hard start when outside temperatures are warm

Hi John,

It could be flooding (which is reverse thinking). There is a potential issue with it causing it to not get off cold start mode which is fine when the temp is cold but once it warms up it floods the engine and makes it hard to start. ie Coolant Temperature Sensor out of range.
The oil pressure sending unit on certain year Blazers, works in conjunction with the fuel pump. If you have a defective oil pressure sending unit, this will cause a hard start, or no start at all. The oil pressure sending unit is a great safety device. If you have no oil pressure, the engine will not run. Let`s say if you're driving down the freeway and your oil pump fails. The sending unit will signal the computer to deactivate fuel delivery, which will shut off the engine immediately.
We have an older discussion about this issue involving several S10 years and engine sizes.

https://www.2carpros.com/questions/chevrolet-s-10-2001-chevy-s-10-oil-sending-unit

I would start with those two. Keep in touch. Glenn

CTS has already been replaced, I will replace oil pressure sensor. OBD1 is a handicap... I would prefer OBD0 or even obd2... I will report back with new findings. Thank you

replaced oil pressure switch yesterday... no noticeable difference.
now I hear a small back fire... too rich ? too lean ?
how can you adjust a TBI?
TBI has been rebuilt and cleaned... to the point where I have two that I have swapped between.
I have TWO ECM that I have swapped between.

still starting hard about 60 degree ambient temperature.

Hi,

I noticed it has been a few days since you were contacted. Has any progress been made? Also, a backfire is usually caused by a rich fuel mixture.

Here is what I suggest. If you haven't already, check for codes. This vehicle has an obd1 system. It doesn't require a scan tool to retrieve codes. All you need is a short jumper wire or even a paper clip. Here is a link showing how it is done:

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

If you find codes, let me know what they are. As far as running rich, oftentimes you will see black or gray smoke from the exhaust.

If you haven't checked fuel pressure, check that as well. Here is a link that shows how it's done in general:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Here are the directions from my manual:

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1992 Chevy Truck S10/T10 P/U 2WD L4-151 2.5L
Fuel System Pressure Test
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Pump Fuel Pressure Testing and Inspection Component Tests and General Diagnostics Fuel System Pressure Test
FUEL SYSTEM PRESSURE TEST
PROCEDURE
- Turn engine "OFF" and relieve system pressure.
- Plug THERMAC vacuum port on TBI.
- Uncouple fuel supply flexible hose in engine compartment. Install fuel pressure gauge between steel line and flexible hose.
- Tighten gauge in line to insure no leaks occur during testing.
- "START" engine and observe fuel pressure reading. It should be 62-90 kPa (9-13 psi).
- Gradually restrict (pinch) outlet side of gauge. Fuel pressure should rise to 90 to 103 kPa (13 to 15 psi). This checks maximum pressure (dead head pressure) and determines if high fuel pressure is due to a restricted fuel return line or a TBI pressure regulator problem.
- Perform Fuel Pressure Release Procedure and remove fuel pressure gauge.
- Reinstall fuel line.
- "START" engine and check for fuel leaks.
- Remove plug from vacuum port and install air cleaner assembly with new gasket.

___________________________________

Let us know what you find.

Joe