Ok, so I'll try and explain this to the best of my ability, so work with me.
Alright, so I have a 1993 K1500 Suburban 4wd 5.7L TBI 200k miles. The story is that it has just horrible power. But before you think you know the answer just hear me out. Here's the story. So I've had this truck since high school (about 5 years), and it has NEVER given me any sort of problems. Never left me stranded. A good dependable truck. I change the fluids religiously. Well I remember back in high school this thing was pretty quick for a truck. I remember I could do burnouts easy. Well, I have since grown up and stopped burning tires down because they are too expensive. Jump to the present, and the truck is just a total dog. We have raced every kind of economy car there is, and lost. This thing just kinda slugs up to speed. Now here's the weird part. On RARE occasions, after it's been sitting for awhile. After it's cooled down. It will start up, and I get that horsepower back. Oh I love it. I get that power back for like 30 seconds and it's great. But then after it warms up, it returns back to it's normal sluggish self. I figure that it's not the transmission because it's clearly capable of accepting the hp and putting it down.

So here is the list of parts that are new. (I didn't buy all of these to try and fix this problem, they are just new.)

New Fuel Filter
New Fuel Pump
New Fuel Pressure Regulator
New O2 Sensor
2 New Fuel Injectors
TBI Gasket Kit Installed
New Coolant Temperature Sensor
New Coolant Temperature Switch

Now I have replaced all of these so don't suggest that one of those is the problem, because it's not. I wish it was, but it's not, haha.
I figured it might be the Coolant Temp. Sensor because it was temperature specific, but no. I have heard about the possibility of being a clogged or bad Cat., but I don't know. And to emphasize how much of a power difference there is when it's cold. When it's warm, and you floor it, it just kinda stumbles up to speed. Barely any throttle response. When it's cold, all the power is right there, and good throttle response. The difference feels like 50hp, no joke. I've also heard the possibility of the PCM going bad, but I don't know. I'm just a junior mechanic trying to solve a problem and any help would be appreciated. Thanks guys.

 

Welcome to the forum.

When the engine is cold and running in the open loop configuration, it will run richer. When it warms up, it goes into a closed-loop configuration and the computer takes over based on sensor inputs. Have you checked for any codes?

Did you replace the fuel pump with an OEM pump? If not, I would check the fuel pressure.

 

Thank you.
Well let's see, it's on an OBD1 Port, so I haven't gotten around to testing any codes yet. And yes, the pump was OEM. It's weird, because It's capable of producing the HP in this "open loop", and let me reiterate, it is a BIG difference in power in comparison to when it's warm. BIG difference. Like when I hit the gas, It actually gets up and moves, haha. It's soooo bad, you have no idea. Getting beaten by some yahoo in a prius is sooo embarassing. And it's not even a close race either. This prius takes off like a rocket compared to my truck. Anyways, I'll look up how to check codes for OBD1 after I get off work, and see what I can do. Thanks for the help.

 

Yeah there were no codes given at all. So I'm stumped. Any thoughts?