FJ62 hard to start when hot

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jonnyd42

jonnyd42

SILVER Star
Joined
Aug 20, 2023
Threads
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Location
Santa Cruz, CA
Update: it was the fuel pump.
Wasn't holding pressure after shutoff (dropping to 0 psi instantly).

Fuel pump actually died on me in the middle of Utah - replaced with a new Denso part and the problem is gone completely.

======
Ok so I'm a bit stumped on this one. My truck starts up very quickly when it's cold (about 2 seconds), or if its been sitting for > 5 hrs. If I get it up to operating temp and then let it sit for a while, it takes a really long time to crank (12s or so). If I drive it, shut it off, and then immediately try to restart it it starts up just fine. It's only when it's been sitting for upwards of 20 mins.

I have replaced the fuel pressure regulator. The fuel pulse damper at the back of the rail (firewall side) looks like it was replaced by the prev owner.

I have tried all of the following permutations:
  • Starting it without letting the fuel pump build pressure
  • Starting it after leaving the key on so that the pump can build pressure
  • Pressing the gas pedal / not pressing the gas pedal
I have checked:
  1. Condition of plugs
  2. Air filter
  3. Fuel filter (it's new)
  4. Cap & rotor wires
  5. Battery cables & ground
The truck has no loss of power or other indications that there's a fuel delivery problem due to the pump. I'm wondering if this is something sensor or computer related, since IIRC the 3FE EFI system has different behavior on cold vs. warm start.

Would love some advice on what to take a look at next...
 
Last edited:
I’ve had/have this same issue for about a year. Ambient temperature doesn’t seem to have an effect in my case.

The pump doesn’t actually come on until the key is in the start position, so just turning the key to accessory on isn’t pressurizing the system (I believe this is what you’re describing). Have you tested when hot and jumper the pump at the diagnostic port to build pressure? I can’t recall the pins but I think it’s B+ and Fp, then turn the key accessory… you should be able to hear the pump (it’s faint). After 10-15 seconds, turn off the key, remove the jumper then try to start.

Pressing the gas pedal won’t really make a difference- that’s old school carb stuff (accelerator pump).

Coincidentally my pump just completely failed 2 weeks ago. I’m still working through some issues so I’m not able to say definitely, but I have a hunch my fuel flow/pressure was perhaps insufficient prior to the failure which *may* have been the cause of the hot start issue.

Also suggest getting a fuel pressure indicator to help you diagnose.
 
toy_tek said:
I’ve had/have this same issue for about a year. Ambient temperature doesn’t seem to have an effect in my case.

The pump doesn’t actually come on until the key is in the start position, so just turning the key to accessory on isn’t pressurizing the system (I believe this is what you’re describing). Have you tested when hot and jumper the pump at the diagnostic port to build pressure? I can’t recall the pins but I think it’s B+ and Fp, then turn the key accessory… you should be able to hear the pump (it’s faint). After 10-15 seconds, turn off the key, remove the jumper then try to start.

Pressing the gas pedal won’t really make a difference- that’s old school carb stuff (accelerator pump).

Coincidentally my pump just completely failed 2 weeks ago. I’m still working through some issues so I’m not able to say definitely, but I have a hunch my fuel flow/pressure was perhaps insufficient prior to the failure which *may* have been the cause of the hot start issue.

Also suggest getting a fuel pressure indicator to help you diagnose.
Click to expand...
I’m thinking since mine is temp dependent it’s not the fuel pump 🤔

When it's cold it starts up just fine, very quickly.

Noted re gas pedal!
 
Last edited:
Remove fuel line to fuel rail and confirm fuel is reaching engine bay. Then check fuel pressure regulator is not blocked or inoperable. Report back.
 
jonnyd42 said:
Ok so I'm a bit stumped on this one. My truck starts up very quickly when it's cold (about 2 seconds), or if its been sitting for > 5 hrs. If I get it up to operating temp and then let it sit for a while, it takes a really long time to crank (12s or so). If I drive it, shut it off, and then immediately try to restart it it starts up just fine. It's only when it's been sitting for upwards of 20 mins.

I have replaced the fuel pressure regulator. The fuel pulse damper at the back of the rail (firewall side) looks like it was replaced by the prev owner.

I have tried all of the following permutations:
  • Starting it without letting the fuel pump build pressure
  • Starting it after leaving the key on so that the pump can build pressure
  • Pressing the gas pedal / not pressing the gas pedal
I have checked:
  1. Condition of plugs
  2. Air filter
  3. Fuel filter (it's new)
  4. Cap & rotor wires
  5. Battery cables & ground
The truck has no loss of power or other indications that there's a fuel delivery problem due to the pump. I'm wondering if this is something sensor or computer related, since IIRC the 3FE EFI system has different behavior on cold vs. warm start.

Would love some advice on what to take a look at next...
Click to expand...
Did you ever end up figuring out what the issue was? I'm currently having the EXACT same problem, down to the video you posted, I have replaced the EFI relay as well and have new grounds on battery and new battery. also new fuel injectors and spark plugs. FJ62 having issues turning on at hot start after EFI relay replaced - https://forum.ih8mud.com/threads/fj62-having-issues-turning-on-at-hot-start-after-efi-relay-replaced.1372287/
 
luckylandcruiser said:
Did you ever end up figuring out what the issue was? I'm currently having the EXACT same problem, down to the video you posted, I have replaced the EFI relay as well and have new grounds on battery and new battery. also new fuel injectors and spark plugs. FJ62 having issues turning on at hot start after EFI relay replaced - https://forum.ih8mud.com/threads/fj62-having-issues-turning-on-at-hot-start-after-efi-relay-replaced.1372287/
Click to expand...
Honestly no. I replaced the fuel pressure regular and damper, that helped marginally. But in the summer heat after a long drive, it'll really struggle to get started again.
 
Try really cleaning your cold start injector.

I was having quite similar issues and this was the magic bullet.

Also, prior to really cleaning my cold start injector, opening my gas cap seemed to help it start better.
 
toy_tek said:
I’ve had/have this same issue for about a year. Ambient temperature doesn’t seem to have an effect in my case.

The pump doesn’t actually come on until the key is in the start position, so just turning the key to accessory on isn’t pressurizing the system (I believe this is what you’re describing). Have you tested when hot and jumper the pump at the diagnostic port to build pressure? I can’t recall the pins but I think it’s B+ and Fp, then turn the key accessory… you should be able to hear the pump (it’s faint). After 10-15 seconds, turn off the key, remove the jumper then try to start.

Pressing the gas pedal won’t really make a difference- that’s old school carb stuff (accelerator pump).

Coincidentally my pump just completely failed 2 weeks ago. I’m still working through some issues so I’m not able to say definitely, but I have a hunch my fuel flow/pressure was perhaps insufficient prior to the failure which *may* have been the cause of the hot start issue.

Also suggest getting a fuel pressure indicator to help you diagnose.
Click to expand...
Did replacing the pump fix this issue?
 
RevISK said:
Try really cleaning your cold start injector.

I was having quite similar issues and this was the magic bullet.

Also, prior to really cleaning my cold start injector, opening my gas cap seemed to help it start better.
Click to expand...
Hm, how would that make a difference? I thought the cold start injector only is active when the engine is below like 100F. My issue is the opposite - super hard to start when hot.
 
jonnyd42 said:
Hm, how would that make a difference? I thought the cold start injector only is active when the engine is below like 100F. My issue is the opposite - super hard to start when hot.
Click to expand...
Give cleaning it a shot and see. It probably needs it.
 
toy_tek said:
Turned out I had a few issues. Fuel results here:
Fuel pump questions: LRA / 3FE -> LS - https://forum.ih8mud.com/threads/fuel-pump-questions-lra-3fe-ls.1351532/post-15853033

Between that, desmog, and rebuilt injectors it starts very fast now.
Click to expand...
I ordered this gauge & adapter kit, will see what kind of pressure I'm getting when cold & hot to see if there's a difference. Once I rule that out, my gut sense is it may be the 37 year old original fuel injectors leaking.... (319k miles on the clock)
 
most often in my experience this issue (usually a lot worse then you are experiencing, no start at all) is the EFI relay sticking closed. Next time it happens pour some cold water on it and give it a few taps. It's right in the engie bay behind the air cleaner housing.
 
Also, you could test the temp sensor for the EFI system that's on the thermostat housing.
If it's out of whack, it can confuse how much fuel the system delivers at start up based on inaccurate coolant temp data.
 
Lead Head said:
Next time you go to try and hot start it, disconnect the vacuum line to the fuel pressure regulator. If that helps, the hot-start solenoid valve may be malfunctioning.
Click to expand...
What is the "hot start solenoid valve"? Can you share a screenshot or picture of what this looks like, or a part number? I'd love to learn more.

EFI system temp sensor tested & all good.
Tried putting cold water & tapping the EFI relay - that also didn't do anything. :(
 
jonnyd42 said:
What is the "hot start solenoid valve"? Can you share a screenshot or picture of what this looks like, or a part number? I'd love to learn more.

EFI system temp sensor tested & all good.
Tried putting cold water & tapping the EFI relay - that also didn't do anything. :(
Click to expand...
On the left side fender, there's a bank of three "VSV" solenoids (vacuum switching valve). One is for the EGR, one is for the smog pump, the other goes to the fuel pressure regulator.
 
Lead Head said:
On the left side fender, there's a bank of three "VSV" solenoids (vacuum switching valve). One is for the EGR, one is for the smog pump, the other goes to the fuel pressure regulator.
Click to expand...
When a 3FE is desmogged those 3 VSV’s on the drivers fender usually get eliminated. However, the one VSV that controls the FPR should be retained and functional, IMO.
I’m not educated on how much it controls the FPR, but it’s another piece of the EFI puzzle.

If OP is desmogged, it’s something to look at.
 
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