1996 GMC Sierra

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  #1  
Old 12-20-03, 01:39 PM
mthomas84
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Unhappy 1996 GMC Sierra

I'm drowning here. I have a 1996 GMC Sierra pickup with 305 engine. I have had to repalce the head gaskets due to failure and after reassy., I can't get the the engine to run. In the "repair" process, I removed the intake manifold, distributor, exhaust mainfolds and cylinder heads. I set the crankshaft at TDC on compresssion stroke prior to removing these parts and noted the orientation of the rotor to distributor base and distributor base to the engine. Since I need the truck for work(no truck,no income) I wiped everything down as clean as possible making sure to remove as much of the mess created by the coolant/oil mix. I cleared al the oil passages in the heads and wherever else I could find it. I dropped the oil pan and cleaned it up and wiped down the crankshaft lobes I could reach from below. I installed new cylinder head, distributor and intake manifold gaskets carefully making sure the distributor went back the way it came out. I reconnected all electrical, added new oil and filter and reset the valves according to the procedure in the Haynes Manual for the truck. When I tried to start the engine, it turned but did not attempt to fire. I prerssed the accelerator to the floor and on next try, I got a "pop" and smoke came out through the intake plenum. I've verified spark, distributor setting, valve set has been redone 3+ times, gas is getting to all cylinders(Looks dark,some grit) and all electrical connections are correct........ What could I have screwed up here?
 
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Old 12-20-03, 01:47 PM
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In all honesty it sounds like you have your distributor 180 degrees out. Take the number 1 spark plug out, with a helper stick your finger in the spark plug hole and have him (or her) bump it over slowly until you feel pressure and air escapes. Look at the harmonic balancer and see where it is. With a socket and ratchet rotate the engine the same direction until the lin on the harmonic balancer is pointing at 0 degrees. Note where #1 spark plug wire is and pop the cap off. Is the rotor pointing at the location of the #1 plug wire??? Start from there go clockwise with the wires in the correct firing order. 1-8-4-3-6-5-7-2.
Hope this is helpful to ya,
Billy
 
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Old 12-20-03, 01:55 PM
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Sounds like Billy's right. The backfire proves you have fuel and spark, just at the wrong time.
 
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Old 12-20-03, 02:06 PM
mthomas84
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Ok, here's how I checked that. Since I had no one around to help, I removed the distributor cap and I already had the valve covers off by now. I bumped the starter around until I could watch the #1 intake valve open and close. I checked the position of the timing mark, moved it to TDC (I went past a little and had to go CCW to correct) and checked the relationship of the rotor to the #1 spark plug terminal in the distributor cap. It was on the mark...Could I be confusing myself further with this method or is it all wrong?
 
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Old 12-20-03, 02:09 PM
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That is the correct procedure, but you are on the wrong stroke. You have to wait for both valves to open and then close. Do it again and check like I explained in the last reply. This will get you where you need to be.
Billy
 
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Old 12-20-03, 03:42 PM
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How is it he is on the wrong stroke? He said the intake valve opened and closed and he is on TDC. That would make it TDC compression.

Turn the crankshaft by hand and do it again while watching the rocker arm move. The intake valve is the second rocker arm.
 
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Old 12-20-03, 06:06 PM
mthomas84
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That's the way I did it. When I saw the intake valve close (2nd rocker), I stopped turning the crankshaft when the timing marks were lined up. The rotor was aligned with #1 spark plug terminal at that point. Still no start, only "pop". If I assume I screwed everything up and didn't get TDC right from the start and got the valves set wrong, how do I start from scratch without pulling the manifold and heads off again? I've done this before with no problems but I can't make that assumption now. Could I be dealing with a piston ring or burned/bent valve? I would think that I should still get better action than the few pops I get when trying to start.
 
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Old 12-20-03, 06:20 PM
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Go back and rotate the crankshaft again just like you did. Get it back to #1 just like before. OK now for [email protected] and GIGGLES, rotate the crank one more time till you line the mark on the harmonic balancer up with 0. Check to see if the rotor is pointed at #1. If it is not (and im sure it will be 180 out) redo the plug wires according to this new orientation.
I think you will find that this is your problem, but if not, you can redo the valves. You can not reset the valves with the heads off. Back off of all of the rocker nuts and rotate the engine. Start with #1 and watch each set of rockers for movement. When the intake rocker comes up and then goes down the exhaust valve will be right behind it. It in fact will start moving before the intake valve is closed. When the exhaust valve is closed, STOP!!! Take the push rod between your thumb and index finger, and roll it back and forth while slowly tightening the rocker nut down. when you feel resistance, STOP!!! Turn the nut 1/4 turn farther. It is ok if you have to check yourself. Its not going to hurt a thing to loosen and redo them over and over again. Just dont overtighten. If you do you will surely bend a valve or push rod. Do this on all 8 cylinders one at a time and if you did it right and your wires are in the correct position you should fire right up.
Hope this is helpful to ya,
Billy
 
  #9  
Old 12-20-03, 11:53 PM
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I agree that it's one of 2 things...either valves too tight, or distributor orientation. Sounds like you did the distributor right though...assuming you were rotating the engine the correct direction.
 
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Old 12-21-03, 04:11 AM
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Originally posted by cheese
I..assuming you were rotating the engine the correct direction.
That's what I'd be questioning about now. Possibly valves too tight also.

A backfire through the intake proves it is firing while an intake valve is open whether is be the firing order, distributor timing or valve staying open. Somehow compression is coming back through the intake valve.

From what I've read it doesn't look like you had the timing chain off at all, right?
 
  #11  
Old 12-21-03, 08:14 PM
mthomas84
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The timing chain was not touched and I rotated the crankshaft clockwise as required. I have to assume I have the valves set too tight. The procedure in Haynes says to tighten until resistance is felt and go 3/4 of a turn more after that point. Tomorrow, I'm starting from scratch with all the valves loose and reset the crank and distributor to TDC compression. Then I'll do one set at a time rotating the shaft 90 deg. for each set in firing order.
 
  #12  
Old 12-22-03, 03:31 AM
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Your issue may be that there is no resistance until you have oil pressure and your cranking right to the bottom and then some. Try just tightening until pushrod stops being loose. Once you get it to fire once, you can go back and adjust things correctly. Doing it with the engine running works better for me. Just tighten till clacking stops and then the appropriate setting.
 
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Old 12-22-03, 07:01 PM
mthomas84
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Hallelujah!
After all your coaching, looks like we got my head on straight. It looks like I was alternating between 2 problems never correcting both at the same time. Valves were set with the crankshaft 180 out and subsequently, I got the distributor jacked around too. Thanks for all your help guys!
 
  #14  
Old 12-23-03, 04:18 AM
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HMMMM.......

Glad you got it going again!!!
Billy
 
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Old 07-25-12, 04:24 PM
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same thing

hey, i read this thread and now this is the place to ask, i have doone the exact same to my 350, vortec. except i redid the timing chain and the sproket onto the crankshft, my truck fires but it shift extremly hard i also lack major power, please help me!
 
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