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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: rusty but trusty on April 11, 2012, 02:38:09 pm
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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
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Do you have a check engine light on?
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no i did but that was a sensor that wasnt hooked up so it hasnt come back
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Weak fuel pump/low fuel pressure will cause that.
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Check the fuel pressure, EGR operation and engine compression; replace the fuel filter and give it a tune-up.
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ok i will start to work down that path
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I would check the timing on it.
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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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the compression is either 175 or 180 alternating cyclinders
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The timing is electronically advanced or retarded, but you still have to time it to 0* before any of that takes effect.
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Ok so on a tbi do you have to disconnect the brown/ tan wire
and then set the timing?
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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.
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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.
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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.
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Did the Check Engine light come on when you disconnected the EST?
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tune it up and set the timing.
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yes the service engine soon light comes on and how would i go about doing a tune up? yes this is a dumb question but i really don't know much. and thanks too all of you
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Replace the spark plugs, wires, cap, rotor, fuel filter, air filter PCV valve, set the timing, disconnect the negative battery cable for a minute to reset the adaptives.
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ok iv done oil change new cap and rotor and new wires new plugs new fuel and air filters but i cant find my pcv valve all of my breather lines on my valvecovers go to my intake manifold
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The PCV valve should be at the end of a 3/8" vacuum line plugged into the top of a valve cover. Since your engine has been replaced, it could be either side.
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The PCV valve should be at the end of a 3/8" vacuum line plugged into the top of a valve cover. Since your engine has been replaced, it could be either side.
You might only see the top black part of the PCV valve, the silver part might be pushed into the rubber grommet.
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bake74 thank you so much i have looked and looked and then i read your post and i felt kinda dumb but enlightned
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So does that mean it is there, but just pushed in the grommet ? If so you are welcome, that is what we are all here for, just to help without judgements. ;D
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the pcv was pushed into the valve cover so bake74 saved the day.
does anybody have any idea why the engine would shake more than is reasonable at idle, the throttle response isn't great either
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Hook up a vacuum gauge and that will let us know what it reads. They are cheap to buy. I keep one hooked up inside my cab.
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Misfiring or crossed plug wires? Incorrect timing? Spark plugs loose? Distributor cap not locked down?
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does anybody have any idea why the engine would shake more than is reasonable at idle, the throttle response isn't great either
Misfiring or crossed plug wires? Incorrect timing? Spark plugs loose? Distributor cap not locked down?
Also, check the motor mounts to see if they are shot.
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OK i have 17 inches of vacuum and the plugs, plug wires and rotor and cap are brand new the cap is tight and the coil is a month old also # 1 is always wet but defiantly has spark
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Not that is has any thing to do with the truck shaking, you said #1 spark plug is always wet. With oil or just moister ?
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wet with gas and #8 was also wet with gas so i switched them but i think iv just lost my firing order completely
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Lost your firing order ? You messed up the wires going to the spark plugs ?
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Hope this helps. If not then I think a compression test is in order (http://img.tapatalk.com/d036569b-ebf1-f65b.jpg)
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That's the wierdest firing diagram I've seen. Like you're laying on the roof putting your plug wires on.
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That's the wierdest firing diagram I've seen. Like you're laying on the roof putting your plug wires on.
It would look better if it was rotated 180 degree's.
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True
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i tried to swich 1 and 8 because both had spark but were always wet but mixed up some wires and things went downhill fast and then i think i fixed it but dont know because next day i double checked it and went to start it and nothing i hooked 2 more running cars to the battery and still nothing no power anywhere