91 Fj80 Won't Start When HOT HELP!!!

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Couple of thoughts.
If the EFI relay/fuse was an issue here, this engine would not run. The OP says that if a secondary fuel is introduced the engine will fire. This eliminates the EFI circuit and points to fuel starvation.

The fuel damper is simply a small expansion tank with a diaphragm. Its job is to absorb the spikes of fuel pressure in the fuel rail as the 2 sets of injectors fire. The screw should be preset to a calibrated pressure and should not be "screwed" with, assuming you purchased OEM parts. It does not have a "return path". It is simply an expansion tank on a very small scale that sits on the fuel rail.

If the injectors were not firing, this engine would not run. Again, pointing to fuel starvation.

Does your 3FE have the OEM intake cooling fan/plenum?
 
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Something just occurred to me after a few cups of coffee and a bathroom visit.
The next time you have a "no start when hot", loosen the fuel filler cap. If there's an inordinate amount of tank pressure, then the fuel rail can become over-pressurzed and the check valve in the fuel pump will not allow fuel flow.
I had this happen after a tank vent line was crushed due to an unfortunate situation years ago.
 
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Thanks Hurleyburly, I actually have changed the starter relay for a heavy duty one as well since it had been giving me grief, I also rebuilt the starter and it now cranks nice and strong but still have that hot non start. I will double check my cold start injector switch resistance and update you, the mystery continues.
 
I will warm up the truck today and check remove the gas tank cap to see if for some reason is not breathing right and get back to you guys, again thanks for your help.

What I did a bit ago is actually clean the vapor canister, I opened it, cleaned it and replaced the charcoal material and put it all back together. I also thought the tank wasn't breathing right because every time I went to fill up there was a vacuum coming from it as I removed the cap, that did disappeared and it did fire up after I did that, nevertheless I will double check and try to start it without the cap on (I HAVEN'T TRIED THAT).
 
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Ok so I warmed up the truck took it for a spin, I tried restarting after loosing the fuel cap a and there was no vacuum or back pressure in the tank and it did not start. I checked the cold start injector switch and it is all within specs.

While driving I did notice something new it hadn't done before, as it warmed up and I floored the gas pedal it hesitates then dies but comes back on after the rpm come down to about 2000, I replaced the EFI relay for a fresh one and the hesitation goes away only for a minute or two but as the relay gets hot it will start hesitating again.

I have tried replacing a fresh relay while it is warm but it still wouldn't start, I have also checked for codes and there are no codes stored. A while back the Coolant temp sensor went bad and I replaced it but the symptoms were different (Wouldn't Idle and it kept dying but it would start).

On the hesitation note I have replaced the fuel filter and the pump runs nice and strong, I will double check the fuel pressure this weekend, does any of you know how much pressure should be held at the fuel rail after the truck is off?

The fan that cools the intake was removed a while back but the truck did start up and run after that for many months, this only started happening after she was put away for a while, I guess she is taking vengeance on me for leaving her behind.

A new plastic EFI relay is on the way.

I still have no idea where the problem could be.
 
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Here I am again, I installed a new plastic cased toyota EFI relay, I am currently stuck and starting to pull my hair out, if there are any ideas out there I greatly appreciate them, again thank you all for your help.

Again it starts right up when cold and will not restart once it warms up unless I use an external fuel source.
 
You obviously have a fuel starvation issue here. There is a VSV that controls vacuum to the FPR to regulate fuel pressure. Is that working?
Early on in this thread it was suggested that you test fuel pressure. Was this done? What are the numbers?
FI 47-49 in the FSM gives a detailed description of how to do this and what the numbers should be.

Try disconnecting the electrical connector to the cold start injector when hot.
 
Any update on fuel pressure? Is the VSV working? Did you disconnect the cold start injector when hot- any change?

Also- is the hesitation still there? Is this hesitation in park/neutral or drive?
 
The fuel pressure was fine but I will retest it (I had tested it before and replaced the fuel regulator), I also tested the pump by jumping the terminals and it runs great (Also replaced recently). I haven't tried disconnecting the cold start when hot, that will be my next test. I removed the VSV (DESMOGED) along with the egr, air injectors and all those bits about 6 years ago and that never affected the truck.

I did remove the Fan that cools the truck down after you shut it off, I don't know if that has anything to do with it (COMPUTER), I don't recall if this started right after I did that or it was there before.

I thought the fuel return line might be blocked but I already blew air through it and it returns to the tank fine.

The hesitation happened when I drove it for a while and then as it warmed up I couldn't floor it because it would hesitate.
 
I've started the truck and left it idle for while until warm, if I shut it off and try to start it again it will at the second or third crank but has to be right away and long cranks, if I wait ten seconds or longer it just will not start, I disconnected the cold start injector and will not start either.

Somehow I am guessing the fuel is drawing back to the tank but there is no vacuum at all, years ago I had vacuum in the tank and I fixed that by dissembling the charcoal canister, cleaning it and pouring new charcoal in it (that took care of that).

I do have spark when cranking and I do have fuel when cranking, could the ECU have gone bad?
 
Test the fuel pressure when you think the it won't start. Read the 4th paragraph down in the first post on how to do.
Here's the thread with the fix we did: Intermittent Starting Problem Solved.
Just noticed I previously posted this in the first page of this thread.
So what is the fuel pressure at the no start?
 
Ok, I've got spark and I've got fuel pressure, the efi relay is working and it does activate when hot.

I just came across an similar case but this was on an early 90's corvette, I don't know if I mentioned that I replaced a few injectors but I didin't check them before installing them. I bought those quite a while ago and they sat for a long time, the injectors are probably loosing impedance when hot or just sticking because I don't smell fuel after long periods of cranking when hot. I did this repair because one of my injector seals was leaking and the truck was running rough.

Same thing happened with the corvette, had spark, fuel pressure but it would crank and only start with a shot of fuel, injectors where replaced and problem was solved, they were stuck.

I will perform a few tests on the injectors but the safest thing to do is just remove them all and have them flow tested.

At least I am getting somewhere with this as it is quite frustrating by now, I will update you once I test the injectors. This is probably next month as I will be leaving the country for a few weeks.
 
thex1231 said:
the injectors are probably loosing impedance when hot or just sticking because I don't smell fuel after long periods of cranking when hot.
Click to expand...
This doesn't make sense to me. If the injectors were faulty the engine wouldn't run.
You said that if you introduce a secondary fuel source during hot starts the engine will run and you can drive normally. This indicates that the injectors are firing correctly. If they were "stuck", then how is the engine running?
 
Just to confirm...When hot and in the no start position, the vehicle has spark and the fuel pressure was checked with a fuel pressure gauge kit? What was the pressure? If you have spark and about 40#'s of fuel pressure then it should start. Injectors are fine as @jonheld mentioned.
 
I haven't checked it again as I mentioned I don't have the gauge right now (have to rent it), I did check it before I did the injector job and after, this non start after it has warmed up was still there before I did anything to the injectors.

The injectors get stuck but with the engine vibration they work again, also when they are hot the impedance on the injectors changes and the pulse strength is much weaker, I did a drive test and after it gets warm, it hesitates when you floor it.
 
Before I get too far on the injectors I will get the fuel pressure gauge and do a test on each one by pulsing them and see if when hot they will release the fuel or not, I'll update you on that.

It is a guessing game but I don't want to just throw money at it anymore.

Thanks
 
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