91 Fj80 Won't Start When HOT HELP!!! (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Make it easy on yourself. Free loaner fuel gauge kit at Autozone. Remove the cold start injector line from the fuel rail and tap into there for the test. The fuel rail is the best place that you can accurately test the fuel pressure required for the injectors. The gauge will be inline so if you can have someone start the vehicle while you are observing the pressure readings that is best.

With the fuel pump bypassed through the diagnostic box, turn the key on, crank the engine and check fuel pressure. FSM states 37 to 46 psi. Results from this test need to be obtained during your no start situation.

Edited: key on, to crank engine. Fuel pump will not come on until engine is cranked over and AFM door is opened
 
Last edited:
Hi, If relays are still getting hot ,your wiring needs to be replaced going to the Efi. Wiring is upgraded to 12 gauge for about 6 inches under the black fuse box under the hood . Mike
 
Sorry for the late reply, I am running around with a house build , work and wherever else.

I finally bought a fuel pressure gauge, the pump installed is aftermarket. The truck will not start unless I use starter fluid, the lines will not hold pressure until the starter is engaged (48 psi).

It will start and hold 48 psi, after about 10 minutes the efi relay will overheat and will let the truck die. I can change the relay and it will start up again with starter fluid. The pump will engage right away and give you 48 psi when the starter is engaged but the pressure will drain right away after you let go and will not start.

I have already upgraded the wiring from the harness that feeds the efi relay. I know the aftermarket pump uses draws more amps than stock ( I will install a stock pump).

I did replace the fuel dampner and pressure regulator, the regulator is used but it came from a working truck. When I pinch the line it will go from 48 to 54 or so. I know this is very high for the 3fe and she will be getting a stock pump soon.

My real question is, who is in charge of holding the pressure, the dampner or the pump?

I love this truck and she used to be my daily driver but has had so many gremlins, this seems to be the last of them.

Thank you all for your help, the pump is on the way and will update you on the results once installed.

2016009
 
Any advice will be greatly appreciated, I will deal with the pump next week and updated this.

Thanks,

Gio
 
Sorry for the late reply, I am running around with a house build , work and wherever else.

I finally bought a fuel pressure gauge, the pump installed is aftermarket. The truck will not start unless I use starter fluid, the lines will not hold pressure until the starter is engaged (48 psi).

It will start and hold 48 psi, after about 10 minutes the efi relay will overheat and will let the truck die. I can change the relay and it will start up again with starter fluid. The pump will engage right away and give you 48 psi when the starter is engaged but the pressure will drain right away after you let go and will not start.

I have already upgraded the wiring from the harness that feeds the efi relay. I know the aftermarket pump uses draws more amps than stock ( I will install a stock pump).

I did replace the fuel dampner and pressure regulator, the regulator is used but it came from a working truck. When I pinch the line it will go from 48 to 54 or so. I know this is very high for the 3fe and she will be getting a stock pump soon.

My real question is, who is in charge of holding the pressure, the dampner or the pump?

I love this truck and she used to be my daily driver but has had so many gremlins, this seems to be the last of them.

Thank you all for your help, the pump is on the way and will update you on the results once installed.

View attachment 2016009

Regulator regulates the pressure. The fuel damper helps smooth out any spikes in pressure changes. A bad damper can act as a relief valve and can dump all the fuel pressure to 0 after shutdown. If your EFI relay is getting hot I think you might want to investigate more in that area.
 
Thanks for the your reply, I did upgrade the harness to a larger caliber wire but the pump I installed draws too much amperage and that is why the relay is getting hot.

I have bought a brand new denso pump and will be installing in a few days, I did replace a leaky injector but I didin't bother checking if the others were leaking into the cylinders preventing it from starting.

I am pretty sure the new pump along with the efi relay wiring will resolve the hot relay, She used to run really bad, that is why I took it apart and upgraded some of the wiring and replaced a couple of injectors. Once she is running it performs like a champ except for the hot efi relay ( to be resolved).

I will update this with some pics and new fuel pressures once the pump is installed.

Thanks again,

Gio
 
Have you checked the coolant temperature sensor? The fact it'll hot restart on some Bill Cosby in a can tells us you have spark, air and compression. Im wondering if the ECU thinks its hotter than the engine really is and causing you to not get enough cranking fuel pulsewidth.
 
Last edited:
I haven't checked it but now that you mention it I did replace it a few years back but I remember getting a check engine light for and it wouldn't start for the life of it.

I will give it a go when the pump and the fuel sender arrives, I will get those replaced and check the coolant temp sensor just to make sure.

Thanks
 
Actually got one of those and I keep a metal one as a spare, my relay overheating is due to the pump amperage is too high.

I will take a reading amps drawn by this pump vs the stock denso.

Thanks for the tip
 
Hello everyone and sorry for taking so long to get back. I hadn't been using my FJ for a while since I am doing construction at my house and with the non start problems it was a big issue.

Long story short I have just replaced the pump with a Denso along with the fuel sending unit since it was giving me grief. The pump works great and it will no longer overheat the relay and the pressure will remain there after shut off, it stays between 38 and 42 PSI.

The issue now is that there are air bubbles in the high pressure fuel line, I don't see a leak anywhere. I just installed the pump back in.

I need to check the pick up tube for pinholes along with the lines.

The pressure gauge is connected to the cold start injector. Anywhere else the bubbles could be coming from?, when I release some fuel from the guage to the clear tube it fills up with tiny bubbles and you can feel it on the trigger as the go by.

The truck will start when cold and once up to temp if you shut it off it will not unless I use starter fluid.

Any ideas or has anyone had this type of issue before?

I thank you all for the input.


Fue Gauge FJ80.jpg
 
I'm thinking out loud here....
When hot: The Fuel pump kicks on when the starter is engaged and you get a proper pressure reading but the truck won't start.
Correct so far?
While cranking, you apply outside fuel source, and the truck starts and continues to run until you turn the key to "off".
Still correct?
So the question then is what is keeping the injectors from firing while hot, while the engine is at low (starter generated rpm) but then allows the injectors to fire when the engine is running at full rpm (700ish)? Could it be something with the crank position sensor and it's pulse counting? I don't have a 3FE electrical manual, so I don't know if the crank position sensor is tied into the EFI or not.

Bubbles will only be formed in the suction side, either you have pin holes in the pick up, as you said, or there is cavitation in the pump. Holes on the pressure side will result in leaks.
 
I don't have a 3FE electrical manual, so I don't know if the crank position sensor is tied into the EFI or not.
The 3FE does not have a CPS like the 1FZ. The ECU uses the pick up coils in the distributor to reference position. If those were not positioned correctly there would be no spark.
 
Spark he has, its fuel at low RPM that's lacking.
Lets see, low RPM also means low/no vacuum. Bad VSV or vacuum lines associated with the EFI system?
Is that even a thing?

So spraying starter fluid would enrich the mix, effectively choking the intake. Is it possible the engine is getting too much air at hot start? A butterfly that gets stuck open, and it's not a fuel problem but an air delivery problem?
 
This could be an air problem but I serviced the whole intake not to long ago, this was happening before I did that and I am still stuck.

The issues I was able to take care were the efi relay cut off (no longer an issue) by replacing the old wiring to it and replacing the aftermarket pump with a denso unit. The other issue was the pump's check valve wasn't working properly, it was letting the gas drain back (solved with new pump).

I am really stuck, I do love my truck but it has been full of gremlins, this started happening after it sat for about 3 months and it hasn't stopped.

First the neutral switch wouldn't allow it to start at all, took care of that, then the starter (replaced and I wired a new relay). I serviced the charcoal canister because it was clogged (replaced active charcoal) and it pulled a vacuum, no more hissing when I remove the gas cap.

At the moment it starts fine when cold and it remains on just fine, it won't start after it's turned off, this is my main issue. I want to be able to drive to the store and not have to open the hood to spray starter fluid and get going.

Again thanks for any ideas, has anyone had this issue before?
 
Last edited:
Could this be a coolant temp sensor?, This happened a while ago but it threw a check engine code, replaced it and everything was ok.

But if this was the case it wouldn't start when cold, right?

A
Does anyone know the resistance the temp sensor should output?
 
Hmm. The common criteria in getting a successful start sounds like it's more fuel, so I wonder if disabling the cold start injector and starting the truck cold is a useful diagnostic step.

I'll agree that it sounds like either too much air or a lack of fuel at startup.

Leland started a great thread on 3FE fueling diag, it might be of use in sussing this out.
 
Thanks, I'm reading through it, it is quite complex. I will check my water temp switch and sensors to make sure they are in spec.

I will also go through the wiring to check there aren't any burned wires that are shorting out.

Gremlins everywhere, hahaha, I still love my truck.


Thanks everyone.
 

Users who are viewing this thread

Back
Top Bottom