1991 r3500n 454 cfi, cold start issues....

[cag]

this cfi 454 on start up runs really rough and backfires sometimes, any idea what is going on???

[Bob B.]

When you shut the engine off, is there fuel leaking from the injectors flooding the intake manifold? Also check to make sure the engine coolant temp. sensor (the one for the computer, not the gauge) is reading properly. You can check it with a scan tool. Sometimes they can be way off and cause hard start problems. Does in run O.K. once it warms up?

[kwmech]

1991 big block is going to be a TBI so first I would check the EGR spacer underneath the throttle body for vacuum leaks. Then I would move on to the coolant temp sensor by the t-stat and make sure the wiring is not messed up. After that?? maintenance for a tune up, plugs wires? what shape are they in. Plugged fuel filter etc.

[cag]

Originally Posted by Bob B.

When you shut the engine off, is there fuel leaking from the injectors flooding the intake manifold? Also check to make sure the engine coolant temp. sensor (the one for the computer, not the gauge) is reading properly. You can check it with a scan tool. Sometimes they can be way off and cause hard start problems. Does in run O.K. once it warms up?

it runs fine after it warms up, will look at injectors, what scan tool?

[cag]

Originally Posted by kwmech

1991 big block is going to be a TBI so first I would check the EGR spacer underneath the throttle body for vacuum leaks. Then I would move on to the coolant temp sensor by the t-stat and make sure the wiring is not messed up. After that?? maintenance for a tune up, plugs wires? what shape are they in. Plugged fuel filter etc.

plugs, wires,coil,dist all brand new.

[kwmech]

So that leaves us with a vacuum leak or a CTS and/or black and yellow wiring at the connector.