why does my truck run the way it does?

[rusty but trusty]

OK my truck is a 1987 GM v1500 that had a tbi 350 but the guy i bought it from said he put in a 305 and to the best of my knowledge it is a 305. but the problem is it starts awful i have to give it 1/2 throttle and it backfires allot and pops and bangs to life the after 5-7 mins it settles down and runs semi smoothly but rocks back and forth a good bit

[zieg85]

Do you have a check engine light on?

[rusty but trusty]

no i did but that was a sensor that wasnt hooked up so it hasnt come back

[zieg85]

Weak fuel pump/low fuel pressure will cause that. 

[bd]

Check the fuel pressure, EGR operation and engine compression; replace the fuel filter and give it a tune-up.

[rusty but trusty]

ok i will start to work down that path

[thirsty]

I would check the timing on it.

[454Man]

If I remember correctly isn't the timing controlled by the computer on a tbi? I remember something about unplugging a brown wire to check timing on a friends truck.

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[rusty but trusty]

the compression is either 175 or 180 alternating cyclinders

[Da67goatman]

The timing is electronically advanced or retarded, but you still have to time it to 0* before any of that takes effect.

[454Man]

Ok so on a tbi do you have to disconnect the brown/ tan wire
and then set the timing?

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[bd]

Ok so on a tbi do you have to disconnect the brown/ tan wire
and then set the timing?

Checking/setting base timing on TBI fueled 305s/350s involves running the engine to operating temperature, then unplugging the timing connector (single brown wire with black stripe) that breaks out of the engine harness near the bulkhead plug below the brake booster, forcing the Electronic Spark Timing (EST) into bypass mode.  Unplugging the timing connector will illuminate the Check Engine light and set code 42.  Cycling the key after reconnecting the timing connector will return timing control to the EST system and extinguish the Check Engine light.

[bake74]

Check the fuel pressure, EGR operation and engine compression; replace the fuel filter and give it a tune-up.

     You said you checked the engine compression, but these other items need to be done and more than likely will solve your problem.

[rusty but trusty]

Ok it rained today and i went to check the timing and i disconnected the electronic spark control wire and i fired up and ran perfect what gives, it has never ran like this ever before.

[bd]

Did the Check Engine light come on when you disconnected the EST?