Hard starting when hot.

[eurasiaoverland]

I recently bought a pretty neglected 3RZ 3rd Gen. It leaked oil (rear crank seal and / or oil pan), coolant (water pump and / or head gasket), the engine would hesitate at 1500 - 2000 rpm (cleared up after driving some), the rear brakes were binding, etc etc etc.

One thing I couldn't explain was hard starting when the engine was hot. When cold, it would start with very little cranking, but once hot it seemed harder to crank and would need to be cranked a bit more before reluctantly starting. Battery is not the problem as I swapped the original for a known good one, plus it started fine from cold.

I've never had a gasoline engine before, so I'm not really sure what might be the cause. A couple of things I have noticed however are dirty injectors and a smell of gasoline in the engine.

Any ideas on what causes slow cranking specifically when hot??

 

[jgue467]

Easy cold starts and tough hard starts Can be an indication of valves needing adjustment, they maybe too tight. Yet it could be other stuff. Lets see what others think.... :cowboy:

 

[eurasiaoverland]

Easy cold starts and tough hard starts Can be an indication of valves needing adjustment, they maybe too tight. Yet it could be other stuff. Lets see what others think.... :cowboy:

Thanks for that. I checked valve clearances and 3 of the intake valves are a little tight, but none were touching....

 

[Kanoe]

Are you saying slower cranking when hot? Or longer cranking and harder to start when hot? Bit hard to tell.

If you are having longer crank times and a slightly grumbly start when hot only, I may have a clue. Searching the web pointed to the IAC valve. Pulling the TB and IAC and cleaning both well seems to have fixed the issue for me. Same engine 3rz. Haven't had any hard start occurances since.

Good luck

 

[LittleCaesar]

When it comes to hard starting when hot, I have found that it can be contributed to:

1. Bad fuel pressure. Check it. I remember that fuel pressure regulators have leaked on the 3RZ before. The pump can be also a culprit. Change the filter even though it isn't a walk in the park.
2. Since the 3RZ has an EGR check it. If it is gummed up try cleaning it with carb cleaner. I have had them go bad and not throw a code.
3. ECT sensor is out of range or just bad. Get a new OEM one.
4. Check all starting circuit relays including ECU main, starter, fuel.
5. A gummed up or dirty IAC as Kanoe pointed out.

 

[eurasiaoverland]

Are you saying slower cranking when hot? Or longer cranking and harder to start when hot? Bit hard to tell.

If you are having longer crank times and a slightly grumbly start when hot only, I may have a clue. Searching the web pointed to the IAC valve. Pulling the TB and IAC and cleaning both well seems to have fixed the issue for me. Same engine 3rz. Haven't had any hard start occurances since.

Good luck

Thanks for that. Cranking is slower when hot and it also seems to take longer to catch. When it does start though, it runs immediately fine.

But the ISCV is a suspect; the PO mentioned having worked on it, and when I pulled the TB I found a cheapo Chinese ISCV which I will replace with a new OEM one. The idle was quite high from memory, taking a long time to come down.

 

[eurasiaoverland]

When it comes to hard starting when hot, I have found that it can be contributed to:

1. Bad fuel pressure. Check it. I remember that fuel pressure regulators have leaked on the 3RZ before. The pump can be also a culprit. Change the filter even though it isn't a walk in the park.
2. Since the 3RZ has an EGR check it. If it is gummed up try cleaning it with carb cleaner. I have had them go bad and not throw a code.
3. ECT sensor is out of range or just bad. Get a new OEM one.
4. Check all starting circuit relays including ECU main, starter, fuel.
5. A gummed up or dirty IAC as Kanoe pointed out.

1. Not sure how to do this now that the whole truck is stripped. Bad regulator could explain the fuel smell in the engine. I'm contemplating replacing the pump but hate to swap a good original one with a new Chinese-made Denso one....

2,. I have a JDM Hilux Surf with no EGR, thank goodness.

3. Is this the one at the back of the cylinder head??

4. Would have to do this once back together

5. This will be replace.

Thanks, plenty of things to try

 

[jeremyc74]

I've never had a gasoline engine before, so I'm not really sure what might be the cause. A couple of things I have noticed however are dirty injectors and a smell of gasoline in the engine.

I'll bet 10 donuts it's a bad fuel pressure regulator. :hungry:

I've seen several posts here with the same symptoms and that's what resolved it. The regulator is vacuum biased, and the fuel smell come from it bypassing the diaphragm and getting into the intake.

If I'm right, when you pull the intake tube off, you'll find fuel sitting in there.

Hope that's all it is, because that's a relatively easy fix. :thumb:

Edit:
https://www.4runners.com/threads/3-4-hard-to-start-when-warm.930/

 

[eurasiaoverland]

I'll bet 10 donuts it's a bad fuel pressure regulator. :hungry:

I've seen several posts here with the same symptoms and that's what resolved it. The regulator is vacuum biased, and the fuel smell come from it bypassing the diaphragm and getting into the intake.

If I'm right, when you pull the intake tube off, you'll find fuel sitting in there.

Hope that's all it is, because that's a relatively easy fix. :thumb:

Edit:
https://www.4runners.com/threads/3-4-hard-to-start-when-warm.930/

Thanks for the suggestion

I also considered the regulator, but cannot think why it would do this when hot??

Unfortunately I just ripped the engine apart to start a rebuild and don't recall if there was fuel in the intake tube. I'll have a look in the intake manifold at the weekend to check for signs of fuel having been in there.

 

[jeremyc74]

Thanks for the suggestion

I also considered the regulator, but cannot think why it would do this when hot??

Unfortunately I just ripped the engine apart to start a rebuild and don't recall if there was fuel in the intake tube. I'll have a look in the intake manifold at the weekend to check for signs of fuel having been in there.

You can probably check it by putting a vacuum pump on it and see if it bleeds down.

I'm not sure why it happens when it's hot, but I've seen at least three separate threads with the same issue.

 

[LittleCaesar]

I don't know why the FPR will start leaking on the 3RZ but it does. The vacuum will be lost when hot and when one goes to crank it again there isn't any pressure on the first crank.

I replaced a FPR and fuel filter as well as cleaning the IAC for a friend's father who had a Tacoma with the 3rz in 2010 and it has been starting fine since.

The filter is under the intake manifold, but is a guess to where it is on the JDM one.