‘97 5.7 Vortec - ̶n̶o̶t̶ your typical crank no start

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wyn97

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I need some help from someone wiser than myself.

‘97 Vortec 350 has me stumped. I was driving it around town, running errands as one does. I got to my last stop of the day, and upon wrapping up and leaving the parking lot became stranded. I fired the truck up, and made it about 200 feet before the engine abruptly but without fanfare died. I attempted to refire it and was greeted with the sounds of the engine trying to start but not at all in a healthy way.

Here are specifically the symptoms I’m seeing:
Free cranking, sputtering but no running
Ether/starter fluid leads to a large fireball out of the throttle body
Gas directly in the intake leads to a backfire

Here’s what I’ve checked so far:
Fuel pressure, 60psi, and does not bleed off. (Not a blown regulator diaphragm)
Spark happens, at least on cylinder 1
Distributor turns, so timing chain is still there supposedly.
Low compression on 1-3-5-7 (60psi)
Cylinder 2 is at 115psi, 4 is at 60. I have not checked 6 or 8 yet.
Plugs were a little wet, from cranking so much with no running I suppose.
Distributor is tightly held down, the base does not turn.
The cap and rotor are brand new Accel parts. The coil is a brand new MSD coil. Plugs wires to match.

I think, somehow, my 25k mile rebuilt motor jumped time. With no tensioner in there I don’t have the foggiest clue how that happens but, if it quacks like a duck and waddles like a duck…

I used a code reader and got no codes displayed, and the data reads on all sensors I recognize. MAP, MAT, CTS, TPS, MAF, RPM, all read normal and respond under cranking.

The only other thought would be a bad distributor / cam sensor pickup. I don’t know how these respond and determine crank timing but if somehow the distributor pickup was giving poor data perhaps it could advance the timing enough to cause the fireballs on ether?

I am absolutely stunned but I am out of ideas. This truck is my daily right now, so getting it fixed is a priority for me. Where would those long in the tooth go from here? Check my work again? Tear into the top end and look? Leap into a river? Any guidance is appreciated.
 
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yevgenievich

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Compression test is poor results, but I would try different cap/rotor/coil combo to see if that makes a difference. If compression test results are accurate, a leak down test would verify why results are bad
 

badco

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Sounds like jumped time. Can't remember if that year had fiber/aluminum gear or not.
 

badco

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Distributor or anything to do with spark will not affect compression test at all
 

badco

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Line up the timing mark on front cover and look under cap and see if it's pointing at #1 or at least on opposite side of 1. If it's anywhere but that the chain jumped
 

Frank Enstein

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Remove the distributor cap.

Rotate the engine with a ratchet on the alternator pulley until the timing marks line up and note the rotor location. if the rotor points to the back turn the crank one more revolution.

Put a piece of masking tape on the distributor housing so you can mark the precise location of the rotor with a mark on the tape.

Rotate the engine the opposite direction SLOWLY to see EXACTLY when the rotor moves.

Stop there.

Look at the timing marks on the damper and timing cover to see how far the crank has turned.

If it is 5 degrees or less the chain is tight but it may have jumped timing. More that 10 degrees the timing chain is loose and needs to be replaced.
 

badco

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Never got mine to turn using alternator nut, usually slipped. If all plugs are out maybe it would work. Of course I usually just bump starter till compression pops on #1 then line up my marks so I know its on correct stroke. Could be a issue if cam timing that far off tho
 

PlainJane98

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Verify your timing with the process described by Frank. Even a rather fresh rebuild can skip around if inferior parts were tossed in, such as aluminum/nylon (fiber) gear sets on a steel chain. If it quacks like a duck, and waddles like a duck, get your waders and duck dog.
 

wyn97

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Thank you all for the replies!
Has the distributor module been replaced?
It has not been. Only a fresh coil, cap, and rotor. Could the distributor module cause spark timing to be out of whack enough to not start? I figured it would just cause a no spark condition but I’m not sure. If so I reckon that could be it.

I understand that the distributor won’t affect compression, but even low compression should still run. It didn’t run poorly before, however. I can admit to being a bit all over the place right now in regards to the issue, I’m trying to avoid the parts cannon approach but it is tempting.

The advice to check the engine timing is good. I will update once I go through that procedure, it sounds simple enough. I see no way for it to be just a loose chain since it was running well and then not in such a hurry, it should be pretty obvious. Time to put my mechanic hat back on and turn some wrenches I suppose.
 
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