Engine Backfiring While in time

[imkwuzn]

Recently dropped in a crate motor from Jeggs into a 2000 Chevy C3500 SWB with the 5.7l 350 Vortec. Everything was running pretty good before all this mess. After 2k it was time to readjust the valves after they fully seated (roller cam with rocker arms and pushrods). Stripped it down past the lower intake manifold re did the valves. Removed the lash, cleaned block of residue and old gasket material, new intake gaskets, torqued down intake bolts accordingly to specs, timed my distributor (cyl 1 on TDC making sure intake just closed rotating crank.) set cap pointing at #1 cyl, put the rest back. Fire it up and it wont turn over. For giggles enjoying the gun shot noises I turned the crank with distributor out a full 360 thinking just maybe it was 180 degrees out and still nothing....Put it all back to TDC and still just backfires through the throttle body and exhaust. Plug wires are in the correct spot, distributor points at #1 cylinder on TDC and it just sits there and back fires over time. Fuel pressure is reading 50-55 psi when primed and 60psi when trying to start. Plugs are firing when grounded, Fuel is there and it is in time. I have no idea why it wont at least sound like it wants to turn over. Any help is appreciated. No compression test has been done yet, but I did have great oil pressure before I did the valves. Im starting to think its the Ignition control module acting up.

I’ve never heard of the need to readjust valve lash on a hydraulic cam unless you’re replacing something? Sounds like the valve lash is too tight and you have hanging valves. I’d have a buddy come over and take a look. A 2nd set of eyes never hurts, especially when you’re frustrated.

 

[Clutchmaster404]

Long story short I found the problem. Valves were too tight by about a 1/2 a turn. Not sure how that happened still, but it did work. However my idle air control valve also failed on me as well. I cleaned out the throttle body when changing gaskets and come to find out it was hanging wide open too. I’ve got it running really good now. Sorry for the delayed response I’ve just been racking my brain over it for weeks and working on other things with the truck. Thanks for all the help.

 

[Clutchmaster404]

Also, if anyone cares why I did this at all. If you’re familiar with buying crate engines from Jegs they come remanufactured from Mexico and I didn’t trust it. The engine sounded like it had a miss, but after several tests I found it to actually be the valves. A few of them had a chatter too them. I also took the intake manifold off to do it because I just wanted to see how it looked down there after 2k miles. I’m a gear head and could care less how long it takes me to put it back together. This is my first crate motor swap and was doing research. It’s all easy to put back together and learned a lot from it. Hope this helps someone

 

[SAATR]

Long story short I found the problem. Valves were too tight by about a 1/2 a turn. Not sure how that happened still, but it did work. However my idle air control valve also failed on me as well. I cleaned out the throttle body when changing gaskets and come to find out it was hanging wide open too. I’ve got it running really good now. Sorry for the delayed response I’ve just been racking my brain over it for weeks and working on other things with the truck. Thanks for all the help.

Also, if anyone cares why I did this at all. If you’re familiar with buying crate engines from Jegs they come remanufactured from Mexico and I didn’t trust it. The engine sounded like it had a miss, but after several tests I found it to actually be the valves. A few of them had a chatter too them. I also took the intake manifold off to do it because I just wanted to see how it looked down there after 2k miles. I’m a gear head and could care less how long it takes me to put it back together. This is my first crate motor swap and was doing research. It’s all easy to put back together and learned a lot from it. Hope this helps someone

Glad you sorted it all out, and thanks for updating this with the solution. Hopefully it will help somebody else with a similar issue in the future.