ElMartillo

Curious what causes you to believe it's "leaning out"? Sounds to me that it's running rich and not leaning out as it should when it arrives at operating temperature. That's why it will run when hot with the throttle part way open, as you say at 2500 rpm, as this introduces the correct amount of air for the fuel provided when the motor is hot.

LiamLikeNeeson

This is most likely not the problem at all but since you said it's when the coolant thermostat opens and I don't know if you checked the coolant level or not but maybe there's a coolant leak in the engine and drowning it out but I'm sure that's highly unlikely.

forthewreckered

I'm pretty sure if it were flooding out I would have a strong gas smell and black smoke coming out of the exhaust right? No smoke at all.

forthewreckered

I don't think that would be the issue. I'm not losing any coolant and I would have some coming out of the exhaust if that was the case.

ElMartillo

Not flooding, but a rich mixture that is correct for a stone cold motor, but too rich for a hot motor to run. I'm no expert, just some thoughts about your symptoms.

It would be like pulling out the choke on a hot carbureted engine. Not flooded, but won't run like that.

forthewreckered

I didn't think of it like that. What might cause that to happen? Stuck injectors?

ElMartillo

Anything that is responsible for changing the mixture as the engine warms. Check all your wiring/connections for your coolant temp sensor, ECU, recheck IAC and TPS. I know you said you replaced a lot of stuff but there's a possibility a new part is malfunctioning. Sorry I don't have the expertise to help diagnose any of those parts. Definately listen to Cruiser54's suggestions.

Oswalla

I would rule fuel problems out with a rental gauge. Fuel pressure regulator is an easy test as well. Fuel ballast is on driver side quarter panel by egr switch.

You posted coolant sensor on thermostat housing. I thought that was 91' and up, unless you did a open cooling conversion with a 91' and radiator, and that was to send temp for electric fan to turn on. Maybe Cruiser can chime in, but I am pretty sure the ecu temp sensor is on the side of block. Regardless I don't think that will prevent a startup ?

cruiser54

ballast resistor is shown in tip 3 but here ya go.

Oswalla

Fuel pressure regulator comes to mind.

ElMartillo

That's fine, but why only when it's hot?

forthewreckered

It has a 91 engine in it. The block does have a plug in the same location the sensor would go. Would moving it there have an affect?

forthewreckered

Got home from work and checking some things. I picked up a fuel pressure tester today and I have 0 fuel pressure at the fuel rail (tested the gauge and yes it works).
I've already had it running before I hooked up the tester so it's dead right now but when it cools off I will check the pressure when it's running.

I feel dumb now but I never could've imagined it would be fuel pump related since it would crank and run with throttle.

forthewreckered

I put a fuse in bypassing the resistor and no effect. That should rule that out right?

forthewreckered

It's the fuel pump. 20 psi at startup drops to 0 the same time it stalls.

What's the best type/brand to get?