Starts fine cold, will not start when hot...already threw a ton at it.

Stop! Order a scanner so you can see what data the ECM is reading! Without out knowing that your pissing in the wind. This is the one I use for quick easy info.

$20 Foseal OBD2 Scanner, WiFi Car Code Reader Check Engine Light Diagnostic Scan Tool for iOS and Android

https://www.amazon.com/Foseal-Impro...ix=obd2+elm+scanner+bluetooth,aps,127&sr=8-13

 

If you have one already. When your vehicle wont start, Go to live data on your scanner app. Screenshot the data, scroll up and keep screenshotting all the data then post the pics.
Do the same after you get it running.

 

Copy. Thank you. I've done security work for 25+ years. This is NOT my wheelhouse, hence why I am struggling. I DO have a scanner. But that was going to be my next issue....I have ZERO idea of what the value show, or acceptable ranges. I'll fire it up and screen shot this evening. Thank you for reading and listening.

 

Did you try new coils yet? (I skimed the thread... excuse me)

 

So I saw a similar thread on another forum, lots of 95-97 4 cyls with hot hard start issue. A couple guys had similar experiences with mechanics as OP, throwing $1000's at this. For several it was dirty MAF if you can believe that. A $5 can of MAF cleaner solved the issue. For one, cleaner helped, he took apart MAF and it had crud on the sensor, he carefully cleaned off the crud and problem solved. One other guy reported tight valves.

It seems that for early 4 cyls the MAF is very sensitive to dirt. Also I did not think that the MAF was used open loop/starting but apparently it is.

I think for at least one the MAF issue started with those oiled filters - I do not like those.

If you do this be very careful cleaning the MAF, do not touch the wire with the spray can tube as the MAF is a $500 part.

I did not even know you can scan these types of non code issues with a generic scanner - the FSM always refers to the Toyota tool that plugs into the connector in the engine bay and I have heard not even the dealership have those! I'll have to try this.

I have that same scanner can confirm it works with older OBDII as many do not. I think you have to purchase SW to get beyond just code reading though but still worth it.

Edit - Oops, just saw OP cleaned, swapped MAF's so no joy there

 

Knowing what normal values should be in the live data feed from a scanner and comparing those to what is showing, is important data to have. Especially in a hard start issue.

 

You said JDM transplant…I’m curious to see if you are still running JDM parts on that motor that your ECM isn’t liking. I’m assuming they knew about those codes before you bought it and probably just reset them considering they showed up a week later. It would explain why shops can’t figure it out. Someone with a waveform diagnostics scanner can see what’s out of wack.

 

I have seen this in fuel injected cars with bad coolent sensors. Car sees super low temp, but the engine is hot so fuel vaporizes readily. Opening the throttle let's enough air in that it gets the mixture close enough to start. Then runs like crap (because it's super rich) until the computer is reading the O2 sensor and it goes into closed loop.

 

im 90 percent confident its your MAF. A bad maf will not see enough air when starting to engage fuel pump or keep it running. Give it more throttle could help the maf see more air moving as they work off the calaric principle, a small heater the measures the amount of heat being wicked away by the air moving across it.

Replacing the fuel pump due to high pressure make no sense, your fuel regulator is resposible pressure located on the back of the fuel rail. Check your vaccum line going to the top of the regulator, its been awhile but seems like it vents to atmosphere or doesn't see vaccum on a stock truck.

 

UPDATE:

I have the vehicle back. Seems a few have maybe overlooked the actual issue or complaint.

Truck starts FINE and runs FINE when cold. Idle settles and it's great. No bobbles or stumbles. After the vehicle is fully hot and operating....if I turn the truck off....I CAN RESTART IT in 30 seconds after turning it off. So it starts when hot. I can wait about 1 minute....Truck WILL START. If I wait any longer, like turn the truck off and attempt to start it 5 minutes later, it WILL NOT START, or rather.....it will fire and light for just a second or two and will not stay lit.

I've removed the gas cap. THere is no Hiss and relieving the negative pressure does nothing to assist in starting and keeping the vehicle running.

I have several screen shots of Live Data taken as soon as the truck is started, and several of data taken when the truck is operating at full temperature. Are these of any value?

 

The concept of the previous owner clearing all codes and CEL and selling it to me is highly probable. But what can you do? I own it now.

 

In the olden days, we used to have carburetors and there's a thing called a choke. You use the choke on cold starts to choke off air and give it a stronger fuel mixture. You don't use the choke or pump the gas on warm starts, otherwise you might flood it. This is where there is too much fuel and not enough air. To get it to start, you hold your foot down on the pedal (do NOT pump it) to open up the butterfly valve and let the most air possible in. In this case, the engine usually stumbles to life slowly as the excess fuel gets burned off.

So, let's just say you have leaky injectors and think about how the truck might behave. Here is my thought.

When you run it and then turn it off, there is fuel pressure built up behind the injectors, and they slowly leak fuel into the intake until the pressure drops enough for them to shut off completely (if ever).

COLD STARTS
- Truck has been sitting a while, some of the leaked fuel has evaporated, and it needs a stronger fuel mixture to start anyway. No problem.

WARM START before 1 minute or so
- Some extra fuel is dropping into the intake, but not enough time has passed for it to cause a flooded condition, engine starts and quickly burns off excess fuel. (but might throw a P0420 code)

WARM START after several minutes
- Enough fuel has leaked into the intake to cause a flooded condition. Engine stumbles and won't start.

Based on your symptoms, I'm saying leaky injectors.

 

I'm 50. I have a 1974 K5 and 1984 K20.....I am familiar with a Choke and that Carburetor thing. lol

^^^ The Above is how I envision the issue. But obviously can't be certain. From what I've read....the fuel is supposed to leak around the rings and ultimately thin the oil and fill the case??? Engine is very tight. Oil at 4000 miles looks brand new. Maybe tight enough where leaking fuel literally sits in the cylinder? You concept is the one that makes the most sense to me.

 

A leaky injector would show up in a static fuel pressure test, if it holds pressure with the engine off it can't be a leaking injector, if it doesn't then yes potentially one is leaking.

 

Per the shop I just picked it up from.....holds pressure just fine. Now I am back to Zero on ideas.

 

You could post them so we can take a look.
Also are you still getting any codes?

 

I had a near identical issue on my 3rz and chased it for months. Finally solved it. Ended up being a cut in the Cam sensor wire through more than half the copper. soldered some new wire into it and good as new.
Ran fine when cold, and even when warmed up as long as I didn't shut it off. Once it shut off, had to wait for it to cool before it would run.
Not saying this is your exact issue, but just an example of how finnicky these computers can be.

 

The same thing happened to me years ago. It was the fuel pump overheating. The vehicle would not start or run until the pump cooled down. Replaced the pump and problem solved. I think I saw that you replaced the pump or at least they claim they replaced it....

 

The thread I read a few years back found it to be leaking fuel injectors.

The only way the mechanic could verify was to snake a bore scope down the intake to film an injectors. He could actually see drops of fuel leaking out of the injector in real time.