Hard start when hot.

[poole]

I have a problem starting my explorer only when hot. It sputters like it wants to start then dies. Sometimes it takes 6-10 attempts before it starts. It always cranks right up cold. When I turn it off hot and immediately try to start it it always fires right up. If it sits more than about 2 minutes the hard starting begins.

I have replaced: coolant temp sensor, coil pack, upper and lower intake gaskets, pcv, air filter, crankshaft position sensor, IAC, spark plugs, fuel pump and fuel filter.
I have tested: MAF/IAT and TPS.
Checked for vacuum leaks, fuel pressure is 64 psi key on engine off, 64 psi running. Holds pressure for half hour or so, does not drop off fast (leaking injectors).

So far 2 mechanics have not been able to figure it out so I thought it was time to reach out on the forum.

 

[poole]

BTW its a 2000 4.0 SOHC and no CEL.

 

[bobflood]

I have a problem starting my explorer only when hot. It sputters like it wants to start then dies. Sometimes it takes 6-10 attempts before it starts. It always cranks right up cold. When I turn it off hot and immediately try to start it it always fires right up. If it sits more than about 2 minutes the hard starting begins.

I have replaced: coolant temp sensor, coil pack, upper and lower intake gaskets, pcv, air filter, crankshaft position sensor, IAC, spark plugs, fuel pump and fuel filter.
I have tested: MAF/IAT and TPS.
Checked for vacuum leaks, fuel pressure is 64 psi key on engine off, 64 psi running. Holds pressure for half hour or so, does not drop off fast (leaking injectors).

So far 2 mechanics have not been able to figure it out so I thought it was time to reach out on the forum.

Did you replace the correct coolant temp sensor? There are two - one drives the temp guage and the other talks to the ECM.

 

[poole]

Yeah did the one that sends to ECM.

I think I may have found the problem. Its definitely a problem, but I dont know if its "the" problem.

After doing some troubleshooting Saturday I noticed some coolant on the ground, but I could not really see where it was coming from. I cranked it back up and let it get to normal operating temp and noticed some coolant coming out around the from passenger head. I have also been losing some coolant, but did not really know where I was losing it. So Im thinking Im losing coolant into at least one cylinder when it gets hot. Head gasket, cracked head maybe both?? My theory is that when I shut it off hot the cylinder starts filling with coolant, causing a hard start. It cranks cold because the coolant has evaporated (assuming a valve is open). If I turn it off hot and immediately crank it back it cranks because the cylinder has not yet accumulated a lot of coolant.

What do you think? Gonna scope that cylinder in a week or too to see if I can see coolant in it.

 

[Mike11675]

Did you every find out what problem was?

 

[dwitte]

On my 1996 Ford Explorer 4.0 I tried everything to get rid of the hard start when warm problem. I finally replaced all of the fuel injectors and the problem disappeared!