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

[jonheld]

I just purchased a 91 FJ80 that has this exact same issue. Starts cold every time, but will just crank over without starting if you try to start it hot. Sometimes it will start when it’s hot, but alot of the time it just cranks. I replaced my EFI relay, and it didn't change anything. Also tried cooling the relay during one of the episodes, without any change. Only way I can get it to start is with started fluid, and then It starts, idles and runs great.

Was there any resolution to this thread? I know it’s atleast 6 years old.

If the CEL is illuminated with the key in the ON position BEFORE cranking the starter, then the EFI relay is NOT the issue.
After reading through this thread, what diagnostics have you done so far?

 

[Crazymonkey2465]

If the CEL is illuminated with the key in the ON position BEFORE cranking the starter, then the EFI relay is NOT the issue.
After reading through this thread, what diagnostics have you done so far?

The CEL IS illuminated with the key in the ON position BEFORE cranking the engine. That, and the fact that ive tried 3 different EFI relays now including the plastic one, tells me its not the EFI relay.

Tonight i was able to connect a fuel pressure gauge to the cold start injector, and my oscilloscope to the cylinder #1 fuel injector. While running, I get 45-50 psig fuel pressure, and can see injector pulses on the scope. All good there.

I had a hard time recreating the issue, but i finally did by idleing with the hood closed, and then turning it off, letting it rest for a few minutes before trying to start again. This should be the hottest situation, since the engine is heat soaking without the radiator fan running. This is when the issue happens.

While hot starting, I still had fuel pressure but did NOT see any injector pulses on the #1 injector. This tells me the ECM isn't commanding the injectors to fire for some reason, and it only happens when the engine is heat soaked.

One thing to note, is that this engine had the EGR removed, and also the under hood blower that's usually behind the driver headlight was removed too. This is likely making whatever issue this is worse since the underhood temps are likely higher.

I'm looking through the FSM now, but does anyone know a list of sensors/etc that would stop the injectors from firing when hot or malfunctioning?

Again: Engine cranks, I have fuel pressure, but no injector pulse, only happens when heat soaked. Why?

 

[jonheld]

The CEL IS illuminated with the key in the ON position BEFORE cranking the engine. That, and the fact that ive tried 3 different EFI relays now including the plastic one, tells me its not the EFI relay.

Tonight i was able to connect a fuel pressure gauge to the cold start injector, and my oscilloscope to the cylinder #1 fuel injector. While running, I get 45-50 psig fuel pressure, and can see injector pulses on the scope. All good there.

I had a hard time recreating the issue, but i finally did by idleing with the hood closed, and then turning it off, letting it rest for a few minutes before trying to start again. This should be the hottest situation, since the engine is heat soaking without the radiator fan running. This is when the issue happens.

While hot starting, I still had fuel pressure but did NOT see any injector pulses on the #1 injector. This tells me the ECM isn't commanding the injectors to fire for some reason, and it only happens when the engine is heat soaked.

One thing to note, is that this engine had the EGR removed, and also the under hood blower that's usually behind the driver headlight was removed too. This is likely making whatever issue this is worse since the underhood temps are likely higher.

I'm looking through the FSM now, but does anyone know a list of sensors/etc that would stop the injectors from firing when hot or malfunctioning?

Again: Engine cranks, I have fuel pressure, but no injector pulse, only happens when heat soaked. Why?

The injectors get a constant +12 on pin 2 (blk/grn) and are pulsed to ground on pin 1 in 2 groups of 3.
In the no run condition, did you verify +12 to the injectors?

Are you getting spark in the no run condition? The ECU will want to "see" the proper pulses from the distributor to "know" that the engine is cranking.

 

[Crazymonkey2465]

The injectors get a constant +12 on pin 2 (blk/grn) and are pulsed to ground on pin 1 in 2 groups of 3.
In the no run condition, did you verify +12 to the injectors?

Are you getting spark in the no run condition? The ECU will want to "see" the proper pulses from the distributor to "know" that the engine is cranking.

Jon, here are the answers to your questions, thanks for the help!

1. Yes I do have +12V to pin 2 on the injectors during the no start condition. Verified with the scope during no start cranking.
2. Yes I am getting spark during the no start condition. Verified with a sight glass style spark tester on cylinder #1.
3. I verified the two sensors in the distributor are outputting a signal during the no start condition. Verified with scope and pinch probes coming out of the distributor. I measured the gap per FSM, and both are within spec. Cold resistance of both were right around 270 ohms. However, I checked my codes, and I had code 12 (RPM SIGNAL) and code 22 (COOLANT SENSOR). I cleared them, recreated the no start condition, and code 12 came back. So something is going on with the RPM signal..

Also, can you explain to me what the EFI relay actually does? I thought it powered the ECM, but somehow I’m actually able to start and run the engine (when the intermittent issue isn’t happening) while the EFI relay is completly unplugged. Is this normal? What am I missing?

Thanks again for the help.

 

[jonheld]

Jon, here are the answers to your questions, thanks for the help!

1. Yes I do have +12V to pin 2 on the injectors during the no start condition. Verified with the scope during no start cranking.
2. Yes I am getting spark during the no start condition. Verified with a sight glass style spark tester on cylinder #1.
3. I verified the two sensors in the distributor are outputting a signal during the no start condition. Verified with scope and pinch probes coming out of the distributor. I measured the gap per FSM, and both are within spec. Cold resistance of both were right around 270 ohms. However, I checked my codes, and I had code 12 (RPM SIGNAL) and code 22 (COOLANT SENSOR). I cleared them, recreated the no start condition, and code 12 came back. So something is going on with the RPM signal..

Also, can you explain to me what the EFI relay actually does? I thought it powered the ECM, but somehow I’m actually able to start and run the engine (when the intermittent issue isn’t happening) while the EFI relay is completly unplugged. Is this normal? What am I missing?

Thanks again for the help.

All pulses are developed in the distributor. RPM and crank position.
Tachometer pulses come from the igniter.

In an unmolested configuration, it would not be possible for the engine to run with the EFI relay removed.
The EFI circuit is initiated from the ECU (E5-pin 3) which energizes the EFI relay coil. The load side of the EFI relay feeds +12 to the ECU (EFI on logic), all 3 VSV valves, both O2 sensors, the ISC valve, pin 8 (B+) on the DIAGNOSTIC connector, and the load side of the circuit opening relay which feeds the fuel pump. All EFI related +12 comes from the 15 amp EFI fuse in the under hood fuse box. This fuse also feeds constant B+ to the ECU.

You should download the Toyota electronic wiring diagram from the resources section. It will answer your questions.
Please see the complete ECU schematic attached below.