Easy cold start but Hard Start After Sitting Several Hours
 

I have a 3.0 with new heads, plugs, wires, coil, fuel pump, etc. Runs like a top and most of the time is easy to start. After sitting overnight she fires right up. After sitting less than an hour she fires up. But theres a zone from about 1-4 hours of sitting where she wont want to start; cranks forever, eventually fires and sort of sputters at low idle and eventually builds, then idles perfectly. Any ideas as to where I should start?

Sounds like a classic case of vapor lock. Check the routing of your fuel line and make sure it's not too close to any heating sources. (i.e. exhaust pipe, header) Try running a longer fuel line at the TB with a loop in it. You could also try shielding the fuel line with foil tape to see if that eliminates the hot start problem.

Did you replace or rebuild your injectors with the new heads ??

Sounds like leaky injectors getting the plugs wet causing them to not fire .

Things are Hot enough for the first hour to keep the plugs dry

Also sitting over night allows them to dry she fires right up

Makes sense. I replaced the components on the injectors but I didn't send them out to be cleaned. If I pull some plugs the next time she wont start will I be able to tell if the plugs are getting wet or would it be hard to tell? Ill mention that if I shut off the engine before it gets warm it always restarts with no issue, regardless of how long I leave it to sit, which makes me think the injectors aren't the issue. I would think that if the injectors were leaking and I let it run for a second, then let it sit for an hour it would have trouble starting because there wasn't enough residual temp to dry the plugs nor enough time for them to dry on their own. Engine always fires quickest when its cold which makes me lean toward the ECT circuit screwing up my fuel mixture when it's "lukewarm." That being said I've already replaced the ECT sensor and I'm not sure how to test the circuit so if anyone has info on that I'd appreciate it.

Quick, easy, cheap maintenance item:
All temp senders, including their mounting threads, need to be cleaned to bare, shiny metal at least once every 20-something years. Some senders rely on mounting threads for grounding.

Not necessarily. Just because you jump out the fuel pump and hear it running or see pressure on a gauge does not mean you have flow through the system. You could be dead heading the pump.

The "hot" start may be prior to fuel vaporizing where the warm start is already vapor locked. Insulating the fuel line in my mind would rule out vapor lock.

Ill keep that in mind but I've verified that fuel is cycling back to the tank through the return line. I don't believe I am dead heading the pump. Ill pick up some insulation this weekend and give it a shot but I am still open to other recommendations.

Revisiting because I am still having issues. Tried a bunch of insulation to see about a vapor lock issue but I didn't see improvement. The problem happens so rarely so it's hard to troubleshoot. Someone mentioned injectors so I will probably go there next because it does seem heat related. Basically if it's real hot or real cold it starts fine but anywhere in the middle it cranks forever and then sorta chugs to life.

one simple test you could try is when it won't start give it a shot of starting fluid (pull the intake tube, open the throttle body, spray a little in, quickly reconnect the tube and crank it ). if it still won't start it is either flooded or not getting spark. if it starts there is a fuel supply issue.

I have a similar problem after rebuilding my '90 3.0 and am looking forward to your resolution. I personally think my cold start injector is behaving badly - flooding me out when the engine doesn't need the fuel. Once I get over the glee of actually getting this thing to run I'll start chasing the small stuff...

Repeat:
https://cimg4.ibsrv.net/gimg/www.yot...f62c741d88.png

try this

Hey awkwheeler, I've had a can of starting fluid on my passenger seat for a few weeks now. To be honest its tough to tell if it makes a difference on its own. Sometimes she'll fire and stay running after a couple tries with no starting fluid, sometime it takes several or more; so when I use the ether its hard to say if that's the ticket or if I'm just getting lucky and the engine decides to fire and live on that particular crank. Not to mention sometimes the engine runs first try. HOWEVER I am finally starting to think that the starting fluid is helping.

The past few days it's had trouble starting even after sitting and completely cooling overnight, starting fluid seems to help.

Basically what I have going on now is anytime sitting about 2 hours or longer, it cranks, fires quickly, chugs for a second, dies. Repeats one or more times, then finally it fires and chugs to life and stays running.

Going to keep testing with the starting fluid, but it does seem to get the truck running faster. Also, gonna try a new fuel filter, pump (already have an extra one to try out) and see about further insulating the fuel lines for vapor lock. Any other things I should think about?

this is a tough call, but it sounds like weak spark. Maybe low compression, have you checked?

How's your fuel pressure?
A few of us installed fuel gages piggybacked on CSI:
https://www.yotatech.com/forums/f199...l#post52312190

Also allows you to see if the fuel-pressure-up vacuum switching valve is doing its job. When actuated, to prevent vapor lock, it should raise fuel pressure. Below, I SIMULATE VSV exposing fuel pressure regulator to atmosphere to raise fuel pressure:

https://photos.app.goo.gl/MiQqvS8wtaMQKmzS6

If it were low fuel pressure or vapor lock the use of starting fluid would make it fire right up and run for a few seconds until it ran out of starting fluid to burn.

I can almost guarantee its not vapor lock. When the truck is shut off and everything works as it should, pressure should remain in the system. With the high pressures of fuel injection the boiling point of the fuel raises to a point where it almost cant boil from engine bay heat. If it were vapor lock, jumping the fuel pump should remedy the problem which you said it didn't. As long as the pressure regulator is operating correctly there should be fuel flow.

Your case sounds exactly like the fuel injectors are bleeding down. If it were a lack of fuel then starting fluid should fire it up. It sounds like it has too much fuel. You need to get a pressure gauge on it and see if the pressure bleeds off in the time it takes to have a hard start. if the pressure bleeds off significantly in that time then its one of four things. Injectors, fuel pump, regulator, or external leak. Chances are it the injectors. When its time for a hard start hold the accelerator to the floor and crank it. That will help clear any flooding. See if it helps. If it does then you probably have your answer. Start looking into injector issues and stop fooling around with the vapor lock idea.