Ok i have a blazer 95 4.3 vortec mi chk engin

Is your "Service Engine Soon" light on?

Have you scanned for fault codes?

I would suspect low fuel rail pressure...caused by a tired fuel pump.

Before considering a faulty PCM see here for more information and diagnostic tips:

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Have 1995 Chevy Blazer V6 4 3 Vortec and It Ran Ok but We Had

Sounds like low fuel pressure.
A GM vortec engine needs at least 65 psi to start and run.

Yes they bolt right in.

Drive belt routing-1994-95 4.3L, 5.0L and 5.7L engines, C/K series (without A.I.R.)

Drive belt routing-1994-95 4.3L, 5.0L and 5.7L engines, C/K series (with A.I.R.)

your statement is fuel pump work ok, have you tested for proper fuel pressure. just because the fuel pump works it could have less pressure needed to start the engine. maybe the fuel filter is plugged. start out by replacing the fuel filter, if this doesn't fix it, you need to pressure test the pump. even 10 psi reduction in pressure will allow the engine not to start.

The color codes will be different so when you take the harness off the 95 make sure that you label ALL the connectors to make it easier to install it on your Blazer. You may also have to change some sensors or switches up to 95 so that the harness will fit. Label all the empty connectors with their location in the 95 because they will be for options that may or may not be on your Blazer. If you have to access a wire diagram to complete the job then use the 95. DON'T let someone else take the 95 harness out for you andtake a rough diagram of your truck with the plug-ins marked for location and # of pins for wires. Basically it should fit but attention to detail is a must.
Also check out faxonautoliterature. They list GM service manuals but also GM books for engine interchanges that may prove to be very helpful. Hope this helps.

A spider injector is located underneath the intake plenum and this is multi-port. Otherwise you have a throttle body injector system. Vortec engines have spider injectors and they are super expensive to replace ($400.00- 850.00) each ! There is only one spider injector for each engine it has 6 legs/fuel tubes that go to each cylinder.

you have to put a guage on it to find out the pressure it may kick on but not enough pressure

you need the firing order?? it is 1, 6, 5, 4, 3, 2 clockwise. Number one on cap is forward position, or 6 o'clock position, just left of the hold down bolt.

95-94-93 4.3 vortec are compatable engines. 97 4.3 will fit but will have problems with sensors and computer