Replaced motor, starting hard. runs fine . how do I check fuel pressure

Possibly bad plugs, fuel filter restrictions, weak fuel pump

Just because you replaced the fuel pressure regulator does not mean it is working correctly; which is the most common cause of your problem. Hook up a fuel pressure guage and watch what happens when you are starting it cold - it should go up to about 47 PSI and once started it should read between 40-47 PSI, then when you turn the engine off: Does the pressure drop? There is a check valve built into the fuel pump also; that can be faulty and if the pressure is generally reading low and the check valve is bad- this can also create your problem. We have run into this before also; When the fuel pump is cold the internal pump seals are sealing great, but after a period of running time the pump seals lose sealing power and if you try to start it again it will be hard to start. The biggest thing with this situation is getting the fuel pressure readings at the following points of time:: Start-up, running cold, running at normal operating temp, engine off, engine re-start.
Pete/ Bambenek Auto LLC

Did you check the fuel pump relay ?
You would need to use a fuel pressure gauge and check pressure before you crank the engine.
When you turn the key switch on, the pump relay is supposed to provide power for 3 seconds to boost fuel pressure.
If fuel pressure is ok, the coolant temp sensor could be telling the computer the engine is warmer than it really is.

Check fuel pressure at motor

Run some tests on fuel pump

Fuel pressure,volume,current or scope it
& check armature pattern for failing pump

hard starting first start of the day , sitting over night ? Fuel pump . Check valve inside that is suppose to keep pressure in fuel lines to the fuel injectors . Checking with a fuel pressure gauge is the proper way to test , not guessing and replacing parts . Your best bet ,take it to a qualified repair shop. Can't help your on a low fixed income . You could spend alot more money if you don't. So do yourself a favor .
Testing for failed fuel pump check valve

Hello Trio1.

First item to check is the fuel pressure. (is it cold where you are?, could have a frozen fuel line?)
Open the fuel filler cap and listen while someone turns the key to the on position. There should be a couple seconds of humming noise when the fuel pump runs. If no noise is heard the fuel pump or the wiring to it is bad.
Here's a quick hint and it often works if the fuel pump is the issue. While someone is cranking the engine over with the starter, hit the bottom of the fuel tank with a baseball bat or something similar. Not too hard! Just enough to vibrate the fuel pump into making contact on the armature motor brushes.
If this gets the car running it's only very temporary, you will need to replace the fuel pump. I guarantee it will happen again, only you may not be so fortunate the next time.

If you do hear the fuel pump run you will need to check that it is developing pressure.
On the fuel rail where the fuel injectors are on the intake manifold the is a fitting where a fuel pressure tester is attached to. There should be 50 to 60 PSI when the key is turned on. If low on pressure you will need a new pump.
A partially plugged fuel filter is hard on fuel pumps, it does make them work hard. Replace it too.
If your fuel pressure is OK then you will need to find out if your fuel injectors are firing.
If you need help with those, let me know here, I doubt we will need to get that far, but just in case.

Thank you for using FixYa.

KL

Try replacing the fuel filter and check the fuel pressure at the shredder valve. Low fuel pressure from a week fuel pump or dirty fuel filter will cause hard starts, a bad ground will also do the same thing so check the ground wire for the fuel pump which is separate from the main wire harness to the fuel pump sending unit.

Good luck and thank you for using FIxya.

check the fuel pressure when it is hard to start, bet it is low.

replace your MAP sensor(manifold absolute pressure) the map sensor is the computer for your fuel pressure regulator telling how much pressure. Unless your tahoe runs like **** going up hill than it inevitably your fuel pump

Hello, yes the check valve is in the fuel pump assembly. The check valve is leaking and the pump will burn out soon. Unfortunately the aftermarket fuel pumps can be very unreliable. A good portion of problems we see on this site are from people who replace the pump sometimes twice and it still doesn't work.