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.

Compression was great as of a few weeks ago. But thank you for reminding me to pull my distributor cap and clean it. It had thick white deposits on all of the contacts as well black on the (graphite?) post. After I cleaned it this morning, she fired first try under the same conditions that she was previously giving me trouble. I've done this a couple times over the past 6 months, seems like my distributor contacts are fouling too quickly. Any thoughts?

EDIT: A clean distributor help my new cold start issues but the problem is still persisting when warm after sitting a couple hours or so. Same issue of cranking, firing for a second then dying. Will start on its own but starting fluid makes it happen faster. Holding the throttle open does not seem to improve the starting but I will try it some more.

Going to order some parts so that I can hook up a fuel pressure gauge. Any thoughts/field tests in the meantime?

Still thinking of ordering some new OEM sensors. Whenever the engine is anything but ice cold, it has trouble finding the right idle on startup. Cold, it fires an immediately revs right to 1000RPM (edit: more like 1200 until its done with cold idle.) and stays there. Hot, when it does stay running, it fires and sorta slowly chugs its way up and eventually settles on 1000. Seems like if it hit it with ether right before a hot start it gets rid of the chug-a-lug. Don't know if that's useful info but there ya go.

Bryce - before wasting your money on new sensors, there are specs in the FSM for them. There is a temp sensor for the ECU, temp sensor for the gauge, and one for the cold start injector. Obviously the gauge one isn't causing you this issue, but I would pull all of them, clean the really well, and then test them. You can put them in the freezer for a bit, put them in warm water, and test the resistance of them as those temps.

I do not know much about the 3.0, but I assume it has an idle air control valve similar to the 22re. Do you get a cold idle? There are also tests in the FSM that involve pinching the hose from the IACV at cold to verify that it is working. I'd do those tests plus clean and test the sensors before just replacing expensive OEM sensors.

Cory do you know if the specs are the same for the 1988 sensors as the ones in the 1993 service manual? I know the array itself is different in my engine versus the one shown in the FSM. But thats good advice I will check the resistances when I'm home from visiting family. That and install a fuel pressure gauge. Today I got the chance to drive all day and stop for few hours at a time, I used starting fluid each time and never got a hard start so I suppose I'll see what happens with the fuel pressure gauge.

I have a little hesitation on mine under these same parameters. I'm also leaning towards injectors and/or fpr @ 265k on the clock. Let us know what u discover.

Revisiting because I finally got around to testing my fuel pressure. In spec while running and the regulator is in spec but the fuel pressure drops to 0 within 5 seconds of shut off.

Any advice here?

Its still is mainly only hard to start when sitting for a specific time (2 to 3 hours OR overnight) even though it never maintains fuel pressure when off. So I'm not sure what that means but maybe someone else knows.

Believe it or not, there is a spec on that: stay above 21psi for at least 5 minutes. http://web.archive.org/web/201003261...87fuelpump.pdf But that's not your problem. It might mean you have to crank a little more if you try to start it within 5 minutes, but even if that's the case it's so little you're not noticing it. I doubt anyone's truck holds pressure for an hour. (Mine will stay above 21psi for only about 3 minutes.) Why does yours? Probably a bad check valve in the fuel pump, or maybe a leaky FPR. But if you're getting the correct pressure numbers (at idle, and off), that isn't it.

No one has mentioned ignition timing. A timing light is only $30 and you should have one anyway. I'd check that. It COULD cause your problem.

scope, I see what you mean. I plugged the fuel return line to rule out the regulator and still got the same pressure drop, and I've tried a new fuel pump as well to rule out a check valve issue. In my mind whats happening is the injector(s) are leaking into the engine and when hot, enough of the fuel is vaporized to keep dry and when sitting overnight it also has a chance to dry out. I think this is why i have a "lukewarm" start issue. I have a timing light and have checked a number of times. I have also checked valve timing and that is good too.

I once "feared" leaking injectors, so here's what I did to check: https://www.yotatech.com/forums/f116.../#post52330847
You have to remove the plenum, but not much else.

Don't forget the temporary fuel return line.

My problem was NOT a leaking injector.

Thats a great idea, man. My buddy has a borescope we're gonna use to look at the injectors tonight but if that doesn't pan out ill try your idea.

Borescope? Let us know how you do that. The injectors don't go into the cylinder, but the lower intake manifold.

Just lifted the plenum enough to slide the camera in. As far as we could tell none of the injectors are leaking. So I don’t know what’s happening to my fuel pressure at shutoff but like scope said, I suppose that isn’t my hard start problem.

Pull the vacuum line off the fuel pressure regulator and make sure its dry. Another issue I've seen before is a leak in the line that comes off of the fuel pump. Its the same as an "external" leak but you'll never see it because it leaks inside the fuel tank.

So something I have noticed is that my CSI only seems to spray on the first crank attempt. SO if I put the key in and crank it will spray, but once the key is turned to "ON" if i crank it subsequent times the CSI wont spray. BUT if I cycle the key all the way off before cranking again it will spray again. My thermo time switch checked out as far as the FSM is concerned.

When cold, the CSI fires even if the thermo time switch is disconnected???? but only on the first crank or after I cycle the key.
When the engine is hot it doesn't spray at all regardless of the thermo switch being connected or disconnected.
If I unplug the time switch AND ground the injector (STJ) it will spray every time without having to cycle the key.

This morning was icy maybe in the 20/30s and it was a no start until my buddy gave it ether while I cranked, fired right up. I didn't cycle the key at that point because I didn't know it made a difference for the CSI but I'll test that idea these next few mornings.

Checked a bunch of voltages at the ECU per the FSM and everything looked good. Also, took out the aftermarket fuel pump I had installed at one point and replaced with an older OEM pump I had. Started well this morning but it was not very cold out. Had a long crank after sitting for 2 hours and got it to start by grounding the STJ wire (green w/ red stripe coming off of the thermo time switch) and forcing the cold start injector to fire. I wouldn't have thought the CSI needed to fire as my engine was considerably warm. Might be something to try as there have been a couple other posters on here having problems like me. I had previously tested my thermo switch with hot/cold water and cleaned the contacts but I guess it is still defective or I have a short somewhere. A new one is close to 200 bucks and I am probably going to start getting things together for a 3.4 swap so I am not looking to sink much more time into chasing this hard start issue, so for now I think I'm just going to throw a toggle on the STJ wire and feed it into the cab for when I'm having hard starts. I'll post again when I figure out if this solved my issue.

Yeah this solved my issue. Something in the CSI/thermo time circuit was/is off. The injector behaves super odd on its own but things are working alright with the toggle installed. Thanks to everyone who chimed in to help!