Hello everyone. Looking for opinions on where I should be looking on this hot start issue I have been having with my 94' 4runner 3VZE 4WD Auto.
This truck starts like a dream when it's cold out. The problem I have been having is after it's been warmed up, then shut off and sitting for about 30 minutes.
After that sometimes, and quite frequently it will start but idle really rough and sometimes die. There is also a strong smell of unburned fuel from the exhaust while it's trying to idle.
It seemed like when this first started happening I could simply turn the engine off and then quickly restart it and the engine would idle smooth and not die. That made me think it may be a poor electrical supply through a set of relay contacts.
Well lately the quick cycle of the key switch and restarting does not clear the problem. The other day I was going through a drive through and when I went to pull out onto a main street the truck died on me and left me sitting there cranking it trying to get it running good enough to get it in drive and get the hell out of the way of oncoming traffic. That took me about 5 restart attempts before it cleared its throat enough to let me get it in drive and out of the way.
That was the first time it ever just up and died on me, and it hasn't happened since. Replaced distributor cap and rotor about 6 months ago and no help with the issue but they needed changed anyway.. I have a new set of ignition wires on order.
So now I'm leaning toward checking fuel pressure. I replaced the FPR about 4 years ago and it was definitely defective. I'd like to hook up the fuel pressure gauge and somehow get it routed up where I can see it.
Other thoughts:
1. Warm the unit up and wait for the hot start issue to occur again and check the fuel pressure gauge.
2. Either that or maybe my CSI is stuck open and leaking fuel.
3. I also read something about the possibility of the AFM flapper being stuck closed occasionally.
4. Maybe I'm losing the proper amount of voltage to the coil?
Thank you!

 

It could also be the VSV that controls the vacuum line that's attached to the top of the FPR. During a heat soak condition, IE: trying to start again when the engine is hotter than normal due to "heat soak". It happens when the truck is fully warmed up, and then shut down, and lasts for a short period of time, until the engine cools down naturally, or is started, and the cooling system begins to function again. You can see it when you first turn the key to On, just before you go to Start. The temperature gauge will rise well above the normal operating range. It's a perfectly normal condition.
The ECU senses this condition through it's input from the engine coolant temperature sensor. It activates the VSV that feeds the vacuum line going into the top of the FPR. It raises the fuel pressure in the fuel rail(s) to the max the fuel pump is capable of. Normally, the FPR reduces the pressure the fuel in the fuel rails is at.
The higher pressure reduces, or eliminates, the formation of bubbles in the fuel rail(s). If the injectors have bubbles going into them, they aren't providing the proper amount of fuel in the correct spray pattern into the engine. It's easy to see the pressure increase with a meter on the fuel rails, usually running off the CSI fuel connection.
I'm not certain, but I believe the FPR normally operates with the vacuum applied to the top port, and during a heat soak start, the VSV opens and removes the vacuum, allowing normal air pressure to be applied to FPR, allowing the full pressure of the fuel pump to be felt in the fuel rail(s).

If the system isn't function properly, it could be the VSV, or the vacuum line to the FPR, or the electrical connection to the VSV, or ECU. If I were take a WAG (Wild A$$ed Guess), I would go with the VSV not opening properly, but I may well be wrong.
Just idling the engine sitting in one place until the thermostat opens isn't enough to crate a heat soak. You need to let it idle, if that's what you're doing, for 30 min or more, until not only the coolant, but the oil as well, and any other fluids, like the power steering, that might contribute heat back into the engine once it's stopped running. The best way is to run the vehicle on the highway for a period, say 10-20 minutes. This allows everything, and all the fluids, to become thoroughly warmed up. Then shut it down, and let it sit for 5-10 minutes. This is normally adequate for the engine to reach it's peak temperature, before it starts naturally cooling down.
A simple way to ensure the FPR is functioning correctly is to connect a pressure gauge to the CSI fuel port and pull the vacuum line off the top of the FPR. You should see a pressure increase in the system. You said you replaced the FPR recently, so that PROBABLY not the problem, but it's easy to check real quick.

Hope this is some small help...
Pat☺

 

Thanks Pat, I forgot to add that the other day I removed the vacuum line to the FPR and ran it the whole day that way. Once again after sitting for about 25 minutes I attempted to start and drive somewhere and it ran crappy and died a couple times before it cleared it's throat and idled normally. I just took the CSI out and plugged the hole in the intake. Watched the CSI spray pattern when I started it and it looked great. Let it idle for 45 minutes and shut it down. Gonna go back out and check in 25 minutes to see if theres any leakage from the now exposed CSI.

Well it doesn't appear to be a leaky CSI. I'm gonna leave it exposed and the connector disconnected to watch it over the next couple days.