GMC no start with new block

OneTon · August 24, 2006

First of all let me say that I genrally deal with Fords, so I have decided to ask for the advice of those that know GM. Now to keep this as breif as possible. I'm working on a friends 95' GMC K-1500 with a 350 and the Z-71 package. This truck experienced a major engine failure "broken crank at the first journal". Engine was replaced with a long block assy. from one of the major chains. Everything is back in the truck, all harnesses and ground in place. Distributor in and phased correctly, plug wires verified to have correct firing order. Now for the fun. When cranked it backfires through the throttle body. It'll turn over a couple of times and backfire. Not a major bang, a definite backfire. I've checked the EGR, it's closed. New components in the distributor, and mechanically verified TDC #1 compression stroke. What am I missing "aside from my sanity!" Give me points and a carb anyday.

Thanks, Wes

95Sierra2500 · August 25, 2006

Timing is probably out. Get the motor back to TDC on cylinder 1, compression stroke. Reset the distributor.

Rookie · August 25, 2006

I would have to agree. back fire thru the intake 9 times out of 10 is timing. the vortec motor is a pain to reset the distrbutor if its pulled from the motor.

Butch 02 Denali · August 25, 2006

Check the cam timing chain, it could be off a tooth.

Check the rocker arms, one or more could be too tight causing a valve to not seat completly.

Are you sure the distributor isn't 180 degrees out? Make sure it's on the compression stroke.

redvett · August 25, 2006

Since your a Ford man maybe you dont know that #1 is on drivers side. That engine isnt a vortec its just a TBI smallblock. 96 is when the vortec engines began in GMT400 trucks.

I too feel its timing.

OneTon · August 25, 2006

Seems timing is the same topic on all our minds, "including mine" And yes I am aware that #1 is Drivers front, but thank you for the comment, these little things are why I'm here. I'm going to pull the valve cover this weekend and re verifiy I'm on the compression stroke. I actually know someone who has had one run 180 degrees out, believe it or not. The TBI gasket was replaced, but I do have concerns about fuel as this thing sat for two years. We thought the tank was empty, but we all know what happens when fuel sits for that long, lets pray no varnish, cause the TBI kit's I've been quoted are @*&$ expensive. I'll keep you guy's posted. And thanks again. You ever need info of 50's - 60's Effie's let me know.

redvett · August 25, 2006

Seems timing is the same topic on all our minds, "including mine" And yes I am aware that #1 is Drivers front, but thank you for the comment, these little things are why I'm here. I'm going to pull the valve cover this weekend and re verifiy I'm on the compression stroke. I actually know someone who has had one run 180 degrees out, believe it or not. The TBI gasket was replaced, but I do have concerns about fuel as this thing sat for two years. We thought the tank was empty, but we all know what happens when fuel sits for that long, lets pray no varnish, cause the TBI kit's I've been quoted are @*&$ expensive. I'll keep you guy's posted. And thanks again. You ever need info of 50's - 60's Effie's let me know.

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I just noted about the #1 cylinder because there are so many different engines and older GM had #1 on the right bank in older engines. If timing is close its got to be the fuel is sour. You may try fresh fuel and override the pump relay for a few minutes to circulate the fuel in the lines.

OnyxMAX · August 26, 2006

yep verify ignition timeing and cam timing. i've worked on several engines were persons lined up the dots across from eachother and not next to each other.

whiel the covers off make sure all the pushrods are straight and lifters pumped up. turn the crank and make sure none stick open.

dewfpo · August 26, 2006

Run a compression check on one cyclinder....if it is good, then chances are your distributor is out of phase 360 degrees. I've seen many people install a distributor on the exhaust stroke of #1 and swear it was on the compression stroke. Happens to all of us.

DEWFPO

ken1mod · September 2, 2006

I had this happen in reverse. carefully rebuilt friends ford 390 , went to start it up, noise and fire. fords number cylinders completely different from chevy and rest of planet. intake manifold is usually numbered.

Ken