engine will not start, shoots flames out of intake and headers
engine will not start, shoots flames out of intake and headers I bought a gen 3 5.3 that ran when pulled. i installed a trailblazer ss cam and updated springs in it with new timing chain. checked pushrod length and installed stock push rods. I adjusted the valves the same as every other engine I've done before. when I first tried to start engine I wasn't getting any spark. trouble shoot and found crank sensor bad. replaced crank sensor. now it shoots flames out of headers and occasionally out of the intake. i also tried running engine on starting fluid with same issues. I am using parts from my run stand. harness, computer fuel pump and ignition. I've double checked all my grounds from battery to block and at computer. I've double checked voltage to computer, 12 volts. installed another computer. What am I missing?
Flames out the headers and/or intake means the valves are open during the combustion cycle. Either your pushrods are too long or you installed the camshaft incorrectly. Do a compression test to verify.
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flames out intake = mechanical or ignition firing order/timing wrong. Or valves stuck open like mentioned above
cam installed wrong, or coils on wrong side, or coil wiring mixed up
cam installed wrong, or coils on wrong side, or coil wiring mixed up
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yes I know that valve train is not adjustable. I have a comp cams pushrod length checker. I checked pushrod length with lifters bled down. I usually take head off and check with a solid lifter I made, but I just put a cam in this engine and over looked lifters being bled down.
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So, you bought push rods that are like 7.525" or some such?
That would explain the valves hanging open.
The CORRECT way to use the adj PR, is to screw it all the way together; install it; then unscrew it until it JUST BARELY takes up all the PLAY in the rocker arm. At the point where the lifter is FULLY extended (as tall as it can be, with the plunger up against the retainer), and BEFORE it begins to depress. Not, "tight"; not, "can't spin it anymore"; only, takes up all the FREE PLAY. The LOOSE SLACK. All of this of course, with the cam known to be on the "heel" of the lobe. My favorite method of determining that, is to look for the PEAK of the same lobe (int/exh) on the cyl 4 cyls away in the firing order (e.g., if you're looking at the #1 int, put the engine at the peak lift of the #6 int) which PEAK LIFT on the #6 int is MIN LIFT on the #1 int; and JUST BARELY take up all the VERTICAL play on the #1 int PR. Do it on acoupla cyls; maybe, the front & rear on each side so you catch the factory's crappy block deck tolerances, and int & exh, since those valves & seats wear VERY differently. (if these are stock "rebuilt" heads, of course, or if the valves you're using - I HOPE if this is any kind of serious effort rebuild, they're not stock) Then add whatever your desired preload is, based on the lifters you're using. Then, take some common sense into account: would you rather the lifter preload be low, for high RPMs; or would you rather it be high, for extreme longevity? IOW, use YOUR BRAIN, instead of slave to, "book" "says".
Sounds to me, overall, like your PRs are too long. And, if you go through the exercise I just gave you, they'll most likely (though of course not "certainly") come out not too terribly far from stock. 7.375" to 7.425" most likely.
That would explain the valves hanging open.
The CORRECT way to use the adj PR, is to screw it all the way together; install it; then unscrew it until it JUST BARELY takes up all the PLAY in the rocker arm. At the point where the lifter is FULLY extended (as tall as it can be, with the plunger up against the retainer), and BEFORE it begins to depress. Not, "tight"; not, "can't spin it anymore"; only, takes up all the FREE PLAY. The LOOSE SLACK. All of this of course, with the cam known to be on the "heel" of the lobe. My favorite method of determining that, is to look for the PEAK of the same lobe (int/exh) on the cyl 4 cyls away in the firing order (e.g., if you're looking at the #1 int, put the engine at the peak lift of the #6 int) which PEAK LIFT on the #6 int is MIN LIFT on the #1 int; and JUST BARELY take up all the VERTICAL play on the #1 int PR. Do it on acoupla cyls; maybe, the front & rear on each side so you catch the factory's crappy block deck tolerances, and int & exh, since those valves & seats wear VERY differently. (if these are stock "rebuilt" heads, of course, or if the valves you're using - I HOPE if this is any kind of serious effort rebuild, they're not stock) Then add whatever your desired preload is, based on the lifters you're using. Then, take some common sense into account: would you rather the lifter preload be low, for high RPMs; or would you rather it be high, for extreme longevity? IOW, use YOUR BRAIN, instead of slave to, "book" "says".
Sounds to me, overall, like your PRs are too long. And, if you go through the exercise I just gave you, they'll most likely (though of course not "certainly") come out not too terribly far from stock. 7.375" to 7.425" most likely.
Last edited by RB04Av; Oct 12, 2023 at 06:02 PM.
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