New 5.7 300 HP- 1994 Z-71 - need help

[JProctor1975]

New here,
I'm the only owner of my 1994 Z-71 short box regular cab. Bought her off the showroom floor. She's 29-1/2 years old and I wanted to get her some new life for her big 30. I purchased a 300 HP 5.7 long block. Installed it and have had some issues with getting to run smooth. first issue is it runs rich. I've replaced all sensors (twice) and fixed any wiring that could have been questionable. With no improvement. The only thing that I can think of is the Fuel Pressure Regulator. I have rebuilt it (new gasket and spring). Thought of installing an after market one. Any advice would be great!

My second issue is overheating. The dash gauge will say 250 but when I use a heat gun the intake is only at 120 -130. I aim the heat gun at the thermostat housing. I also take a temp reading at the heads and they show 250 to 260. This is by the exhaust manifolds. Because of the location I'm not sure if the reading is a good location or not. Is there a proper location to use a temp gun? I have tested the thermostat and it opened at 190. I replaced the radiator and used a vacuum system to fill the coolant each time. I have also replaced the coolant sensor twice and fixed / replaced the connector. I've checked the ohms and it seemed to be good. Sorry I do not recall the reading I got. Any advice would be great!

 

[L31MaxExpress]

Intake gaskets installed backwards by chance?

What makes you think it is rich? I bet it is lean as can be atleast off-idle and under load. The stock TBI system runs crazy lean if it does not have 13-14 psi of fuel pressure even on a stock engine. At 100% DC which the TBI system will actually run at in stock form, the twin 61# injectors flow enough fuel for ~270 hp at the crankshaft which is about what the engine makes at the flywheel. There is some debate if the stock injectors were rated at 12 psi or 13 psi and I have seen the best results basing the math off 13 psi. When I work with a stock TBI 13 psi is the minimum pressure I want to see on an accurate gauge. From that starting point, I use the fuel trims and 02 voltage to know if it needs more. A solid 300 hp 350 needs about 15-18 psi of fuel pressure and chip tuning to run right.

 

[jd33173]

New here,
I'm the only owner of my 1994 Z-71 short box regular cab. Bought her off the showroom floor. She's 29-1/2 years old and I wanted to get her some new life for her big 30. I purchased a 300 HP 5.7 long block. Installed it and have had some issues with getting to run smooth. first issue is it runs rich. I've replaced all sensors (twice) and fixed any wiring that could have been questionable. With no improvement. The only thing that I can think of is the Fuel Pressure Regulator. I have rebuilt it (new gasket and spring). Thought of installing an after market one. Any advice would be great!

My second issue is overheating. The dash gauge will say 250 but when I use a heat gun the intake is only at 120 -130. I aim the heat gun at the thermostat housing. I also take a temp reading at the heads and they show 250 to 260. This is by the exhaust manifolds. Because of the location I'm not sure if the reading is a good location or not. Is there a proper location to use a temp gun? I have tested the thermostat and it opened at 190. I replaced the radiator and used a vacuum system to fill the coolant each time. I have also replaced the coolant sensor twice and fixed / replaced the connector. I've checked the ohms and it seemed to be good. Sorry I do not recall the reading I got. Any advice would be great!

where did you source the engine? asking for a friend that wants 300hp tbi solution for his 1988 k1500 that is parked at my house...

 

[jd33173]

New here,
I'm the only owner of my 1994 Z-71 short box regular cab. Bought her off the showroom floor. She's 29-1/2 years old and I wanted to get her some new life for her big 30. I purchased a 300 HP 5.7 long block. Installed it and have had some issues with getting to run smooth. first issue is it runs rich. I've replaced all sensors (twice) and fixed any wiring that could have been questionable. With no improvement. The only thing that I can think of is the Fuel Pressure Regulator. I have rebuilt it (new gasket and spring). Thought of installing an after market one. Any advice would be great!

My second issue is overheating. The dash gauge will say 250 but when I use a heat gun the intake is only at 120 -130. I aim the heat gun at the thermostat housing. I also take a temp reading at the heads and they show 250 to 260. This is by the exhaust manifolds. Because of the location I'm not sure if the reading is a good location or not. Is there a proper location to use a temp gun? I have tested the thermostat and it opened at 190. I replaced the radiator and used a vacuum system to fill the coolant each time. I have also replaced the coolant sensor twice and fixed / replaced the connector. I've checked the ohms and it seemed to be good. Sorry I do not recall the reading I got. Any advice would be great!

also, how long does it take to hit 250? Electric fans? Mechanical?

 

[GoToGuy]

An IR thermometer can be inaccurate on engine finite troubleshooting. As the temp can be misread by nearby higher or lower spots on an engine. You tested thermostat opens at correct temp, and is installed correctly, I would take temp readings at point where water enters radiator tubes. Or start leave cap off , with a thermometer in radiator cap neck fill and watch temp. Have considered your gauge may be incorrect? Is the temp sensor correct part for location?
Recheck everything you touched, as things were normal until you touched them. So either something suddenly failed, broke or you did or didn't do something correctly.

 

[Schurkey]

Connect a scan tool, verify EVERY sensor and computer output. HOW do you know that it runs rich? If that's not based on O2 sensor voltage from a fresh and properly-operating O2 sensor, it's very questionable. "Smells rich" is extremely unreliable.

Infrared thermometers are notoriously unreliable for multiple reasons.

 

[FLGS400]

Infrared thermometers are notoriously unreliable for multiple reasons.

To expand on this, for most IR Thermometers, there is a few things that you need to be aware of to get somewhat accurate readings. First, all of those things have a "distance to spot size ratio" (usually abbreviated DS). Most cheap ones is like 1:1 or lower. This means at 4", it averages every temperature it sees within a 4" spot size. It is proportional the farther back you are. All of them have a "minimum spot size" too.

The second issue is called emissivity. Most have a preset emissivity of .9 or 1, which is great as long as you're measuring something as unreflective as flat black. Anything shiny is not going to give you an accurate reading on the display. The best thing you can do to remedy this is to put a piece of black electrical tape on whatever you want a somewhat accurate reading for, or paint it a flat, non reflective color. The only thing I use those for is to see a temperature difference on the same surface (looking for hot spots on a radiator core for example). On glass, thin plastic (like grocery bag thin), and chrome plated stuff they are useless, so don't even try.

Lastly, they only measure surface temperature. There is no penetration with the IR.

To qualify this, I am trained in Level 1 thermography. I used to rep 2 different companies that sold the IR thermometers, IR cameras, and fixed mount industrial IR sensors.

Here's a pretty good article if you're really interested:
www.fluke.com/en-us/learn/blog/temperature/how-to-get-great-results-with-an-infrared-thermometer#:~:text=Distance%2Dto%2Dspot%20ratios%20vary,thermometer%20or%20in%20the%20manual.

Sorry to hijack your thread...

 

[JProctor1975]

Intake gaskets installed backwards by chance?

What makes you think it is rich? I bet it is lean as can be atleast off-idle and under load. The stock TBI system runs crazy lean if it does not have 13-14 psi of fuel pressure even on a stock engine. At 100% DC which the TBI system will actually run at in stock form, the twin 61# injectors flow enough fuel for ~270 hp at the crankshaft which is about what the engine makes at the flywheel. There is some debate if the stock injectors were rated at 12 psi or 13 psi and I have seen the best results basing the math off 13 psi. When I work with a stock TBI 13 psi is the minimum pressure I want to see on an accurate gauge. From that starting point, I use the fuel trims and 02 voltage to know if it needs more. A solid 300 hp 350 needs about 15-18 psi of fuel pressure and chip tuning to run right.

The reason I think it's running rich is because it's its shooting black residue out of the exhaust and the exhaust smells like fuel. I tested the PSI at the fuel filter and it was 13 to 14 PSI. The fuel pump is new and the filter is new. I blew out the both fuel lines so I know there isn't an obstruction. I pulled the oil dipstick and the oil is very dark for being a new engine. It also has an exhaust smell to it. I have not pulled any spark plugs yet. My next test is going to be removing the valve covers and turning the block over by hand to see if the values are opening up like they should. I'm also going to pull the plugs to test compression. I know all you need if fuel, Air and spark to get a mortar to run. The mortar runs and seem to idle fine. But something is not right. After I check the valves and compression I'm going to pull the intake to make sure I installed the gaskets correctly.

 

[Schurkey]

The reason I think it's running rich is because it's its shooting black residue out of the exhaust and the exhaust smells like fuel.

Maybe rich. Just as likely it's got misfire, and the catalyst is failing/failed.

I tested the PSI at the fuel filter and it was 13 to 14 PSI. The fuel pump is new and the filter is new. I blew out the both fuel lines so I know there isn't an obstruction.

OK.

My next test is going to be removing the valve covers and turning the block over by hand to see if the values are opening up like they should. I'm also going to pull the plugs to test compression. I know all you need if fuel, Air and spark to get a mortar to run. The mortar runs and seem to idle fine. But something is not right. After I check the valves and compression I'm going to pull the intake to make sure I installed the gaskets correctly.

You're getting ahead of yourself.

Connect a scan tool, verify EVERY sensor and computer output. Investigate fuel trims.

Consider a cylinder-balance test. Might identify misfiring cylinder(s).

Do the non-destructive testing before disassembling stuff.