. So, I’m not entirely sure I love this cam and the way it idles. Changing it may resolve my dismay with idle and hotly starts. Anyone know of a descent cam I might try? Engine builder? Specs?

jjswenn

Update: So I started experimenting with removing vacuum from the fuel pressure regulator at hot starts, and this seems to fix the problem completely. This would lead us to believe that the VSV is not receiving the signal at hot starts opening to atmosphere. I even had someone crank while looking for voltage when hot, nothing there at the pigtail. There is 12 V present when I physically ground the Black negative probe anywhere off the pigtail, so I know I have power, but the ecu is not completing the circuit to ground when needed. The solution: (a solution): I read in another thread how a guy wired a switch into the cab to complete the circuit manually on hot starts. So, that’s what I did yesterday and it seems to be working wonderfully. Of course, time will tell and I will update when I have a larger sample size (more tests). By the way, my 1995 does not have a switch at the thermostat housing, just the blue vsv for pressure regulation, and so the vsv signal is the one I tapped into, enabling myself to complete ground circuit via toggle switch. Thanks

scope103

When testing with a multimeter you can't ... get ... nothing. You can get 250 ohms or 300ma or even 0.00 volts from Pin 1 to Ground, but you can't get nothing.

From your description, I'm guessing your partner was looking for voltage from pin 1 to pin 2 of the FPU VSV connector on the harness side. He got a very low (less than 1volt) reading. You may or may not have "power," but your multimeter can't measure power.

On a '94 3VZE, the FPU VSV has W-R to ground, and G-Y to switched battery at the ECU. It's switched-supply, not switched-ground as you are inferring. So if you have battery voltage from either pin on the harness-side connector to ground with KOEO, you have a problem. Your problem was originally described as over-rich, which could be a sign of an always-on FPU (where you might find 12v to ground on G-Y).

If you're happy with your manual system, just hang onto it. You don't need to fix what's not "broken." But if not, you could follow the procedure for testing the VSV. http://web.archive.org/web/201501160...ne/41fuelp.pdf (this is the link I provided to you earlier). If the VSV meets specs, you might want to test the signal to the VSV. For that, you'll want to measure voltage to ground on each pin, with key-off, KOEO, and cranking. (Don't forget to note your estimate of ECT.)

jjswenn

Hey scope,
I have used those procedures to check my VSV numerous times, it always passed the test. I see what you’re saying about switched supply versus switched ground. For some reason the VSV is not being activated when necessary. I chose to put a switch on the ground side only because when I put a meter on the VSV, I could see that when the key was on I had 12 V at the valve, so long as I completed the ground somewhere manually (negative probe to body/neg terminal), and at all temperatures as well (as I checked several times over time). So, what problem does this tell me I have, if I always have 12 V at that VSV with the key on, which shouldn’t be possible given switched supply, activated by ecu/water temp switch..? To me, with my limited ability, manipulating the ground side seemed to be the simplest way. By all means, if somehow the information I have here enables you to figure out the issue, please let me know or what I should test next. It would be pretty easy, and PREFERRED for me to repair the wire I cut where I installed the toggle switch, if we figure it out. I’ve swapped computers and tried everything within my abilities, nothing seems to work. Also, I have numerous VSV‘s of every kind on hand, and have gone that route as well (swapping in and out). In any case, after testing for two days now driving around, hot starting the truck numerous times, I can say definitively that this fix has solved the problem for me. I can actually see my RPMs go up or down depending on whether I have completed the circuit via toggle switch. It’s working wonderfully. Even so, I keep going back to the fact that I have all of my emissions and VSV switches deleted except for the fuel pressure regulator VSV. I keep asking myself if it’s possible that removing all of that stuff may be causing my problem, despite the fact that I have found a way around it and solved the issue. However, and it’s been many years of dealing with this issue, I really want to say that the problem was there well before I removed all of my emissions and other VSV’s, yes, I’m sure of it. I tend to be a bit of a purist, and would not of gone this far removing things have the truck been behaving correctly.

Picture of my vacuum line and emissions diagram.
For me, I know there has to be a solution or reason for this problem. I know there has been TSB’s for older model 22re’s water temp senders, so Ive checked around, but never found a replacement for this late model of a temp switch (which I also replaced with a new one from Toyota). I’m always up for solutions and tests, so let me know please. Thanks again scope!!

Co_94_PU

iTrader: (-1)

The first gen 22re has switched ground on this VSV, yours may also based on your readings it does get its power from the efi relay.

Is your TSW, on top of the thermostat housing is you have one, switching? If so at what temperature? (I know this sensor isn't present on my 94 2wd..) (You could try throwing a variable resistor in place of the ECT/THW and seeing if you can trigger the ecu to ground the vsv? This can be compared with the temp scale and give a temp it triggers at.)

Blueman

My '87 with 22RE picked up this behavior as soon as the switch to gasohol was made. Try some non-ethanol fuel and see if the problem persists. I saw the same issue appear at the fuel transition time in my V4-powered motorcycle as well.

For both vehicles there's a window of time in which restarts are difficult, but then it passes.

jjswenn

Unfortunately I live right down the road from gas station with ethanol free, it does this with ANY fuel I use. Remember, as pathetic as it sounds, I’ve been at this for ~7 years, maybe a touch longer. No, my truck doesn’t have the TSW on the thermostat housing, it’s smooth and original (never did have it). So far, the switch to ground is working wonderfully. But I’d still love to know why this happened. Let me know if you find something to test or try. Thanks

jjswenn

PS-
Is it possible, at all, and this may be a somewhat stupid question.. that I have the wrong EFI relay in my truck? Would it still function at a/some level, but not enable the FPU system to function correctly? I know there’s something! Another culprit I’m suspicious of is my alarm. Foolishly, I had car toys install an alarm way back when (circa the time I started noticing issues). However, at the time my knowledge was even more limited than it is now, hence, paying someone to install the alarm. I plan to remove their rats nest mess they made soon.. I’m more curious about the EFI relay though, so help me out if you can. I’ll provide a picture ASAP, when my phone charges.