1989 Isuzu Trooper Starting problem

I have a 1989 Isuzu trooper 4 cyl engine. Sometimes after is has been driven and sits for 10-20 minutes I can not start it. It just cranks, Has new battery and starter. It finally starts after about 5-10 minutes of trying. I have used starting fluid to start it. Does not always work. It is getting a spark. Feels like it is not getting any fuel but do not know that for a fact Had the fuel pressure tested and it tests normal. Someone mentioned the fuel pressure regulator but said that it would not start cold if that was a problem since the pressure would seep out overnight. Does that sound right? Only does it when the engine is warm and it does not always do it. It seems to do it more frequently now then a few weeks ago. I was going to have the fuel pump changed but that tested ok for pressure. Is there some type of electronic sensor that might be causing this problem. I do not have the ability to evaluate the electronic portion of the car. I drove to work today and let it sit for 20 minutes and it would not start. I left it sit for the rest of the day and it started fine since the engine was cold. I was told that the fuel pump might be overheating even though it is submerged in the tank and will not work until it cools down. I am baffled by this. Any help will be appreciated.Thank you

Optional Information:
1989 Isuzu Trooper 4 cyl 2.6

Already Tried:
new plugs, new plug wires, fuel treatment/injector cleaner, new fuel filter, new air cleaner

I’m not inclined to believe that the pressure regulator is bad, otherwise starting problems would likely present themselves no matter the engine temperature.

Honestly it sounds a lot like vapor lock, though that’s a somewhat rare thing to come across anymore.

Who says you don’t have the ability to evaluate the electronic portion of the car? It’s pretty easy-- all you need is a service manual and a volt/ohm meter. The manual will have tests for all the components that could be at fault. I’d pay specific attention to the ignition coil, the pickup coil/ignition module, and the coolant temp sensor.

One other possibility is that because on these rigs I believe the fuel pump is grounded through the oil pressure switch (so if you lose oil pressure it’ll stop running) one possibility is that you have marginal oil pressure that doesn’t get high enough at starting RPM’s when the oil is hot. Or, along the same lines, it could be as simple as a bad oil pressure sender.

Most times, only one fuel pressure check is done with the fuel pressure test gauge: before engine run, or, at idle. There are several other engine conditions where fuel pressure readings should be taken: under load; during acceleration; during cruise; and AFTER ENGINE SHUT DOWN.
Check fuel pressure after the engine has been just shut off, and 10 to 20 minuets later. The fuel pressure should still hold. If it doesn’t, the fuel could have released, into the engine, through leaking fuel injectors. This can flood an engine.
To start an engine suspected of being flooded, hold the gas pedal to the floor while cranking. Ease up on the gas as (if) the engine starts. Crank, with it floored for 10 seconds, let the starter motor rest for a couple of minuets, and crank again for 10 seconds (with gas pedal held to the floor).
Here are instruction on how to do fuel pressure testing in a thorough manner (which many don’t do): http://www.aa1car.com/library/fuel_pump_diagnose.htm

I have used starting fluid to start it. Does not always work.

Exactly what happens when you try and it does not work?

It just keeps cranking like it did before I used the fluid.

The engine always starts after sitting for a few hours. If the fuel pressure regulator was bad then why would it start when it was cold if the pressure leaked out. When it will not start it is always after the engine is warm.

I know you said it is getting spark, but this still sounds ignition related to me. Have you checked it for spark while the symptoms are presenting themselves (when it won’t start)? If not, you really need to. If you have a tachometer in the dash, look at it when you’re cranking it when it won’t start. The needle should normally jump as it’s cranked. If it doesn’t, this indicates a problem with a crank position sensor or engine management computer. If it does, it is likely a bad ignition coil ignition module, or distributor.

It doesn’t run for a second or two when you use the starting fluid?

If so, I’d agree-- that’s almost certainly a spark problem. On this truck the ignition module is the only thing that’s likely to have heat related problems. They’re kind of expensive so if I were you I’d get a manual and an electrical tester and double check, but I’ll bet that’s your problem.

I have almost the same exact problem with my 94 Isuzu truck. My uncle had a similar problem with his 89 Isuzu truck. I can drive it for weeks, months, and then one day it will cut out ( usually when pulling away from a stop sign or red light). It will just kind of - chug a chung a and quit. I catch a bus back home come back the next day. It starts right up. It is very weird. I cannot figure it out. I just try not to veer too far away from bus routes and only use it for garage saling and lesiurely events. Anyone have any idea what this could be???