Hard to start when hot

[RyanHeo]

Hi, guys.
I have a 96' Infiniti I30 which 124k on it. The car is good start in the morning or the engine is cool but when the engine is hot, it makes hard to start. The engine is needed a long crank time more than 5~15 sec. Sometime it was failed. What's wrong?

 

[gulledge]

Possible fuel pump relay failure as the engine gets hot and creates resistance/failure of the circuit. This is a cheap part that can be purchased and done yourself. This was the exact problem my neighbor had except his car would fail to start when the car was hot. I would start again after it cooled down. Replacing the fuel pump relay fixed the problem.
However this is a guess, and I am not an expert on this. Are you getting a check engine light at all? If not, I guessing the computer, because it's not a total failure, is unable to give you a code. I don't know where the relay is located on your car, put my friends was a small plug in device similar to a fuse in a electrical box in the engine compartment. Very easy to replace once you locate where it is.

 

[RyanHeo]

I will try tomorrow.
Thanks man.

 

[RyanHeo]

I got the OEM part today and replaced it but it doesn't help me at all. Anyway thanks.

 

[dkryan]

Perform a search for "Mokanic" and PM him with your question tomorrow (Saturday) if he does not respond to your post by then. He seems to know I30s fairly well.

 

[porcupine73]

Engine coolant temp sensor is a common cause of hot/cold start issues on fuel injected vehicles.

 

[RyanHeo]

But I don't have a "check engine light".
Doesn't the sensor make CEL if it is fail?
Thanks.

 

[porcupine73]

The ECU can only set the CEL/MIL if it can tell there is a problem with the circuit. If a sensor output is just inaccurate, the CEL/MIL may not illuminate.

i.e. if the engine coolant temp sensor is telling the ECU the coolant temp is say 120 deg F and it is really only say 60 deg F the ECU may try to start it too lean.

 

[Rickey]

I'm no Infiniti expert.

It sounds like it could be loosing prime on the fuel rail.
Is there a check valve either in the fuel pump or fuel pressure regulator that is leaking the prime back into the tank?

Just a wild guess on my part.

I would have guessed the fuel pump relay first also.

Good luck sir.

Rickey

 

[mechtech2]

Once it is started hot, does everything work OK?
Are there any misfires, or is is just a starting problem?
I vote for a sensor problem, like the coolant or air inlet temp sensors. Maybe a vacuum leak in an intake hose or PCV system. You may have a fuel pump problem, but you would see problems when cold, also.

 

[NYEngineer]

This may or may not help, but years ago I had a Ford van that started cold in maybe a half rotation of the starter but hot, took forever. Ended up being the ignition module. I replaced it and put in a new layer of dielectric grease for it to lay on. End of problem.

 

[RyanHeo]

The CEL came on again today morning.
So I scaned it, it was coolant temp sensor malfunction.
The sensor was replaced today. However the starting problem is still pain in the aXX.

As I told you, I replaced the starter, fuel pump relay, and ignition switch. Do I have to give up now?
Thanks.

 

[benjamming]

What is the actual code(s) #?

 

[RyanHeo]

I think it was P0115 and P0125.

 

[RyanHeo]

The engine would be misfired when the start is too hard. I'm not sure but the cranking sound is like misfire.

 

[VK56VD]

maybe a faulty fuel injector?

 

[porcupine73]

Do you still get any codes now after replacing the engine coolant temp sensor?

Quote:

---

I think it was P0115 and P0125.

---

DTC P0115: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT MALFUNCTION
Immediately at fault recognition
TROUBLE SYMPTOM: Hard to start, Erroneous idling, Poor driving performance

DTC PO125: INSUFFICIENT COOLANT TEMPERATURE FOR CLOSED LOOP FUEL CONTROL
Two consecutive trips with fault
TROUBLE SYMPTOM: Engine would not return to idling.
NOTE: If P0115 is also present it should be inspected first.

 

[RyanHeo]

I replaced the coolant temp sensor and them reset the ECU.
The CEL was gone. However the starting is still problem when engine is hot. Also I'm sure the fuel pressure is good.
Thanks.

 

[rokky]

Have a shop test the ignition.
Could be just a bad wire. When cold, the wire contracts making the connection. When the wire is hot it expands the connection causing an arc which results in poor spark. Very common for carbon spark plug wires to do this.
Weak spark on a couple of cylinders could easily cause hard starting.

 

[RyanHeo]

I30 doesn't have ignition wire set. It has a direct coil type.

Anyway.
I found the new clue related to the hard starting problem. I thought it was hard to start when the engine is hot. However the engine isn't hot but it has the same symptom when the car was parked in which directly exposed to the sun. My parking lot is under tree in my house, but the school parking lot has not any celling upon the car like the street parking. Today's temp is 85F~90F. When I came back to home from school, it happen again.
What kinds of parts are related to the outside temp?

Thanks.